Evaluation of hay-type and grazing-tolerant alfalfa cultivars in

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Evaluation of hay-type and grazing-tolerant alfalfa cultivars in Powered By Docstoc
					    Evaluation of hay-type and grazing-tolerant alfalfa cultivars in season-long or
             complementary rotational stocking systems for beef cows

                      M. L. Hermann, J. R. Russell and S. K. Barnhart


                               J Anim Sci 2002. 80:768-779.




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  Evaluation of hay-type and grazing-tolerant alfalfa cultivars in season-long or
           complementary rotational stocking systems for beef cows1

                               M. L. Hermann, J. R. Russell2, and S. K. Barnhart3

        Department of Animal Science and Department of Agronomy, Iowa State University, Ames 50011



ABSTRACT: Alfalfa (Medicago sativa L.) persistence                          of the pasture seeded with the alfalfa-smooth brome-
and forage and cow-calf production were evaluated on                        grass mixtures for pastures with the complementary
pastures containing smooth bromegrass with or with-                         stocking systems. In yr 1 and 2, the remaining 60% of
out grazing-tolerant or hay-type alfalfa cultivars rota-                    each pasture was grazed for the first 44 and 54 d, and
tionally stocked in either a season-long or complemen-                      100% of each pasture was grazed on d 45 to 120 and d
tary system. In 1997, six 2.02-ha pastures were seeded                      55 to 141, respectively. Proportions of alfalfa in the live
with smooth bromegrass, a mixture of a grazing-toler-                       dry matter of pastures seeded with the grazing-tolerant
ant alfalfa (Amerigraze variety) and smooth brome-                          and hay-type alfalfa cultivars decreased by 70 and 55%
grass, or a mixture of a hay-type alfalfa (Affinity vari-                    in paddocks stocked season-long and by 60 and 42%
ety) and smooth bromegrass to be used in season-long                        in paddocks used for complementary stocking (alfalfa
stocking systems. Four 2.02-ha pastures were seeded                         cultivar, P < 0.05; stocking system, P < 0.05) in yr 1,
with smooth bromegrass on 1.21 ha of each pasture,                          but decreased by 72% across cultivars and stocking sys-
and mixtures of either the grazing-tolerant or hay-type                     tems in yr 2. Total (P < 0.08) forage masses in Septem-
alfalfa cultivars and smooth bromegrass on the 0.81 ha                      ber of yr 1 and in August of yr 2 were greater in pastures
of each pasture to be used in complementary stocking                        in which alfalfa paddocks were stocked season-long
systems. All 10 pastures were divided into 10 paddocks                      than in those with complementary alfalfa stocking.
and rotationally strip-stocked at 1.98 cow-calf units/ha                    Grazing of alfalfa in grass mixtures increased calf and
with crossbred cows and calves for 120 and 141 d start-                     total cow/calf weight gains in comparison with grazing
ing May 18, 1998 (yr 1), and May 6, 1999 (yr 2), respec-                    of smooth bromegrass, but alfalfa persistence, mea-
tively. Each year, first harvest forage was harvested as                     sured as a proportion of the live dry matter, was not
hay from 40% of all 10 pastures, this being the portions                    affected by alfalfa cultivar.

                                            Key Words: Alfalfa, Beef Cattle, Grazing

2002 American Society of Animal Science. All rights reserved.                                       J. Anim. Sci. 2002. 80:768–779


                         Introduction                                       forage nutritive value because of its high concentrations
                                                                            of digestible DM, CP, calcium, phosphorus, and magne-
   Incorporation of alfalfa (Medicago sativa L.) into cool-                 sium (Van Keuren and Matches, 1988). Problems with
season grass pastures seems advantageous because of                         bloat (Majak et al., 1995) and poor plant persistence
its high yields and ability to fix nitrogen (Van Keuren                      (Brummer and Bouton, 1991; Smith and Bouton, 1993),
and Marten, 1972). Alfalfa incorporation also increases                     however, have limited the use of alfalfa in grazing sys-
                                                                            tems. Recent alfalfa cultivars have been developed to
                                                                            minimize these problems (Smith et al., 1989; Smith et
  1
    Journal paper no. J# 19008 of the Iowa Agric. and Home Econ.            al., 1992; Bittman and McCartney, 1994).
Exp. Sta., Ames. Project no. 3237, and supported by Hatch Act and              Complementary stocking is a form of sequential graz-
State of Iowa funds. This project was funded, in part, by a grant
                                                                            ing in which pastures with different forage species or
from the Leopold Center for Sustainable Agriculture, Iowa State
Univ., Ames.
                                                                            species mixtures are grazed when environmental condi-
   2
    Correspondence: 337 Kildee Hall (phone: 515-294-4631; fax: 515-         tions optimize the productivity and(or) nutritional qual-
294-3795; E-mail: jrussell@iastate.edu).                                    ity of the forage from those species. Because of their
   3
    The authors gratefully acknowledge R. Berryman, M. Hersom,              seasonal growth distributions, legumes could supply
M. Kruse, D. Primm, A. Pugh, and the animal caretakers at the Iowa          forage in mid-summer when the productivity and nutri-
State University Beef Nutrition Research Center for assistance in
                                                                            tional quality of cool-season grass species are limited by
conducting this experiment and P. M. Dixon for assistance in the
statistical analysis of the data.                                           environmental temperature and moisture deprivation
   Received August 24, 2000.                                                (Allen et al., 1986). Furthermore, because forage persis-
   Accepted September 19, 2000.                                             tence problems have been associated with grazing un-

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                                               Alfalfa grazing by beef cows                                             769
der heavy rainfall in the early part of the grazing season        of sward height determined with a falling plane meter
(Whitear et al., 1962; Wilman, 1977; Hutchinson et al.,           (4.8 kg/m2) in six locations per paddock. The falling
1995), limiting the grazing of alfalfa to mid- to late            plane meter measurements were correlated to live DM
season may reduce alfalfa persistence problems.                   density (r2 = 0.71) in a previous experiment with 100
  The objectives of this experiment were to evaluate              measurements in pastures containing smooth brome-
cow-calf productivity, forage productivity, and alfalfa           grass or a mixture of alfalfa and cool season grasses
persistence from pastures containing hay-type and                 grazed by continuous or rotational stocking (unpub-
grazing-tolerant alfalfa cultivars grazed in either sea-          lished data). Animals were moved to new strips daily
son-long or complementary rotational stocking systems             and to new paddocks after the total area of each paddock
for beef cows.                                                    had been grazed. First harvest forage from the re-
                                                                  maining 40% of each pasture was mowed on June 1
               Materials and Methods                              and May 26 and baled as hay on June 16 and May 30
                                                                  in yr 1 and 2, respectively. Bales were weighed and
                                                                  core-sampled in two locations on each side. Harvested
Pastures                                                          paddocks were incorporated into the stocking system
                                                                  after a minimum regrowth period of 33 d after mowing.
   In the spring of 1997, 20.2 ha at the Iowa State Uni-          The total grazing season lengths were 120 and 141 d
versity Beef Nutrition Research Center near Ames, IA,             in yr 1 and 2, respectively.
were divided into ten 2.02-ha fields. Replicate fields
were seeded with smooth bromegrass (Bromus inermis;               Animal Management
Barton variety; season-long stocking smooth brome-
grass treatment, 2.02 ha each), a mixture of smooth                  At grazing initiation in each year, four Simmental ×
bromegrass and a hay-type alfalfa cultivar (Affinity va-           Angus × Charolais cows (one primiparous and three
riety; season-long stocking hay-type alfalfa treatment,           multiparous) with calves were allotted at a stocking
2.02 ha each), a mixture of smooth bromegrass and a               rate of 1.98 cow-calf units/ha to each pasture based on
grazing-tolerant alfalfa cultivar (Amerigraze variety;            cow weight, condition score, age, and sex of the calf.
season-long stocking grazing-tolerant alfalfa treat-              Mean initial cow and calf BW (kilograms) and cow body
ment, 2.02 ha each), smooth bromegrass on 1.21 ha                 condition scores were 613, 81, and 5.2 in yr 1 and 532,
and a mixture of smooth bromegrass and the hay-type               68, and 4.8 in yr 2. All cows received mineral supple-
alfalfa cultivar on 0.81 ha of the pastures (complemen-           ments; those grazing alfalfa-smooth bromegrass re-
tary stocking hay-type alfalfa treatment), or smooth              ceived poloxalene as a bloat preventative. Compositions
bromegrass on 1.21 ha and a mixture of smooth brome-              of these mineral supplements were 0.2% Mg, 1,250 ppm
grass and the grazing-tolerant alfalfa cultivar on 0.81           Cu, 3,000 ppm Zn, and 26.4 ppm Se; and 4% Mg, 625
ha of the pastures (complementary stocking grazing-               ppm Cu, 1,500 ppm Zn, and 8.8 ppm Se on a DM basis,
tolerant alfalfa treatment). Smooth bromegrass was                respectively. Cows were time-bred on June 23 of each
seeded at rates of 12 and 9 kg/ha in monoculture and              year by artificial insemination after estrus synchroniza-
mixtures, respectively. Alfalfa was seeded at a rate of           tion followed by a 42-d breeding season by natural ser-
12 kg/ha. Forage was harvested as hay in two cuttings             vice. Although conception rates and calving intervals
from the pasture in 1997. In the spring of 1998 (yr 1)            were measured, they are not presented because of the
and 1999 (yr 2), each full pasture or portion of pasture          low cow numbers.
containing smooth bromegrass in monoculture was fer-                 Cows and calves were weighed monthly without fast-
tilized with 112 kg nitrogen/ha.                                  ing. Cows were condition-scored monthly using a 9-
                                                                  point scale (1 = severely emaciated, 5 = thin to moderate,
Stocking Management                                               9 = very obese) based on a visual appraisal by two
                                                                  individuals (Neumann and Lusby, 1986). The study was
  Pastures were divided with electric fence into ten              reviewed and approved by the Institutional Animal
0.20-ha paddocks (47.0 × 43.1 m) with a lane. Grazing             Care and Use Committee at Iowa State University.
was initiated on May 18 and May 6 in yr 1 and 2,
respectively. During the first 44 and 54 d in yr 1 and 2,          Pasture Sampling
six of the paddocks in all 10 pastures were rotationally
strip-stocked to assist in the control of bloat and forage           Forage masses in portions of the pastures that were
waste. In pastures with the complementary treatments,             stocked season-long or stocked in mid- to late season
this area of the pastures was planted with smooth                 after hay harvest were determined by monthly hand-
bromegrass. The forage allowance for strip-stocking               clipping to a height of 2.5 cm in two 0.25-m2 locations
paddocks in each pasture was calculated and provided              per paddock composited by the season grazed. To deter-
daily assuming that a cow-calf pair consumed 3.5% of              mine the effect of 2 yr of stocking treatments on botani-
the cow’s initial BW per day as live forage mass of that          cal composition in the spring of the third year, pastures
paddock at an estimated harvest efficiency of 50%. Live            were sampled in a similar manner in May of 2000 (yr
forage DM density was estimated as 112 kg/(ha cm)                 3). Clipped forage samples were hand-sorted into the

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770                                                     Hermann et al.

dead forage and live grass, alfalfa, and broadleaf weed            fate-potassium bromate-phosphoric acid extracts of
fractions. No other legume species were present in these           ashed samples (Williams et al., 1962). Fecal output was
pastures. Each fraction was weighed, dried in a forced             estimated from the passage kinetics of chromium-mor-
air oven at 65°C for 48 h, and weighed again to deter-             danted fiber using a two-compartment model (Pond et
mine DM concentration. Dried samples were ground                   al., 1988) and nonlinear regression analysis (SAS Inst.
through a 1-mm screen of a Wiley mill. A weighted                  Inc., Cary, NC). Dry matter intake (DMI) was calcu-
composite of live forage from each pasture was prepared            lated as DMI = fecal output/(1 − % IVDMD of the masti-
for chemical analysis from each monthly sample by mix-             cate/100). Intake of IVDMD, CP, indigestible NDF, and
ing ground grass, alfalfa, and weed fractions based on             ADF were calculated by multiplying their concentra-
their proportions in the DM of the hand-clipped sample.            tions in the masticate by the DMI of the cows.
For statistical analysis, the proportions of weeds in the
live DM and dead forage in the total DM in the whole                 Analyses
pastures were calculated as means adjusted for the area
of the six paddocks stocked season-long and the four                  Monthly dead and composited live forage samples
paddocks stocked after hay harvest. To test the effects            and the masticate and pasture forage samples from
of season-long and mid- to late-season grazing on the              the grazing selection determinations were analyzed for
proportion of alfalfa in the live DM of paddocks planted           IVDMD, CP, NDF, and ADF. Forage IVDMD concentra-
with the alfalfa-smooth bromegrass mixtures, these                 tions were determined by the Tilley and Terry (1963)
data were analyzed as separate effects.                            procedure modified to use the NC-64 buffer with 48-h
                                                                   ruminal and 24-h acid-pepsin incubation periods (Mar-
Forage Selection and Intake                                        ten and Barnes, 1979). Ruminal inoculum for this proce-
                                                                   dure was obtained from a fistulated steer fed an alfalfa
   Forage selection was determined after 21 and 84 d               diet. Thus, IVDMD measurements of smooth brome-
of grazing in yr 1 and 32 and 94 d of grazing in yr 2.             grass may have been underestimated. Forage CP con-
One ruminally fistulated Simmental × Angus × Jersey                 centrations were calculated as the product of 6.25 times
steer (8 yr old) was placed in each pasture for an adapta-         the total N concentration as determined by the Kjeldahl
tion period of 5 d and a collection period of 2 d. Masticate       procedure (AOAC, 1990). Forage NDF and ADF concen-
was collected during 2 h of grazing by ruminal evacua-             trations were determined by sequential analysis using
tion on two consecutive days (Hitz and Russell, 1998).             an ANKOM200 Fiber Analyzer (ANKOM Technology
Forages selected by steers were subsampled, frozen,                Corporation, Fairport, NY) according to the procedures
and freeze-dried. Pasture sward heights were measured              or Van Soest and Robertson (1979) and Goering and
with a falling plane meter (4.8 kg/m2), and forage was             Van Soest (1970), respectively. Composition of total for-
hand-clipped in two 0.25-m2 locations in the forage                age in the monthly samples was estimated as the mean
strips grazed by the cattle on those days. Pasture forage          of the concentrations of each component in the dead
samples were weighed, dried at 65°C for 48 h, and re-              and live forage fractions weighted for the proportion of
weighed to determine DM mass and concentration.                    these fractions in the total forage. The concentration
Dried selected and pasture forage samples were ground              of indigestible NDF in masticate and pasture forage
through a 1-mm screen of a Wiley mill in preparation               samples were determined by subjecting samples to a
for further analyses. Selection indices for the analyzed           96-h incubation in ruminal fluid with the NC-64 buffer
forage fractions were determined as the ratio of their             followed by neutral detergent extraction.
concentrations in the selected and pasture forages.
   In conjunction with the determination of forage selec-          Statistical Analyses
tion, two cows of similar age, condition score, and body
weight in each pasture were pulse-dosed with 30 g of                  All data were analyzed by the GLM procedure (SAS
chromium-mordanted fiber in five gelatin capsules to                 Inst., Inc.) with pasture as the experimental unit. Al-
quantify digesta passage kinetics (Russell et al., 1993).          falfa proportions in paddocks seeded with alfalfa were
Mordanted fiber was prepared by NDF from masticate                  analyzed as a split-split-split-plot design with alfalfa
selected by ruminally fistulated steers with 2% chro-               cultivar as the main plot, season grazed (full vs mid-
mium as sodium dichromate (Russell et al., 1993). Chro-            to late season) as the subplot, month as the sub-subplot,
mium concentrations of the mordanted fibers from pas-               and year as the sub-sub-subplot. The alfalfa cultivar ×
tures containing hay-type alfalfa, grazing-tolerant al-            replicate, alfalfa cultivar × season grazed × replicate,
falfa, and smooth bromegrass were 1.14, 1.25, and                  and alfalfa cultivar × season grazed × month × replicate
1.12% in yr 1, and 1.40, 1.27, and 1.62% in yr 2. Fecal            interactions were used as the error terms for the main
samples were collected at 0, 18, 22, 26, 30, 42, 54, 66,           plot, subplot, and sub-subplot. Monthly forage botanical
78, 90, 102, and 114 h after dosing, dried at 65°C for 7           composition, total and live mass, and the composition
d, and ground through the 1-mm screen of a Wiley mill.             of total and live forage in the pastures, pre- and post-
Chromium concentrations of mordanted fibers and feces               grazing sward heights, and forage selection and intake
were determined by atomic absorption spectrophotome-               were analyzed as a split-split-plot design with treat-
try with an air-acetylene flame using manganese sul-                ment as the main plot, month as the subplot, and year

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                                                 Alfalfa grazing by beef cows                                             771
as the sub-subplot. Effects of treatment were tested by
the treatment by replicate interaction. Changes in cow
BW and condition score before, during, and after breed-
ing; calf and cow/calf production; and hay yield data
were analyzed as a split-plot design with treatment as
the main plot, and year as the subplot. The effects of
treatment were tested by the treatment × replicate in-
teraction. For all variables except the proportion of le-
gumes in the live DM in which there were significant
interactions between the treatments and month and(or)
year, data were analyzed as a randomized complete
block design by month within years. Orthogonal com-
parisons for the effects of forage species, alfalfa cultivar,
and stocking system were conducted on variables with
significant (P < 0.10) treatment effects. Forage species
compared the season-long smooth bromegrass treat-
ment to all alfalfa treatments. Alfalfa cultivar com-
pared the hay-type alfalfa treatment to the grazing-
tolerant alfalfa treatment. Stocking system compared
the season-long alfalfa systems to the complementary
alfalfa systems. To estimate cow DMI, as a percentage
of BW, linear regression analysis was conducted using
total mass and sward height of pasture forage and the
concentrations of IVDMD, CP, INDF, NDF, and ADF
in masticate samples from fistulated steers as indepen-
dent variables.

                         Results

Sward Botanical Composition                                            Figure 1. Proportion of alfalfa in live forage DM from
                                                                    paddocks containing grazing tolerant (GT) and hay-type
   The proportions of alfalfa in the live DM in all pad-            (HT) alfalfa cultivars stocked either full season (FS, n =
docks seeded with alfalfa were greater (P < 0.01) in yr             2, SEM = 8.4) or mid- to late season (MLS, n = 4, SEM =
1 than in yr 2 (Figure 1). Furthermore, the proportions             6.56) in yr 1 and 2.
of alfalfa decreased (P < 0.01) steadily throughout the                                      Significance
grazing season in each year. Paddocks that were only                Alfalfa cultivar (a)                0.02
stocked in mid- to late season had greater (P < 0.01)               Season grazed (s)                  <0.01
                                                                    a×s                                 0.08
mean proportions of alfalfa than paddocks stocked for               Month (mo)                         <0.01
the full season (57.3 vs 42.2%). This effect was greater            a × mo                             >0.10
in yr 2 than in yr 1 (year × stocking, P = 0.08) and was            s × mo                             >0.10
                                                                    a × s × mo                         >0.10
less in each succeeding month of the grazing season                 Year (yr)                          <0.01
(month × stocking, P = 0.02). The adverse effect of full-           a × yr                             >0.10
season grazing on alfalfa persistence likely resulted               s × yr                             >0.10
                                                                    a × s × yr                         >0.10
from excessive rain in June of each year. Rainfalls were            mo × yr                            >0.10
27.4 and 18.5 cm in June of yr 1 and 2, which were 14.8             a × mo × yr                        >0.10
and 5.9 cm over the 30-yr average of June rainfall for              s × mo × yr                        >0.10
                                                                    a × s × mo × yr                    >0.10
the experimental site. Furthermore, soil classes at the
experimental site typically have little slope and vari-
able drainage. Mean proportions of alfalfa in paddocks
containing the hay-type alfalfa cultivar were greater               65, 43, and 69% in May of 1999 (yr 2; year, P < 0.01;
(P < 0.02) than in paddocks containing the grazing-                 stocking, P < 0.01; year × stocking, P < 0.01).
tolerant alfalfa cultivar (54.7 vs 49.9%), primarily be-               Mean proportions of broadleaf weeds in the live DM
cause of differences in yr 1. In May of 2000 (yr 3), mean           of all pastures were greater (P < 0.01) in yr 2 (9%) than
proportions of alfalfa in the live DM of paddocks that              in yr 1 (3%) and increased in each succeeding month
were stocked during the full and mid- to late-season                of the grazing season (P < 0.01). Pasture treatments
periods were 35 and 66% for the hay-type cultivar and               had no significant main effects or interactions on the
35 and 71% for the grazing-tolerant cultivar. Mean pro-             proportions of broadleaf weeds in the live DM.
portions of alfalfa in the live DM for these treatments                In both years, the proportions of dead forage in all
were 87, 86, 81, and 82% in May of 1998 (yr 1) and 49,              pastures increased (P < 0.01) in each succeeding month

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772                                                     Hermann et al.

                                                                   Herbage Masses
                                                                      Mean total and live herbage masses (P < 0.01) were
                                                                   greater in yr 1 (2,278 and 1,536 kg DM/ha) than in yr
                                                                   2 (2,017 and 1,160 kg DM/ha) and were greater in the
                                                                   month of May than in the months of June, July, August,
                                                                   and September (P < 0.01). There were no significant
                                                                   treatment × month or treatment × month × year interac-
                                                                   tions in mean live herbage masses. Similarly, mean and
                                                                   SEM of total herbage masses in May, June, July, and
                                                                   August of yr 1 were 4,476 ± 1141, 1,858 ± 725, 1,695 ±
                                                                   798, and 1,500 ± 556 kg DM/ha and did not differ across
                                                                   treatments. But in September of yr 1, total herbage
                                                                   masses of pastures with the season-long alfalfa treat-
                                                                   ments were greater (P = 0.08) than those with comple-
                                                                   mentary alfalfa grazing (2,637 and 1,411 ± 533 DM kg/
                                                                   ha, respectively). In yr 2, mean and SEM of total herb-
                                                                   age masses in May, early June, late June, July, and
                                                                   September were 2,558 ± 818, 1,472 ± 634, 1,835 ± 673,
                                                                   1,701 ± 726, and 1,950 ± 765 kg DM/ha, which did not
                                                                   differ across treatments. Similar to September of yr 1,
                                                                   total herbage masses in August of yr 2 were greater (P
                                                                   = 0.06) for pastures with season-long alfalfa grazing
                                                                   than pastures with complementary alfalfa grazing
                                                                   (2,776 and 1,349 ± 534 kg DM/ha).

                                                                   Forage Sward Height
                                                                      Mean sward heights as cattle entered each paddock
   Figure 2. Proportions of dead material in total forage
                                                                   were greater in yr 1 than in yr 2 (22 vs 21 cm; P = 0.03).
DM from smooth bromegrass (SB) and alfalfa/smooth
                                                                   This effect was greatest in May and June when the
bromegrass pastures grazed with season-long (Season)
                                                                   average sward heights as cattle entered the paddocks
or complementary (Comp) stocking of grazing tolerant
                                                                   were 36 and 24 cm in yr 1 and 24 and 18 cm in yr 2
(GT) or hay-type (HT) alfalfa cultivars in yr 1 and 2 (SEM
                                                                   compared with mean sward heights of 17 and 18 cm as
= 4.5; n = 2). Significant (P < 0.10) orthogonal comparisons
                                                                   cattle entered paddocks in July through September in
within months are: f = season-long smooth bromegrass
                                                                   yr 1 and 2 (month × year, P = 0.02). Mean sward heights
treatment vs all alfalfa treatments; s = season-long alfalfa
                                                                   as cattle entered paddocks in pastures with season-long
stocking vs complementary alfalfa stocking; and a = hay-
                                                                   smooth bromegrass or complementary alfalfa stocking
type alfalfa vs grazing tolerant alfalfa.
                                                                   were greater in yr 1 than in yr 2 but were greater in
                                                                   pastures with season-long alfalfa stocking in yr 2 than
                                                                   in yr 1 (treatment × year, P = 0.02). However, there
                                                                   were no significant main effects of treatments or inter-
of the grazing season (Figure 2). The mean proportions             action of treatments with month on the sward height
of dead forage in the total DM of all pastures were                as cattle entered the paddocks. These sward heights
greater in yr 2 (31%) than in yr 1 (29%; P = 0.04), and            resulted in paddocks being grazed in May, June, July,
this effect was greater in May of yr 2 than in each                August, and September for an average ± SEM (n = 10)
succeeding month of the grazing season (month × year,              of 4.1 ± 0.35, 3.2 ± 0.60, 2.2 ± 0.17, 2.2 ± 0.29, and 2.3
P < 0.01). The mean proportions of dead forage in the              ± 0.27 d in yr 1 and 4.0 ± 0.33, 2.7 ± 0.35, 2.4 ± 0.23,
total DM of pastures with the season-long alfalfa treat-           2.7 ± 0.37, and 2.5 ± 0.35 d in yr 2.
ments were lower (P = 0.02) than the complementary                    Mean sward heights of paddocks as cattle were moved
alfalfa treatments and the season-long smooth brome-               from them did not differ between the 2 yr. However,
grass treatments. This effect was greater in the mid-              mean sward heights of paddocks as cattle were moved
to late part of the grazing season (treatment × month,             from them were greater in May of yr 1 than in yr 2 and
P < 0.01). There were no differences in the proportions            greater in June through September of yr 2 than yr 1
of dead forage in pastures between the two alfalfa culti-          (month × year, P < 0.01). Alfalfa cultivar or stocking
vars in yr 1. At the initiation of grazing in yr 2, however,       system had no significant main effects on the sward
the proportions of total DM that were dead were less               height as cattle were moved from the paddocks. But
(P = 0.09) in pastures with the hay-type cultivar than             the sward heights as cattle were moved from paddocks
in those with the grazing type cultivar.                           in pastures with season-long alfalfa stocking were

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                                              Alfalfa grazing by beef cows                                               773
shorter than those of pastures with season-long smooth
bromegrass or complementary alfalfa stocking in yr 1
and longer than those of pastures with the later treat-
ments in yr 2 (treatment × year, P = 0.03).
  Over 2 yr, the mean sward heights of paddocks as
cattle entered were greater (P = 0.07) than when cattle
were moved out (22 vs 10 cm). Calculated from forage
sward heights as cattle were moved into and out of
paddocks, forage removal rates in May, June, July, Au-
gust, and September were 56, 67, 50, 53, and 59% in
yr 1 and 55, 44, 44, 55, and 53% in yr 2. Because the
mean utilization rate of 54 was 8% over the estimated
utilization used in calculation of the forage allowance,
the apparent forage DM intake of a cow-calf pair was
3.78% of the cow’s BW instead of the 3.5% used in the
estimation of grazing days. However, because forage
sward heights likely reflect the effects of trampling as
well as consumption of forage, forage utilization rates
calculated from sward height measurements likely
overestimated actual forage utilization rates.

Forage Chemical Composition
   Mean IVDMD concentrations of the total and live
forage in all pastures were greater in yr 2 (50.9 and
57.3%) than in yr 1 (48.3 and 54.2%) and were greater
in May (58.6 and 61.2%) than in June, July, August,
and September (47.3 and 54.4%; year, P < 0.01; month,
P < 0.01; Figure 3). Over 2 yr, all alfalfa treatments
had greater (P = 0.01) total forage IVDMD concentra-                Figure 3. Mean IVDMD in total forage samples from
tions than the season-long smooth bromegrass treat-              smooth bromegrass (SB) and alfalfa/smooth bromegrass
ments (49.9 vs 48.4%). The season-long alfalfa treat-            pastures grazed with season-long (Season) or
ments had greater (P < 0.01) total forage IVDMD con-             complementary (Comp) stocking of grazing tolerant (GT)
centrations than the complementary alfalfa treatments            or hay-type (HT) alfalfa cultivars in yr 1 and 2 (SEM =
(51.0 vs 48.8%). There were no significant treatment ×            1.61; n = 2). Significant (P < 0.10) orthogonal comparisons
month or treatment × month × year interactions in live           within months are: f = season-long smooth bromegrass
forage IVDMD concentrations. There were treatment                treatment vs all alfalfa treatments; s = season-long alfalfa
× month interactions for total forage IVDMD concentra-           stocking vs complementary alfalfa stocking; and a = hay-
tion (P = 0.04). Although IVDMD concentrations of the            type alfalfa vs grazing-tolerant alfalfa.
total forage of pastures with the season-long smooth
bromegrass treatment did not differ from pastures with
any alfalfa treatment in May through August of yr 1              of total forage in pastures with the hay-type alfalfa
and May and June of yr 2, IVDMD concentrations of                cultivar was greater (P = 0.07) than pastures containing
total forage in pastures with the season-long smooth             the grazing-tolerant alfalfa cultivar at grazing initia-
bromegrass treatment were less (P < 0.10) than alfalfa           tion in May of yr 2 (60.6 vs 57.1%).
treatments in September of yr 1 (41.4 vs 47.4%) and                 Over 2 yr, mean CP concentrations of the total and
July (45.1 vs 49.3%), August (46.1 vs 49.1%), and Sep-           live forage of all pastures were greater in May (20.0
tember (46.9 vs 49.1%) in yr 2. Similar to pastures              and 21.2%) than throughout the rest of the grazing
containing the season-long smooth bromegrass treat-              season (12.7 and 14.7%; P < 0.01; Figure 4). Mean CP
ment, mean IVDMD concentrations of total forage from             concentrations of total and live forage in pastures with
pastures with complementary alfalfa stocking were                the season-long smooth bromegrass treatments (12.9
lower (P < 0.05) than those with the season-long alfalfa         and 14.5%) were less (P < 0.01) than pastures with all
stocking in May (57.3 vs 59.5%) and September (44.7              alfalfa treatments (14.5 and 16.3%). Mean CP concen-
vs 51.1%) of yr 1 and in July (47.8 vs 50.7%), August            trations of total (P < 0.01) and live (P = 0.06) forage in
(45.9 vs 52.4%), and September (47.6 vs 50.3%) of yr 2.          pastures with complementary alfalfa stocking were less
Mean IVDMD concentrations of total forage did not                than in pastures with season-long alfalfa stocking (13.9
differ between pastures planted with either alfalfa cul-         and 16.0 vs 15.2 and 16.7%). Crude protein concentra-
tivar in any month in yr 1 or from June through Septem-          tions of total and live forage did not differ between
ber of yr 2. However, the mean IVDMD concentration               pastures with either alfalfa cultivar. Furthermore,

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  Figure 4. Mean CP concentrations in total forage                   Figure 5. Mean NDF concentrations in total forage
samples from smooth bromegrass (SB) and alfalfa/                   samples from smooth bromegrass (SB) and alfalfa/
smooth bromegrass pastures grazed with season-long                 smooth bromegrass pastures grazed with season-long
(Season) or complementary (Comp) stocking of grazing               (Season) or complementary (Comp) stocking of grazing
tolerant (GT) or hay-type (HT) alfalfa cultivars in yr 1           tolerant (GT) or hay-type (HT) alfalfa cultivars in yr 1
and 2 (SEM = 0.94; n = 2). Significant (P < 0.10) orthogonal        and 2 (SEM = 1.72; n = 2). Significant (P < 0.10) orthogonal
comparisons within months are: f = season-long smooth              comparisons within months are: f = season-long smooth
bromegrass treatment vs all alfalfa treatments; s = season-        bromegrass treatment vs all alfalfa treatments; s = season-
long alfalfa stocking vs complementary alfalfa stocking;           long alfalfa stocking vs complementary alfalfa stocking;
and a = hay-type alfalfa vs grazing-tolerant alfalfa.              and a = hay-type alfalfa vs grazing-tolerant alfalfa.



there were no significant treatment × month or treat-
ment × month × year interactions in mean CP concen-                grazing season were less (P < 0.01) on the season-long
trations of total and live forage.                                 alfalfa treatments than the complementary alfalfa
   Apparently because of the later date of grazing initia-         treatments (53.5 and 49.1 vs 56.9 and 52.0%), primarily
tion in yr 1 than in yr 2, mean NDF concentrations of              because of differences between these treatments in May
total and live forage were greater (P < 0.01) in yr 1 than         and June. Concentrations of NDF in the total and live
in yr 2 (57.0 and 52.8 vs 55.2 and 50.5%; Figure 5).               forage did not differ between alfalfa cultivars.
Across both years, mean NDF concentrations of total                   Similar to NDF concentrations, mean ADF concen-
and live forage were less (P < 0.01) in May than through-          trations of total and live forage were greater (P < 0.01)
out the rest of the grazing season (46.3 and 44.1 vs 58.6          in yr 1 than in yr 2 (35.9 and 32.4 vs 31.7 and 27.9%).
and 53.6%). Mean NDF concentrations of total and live              Mean ADF concentrations of total and live forage were
forage were also less (P < 0.01) on all alfalfa treatments         less (P < 0.01) in May than throughout the rest of the
than the season-long smooth bromegrass treatment                   grazing season (27.0 and 25.2 vs 35.5 and 31.4%). Over
(55.2 and 50.5 vs 59.9 and 56.3%), largely because of              2 yr, there were no significant differences between
differences between the smooth bromegrass and the                  treatments and no treatment × month or treatment ×
alfalfa treatments early in the season. Similarly, mean            month × year interactions for the mean ADF concentra-
NDF concentrations of total and live forage over the               tions of total and live forage.

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                                                      Alfalfa grazing by beef cows                                                    775
       Table 1. Condition scoresa of cows grazing alfalfa/smooth bromegrass and smooth bromegrass pastures
                      in season-long and complementary systems in 1998 (yr 1) and 1999 (yr 2)
                                                             Alfalfa cultivar

                                          Grazing tolerant                       Hay-type                            Significancec
                    Smooth
Item              bromegrass     Seasonb        Complementary           Season     Complementary    SEM        f          s           a

                                                        Yr 1
Initial change        5.4           5.1                5.1                5.1             5.2       0.12    > 0.10      > 0.10      > 0.10
 Prebreedingd        −0.2           0.0                0.2               −0.1             0.0       0.04     0.01        0.02        0.02
 Breeding             0.0           0.3               −0.3                0.4             0.0       0.16    > 0.10       0.05       > 0.10
 Postbreeding        −0.1          −0.1                0.1               −0.3            −0.3       0.27    >0.10       >0.10       >0.10
 Total               −0.3           0.2                0.0                0.0            −0.3       0.25    >0.10       >0.10       >0.10
                                                        Yr 2
Initial change        4.8           4.9                4.7                4.8             4.8       0.13     >0.10      >0.10       >0.10
 Prebreedinge         0.1           0.1               −0.3                0.2            −0.2       0.11     >0.10       0.03       >0.10
 Breeding            −0.1          −0.1                0.2                0.3             0.2       0.16     >0.10      >0.10       >0.10
 Postbreeding         0.2           0.3                0.1                0.0             0.0       0.25     >0.10      >0.10       >0.10
 Total                0.2           0.3                0.0                0.5             0.0       0.26     >0.10      >0.10       >0.10
  a
    Condition scores are on a 9-point scale.
  b
    In this and later tables, the terms season and complementary refer to season-long and complementary stocking, respectively.
  c
   Orthogonal comparisons: f = season-long smooth bromegrass treatment vs all alfalfa treatments; s = season-long alfalfa stocking vs
complementary alfalfa stocking; and a = hay-type alfalfa vs grazing tolerant alfalfa.
  d
    1998: prebreeding 5/18 to 6/12, breeding 6/13 to 8/14, postbreeding 8/15 to 9/15.
  e
   1999: prebreeding 5/6 to 7/1, breeding 7/2 to 7/29, postbreeding 7/30 to 9/24.



Cow Body Weights and Condition Scores                                      cows grazing alfalfa season-long during the prebreeding
                                                                           period (−0.3 vs 0.2).
   Initial cow BW in yr 1 were greater (P < 0.01) than
in yr 2 (612 vs 531 kg/cow). Cow BW increased more                         Animal and Hay Production
(P < 0.01) during yr 2 than yr 1 (41 vs − 12 kg/cow),
primarily as a result of differences in BW change during                     Daily calf BW gains were greater (P = 0.05) in yr 1
the postbreeding period between years (31 vs − 14 kg/                      than yr 2 (1.2 vs 1.1 kg/d; Table 2). Because the grazing
cow). There were no significant differences between                         season was 21 d longer in yr 2 than in yr 1, seasonal
treatments and no treatment × year interactions for                        BW gains by calves (P = 0.01) and cow-calf pairs (P <
pasture means of the initial and changes in cow BW                         0.01) were greater in yr 2 (301 and 381 kg/ha) than in
before, during, and after breeding.                                        yr 1 (272 and 248 kg/ha). Over 2 yr, daily calf BW gains
   Similar to BW, mean cow body condition scores at                        were greater (P = 0.01) in all alfalfa treatments than
the initiation of grazing in yr 1 were greater (P = 0.01)                  the season-long smooth bromegrass treatment (1.2 vs
than in yr 2 (5.2 vs 4.8; Table 1). Furthermore, mean                      1.0 kg/d). Seasonal BW gains by calves and cow-calf
cow body condition score increased more during the                         pairs were also greater (P < 0.01) in all alfalfa treat-
postbreeding period (P = 0.01) and throughout the en-                      ments (294 and 330 kg/ha) than the season-long smooth
tire grazing season (P = 0.03) in yr 2 (0.1 and 0.2) than                  bromegrass treatment (257 and 253 kg/ha). Season-long
in yr 1 (−0.1 and −0.1). There were no significant treat-                   stocking of alfalfa resulted in greater daily calf BW
ment effects for means of the initial and changes in                       gains (P = 0.08), seasonal calf BW gains (P = 0.07), and
cow condition scores before, during, and after breeding.                   seasonal BW gains of cow-calf pairs (P < 0.01) than
However, during the prebreeding period of yr 1, body                       complementary stocking of alfalfa. Grazing of the hay-
condition scores of cows grazing smooth bromegrass                         type alfalfa cultivars also resulted in greater daily calf
season-long decreased more (P = 0.01) than cows graz-                      BW gains (P = 0.08), seasonal calf BW gains (P = 0.07),
ing all alfalfa treatments (−0.2 vs 0) and cows grazing                    and seasonal BW gains of cow-calf pairs (P = 0.02) than
in the complementary alfalfa stocking system had an                        grazing of treatments seeded with grazing-tolerant al-
increase in body condition score while body condition                      falfa. There were no year × treatment interactions for
of those grazing alfalfa season-long decreased (0.1 vs                     calf daily and seasonal production, and cow-calf sea-
−0.1; P = 0.02). Furthermore, during the prebreeding                       sonal production.
period of yr 1, body condition scores of cows grazing the                    Mean first harvest hay yields were greater (P < 0.01)
grazing- tolerant alfalfa cultivars increased more (P =                    in yr 2 than in yr 1 (2,498 vs 2,288 kg/ha). Over 2 yr,
0.02) than cows grazing the hay-type alfalfa cultivars                     mean first harvest hay yields were greater (P < 0.01)
(0.1 vs −0.1). In contrast to yr 1, cows grazing in the                    from the season-long smooth bromegrass treatments
complementary alfalfa stocking system in yr 2 had                          than all alfalfa treatments (2,680 vs 2,322 kg/ha). Al-
greater (P = 0.03) losses in body condition scores than                    though both treatments had alfalfa seeded in the acres

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 Table 2. Mean calf and cow-calf production from alfalfa/smooth bromegrass and smooth bromegrass pastures in
                           season-long and complementary systems in 1998 and 1999
                                                         Alfalfa cultivar

                                     Grazing tolerant                          Hay-type                               Significancea
               Smooth
Item         bromegrass       Season        Complementary           Season        Complementary     SEM           f            s       a

Calf
 kg/d             1.0            1.2               1.1                 1.2              1.2         0.04      0.01         0.08       0.08
 kg/ha          257            297               274                 309              297           9.7      <0.01         0.07       0.07
Cow/calf
 kg/ha          253            348               269                 393              310          15.6      <0.01        <0.01       0.02

  Orthogonal comparisons: f = season-long smooth bromegrass treatment vs all alfalfa treatments; s = season-long alfalfa stocking vs
  a

complementary alfalfa stocking; and a = hay-type alfalfa vs grazing tolerant alfalfa.



harvested for hay, mean first harvest hay yields were                        (62.8 vs 59.5%). In contrast, mean concentrations of CP
greater (P < 0.01) from treatments with season-long                         (P < 0.01) and indigestible NDF (P = 0.05) in masticate
alfalfa stocking than from treatments with complemen-                       were greater in June than in August of both years (18.8
tary alfalfa stocking (2,467 vs 2,176 kg/ha). Mean first                     and 16.4% vs 15.3 and 14.3%). Over the two years,
harvest hay yields were greater (P < 0.01) from pastures                    masticate IVDMD concentrations were greater (P =
with the hay-type alfalfa cultivars than from pastures                      0.07) and indigestible NDF concentrations were less (P
with the grazing-tolerant alfalfa cultivars (2,642 vs                       = 0.08) from pastures with alfalfa treatments than from
2,002 kg/ha).                                                               pastures with season-long stocking of smooth brome-
                                                                            grass (61.7 and 14.9% vs 58.9 and 17.2%). Masticate
Forage Selection and Intake                                                 IVDMD concentrations were also greater (P < 0.01) and
                                                                            indigestible NDF concentrations were less (P < 0.01)
   Selected forage composition and selection index data                     from pastures with season-long alfalfa stocking than
were combined across yr 1 and 2 for treatments in June                      from pastures with complementary alfalfa stocking
and August because there were no treatment × year                           (63.9 and 13.2% vs 59.6 and 16.6%). Masticate NDF
interactions (Tables 3 and 4). Furthermore, concentra-                      and ADF concentrations were greater (P < 0.01) from
tions of IVDMD, CP, NDF, and ADF in the masticate                           pastures with complementary alfalfa stocking than
of fistulated steers did not differ between the 2 yr. How-                   from pastures with season-long alfalfa stocking (46.5
ever, the concentrations of indigestible NDF in the mas-                    and 27.7% vs 40.8 and 25.2%). Masticate NDF and ADF
ticate of fistulated steers were greater (P = 0.04) in                       concentrations increased from June to August in pas-
yr 1 than in yr 2 (16.4 vs 14.3%). Over 2 yr, mean                          tures with season-long alfalfa stocking, but decreased
concentrations of IVDMD in masticate of grazing steers                      or did not change from June to August in pastures with
grazing were greater (P < 0.01) in August than in June                      complementary alfalfa and season-long smooth brome-


 Table 3. Mean composition of selected forage collected from fistulated steers grazing alfalfa/smooth bromegrass
          and smooth bromegrass pastures in season-long and complementary systems in 1998 and 1999
                                                         Alfalfa cultivar

                                     Grazing tolerant                         Hay-type                                Significancea
               Smooth
Item         bromegrass      Season        Complementary            Season       Complementary     SEM        f            s          a

                                                                     June
IVDMD           56.7          64.2               56.0                61.9             58.7         1.61     >0.10         0.02       >0.10
CP              17.6          21.1               16.7                21.2             17.5         1.64     >0.10         0.07       >0.10
INDF            17.8          13.0               19.9                14.4             16.8         1.25     >0.10         0.02       >0.10
NDF             47.7          33.3               49.7                36.4             45.1         2.45      0.07        <0.01       >0.10
ADF             28.2          23.0               29.9                25.0             28.3         0.95     >0.10        <0.01       >0.10
                                                                    August
IVDMD           61.2]         64.2               61.3                65.0             62.3         1.90     >0.10        >0.10       >0.10
CP              14.4          14.8               15.8                15.6             16.1         1.44     >0.10        >0.10       >0.10
INDF            16.6          12.6               15.4                12.6             14.4         1.85     >0.10        >0.10       >0.10
NDF             45.3          47.0               45.5                46.2             45.7         2.07     >0.10        >0.10       >0.10
ADF             26.4          26.4               26.3                26.4             26.3         0.90     >0.10        >0.10       >0.10
  a
   Orthogonal comparisons: f = season-long smooth bromegrass treatment vs all alfalfa treatments; s = season-long alfalfa stocking vs
complementary alfalfa stocking; and a = hay-type alfalfa vs grazing tolerant alfalfa.

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                                                          Alfalfa grazing by beef cows                                                 777
  Table 4. Mean selection indicesa of fistulated steers grazing alfalfa/smooth bromegrass and smooth bromegrass
                      pastures in season-long and complementary systems in 1998 and 1999
                                                          Alfalfa cultivar

                                       Grazing tolerant                        Hay-type                                Significanceb
               Smooth
Item         bromegrass        Season        Complementary           Season       Complementary      SEM          f          s          a

                                                                      June
IVDMD            1.19           1.27               1.20               1.22              1.29         0.039     >0.10       >0.10      >0.10
CP               1.37           1.56               1.25               1.48              1.70         0.085     >0.10       >0.10       0.09
INDF             0.52           0.41               0.54               0.45              0.46         0.033     >0.10        0.09      >0.10
NDF              0.80           0.61               0.81               0.67              0.73         0.022      0.02       <0.01      >0.10
ADF              0.82           0.64               0.81               0.69              0.75         0.034      0.06        0.03      >0.10
                                                                     August
IVDMD            1.28           1.21               1.25               1.29              1.30         0.061     >0.10       >0.10      >0.10
CP               1.27           1.14               1.36               1.10              1.30         0.079     >0.10        0.06      >0.10
INDF             0.52           0.50               0.51               0.46              0.45         0.051     >0.10       >0.10      >0.10
NDF              0.76           0.83               0.77               0.84              0.80         0.033     >0.10       >0.10      >0.10
ADF              0.76           0.80               0.74               0.77              0.75         0.031     >0.10       >0.10      >0.10
   a
    Selection index is the ratio of the component’s concentration in masticate of fistulated steers to the component’s concentration in hand-
clipped pasture forage samples.
   b
    Orthogonal comparisons: f = season-long smooth bromegrass treatment vs all alfalfa treatments; s = season-long alfalfa stocking vs
complementary alfalfa stocking; and a = hay-type alfalfa vs grazing tolerant alfalfa.




grass stocking (treatment × month, P < 0.05). The differ-                       In yr 1 and 2, mean DMI across treatments were 16.0
ences in composition between months reflect the areas                         and 19.0, expressed as kg/d (P = 0.06), and 2.60 and
of the fields that were grazed by cattle in the comple-                       3.38, expressed as a percentage of BW (P < 0.01; Table
mentary system. In June, cattle only grazed those areas                      5). There were no treatment or month effects on DMI.
of the pastures planted in smooth bromegrass. In Au-                         The lack of treatment differences may have been related
gust of yr 1, however, cattle grazing in one replicate of                    to our strip-stocking system that provided a daily live
the complementary stocking hay-type alfalfa system                           forage allowance of 7% of the cows’ BW. In contrast to
grazed in a smooth bromegrass paddock while the cattle                       previous studies (Baker et al., 1981; Forbes and Cole-
in the other replicate grazed in an alfalfa-smooth                           man, 1993), DMI by grazing cattle was not significantly
bromegrass mixture during the selection study. Simi-                         related to herbage mass. Furthermore, DMI was not
larly, in August of yr 2, cattle grazing in one replicate                    related to sward height. However, in linear regressions,
of the complementary stocking grazing-tolerant alfalfa                       DMI increased (P < 0.01) with increasing IVDMD con-
system grazed in a smooth bromegrass paddock during                          centration of the masticate of fistulated steers (DMI, %
the selection study.                                                         BW = −4.15 + 0.12x; r2 = 0.21) and decreased (P < 0.01)
   Apparently because of the greater mass and lower                          with increasing indigestible NDF concentration in the
IVDMD concentrations of available forage in yr 1 than                        masticate of fistulated steers (DMI, % BW = 4.97 −0.13x;
in yr 2, the mean selection index by grazing steers for                      r2 = 0.21).
IVDMD was greater (P = 0.02) in yr 1 than in yr 2 (1.29                         Intakes of IVDMD, as a percentage of BW, in cows
vs 1.21). Similarly, steers were more selective against                      grazing the alfalfa treatments were greater (P = 0.08)
indigestible NDF (P = 0.07), NDF (P = 0.09), and ADF                         than cows grazing season-long smooth bromegrass pas-
(P < 0.01) in yr 1 (0.46, 0.75, and 0.72) than in yr 2                       tures in June (1.79 vs 1.41). Intakes of CP were greater
(0.50, 0.78, and 0.79). In both years, steers were more                      (P = 0.07) and intakes of total (P = 0.03) and indigestible
selective for CP (P < 0.01; 1.53 vs 1.47) but less selective                 NDF (P = 0.06) were lower in June in cows grazing in
against NDF (P < 0.01; 0.80 vs 0.75) in August than in                       the season-long alfalfa system than cows grazing in the
June. In both years, there were no treatment differ-                         complementary alfalfa system.
ences in mean selection indices. Steers grazing pastures
with season-long alfalfa stocking and the complemen-                                               Discussion
tary stocking of the hay-type alfalfa cultivar were more
selective for CP in June than in August (1.58 vs 1.18,                         In this experiment, incorporating alfalfa with smooth
treatment × month, P = 0.03). In contrast, steers grazing                    bromegrass into pastures resulted in 17.8% greater calf
pastures with season-long alfalfa stocking and comple-                       production per hectare than N-fertilized smooth brome-
mentary stocking of the hay-type alfalfa cultivar were                       grass. This is slightly greater than the average 15%
more selective for NDF (treatment × month, P < 0.01)                         increase in animal production from legume-grass pas-
and ADF (treatment × month, P = 0.03) in August than                         tures reported in a review by Burns and Standaert
in June (0.82 and 0.77 vs 0.67 and 0.69).                                    (1985). The improvements in calf production was re-

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778                                                           Hermann et al.

       Table 5. Mean intakes of DM and its components, as a percentage of BW, in cows grazing alfalfa/smooth
       bromegrass and smooth bromegrass pastures in season-long and complementary systems in 1998 and 1999
                                                        Alfalfa cultivar

                                     Grazing tolerant                        Hay-type                               Significanceb
               Smooth
Item         bromegrass      Season        Complementary           Season       Complementary      SEM        f          s          a

                                                                    June
DM              2.51          3.25               2.74               2.84              3.06         0.309    >0.10      >0.10       >0.10
IVDMD           1.41          2.08               1.52               1.76              1.80         0.146     0.08      >0.10       >0.10
CP              0.43          0.69               0.46               0.60              0.53         0.059    >0.10       0.07       >0.10
INDF            0.45          0.42               0.54               0.41              0.51         0.044    >0.10       0.06       >0.10
NDF             1.21          1.08               1.35               1.04              1.38         0.090    >0.10       0.03       >0.10
ADF             0.71          0.74               0.82               0.71              0.87         0.057    >0.10      >0.10       >0.10
                                                                   August
DM              3.08          3.01               2.55               3.79              3.08         0.362    >0.10      >0.10       >0.10
IVDMD           1.89          1.94               1.57               2.47              1.91         0.288    >0.10      >0.10       >0.10
CP              0.44          0.45               0.39               0.59              0.50         0.063    >0.10      >0.10       >0.10
INDF            0.50          0.37               0.39               0.48              0.44         0.029     0.08      >0.10        0.05
NDF             1.39          1.40               1.17               1.75              1.40         0.180    >0.10      >0.10       >0.10
ADF             0.81          0.79               0.67               1.00              0.81         0.092    >0.10      >0.10       >0.10
  a
   Orthogonal comparisons: f = season-long smooth bromegrass treatment vs all alfalfa treatments; s = season-long alfalfa stocking vs
complementary alfalfa stocking; and a = hay-type alfalfa vs grazing tolerant alfalfa.



lated to greater intakes of IVDMD and CP in June and                       igraze’ has been identified as a grazing-tolerant alfalfa
lower proportions of dead forage and greater concentra-                    that is more resistant to excessively cold temperatures
tions of IVDMD in the total forage late in the grazing                     and moist conditions than ‘Alfagraze’ (Brummer and
season in alfalfa-grass pastures. One limitation to the                    Moore, 2000). Over the 120-d grazing season in yr 1 of
utilization of alfalfa in grazing systems, however, is                     this experiment, the proportions of alfalfa in the live
poor alfalfa persistence. In this experiment, the mean                     DM of pastures containing the grazing-tolerant and
proportion of alfalfa in the live forage in May decreased                  hay-type alfalfa cultivars decreased by 70 and 55% in
from 84% before grazing in 1998 to 35% in 2000 in                          paddocks that were stocked for the full season and by
paddocks grazed for the full season in 2 yr.                               60 and 42% in paddocks grazed in mid- to late season.
   Alfalfa persistence in paddocks grazed during the full                  In yr 2, however, the proportions of alfalfa in the live
season may have been adversely affected by heavy June                      DM decreased by 72% over the 141-d grazing season
rainfall and animal trampling (Whitear et al., 1962;                       across the two cultivars. Furthermore, initial pasture
Wilman, 1977; Hutchinson et al., 1995). In this experi-                    forage samples taken in May of yr 3 were not different
ment, deferring grazing of alfalfa in a complementary                      in alfalfa proportions in the live DM between alfalfa
system until mid- to late season resulted in greater                       cultivars. Thus, when expressed as a proportion of live
legume persistence than season-long alfalfa grazing as                     DM, there was little difference in persistence of the two
defined by the proportion of alfalfa in the live DM.                        alfalfa cultivars when grazed either during the full-
Paddocks grazed in mid- to late season were allowed                        season or during mid- to late season. Similarly, the use
minimum regrowth periods of 30 d after a first-cutting                      of the grazing-tolerant alfalfa cultivar did not improve
hay harvest before grazing was begun that may have                         forage production, forage nutritional value, or animal
assisted in persistence (Van Keuren and Matches,                           production compared with the hay-type cultivar.
1988). The mean number of rest days for paddocks in-                          In conclusion, complementary stocking of alfalfa-
corporated into the grazing systems were 24.8 and 25.4                     smooth bromegrass pastures after a first-cutting hay
in yr 1 and 2. Furthermore, complementary grazing of                       harvest resulted in improved alfalfa persistence in pas-
alfalfa resulted in 6% lower calf production than season-                  tures and small decreases in calf production compared
long alfalfa grazing, but still resulted in 11% greater                    with season-long alfalfa stocking. Incorporation of the
calf production than season-long grazing of N-fertilized                   grazing-tolerant alfalfa cultivar, Amerigraze, into
smooth bromegrass. This result is likely associated with                   smooth bromegrass pastures did not improve calf pro-
the greater total herbage mass and IVDMD concentra-                        duction or legume persistence compared with the hay-
tion of alfalfa in mid- to late season than the cool season                type alfalfa cultivar, Affinity.
grass, smooth bromegrass.
   Grazing-tolerant alfalfa cultivars such as ‘Alfagraze’                                        Implications
have yields comparable to hay-type cultivars and per-
sist even when continuously grazed in mixed stands                           The results of this experiment indicate that the incor-
(Brummer and Bouton, 1991; Smith et al., 1992). ‘Amer-                     poration of alfalfa into smooth bromegrass pastures

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                                                                                 rainfall, moisture stress, and stocking rate on the persistence
greater body weight and condition score increases of
                                                                                 of white clover over 30 years. Aust. J. Exp. Agric. 35:1039–1047.
cows. There is little difference in alfalfa persistence                     Majak, W., J. W. Hall, and W. P. McCaughey. 1995. Pasture manage-
from grazing systems between the hay-type alfalfa cul-                           ment strategies for reducing the risk of legume bloat in cattle.
tivar, Affinity, and a cultivar bred for grazing tolerance,                       J. Anim. Sci. 73:1493–1498.
Amerigraze. However, cow-calf production was greater                        Marten, G. C., and R. F. Barnes. 1979. Prediction of energy digestibil-
                                                                                 ity of forages with in vitro rumen fermentation and fungal en-
from grazing systems seeded with the hay-type alfalfa
                                                                                 zyme systems. In: Proc. Int. Workshop Standardization of Ana-
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