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                  G. H. KIRACOFE

                     J ANIM SCI 1980, 51:16-28.

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               U T E R I N E I N V O L U T I O N : I T S R O L E IN R E G U L A T I N G
                                 POSTPARTUM INTERVALS                    1

                                          G. H, K I R A C O F E
                            Kansas State University, Manhattan           66506

                   Summary                                Uterine size has not been a good indicator
                                                       of subsequent fertility, but more subtle ana-
AN involuting uterus is a temporary barrier to
                                                       tomical changes may continue well beyond the
fertility in cows, ewes and sows. Parturition is
                                                       dramatic changes in size noted shortly after
followed by a period when conception is not
                                                       parturition. Subsequent fertility is impaired
possible: about 1 week in sows and about 3
                                                       when uterine involution is complicated by
weeks in cows and ewes. Estrus and ovulation
                                                       pathological conditions induced by dystocia,
seldom occur together during this period and,
                                                       retained fetal membranes, metritis or other
if fertilization occurred and the embryo
                                                       disorders. However, whether these factors di-
reached the uterus, placentation would be vir-
                                                       rectly affect postpartum endocrinology or re-
tually impossible. T h e period of no fertility is
                                                       duce fertility by providing an improper milieu
followed by 2 to 3 weeks when fertility is
                                                       for spermatozoa and embryos has not been
possible, but not optimal. T h e extent to which
                                                       established. Lack of a precise definition of
the involuting uterus contributes to infertility
                                                       uterine involution prevents direct comparisons
during the second period is difficult to deter-
                                                       of many data. Despite voluminous data con-
mine. Embryonic mortality in sows bred dur-
                                                       cerning uterine involution and postpartum
ing this latter period appears to be a major
                                                       fertility, specific studies correlating the two
cause of reduced litter size, so changes in
                                                       are lacking.
uterine environment associated with involution
may be essential for optimum fertility. Con-              This review describes normal processes of
ception rate is lower up to 4 0 days after par-        uterine involution in cows, ewes and sows.
turition than later in cows and ewes. Uterine          Factors related to normal uterine involution
involution appears not to be a barrier to ferti-       are considered to determine if the uterus limits
lity after 3 to 4 weeks postpartum in sows or          postpartum fertility.
5 to 6 weeks postpartum in cows and ewes
                                                                             Bovine Species
unless delayed b y inflammation or infection.
 (Key Words: Uterine Involution, Postpartum               The Process of Uterine Involution. Before
Intervals, Postpartum Conception, Short Es-            1950, postpartum changes in the bovine uterus
trous Cycles, Cattle, Sheep, Swine.)                   received little attention. Studies were limited
                                                       primarily to pathological situations and to pal-
                  Introduction                         pation per rectum to determine uterine size,
   Processes involved in the return of the post-       tone and positional changes; a few uterine
partum uterus to a state capable of support-           weights and measures were recorded. Pioneer-
ing another conceptus after parturition are            ing studies included those of Hilty ( 1 9 0 8 ) ,
complex and the interrelationship of the uterus        Boyd ( 1 9 2 5 ) , Casida and Venzke ( 1 9 3 6 ) and
with the ovaries is not understood. That the           Casida and Wisnicky ( 1 9 5 0 ) . Rasbeck ( 1 9 5 0 )
time required for uterine involution limits post-      reviewed much of the early research and later
partum fertility under current livestock man-          reviews on uterine involution were done by
agement systems is questionable. Considering           Casida et al. ( 1 9 6 8 ) , Morrow et al. ( 1 9 6 9 )
only the basics of normal uterine involution,          and Moller ( 1 9 7 0 a ) .
the uterus rarely is unprepared for pregnancy             Since 1950, regression of uterine size, fac-
when ovulation and estrus occur together, fer-         tors affecting postcalving uterine changes, and
tilization has taken place, and the embryo is          descriptions of tissue sloughing, vascular
ready for placentation.                                changes and tissue regeneration have been re-
                                                       ported. T h e complexity of the involutionary
    Contribution 79-379-J, Dept. of Animal Sci-        process and the difficulty in determining ex-
ences and Industry, Kansas Agr. Exp. Sta., Man-
                                                       actly when uterine involution is complete has

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                  U T E R I N E I N V O L U T I O N AND P O S T P A R T U M   INTERVALS                   17

made comparison of data among investigators              which occurred during the first day postcalv-
difficult. Conditions that signify complete uter-        ing, receded b y day 8. Rasbeck ( 1 9 5 0 ) , Gier
ine involution are nebulous. Casida et al.               and Marion ( 1 9 6 8 ) and Wagner and Hansel
 ( 1 9 6 8 ) defined uterine involution as complete       ( 1 9 6 9 ) described sloughing and regenerative
when the uterus returned to its normal non-              changes in histological preparations from ex-
pregnant position and when the two horns                 cised uteri at various times postpartum. J o -
were similar in diameter and showed normal               hanns et al. ( 1 9 6 7 ) , through radiographic stu-
consistency and tonus. Palpation estimates dif-          dies of postpartum uteri, showed degenerative
fer widely because of methods used to mea-               changes in the epithelium as well as changes
sure the uterus and inherent variation among             in the circulatory system.
individuals. Gier and Marion ( 1 9 6 8 ) reasoned             Morrow ( 1 9 6 9 ) reported that the caruncular
that a variety of histological and physical              stalk disappears, the superficial layer of the
changes must take place in the uterus before             caruncle dissolves and uterine lochia form.
involution could be termed complete. They de-            T h e bulk of the caruncle had dissolved by 10
scribed uterine involution as having three over-         days after calving. Johanns et al. ( 1 9 6 7 ) de-
lapping processes: ( 1 ) reduction in size, ( 2 )        scribed constriction of the caruncular arteries
loss of tissue, and ( 3 ) repair.                        and decreasing caruncular blood supply dur-
    Reduction in Size. Estimates of the time re-         ing these 10 days. Endometrial changes re-
quired for complete reduction of uterine size            sulting in edema, then regression and folding,
after calving range from 18 (Rasbeck, 1 9 5 0 )          and a general "stalked" appearance of the car-
to 5 6 days (Wiltbank and Cook, 1 9 5 8 ) . Esti-        uncle were described by Rasbeck ( 1 9 5 0 ) and
mated intervals from parturition to complete             Gier and Marion ( 1 9 6 8 ) . Sloughing of the
uterine involution, ovulation and estrus for             necrotic tissue progressed to an extent that
various breeds are listed in table 1. Palpable           material of the caruncle came off in chunks
changes in uterine size, tone and position af-           b y day 5 and most of the necrotic layer was
ter calving were described by Rasbeck ( 1 9 5 0 ) ,      gone by 10 days. By 15 days all of the car-
Buch et al. ( 1 9 5 5 ) , Morrow et al. ( 1 9 6 6 ) ,    uncular mass involved in the placentome was
Bhalla et al. ( 1 9 6 6 ) , Moller ( 1 9 7 0 b ) , Mo-   sloughed, and by day 19 the arterioles within
hamed ( 1 9 7 4 ) and El-Fouly et al. ( 1 9 7 6 ) .      and beyond the stratum compactum had dis-
    Early reduction of uterine size after calving        appeared leaving the caruncles relatively
results from vasoconstriction (Morrow, 1 9 6 9 )         smooth (Gier and Marion, 1 9 6 8 ) . T h e deci-
and peristaltic contractions that persist for sev-       duum of the caruncle sloughed just basal to the
eral days (Jordan, 1952; Venable and McDon-              crypts and regeneration of the epithelium oc-
ald, 1 9 5 8 ) . Weight and size of the uterus           curred from the margin of the slough (Wag-
after calving decrease in similar patterns.              ner and Hansel, 1 9 6 9 ) .
Riesen ( 1 9 6 8 ) and Gier and Marion ( 1 9 6 8 ) ,         Repair. Several descriptions of tissue repair
who weighed uteri from cows after calving,               have been reported. T h e intercaruncular areas
reported the uterine weight at calving was ap-           never were devoid of epithelium, and both
proximately 9 kg and was reduced to approxi-             degenerative and regenerative epithelial cells
mately 3 kg by 10 days, to 1 kg by 20 to                 were observed in the intercaruncular areas
3 0 days and to 7 5 0 g by 5 0 days postpartum.          before day 15, but after day 15 no degenera-
Fluid is present in the uterus after calving             tive cells were observed (Archbald et al,
 (Johanns et al, 1967; Gier and Marion, 1 9 6 8 ;        1 9 7 2 ) . Epithelium was reestablished over the
Morrow, 1969; Morrow et al, 1 9 6 9 ) . T h e            caruncle 9 to 2 0 days after parturition (Arch-
maximum amount of lochia ( 1 , 0 0 0 to 1,600            bald et al, 1972; Rasbeck, 1950; Roberts,
m l ) is present during the first 4 8 hr and then        1 9 5 6 ) . Gier and Marion ( 1 9 6 8 ) found that
decreases to 4 0 0 to 100 ml by day 8 and                epithelial regeneration was not complete b e -
is absent by 14 to 24 days postpartum.                   fore day 2 5 ; or for at least 10 days after
   Loss of Tissue. Gier and Marion ( 1 9 6 8 ) de-       sloughing had ceased. Caruncle sites were
scribed early uterine changes. Shedding of fetal         covered with epithelium b y postpartum days
membranes appeared to be associated with                 10 to 2 0 in the previously nongravid horn,
peristaltic muscular contractions. Reduction in          but not until 20 to 3 0 days in the horn which
uterine size progressed in a negative logarith-          had been gravid (Riesen, 1 9 6 8 ) .
mic manner so that the postgravid horn dia-                  Gier and Marion ( 1 9 6 8 ) considered involu-
meter decreased by 50% by day 5 . Loss of                tion to be complete and the uterus to be
tissue fluids appeared to be a major factor in           restored to a cycling condition by 4 0 to 6 0
early size reduction. Endometrial edema,                 days when the caruncle had regressed to a
18                                               KIRACOFE

smooth, oblong, epithelial covered, avascular             T h e net effect of nutrition on uterine involu-
knob. Caruncles which had been in the proxi-              tion appeared to be minimal in the absence of
mity of the fetus required the longest interval           specific deficiencies.
to return to normal. Obviously, involution con-              A remarkable feature of uterine involution
tinues past the time that uterine regression is           in the rat is the loss of collagen (Harkness and
detectable by palpation, but the degree of                Harkness, 1954; Harkness and Moralee, 1956;
involution required to support another preg-              Woessner, 1 9 6 9 ) ; 85% of the total collagen of
nancy has not been established.                           the term uterus was removed in the first 4
    Many factors delay the normal process of              days postpartum. Similar research with large
involution: uterine infections, retained fetal            animals on this aspect of involution is lacking.
membranes (Boyd, 1 9 2 5 ; Rasbeck, 1950; Buch            Since relaxin can induce breakdown of col-
et al, 1 9 5 5 ; Norwood, 1 9 6 3 ; Gier and Marion,      lagen in some circumstances (Frieden and
1 9 6 8 ; Marion et al., 1968; Tennant and Peddi-         Hisaw, 1 9 5 3 ) , it would be of interest to deter-
cord, 1 9 6 8 ; Morrow, 1 9 6 9 ) and other peri-         mine if relaxin plays a role in uterine involu-
parturient diseases (see reviews by Morrow                tion. Kiracofe et al ( 1 9 7 3 a ) did not alter the
et al, 1969; Moller, 1 9 7 0 a ) .                        involution rate in postpartum cows by intra-
    Factors Influencing the Time to Involution.           uterine infusion of collagenase. Treating the
Suckling, in contrast to nonsuckling, has been            uterus with enzymes, antibiotics or antibac-
reported to promote uterine involution (Casida            terial compounds failed to hasten uterine in-
et al., 1 9 6 8 ; Riesen, 1 9 6 8 ) , delay uterine in-   volution, but they frequently prolonged the
volution (Wiltank and Cook, 1 9 5 8 ) or have             time to involution (Homan, 1969; Kiracofe
little effect on the rate of uterine involution           et al, 1973b; Oxender and Seguin, 1976; Se-
 (Wagner and Hansel, 1969; Moller, 1970b;                 guin et al, 1 9 7 4 ) .
Oxenreider and Wagner, 1 9 7 1 ; El-Fouly et al.,              A profound effect on the size of the post-
1 9 7 6 ) . However, limited or no suckling has-          partum uterus resulted from injecting cows
tens resumption of estrous cycles (Wiltbank               with GnRH (gonadotropin releasing hormone)
and Cook, 1 9 5 8 ; Moller, 1970b; Oxenreider             14 days after calving (Britt et al, 1974a;
and Wagner, 1 9 7 1 ; Short et al., 1972; Randel          Fernandes et al, 1 9 7 8 ) . T h e GnRH accele-
and Welker, 1977; Radford et al, 1 9 7 8 ; Wet-           rated reduction in uterine size between 14 and
temann et al., 1 9 7 8 ) .                                24 days postpartum. No beneficial effect on
   Generally, uterine involution takes a few              conception was associated with decreased
days longer in pluriparous cows than in primi-            uterine size after GnRH. An increase in serum
parous cows (Rasbeck, 1 9 5 0 ; Buch et al., 1 9 5 5 ;    progesterone concentrations after GnRH, noted
Quevedo et al, 1 9 6 5 ; Morrow et al, 1966;              by Fernandes et al. ( 1 9 7 8 ) , may have ac-
Marion and Gier, 1 9 6 8 ; Araujo et al, 1 9 7 4 ) .      celerated uterine involution by affecting uter-
However, Tennant et al. ( 1 9 6 7 ) and El-Fouly          ine blood flow and water imbibition. Riek et al.
et al. ( 1 9 7 6 ) reported that age or number of          ( 1 9 7 7 ) showed that GnRH partially syn-
previous pregnancies had no effect on involu-             chronized cows in the early puerperium, but the
tion. Several investigators have reported sea-            condition of the postpartum uterus appeared
sonal effects on rate of uterine involution.              to affect the ability of GnRH to initiate cyclic
Norwood ( 1 9 6 3 ) , Marion et al. ( 1 9 6 8 ) , El-     progesterone production. Other postpartum
Fouly et al. ( 1 9 7 6 ) and Gospodinov and Ros-          hormone treatments have hastened onset of
tov ( 1 9 7 6 ) found slower involution in the            estrous cycles and subsequent conception.
fall than in the spring.                                  Shorter intervals from calving to conception
                                                          after administration of progesterone or syn-
   Energy and protein level of the diet only
                                                          thetic progestogens during the postpartum
slightly affect the rate of uterine involution
                                                          period have been reported by Fosgate et al.
but drastically affect the interval from par-
                                                           ( 1 9 6 2 ) , Norwood ( 1 9 6 3 ) , Foote and Hunter
turition to resumption of estrous cycles (Wilt-
                                                           ( 1 9 6 4 ) , Saiduddin et al. ( 1 9 6 8 ) , Boyd
bank et al, 1962; Dunn et al., 1969; Clemente
                                                           ( 1 9 7 0 ) , Britt et al ( 1 9 7 2 ) , Huertas-Vega et
et al, 1 9 7 8 ) . Uteri of cows fed high energy
                                                          al. ( 1 9 7 2 ) and Britt et al. ( 1 9 7 4 b ) . Likewise,
diets after calving involuted 3 days sooner than
                                                          Casida and Wisnicky                  (1950),     Norwood
uteri of cows fed moderate energy diets, and
                                                           ( 1 9 6 3 ) , Ulberg and Lindley ( 1 9 6 0 ) , Foote
uteri of Angus cows involuted 3 days sooner
                                                          and Hunter ( 1 9 6 4 ) and Brown et al. ( 1 9 7 2 )
than uteri of Hereford cows (Dunn, 1 9 6 4 ) .
                                                          reported some beneficial results with either
Kiracofe et al. ( 1 9 6 9 ) found no significant
                                                          estrogens or synthetic estrogens alone or in
difference in uterine involution rates in cows
                                                          combination with progestogens. However, ef-
fed low or high levels of energy or protein.
                 UTERINE INVOLUTION AND POSTPARTUM                            INTERVALS                      19

fects of exogenous steriods on conception vary            ( 1 9 6 8 ) showed uterine involution time was
widely and the beneficial effects of exogenous           unaltered in ovariectomized cows. When beef
steriods cannot be related to hastened uterine           heifers were subjected to hypophysial stalk
involution. Marion et al. ( 1 9 6 8 ) showed that        transection in middle or late pregnancy, preg-
progesterone actually lengthened the period              nancy was maintained and live calves were
of uterine involution. Therefore, if exogenous           born, and then the uterus involuted to a size
steriod hormones prove beneficial to postpar-            similar to that of a prepuberal heifer (Ander-
tum conception, it is unlikely that success will         son et al, 1 9 7 9 ) . Cows can conceive before
be attributed to an effect on uterine involution.        uterine involution would b e expected to have
    The postpartum uterus contains many types            been complete (Buch et al, 1 9 5 5 ; Perkins and
of bacteria (Dawson, 1950; Wulf and Dracy,               Kidder, 1 9 6 3 ; Moller, 1 9 7 0 a ; Odde and Kira-
1952; Lindley, 1954; Gunter et al, 1 9 5 5 ;             cofe, 1 9 7 8 ) . Olds and Cooper ( 1 9 7 0 ) found
Eliot et al, 1 9 6 8 ; Griffin et al, 1 9 7 4 ; Studer   no difference in conception rates of dairy cows
and Morrow, 1 9 7 8 ) . Bacteria of the early post-      bred 4 0 to 6 0 days postpartum and those bred
partum uterus do not appear to affect involu-            later, although uterine involution would not
tion rate and may or may not b e associated              be complete in all cows by day 4 0 . Tudorascu
with subsequent fertility (Graden et al., 1 9 6 8 ;       ( 1 9 6 9 ) and Casida et al, ( 1 9 6 8 ) found no
Fuquay et al, 1 9 7 5 ) . Kiracofe et al ( 1 9 7 3 a )   relationship between the postpartum interval
showed no effect on uterine involution and               to breeding and embryonic mortality in ani-
fertility from innoculating the early postpar-           mals bred after day 3 0 postpartum. Concep-
tum uterus with lactobacillus        acidophilus.        tion rates appear to b e rather low at less than
    Involution and Resumption of Cycles. F e w           3 0 days postpartum (Olds et al., 1949; Van
direct relationships can be made between the             Demark and Salisbury, 1950; Norwood, 1 9 6 3 ;
rate of uterine involution and subsequent fer-           Perkins and Kidder, 1 9 6 3 ; Odde and Kiracofe,
tility. Albrechtsen ( 1 9 1 7 ) found that if uter-      1 9 7 8 ; also see review by Casida et al., 1 9 6 8 ) .
ine involution required more than 4 weeks the            Perkins and Kidder ( 1 9 6 3 ) reported concep-
onset of first estrus was delayed. However,              tion rate to be unaffected b y involutionary
Buch et al. ( 1 9 5 5 ) found only a slight associa-     state after directly comparing conception rates
tion between interval to first estrus and degree         of cows in which uterine involution was com-
of uterine involution. Other researchers have            plete and cows in which uterine involution
found no relationship between uterine involu-            was not complete.
tion and interval from calving to first estrus or             Another approach to determine factors lim-
conception of clinically normal cows (Foote              iting early postpartum conception is to induce
et al, 1960a; Perkins and Kidder, 1963; Dunn,            ovulation and inseminate at various postpar-
1964; Tennant and Peddicord, 1 9 6 8 ; Kiracofe          tum intervals. Henderson ( 1 9 7 8 ) bred cows
et al, 1 9 6 9 ) .                                       after progestogen and estrogen treatment ( a
    Some conditions can delay uterine involu-            6 mg norgestomet implant for 9 days and an

tion, resumption of cycling and conception               injection of 6 mg estradiol valerate and 3 mg
 (see review by Morrow, 1969; Studer and Mor-            norgestomet at the time of implanting). Con-
row, 1 9 7 8 ) . An abnormal uterus may delay            ception rates did not differ among cows bred
follicle development and ovulation, but it is            less than 4 2 days postpartum and those bred
doubtful that a normal involuting uterus plays           later. Further attempts to breed cattle or trans-
a role in reestablishing estrous cycles. Pituitary       fer fertilized ova at specific postpartum inter-
gonadotropin content was not altered in cows             vals and relate pregnancy maintenance to the
hysterectomized within 2 4 hr after calving              degree of involution at the time of insemina-
 (Foote, 1 9 7 1 ) . Vital information in regard to      tion or transfer are needed.
the role of the uterus in initiating postpartum              Follicular activity begins soon after parturi-
estrous cycles might be obtained by observing            tion (Morrow, 1969; Wagner and Hansel,
the intervals to ovulation and estrus in cows            1969; Moller, 1 9 7 0 b ) . T h e corpus luteum of
hysterectomized at calving. It had been pro-             pregnancy is palpable for about 2 weeks post-
posed that the corpus luteum of pregnancy                partum but does not prevent follicular develop-
might delay the onset of the first postpartum            ment (Moller, 1970b; Wagner and Hansel,
estrus (McNutt, 1 9 2 7 ) ; however, Morrow              1 9 6 9 ) . Small corpora lutea, similar in size to
( 1 9 6 9 ) showed that the corpus luteum of
pregnancy is nonfunctional after parturition.              3
                                                             Progestogen (17a acetoxy — 11/3 methyl —
Apparently the ovaries do not affect the rate            19 norpreg — 4 — ene — 3, 20 — dione) used
                                                         in the Syncro-Mate B treatment of G. D. Searle
of uterine involution because Marion et al.              and Co.
 20                                            KIRACOFE
  follicles during the first 3 weeks postpartum,       dairy cows than in beef cows; however, this
  occasionally are huried in the ovarian stroma        difference has not been studied independent
   (Moller, 1970b). Moller (1970b) suggested           of nutritional level. Many dairy cows have an
  that the early developing small corpora lutea        ovulation without estrus before their first overt
  were inactive and speculated that ovulations         estrus (Morrow et ol., 1966; Marion and Cier,
  leading to their formation were infertile.           1968; Callahan et al., 1971; Whitmore et al.,
     Evidence indicates that the postpartum uter-      1974). In both beef and dairy cows, the corpus
 us may influence ovulation. A high percentage         luteum resulting from the first ovulation has
  of ovulations in the first 20 days postpartum       a short life span (Menge et al., 1962; Morrow,
 occurs on the ovary opposite the previously           1969; Kiracofe et al., 1969). Perhaps the in-
  gravid hom (Saiduddin et ol., 1967; Foote and       voluting uterus could affect both the ovula-
 Peterson, 1968; Kiracofe et al., 1969); how-         tory pattern (i.e., which ovary is involved in
 ever, Wagner and Hansel (1969) were unable           ovulation) and the life span of the first corpus
 to confirm these observations. Ovulations            luteum after calving by a mechanism similar
 which occur on the ovary opposite the previ-         to that shown for uterine dilatation (Hansel
 ously gravid horn are more numerous in dairy         and Wagner, 1960). However, Ward et al.
 cows than in beef cows, and conception at             (1979) found that short cycles were frequent
 first service is lower if ovulation occurs on the    when calves were weaned from anestrous post-
 ovary ipsilateral to the previously gravid horn      partum cows as late as 68 days after calving
  (Foote and Peterson, 1968).                         when uterine involution should have been
    Table 1 lists estimates of the time required     completed.
 for uterine involution in early studies in which        Many attempts have been made to elucidate
breeds were identified and the time of first         ovarian function and reproductive hormone
ovulation and estrus were determined. The            levels prior to resumption of estrous cycles
average postpartum interval to the first ovula-      after calving. An increase in serum or blood
tion is less than that to the first estrus. Data     progesterone level occurs in postpartum cows
presented from these early studies indicated         before the first estrus (Donaldson et al., 1970;
first ovulation occurred from 35 to 60 days          Erb et al., 1971; Henricks et al., 1972; Hum-
postpartum. Other studies, especially with           phrey et al., 1976; Echtemkamp and Hansel,
dairy cows, have shown that ovulation oc-            1973; Tribble et al., 1973; Arije et al., 1974;
curred approximately 14 to 22 days postpar-          Corah et al., 1974; Prybil and Butler, 1978;
tum (Menge et al., 1962; Morrow et al., 1966;        LaVoie et al., 1980). LaVoie et al. (1980)
Marion and Cier, 1968; Callahan et al., 1971;        found that when data from cows that had an
Morrow, 1971; Whitmore et al., 1974). The            ovulation without estrus were removed, no cow
first postpartum ovulation occurs earlier in         had a cyclic luteal phase pattern of preestrus

                           FUNCTION IN THE BOVI~E SPECIES

                                                                   Days postpartum

                                                       Uterine           First            First
              Reference              Breed           invol ution       ovulation          estrus

Casida and Wisnicky (1950)         Holstein             28                35                63
Wiltbank and Cook (1958)          Shorthorn"            56                53                84
Wiltbank and Cook (1958)          Shorthorn"            44                36                M
Foote et al. (1960a)               Hereford             44                38                59
Foote et al. (1960b)                Angus               41                61                86
Foote et al. (1960b)              Shorthorn             43                62                76
Ulberg and Lindley (1960)          Hereford             46                38                46
Fosgate ei al. (1962)              Holstein             28                45                51
Fosgate et al. (1962)               Jersey              27                3.5               45
Foote and Hunter (1964)            Hereford             47                44                49
Foote and Saiduddin (1964)         Hereford             46                38                46
Saiduddin et al. (1968)            Hereford             46                38                46
                U T E R I N E I N V O L U T I O N AND P O S T P A R T U M   INTERVALS                    21

plasma progesterone, but all cows with normal         however, suckling intensity or milk removal
postpartum estrous cycles had a preestrus in-         appears to be the primary influence (Ward
crease in plasma progesterone level. T h e pro-       et al, 1 9 7 9 ) .
gesterone increase was not associated with a              Perhaps depressions in conception rate at
palpable corpus luteum. W a r d ( 1 9 7 8 ) demon-    the first postpartum estrus have been affected
strated that most postpartum anestrous cows           by formation of abnormal corpora lutea, failure
that were suckling a calf had a short estrous         to maintain luteal tissue and other factors
cycle (7 to 11 days) if they exhibited the first      rather than by delayed uterine involution. Un-
estrus within 12 days after the calf was weaned.      der normal conditions, the involuting uterus
It appeared that ovulation did occur, but the         appears to be a contributing factor to lowered
corpus luteum in most cases was not palpable          fertility for approximately 4 0 days postpartum.
during the short cycle and the corpus luteum          Lack of early large follicle development, ovula-
regressed before it was fully formed ( W a r d        tion in the absence of behavioral estrus, the
et al, 1 9 7 9 ) . Corpora lutea induced by G n R H   requirement of preestrus progesterone secre-
at 30 or 4 8 days postpartum in anestrous cows        tion to establish cycle patterns, failure of the
also had a short life span (Lishman et al.,           first ovulation to result in a normal corpus
1 9 7 9 ) . Cows with a short estrous cycle did       luteum and other factors may supercede the
not have a preestrus blood progesterone peak          effects of the involuting uterus. In dairy cat-
in data reported b y Corah et al ( 1 9 7 4 ) and      tle, in which ovulation frequently occurs be-
LaVoie et al. ( 1 9 8 0 ) . T h e preestrus blood     fore day 2 0 , uterine involution certainly could
progesterone measured by many researchers             contribute to infertility. However, a low per-
before the first postpartum estrus of a normal        centage of cows displays an estrus accompany-
cycle may have come from a corpus luteum              ing ovulation before day 2 0 and conception
formed from the first postpartum ovulation,           before uterine sloughing would be difficult.
since the first ovulation in lactating cows is        Once the uterine milieu returns to near the
sometimes unaccompanied by estrus and the             nonpregnant condition (i.e., relatively sterile,
resulting corpus luteum has a short life span         repaired, cleared of lochia, e t c . ) , there appears
 (Ward et al, 1 9 7 9 ) . A source of preestrus       to be no direct evidence that the uterus inter-
progesterone appears to be important to the           feres with conception. Unless complications
resumption of normal cycles; however, the             develop, the uterus is apparently repaired b y
source of this progeterone in the postpartum          4 0 days after calving.
cow has not been determined and may or may
not be different in postpartum cows and                                 Ovine Species
prepuberal heifers. T h e source of preestrus
                                                          Uterine Involution and Associated          Factors
progesterone in prepuberal heifers appears to
                                                      Affecting Fertility. Limited data are available
be from small stromal follicles that luteinized
                                                      on uterine involution in the ewe. However, the
 (Berardinelli et al, 1 9 7 8 ) . Connor et al.
                                                      process appears to be similar to that in the
 ( 1 9 7 4 ) postulated that luteinization of fol-
                                                      cow, in that necrotic tissue over the caruncle
licles may be necessary to initiate the first
                                                      was very loosely attached b y day 15 postpar-
postpartum estrus with ovulation, and others
                                                      tum and was sloughed b y day 2 0 to 2 5 (Uren,
have suggested that luteal function may be
                                                      1 9 3 5 ) . Kohl ( 1 9 7 1 ) found shrinkage in uter-
deficient during early estrous cycles (Short et
                                                      ine size relatively complete and necrotic tissue
al., 1972; Edgerton and Hafs, 1 9 7 3 ) .
                                                      absent from the uterus by 25 days. Epithelium
    Since the short life span of the first corpus     had also regenerated from the uterine glands
luteum occurs independent of the time post-           and intercaruncular areas. Caruncles were cov-
partum, uterine involution appears to have no         ered with epithelium by 2 5 to 3 0 days. In-
role in early regression of the first corpus          vestigators agree on description of involution
luteum unless a different mechanism is in-            processes and the time they occur. T h e uterus
volved during the early postpartum period             appears to be near its nonpregant state by 2 5
than is involved later. Lack of an overt estrus       days after lambing (Uren, 1 9 3 5 ; Foote et al,
at the first postpartum ovulation is related to       1967; Foote, 1 9 6 8 ; Hulet, 1968; Kohl, 1 9 7 1 ;
deficient ovarian function (Whitemore et al,          Jennings and Tisdall, 1974; Call et al, 1 9 7 6 ) .
1 9 7 4 ) . Nonstanding estrous behavior decreases       Time of first ovulation after lambing has
as the postpartum interval increases (Saidud-         not been adequately determined in the ewe.
din et al, 1968; LaVoie et al, 1 9 8 0 ) . Lack of    Thus, the role of the uterus in regulating the
uterine involution could be a factor in sup-          first postpartum ovulation is unknown. T h e
pressing ovarian function and, thus, estrus;          first postpartum ovulation usually is not as-
22                                           KIRACOFE

sociated with estrus (Call et al, 1 9 7 6 ; Hulet,    uterine weight remained fairly constant, ex-
1 9 7 9 ) . Estimates of the interval from lambing    cept that Svajgr et al ( 1 9 7 4 ) reported that
to ovulation have ranged from 18 days (Hulet,         involution time was slightly longer, with endo-
1 9 7 9 ) to approximately 3 5 days (Foote et         metrial repair essentially complete beween 13
al, 1967; Hunter and Lishman, 1 9 6 7 ) unless        and 17 days.
lambing occurred during seasonal anestrus. A               T h e number of muscle cells of the myo-
review of postpartum anestrous intervals and          metrium declines with involution, and muscle
factors that influence those intervals in ewes        cell size and amount of connective tissue de-
was reported by Hunter ( 1 9 6 8 ) . T h e average    creases (Graves et al., 1 9 6 7 ) . Palmer et al.
interval from lambing to first estrus was found        ( 1 9 6 5 b ) found that the uterine epithelium,
to b e 3 5 days (Hulet, 1 9 7 9 ) ; however, the      which is degenerated during the early post-
interval to conception was 44 days. Barker and        partum period, started regenerating 7 days
Wiggins ( 1 9 6 4 ) found the postpartum interval     postpartum and appeared complete by 2 1 days.
to conception to be about 8 0 days for Ram-           T h e uterus involutes more rapidly in the sow
bouillet and 5 5 days for Dorset ewes. T h e          than in the ewe or cow; the sow's lack of
single earliest postpartum conception reported        necrotic tissue to be sloughed appears to be
has been 9 days, but average time of concep-          the primary difference.
tion was greater than 4 0 days postpartum                  One cannot consider uterine involution and
 (Hulet, 1 9 6 8 ) .                                  its relation to postpartum fertility in the sow
    Suckling inhibits estrus (Shevah et al.,          without considering weaning effects. To deter-
1 9 7 5 ) and ovulation (Foote et al, 1 9 6 7 ) .     mine how quickly the uterus can support a
Since no difference in uterine involution rates       new pregnancy, one must eliminate the sup-
was found between lactating and nonlactating          pressing effect of suckling on the reproductive
ewes (Foote, 1 9 6 8 ) , the suckling effect on       endocrine system. Morphologically and his-
resumption of estrous cycles apparently was           tologically, uterine involution requires approxi-
not mediated through delayed uterine involu-          mately 3 weeks. In the sow, however, uterine
tion. Follicles larger than 3mm in diameter           size has decreased considerably and epithelial
began appearing on the ovaries after 10 days          repair is well underway by 1 week postpartum.
postpartum, and the number of follicles ex-           There is no evidence to suggest the extent of
ceeding 3mm remained constant after 14 or             repair or reduction in size required before
2 0 days postpartum (Kohl, 1 9 7 1 ) . B y 2 0 days   conception can occur in the postpartum sow.
postpartum, follicle growth and turnover were         According to Polge ( 1 9 7 2 ) , uterine involution
normal. Ovaries appear capable of responding          may not limit reproductive ability after par-
to gonadotropins relatively early postpartum          turition because blastocyst attachment does not
 (Hulet, 1 9 6 8 ) . However, the estrogen-induced    occur until 12 to 13 days after ovulation.
luteinizing-hormone-release mechanism appears              Hays et al. ( 1 9 7 8 ) found at 3 days post-
to recover relatively slowly after parturition        mating that ovulation rate, ova recovered and
 (Wright and Findlay, 1 9 7 7 ) .                     fertilization rate were not affected by length
   Seasonal anestrus has been a complicating          of lactation ( 6 , 12, 18, or 24 days). Generally,
factor in determining the influence of uterine        ovulation and fertilization rates have been
involution on early postpartum fertility. T h e       similar in sows bred before 2 1 days postpar-
uterus appears to be completely involuted b y         tum and those bred later (Baker et al, 1953;
30 to 3 5 days after lambing, and no direct evi-      Moody and Speer, 1 9 7 1 ; Svajgr et al., 1974;
dence is available to attribute low fertility         Rampacek, 1974; Varley and Cole, 1 9 7 6 ) . Far-
after lambing to a lack of involution of the          rowing rates were slightly lower in sows bred
uterus. Data concerning fertility at the first        after 6- and 12-day lactations than in sows
ovulation after lambing, a time when uterine          bred after 18- or 24-day lactations (Hays et
involution might be incomplete, is lacking.           al, 1 9 7 8 ) . Pay ( 1 9 7 3 ) and Svajgr et al.
                                                       ( 1 9 7 4 ) found that reductions in litter size
                Porcine Species                       were more pronounced when sows were
   Uterine Involution and Associated    Factors       weaned less than 7 days postpartum than in
Affecting  Fertility. Numerous investigators          those weaned later. Reduced litter size from
have reported similar decreases in uterine size       sows bred less than 3 weeks postpartum has
until 3 weeks after farrowing (Palmer et al.,         been attributed to increased embryonic loss
1965a,b; Graves et al, 1967; Smidt et al.,            by Varley and Cole ( 1 9 7 6 ) and Svajgr et al.
1969; Svajgr et al, 1974; Varley and Cole,             ( 1 9 7 4 ) . T h e involuting uterus may limit re-
1976; Hays et al, 1 9 7 8 ) . After 3 weeks,          productive efficiency if the sow is bred less
                  UTERINE INVOLUTION AND POSTPARTUM                           INTERVALS                    23

than 2 1 days postpartum. Embryo mortality                  histological study of the post partum bovine
                                                            uterus. J . Reprod. Fertil. 29:133.
rather than fertilization failure appears to
                                                          Arije, F. R., J . N. Wiltbank and M. L. Hopwood.
cause smaller litter size in sows bred early                1974. Hormone levels in pre- and post-parturient
postpartum. Hays et al. ( 1 9 7 8 ) concluded that          beef cows. J . Anini. Sci. 39:338.
weaning pigs when they are 1 8 days old re-               Baker, L. N., H. L. Woehling, L. E . Casida and
                                                            R. H. Grummer. 1953. Occurrence of estrus in
sults in maximum sow productivity in terms
                                                            sows following parturition. J . Anim. Sci. 12:33.
of the number of pigs produced per year.                  Barker, H. B. and E. L. Wiggins. 1964. Estrual
   Other data also indicate that weaning less               activity in lactating ewes. J . Anim. Sci. 23:973.
than 3 weeks after farrowing increases the in-            Berardinelli, J . G., R. L. Butcher and R. A. Daily.
                                                            1978. Source of progesterone prior to puberty
terval from weaning to estrus, reduces litter
                                                            in beef heifers. Beltsville Symp. in Agr. Res.
size, and increases both frequency of cystic                 (BARC) III. Anim. Reprod. (Abstr.).
follicles and embryo mortality (Baker et al.,             Bhalla, R. C , B. K. Soni and D. P. S. Sengai.
1953; Self and Grummer, 1 9 5 8 ; Smidt et al.,             1966. Studies on reproduction in Murrah buf-
1965; Moody et al, 1 9 6 9 ; Peters et al, 1969;            faloes. II. Involution of the uterus. Indian Vet.
                                                            J . 43:892.
van der Heyde, 1972; Cole et al., 1975; Hays              Boyd, W. L. 1925. A study of the physiological
et al, 1 9 7 8 ) .                                          and pathological changes occurring in the re-
   Attempts to accelerate normal postpartum                 productive organs of the cow following parturi-
uterine involution in the sow have been unsuc-              tion. Minnesota Agr. Exp. Sta. Bull. No. 23.
                                                          Boyd, L. J . 1970. Effects of feeding melengestrol
cessful. Hayes et al. ( 1 9 7 8 ) found no change           acetate (MGA) on occurrence of estrus fertility
in involution rate after administration of pro-             and milk yield in dairy cows. J . Anim. Sci. 3 1 :
staglandin or aspirin.                                      751.
   If uterine involution is a limiting factor in          Britt, J . H., E . Huertas-Vega and L. C. Ulberg.
                                                            1972. Managing reproduction in dairy cattle.
reproductive efficiency in the sow, the limiting            1. Progrestogens for control of estrus in dairy
factor is an unsuitable milieu for embryo sur-              cows. J . Dairy Sci. 55:598.
vival for approximately the first 3 weeks after           Britt, I. H., R. I. Kittok and D. S. Harrison.
farrowing. Segerson and Murray ( 1 9 7 8 ) have             1974a. Ovulation, estrus, and endocrine response
                                                            after GnRH in early postpartum cows. J. Anim.
shown that the uterus may not be completely                 Sci. 39:915.
functional until 3 to 4 weeks postpartum be-              Britt, J . H., D. A. Morrow, R. J . Kittok and B.
cause the percentage and quantity of uterine-               E . Seguin. 1974b. Uterine involution, ovarian
specific acidic proteins secreted before this               activity, and fertility after melengestrol acetate
                                                            and estradiol in early postpartum cows. J . Dairy
stage were lower than at later stages. Total                Sci. 57:89.
uterine protein per corpus luteum, percentages            Brown, J . G., D. W. Peterson and W. D. Foote.
of uterine serum-like protein, total uterine-               1972. Reproductive response of beef cows to
specific acidic protein were all significantly af-          exogenous progestogen, estrogen and gonado-
                                                            tropins at various stages of postpartum. J . Anim.
fected by postpartum interval. Whether these                Sci. 35:362.
secretions contribute to embryonic survival or            Buch, N. C , W. J . Tyler and L. E . Casida. 1955.
mortality during the early postpartum period                Postpartum estrus and involution of the uterus
or are associated with involutionary changes                in an experimental herd of Holstein-Fresian
                                                            cows. J . Dairy Sci. 38:73.
in the uterus has not been established. There
                                                          Call, T. W., W. C. Foote, C. D. Ecker and C. V.
seems to be little doubt, however, that repro-              Hulet. 1976. Postpartum uterine and ovarian
ductive efficiency is impaired in sows bred                 changes, and estrous behavior from lactation
early postpartum even though the role of the                effects in normal and hormone treated ewes.
                                                            Theriogenology 6:495.
uterus is not clear.
                                                          Callahan, C. J., R. E. Erb, A. H. Surve and R . D .
                                                            Randel. 1971. Variables influencing ovarian
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24                                                KIRACOFE

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                U T E R I N E INVOLUTION AND POSTPARTUM                    INTERVALS                     25

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Question: Dr.   Bellows                                Cooper ( J . Amer. Vet. Med. Assoc. 1 5 7 :
  Your paper was very interesting, but I am            9 2 ) . I think data can be found both ways;
  not sure if I followed one point that you            some have reported no effect and others
  made regarding the reason for short cycles.          indicate a detrimental effect.
  Specifically, in relation to the size of the       Question: Dr. Pickett
  follicle from which the C L was derived. If
  I understand you correctly, you were imply-          Do you think it has an effect?
  ing that the size of the ovulating follicle        Dr. Kiracofe: In my opinion there is no effect,
  was involved here?                                    although I do not have the data to support
                                                       that opinion. I do not feel that breeding
Dr. Kiracofe: I do not think size of the ovulat-
                                                       cows during the early postpartum period
  ing follicle is playing a role in short cycles
                                                        effects subsequent fertility.
  in our data. In that respect, I was referring
  to the research of Moller in Australia, who        Question: Dr. Pickett
  observed luteinized stromal follicles in post-
  partum cows. I think they were similar to            Is there a possibility that there is a differ-
  the luteinization noted b y the West Virginia        ence between dairy and beef cattle in this
  investigators in prepuberal heifers. T h e data      regard?
  of Berardinelli et al. at West Virginia indi-      Dr. Kiracofe: There could be. B y putting se-
  cates that these are stromal follicles that are      men in the early postpartum uterus there
  small and luteinized. However, in postpar-           may be a chance of causing an inflammatory
  tum cows we do not feel that it was a                response or low grade bacterial infection.
  small follicle that ovulated.                        Since the dairy cow tends to ovulate earlier,
                                                       many times before uterine involution is com-
Question: Dr. Pickett
                                                       plete, she could be more susceptible.
  D o you have any information on the effect
                                                     Question: A   Questioner
  on subsequent fertility of those animals that
  were bred early, say quite soon after par-           On the basis of our knowledge of follicular
  turition, and did not conceive?                      development, is it not true that follicles
                                                       have to pass through a certain stage before
Dr. Kiracofe: I do not have any data on the
                                                       they will ovulate and that the size of the
  effect of early postpartum insemination on
                                                       follicles that ovulate really is fairly consis-
  subsequent fertility. I think there are some
                                                       tent within species?
  in the literature, particularly the earlier re-
  search of Van Demark and Salisbury ( J .           Dr. Kiracofe: That may be true in cycling
   Anim. Sci. 9 : 3 0 7 ) and that of Olds and         animals where definite endocrine patterns
28                                            KIRACOFE

     exist, but in animals that are ovulating for        matter of observing small luteinized follicles
     the first time in their life or after a pro-        or corpora lutea in the ovary.
     longed period of anestrus, such as postpar-       Question: A Questioner
     tum animals, it could be different. In the
                                                         In these luteinized follicles, were ova
     case of prepuberal heifers, the follicle is
                                                         trapped in them or were they actually small
     probably luteinizing without ovulation; how-
                                                         corpora lutea?
     ever, our limited data in the postpartum
     cow indicate she does ovulate, but we do          Dr. Kiracofe: Maybe there is someone here
     not know anything about the size of follicle.       who could comment on the West Virginia
Question: A      Questioner
                                                       Question: Dr.   Lauderdale
     T h e evidence is that the corpora lutea are        You are talking about short cycles, there-
     smaller that develop from these ovulations.         fore, the corpus luteum ( C L ) has obtained
     Did you find any of these small follicles or        its lifespan and the discussion so far has
     follicles of large size prior to the ovulation?     indicated what I would refer to as an in-
     What kind of evidence is there for smaller          herent decrease in its lifespan. Does the CL
     follicles ovulating?                                have an inherent lifespan, and with short
Dr. Kiracofe: I may be misinterpreting your              cycles is the inherent lifespan of the C L
                                                         altered or is there a "superluteolytic" factor

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  question. All data that we have with respect
                                                         in the postpartum animal?
  to the postpartum cow indicate the corpus
  luteum is normal size at day 4 of the short          Dr. Kiracofe: W e have investigated this to
  cycle and that short cycles are a result of            some extent. T h e data are incomplete so
  failure to maintain the corpus luteum, not             far, but I think that in this respect an in-
   a result of small follicles that luteinize. T h e     herent lifespan might be a possibility. I
  only evidence where there is a possibility             think that the inherent lifespan would be
  of ovulation of small follicles, is in the cases       due to a lack of gonadotropin or lack of a
  I indicated, i.e., the prepuberal heifers in           luteotropic substance rather than a luteolytic
  the research at West Virginia or the research          factor. However, we have not tested the
  of Moller in Australia, and this is just a             luteolytic aspect.
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