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Factors affecting the
Mike A. VARLEY
University of Leeds - United Kingdom
There are many diverse factors which can have a criticism is directed. Different environmental
profound effect on the reproductive performance of conditions in addition to the imposition of good or
the breeding herd. Not the least of theseare: poor welfare to the animal, can alsobe associated
the genotype of the sow and boar, the health status with a different levelproductive efficiency. of
of the herd and the general environment provided
for the breeding females. It is intended in this Light and temperature are two environmental
paper to concentrate on those factors which are componentswhichmayplay a r o l ei nt h e
under direct management control and which are determination of litter size although more datais
e c o n o m i c a l l ys i g n i f i c a n t .C o m p o n e n t so f needed. Sainsbury (1971) has suggested that high
reproductive performance to be considered are: ambient temperature at mating associated with is
lactation length, climatic and social environment poor litter size a t full term, although Tomes and
and prolificacy. Neilson (1979)have presented data showing this is
notalways so. Obviously the effects of high
There has been progressive improvement i n recent ambient temperature on litter size in the female
years in sow productivity and this trend seems pig are confounded by effects on the male. Svajgr
likely to continue. Data from the Meat and (1975) has demonstrated that high environmental
Livestock Commission show that over the years temperatures occurring two or three weeks after
1970-1984,sowproductivity in theUnited mating are extremely detrimental to prolificacy.
Kingdom for all recorded herds rose from 15.5 Table 1 presents data from a recent study by
piglets reared per sow per year to 20.0 reared per Wettermann and Bazer (1985) showing that heat
sow per year. There is great variation between s t r e s si nv e r ye a r l yp r e g n a n c yc a nh a v e
herds in this respect and in 1984 the top 10% of detrimental effects on uterine function and the
herds weaning piglets between 14 and 18 days of development of embryos.
age were recorded as rearing 26.8 piglets per sow
Table 1 Heat stress
per year (2.6 litters per sow per year;11.1 piglets ,
after Wettermann& Bazer (1985) Pregnant Gilts
born alive per litter). Not every producer can
achieve performances at this level but there may be
Control Heat stressed
lessons to learn from these top herds which could
help the average farmer.
I - Environmental effects I Embryowet
There is increasing concern about the effects of the 3H Leucine
environment on the general welfare of t h e incorporated in
breeding sow. Individual stalls, slatted floors and uterine explants
farrowing crates are but three examples where
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The summer months and early autumn are the Table 2: Correlation coefficients between
times when deficiency in the numbers of piglets reproductive performance
born alive per litter is most likely to be seen. In of
and the quality stockmanship
practice this means that inseminations for this from Hemsworth, Brand and Willems (1981)
period are carried out in the spring, not usually I I I i
the hottest part the year. Changing photoperiod No. of piglets
is likely to be another factor involved in seasonal Farrowing
effects. The experimental data which exist refute %
this possibility (Greenberg and Mahone, 1982;
Hacker and Perera,
study to date has
1981; Mabry et al., 1982) In no
a significant effect of photoperiod
score of sows - 0.77 - 0.55
on litter size been reported. Seasonal effects with humans
therefore are still unpredictable and difficult to
understand fully. Many conclusions can be drawn from these simple
observations, but it does seem that reproductive
The social environment of breeding females (and processes in the sow are affected by good and bad
boars)couldbeone of the most significant stockmanship in the same way that milk yield in
d e t e r m i n a n t s of reproductive efficiency and be
dairy cattle can influencedby the personalityof
prolificacy. At the present time there is much the cowman (Seabrook, 1972). This relationship
endeavour in the fieldanimal behaviour and the probably has some bearing the fact that adrenal on
pig is an excellent model for this. Moreover, with function,steroidhormonesandstress are
the current awareness of the general public in inextricably linked together. Some individual
matters of animal rights and welfare, there is a sows or some herds may be more stress prone OF
need to understand the relationships involved in subjected to more stress via the system of
social interaction between animals in order that buildings and management than others. This
we may develop systems of production and manifests itself either as complete reproductive
building designswhich fulfil1 the welfare needs of failure or reduced profilicacy, and may account for
the animal whilst still remaining productive. much of the variability in litter size and hence
overall sow productivity seen in practice.
There is evidence that alterations to the social
environment of sows and gilts can be responsible
for changes in reproductive function. The group - II Sow nutrition, body condition and
working a t Werribee in Australia has been very prolificacy
active in this area. Hemsworth, Beilharz and
Brown (1978), for example, showed that sows
housed in pairs between weaning and remating a
There has been n abundance of published reports
had a higher litter size the next farrowing than over the last20 years regarding various aspects of
sows housed individually. sow nutrition, body composition and reproduction.
This work has provided a database from which
I na d d i t i o nt oa n i m a ls o c i a li n t e r a c t i o n s , sound guidelines for the feeding of breeding
Hemsworth, Brand and Willems (1981) reported a females have been derived. I t is established
man-animal interaction which influenced the practice to offer sows throughout pregnancy an
litter size. These authors subjectively scored sows energy intake only a fraction above maintenance.
from 12 separate herds for their "withdrawal" to Under average circumstances this is a cost
the human experimenters' approach. In those effective means of converting feedstuffs into
herds in which sows showed decreased affinity weaners for sale.
with humans, there were significantly fewer
piglets born alive per litter. Table 2 gives the It hasnow become apparent that although average
correlation coefficients observed by Hemsworth et sow,
levels of energy intake suit the average there
al. (1981) between the "aversion score" for each are too many animals without the middle band of
farm in the study and either the farrowing rate body condition. It may be more efficacious at low
percentage or the number of piglets farrowed per energy and protein intakes to carefully monitor
litter. Those herds containing sows which showed individual sow body condition and adjust feed
aversion to humans for whatever reason were scales accordingly. At this point in time, however,
t h o s eh e r d sw i t ht h el o w e s tr e p r o d u c t i v e the ideal body condition and body weight change
performance. have not been. clearly identified for the various
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phases of a sow's life. As far as prolificacy is where Y = littersize(bornalive)and X =
concerned, there is little doubt that the sow can weaning age (days). In most the conclusion is
experience large variations in weight change drawn that with early weaning (7-20 days) there
without loss of numbers born alive per litter are no benefits accruing in terms of annual sow
(Varley and Cole, 1978b; Hovel1 and McPherson, productivity even though it is possible to produce
1977). At the extremes of body condition, the 2.8 litters/sow/year. The general recommendation
incidence of conception failure, anoestrus and has been made that the optimisation of weaning
ovarian dysfunction are likely to increase. age is over the range three to four
There has been an ongoing debate over the last
The questionof when to weanis not so simple and
few years as to appropriate energy allowance for
there may in fact be many answers for different
sows and gilts in very early pregnancy (i.e. up to
farmers. Not the leastthe considerations the are
available buildings on a particular farm and the
whether overfeeding in the immediate coitum
available management skills. Most people would
period causes increased embryonic mortality has
agree however that if sow productivity is the main
been open to much discussion. The evidence
goal then weaning at 21 days is the appropriate
indicates that at least in gilts, it is advisable to
age to wean. This conclusion does not alter
restrict daily feed intake in the first three weeks
significantly over a period time. What of does alter
after mating (Dutt and Chaney, 1968).
is the optimum age to wean with regard to
financial performance. These relationships are
Evidence for multiparous sows has not been so
derived from a computer model of the sow breeding
well defined but a recent study by Toplis, Ginesi
herd (Varley, 1985, unpublished) which integrates
and Wrathall (1983) showed whensowswere
all of the known biological facts and the economic
offered either 2 or 4 kg per day a diet containing
factors involved.The data depicted in Figure 1are
13 MJ/kg of DE between 3 a n d 30 days post
for a new farm with an intensive building system
coitum, there were no differences in either the
and average to good management. It can be seen
number of viable embryosa t day 30 post coitum or
that physical productivity peaks at slightly less
in the percentage embryo survival rate. It may
t h a n a 2 0d a yl a c t a t i o nl e n g t h .F i n a n c i a l
therefore be prudent not to increase the daily
p e r f o r m a n c e ,i nc o n t r a s t ,s h o w sm a x i m u m
energy intake in very early pregnancy. But in
expression for a weaning ageof about 35 days. It is
multiparous sows there is often a real need to
interesting to note also that return on capital at
restore body condition losses resulting from the
current interest rates and price structures never
previous lactation. It should be possible to apply
shows a positive value.
an increased plane of energy intake following
mating without extra lossesembryos.
Figure 2 illustrates the point that financial and
physical performance peaked at the same pointas
III Early weaning the pricing structure prevailing in 1975 (in the
UK a t least). The weanerprice/feed cost ratio was
much greater in the early 1970s. The optimum age
The application of early weaning over the last 20 to wean appears to change considerably over time
years hasplayed a major role in the increases seen and although it currently seems to be around five
in sow productivity on modern pig units. The weeks of age, it may decrease if the economic
biological effects of early weaning are now well is
situation changes. What needed are inexpensive
known: for example,as lactation length is reduced creep diets for early-weaned piglets based soya on
there are concomitant effects on the interval from protein and other low cost ingredients. This will
weaning to conception, conception rates and the not happen until our knowledge of the nutrition of
subsequent litter size (Varley and Cole, 1978b). the young pig is much further advanced.
The problem with litter size is probably the
biggest single drawback and the author has
Although most farmers pursue 25 piglets per sow
per year from a three week weaning system, they
relationship between weaning age and subsequent
may maximise their profits accepting 22 piglets
litter sizeis given by the equation:
from a five week weaning systemat today's prices
with current knowledge.
Y = 6.8 1.1log, X
l CIHEAM - Options Mediterraneennes
profitability. Without a high order of prolificacy it
is i m p o s s i b l eo a x i m i s e n n u as o w
tm a l
IV - Endocrine status productivity. Survey data highlight the enormous
of early-weaned sows variation that exists on farms and the best herds
achieve12.5pigletdlitterand at t h e o t h e r
extreme, the poorest record 7.8 (McIntyre, 1984,
Recentworkhasfocusedontheendocrine personal communicationMLC data).
background of early-weanedsows(Varley,
Atkinson and Ross, 1981; Varley, Peaker and
N e o n a t a 1m o r t a l i t y is a l s o of p a r a m o u n t
Atkinson, 1984; EdwardsandFoxcroft, 1983).
importance. It is little consequence producing 12
Plasma concentrations of the steroid hormone
piglets per litter born alive if 15% of these die
progesterone do not differ in early pregnancy
within 48 hours of birth, asoften is the case. There
between early-weaned sows and conventionally
are many management aids for reducing the
teated sows (weaned a t six weeks) but there is
incidence of neonata1 deaths and these include
evidence (Edwards and Foxcroft, 1983; Kirkwood
h i g ht e c h n o l o g yf a r r o w i n gc r a t e s , E . coli
et al., 1984) that the luteinising hormone (LH)
vaccination and synchronised farrowing.
surge at ovulation is significantly reduced for
early-weaned sows. This could influence the
timing of ovulation relative to other endocrine Supplementary rearing devices for the artificial
signals, leading ultimately to early embryonic rearing of surplus piglets are now being used
death. Surprisingly, the reduced peak does not widely in the UK. In otherwords, there are many
affect the ovulation rate. technicaloptionsopento farmers with special
problems in this area.
Oestrogens have been given some attention by
Varley et al., 1984. Some sows have very high
blood levels of circulating oestrogens between
weaning and remating and in early pregnancy.
VI - Conclusions
transport and poor implantation of blastocysts.
From a practical viewpoint, there is a glimmer of
The source this oestrogen is open at the moment
hope t h a t it may be possible in the future to
to speculation but early-weaned sows show a very
h i g hi n c i d e n c eo fe l e v a t e do e s t r o g e n s . A
reproductive performances. There is a vigorous
proportion of conventionally weaned sows show
effort beingmade by hybrid breeding companies to
the same response but the overall incidence is
develop hyper-prolific female lines and Meat and
much lower than for early-weaned sows.
Livestock Commission evaluations strongly
suggest that there are significant differences
One possibility is that the oestrogens originate
between companies in breeding value of t h e i r
from the adrenal glands. This known to occur as
animals for litter size. Producers now have the
a reaction to stress. Itmay be that some animals
option to select a company’s gilts on the basis of
. are predisposedto stressand willproduce more
published comparative information. From the
oestrogens as a result. Early-weaning tends to
starting point of agood genotype, it is t h e n
compound together two very stressful events in
n e c e s s a r yt oa d h e r et ot h ee s t a b l i s h e d
the reproductive life of a breeding female. These
recommendations of good husbandry and due
are parturition and weaning. There is more work
consideration of some of the points listed below.
to be done in this before firm conclusions are
drawn but it does seem that elevated oestrogens
may lead to embryonic deaths. Use of an appropriate housing system with good
V - Prolificacy and neonata1 Stocking densityfor sows not too high;
Feed sows and gilts as individuals where possible
and monitorbody condition;
Prolificacy, or the number piglets born alive per
litter, is usually considered by most pig farmers
to o ie p
A v o i d v e r f e e d i n gn a r l y r e g n a n c y ,
be the single most important determinant of particularly with gilts and primiparous sows.
CIHEAM - Options Mediterraneennes
Consider the use a constant light pattern in dry Hovell, F.D. De B. and R.M. Macpherson, 1977. Thin sows. 1.
sow accommodation; Observations on the fecundity of sows when underfed for
several parities. Agric. Sci.,Camb. 89:513-622.
Avoid high environmental temperatures between
weaning and mating and over the course early
Kirkwood, P.N., K.R. Lapwood, W.C. Smith, andI.L. Anderson,
1944. Plasma concentrations of LH, protein, oestradiol-l7 and
progesterone in sows weaned afterlactation for 10 or 35 days. J.
Avoid the imposition of any stress on the animal,
particularly at farrowing and between weaning
and service and in early pregnancy.
Mabry, J.W., F.L. Cunningham, R.R. Kraeling and G.B.
Rampacek, 1982. The effect of artificially extended photoperiod
T h i sl a s tp o i n tr e l a t e st ot h eq u a l i t y of
during lactation on maternal performance of the sow, J.Anim.
s t o c k m a n s h i pa sw e l l as t om a n a g e m e n t
techniques. In recent years there has been an
increase in the ratioof pigs to stockman as herds
Sainsbury, D.W.B, 1971. Climatic environment and pig
have increased in size. I t is of p a r a m o u n t
performance. IN: Pig Production, ed. D.J.A. Cole, pp. 91-106.
importance to ensure that those still working in
the industry are fully trained and of the highest
calibre. However good the genotype, the housing,
Seabrook, M.F, 1972. A study to determine theinfluence of the
the feeding and the style of management, the
herdman's personality on milk yield. J. Agric. Labour. Sci. 1:l-
primary constraint may always be the person
actually tendingto the animal'sneeds.
Svajgr, A.G., 1975. Stretching the feed dollar. Feedstuffs.
In the future, with the introduction to Europe of
March 17, p.14.
Chinese breeds capable of producing 16 to 20
liveborn piglets per litter, and with our increasing
Tomes, G.J. and H.E. Nielsen, 1979. Seasonal variations in the
u n d e r s t a n d i n g of t h e , b a s i c m e c h a n i s m s
reproductive performance of sows under different climatic
controlling embryonic mortality, it might yet be
conditions. Wld. Rev. Anim. Prod. 15:(1) 9-19.
possible to sell 3,000bacon pigs a year from 100
Toplis,P., M.F.J. Ginesi, and A.E. W r a t h a l l , 1983. The
influence of high food levels in early pregnancy on embryo
survival in multiparous,sows.Anim. Prod. 37:45-48.
Dutt, R.H. and C.H. Chaney, 1968. Feed intake and embryo
Varley, M.A. and D.J.A. Cole, 1978a. The relationshipbetween
survival ingilts. Prop.Rep. Ky. Agric. Exp. Stu. No. 176:33-35.
the weight changethe sow and her reproductive output. Proc.
Brit. Soc. Anim. Prod. 1978. Page 368 (abstr.).
Edwards, S. and G.R. Foxcroft, 1983. Endocrine changes in
sows weaned a t two stages of lactation. J. Reprod. Fert. 67:161-
Varley, M.A. a n d D.J.A. Cole, 1978b. Studies. in sow
reproduction. 6 . Theeffect of lactation length on pre-
implantation losses. Anim. Prod. 27:209-214.
Greenberg, L.G. and J.P. Mahone, 1982. Failure of a 16 h L =
8hD or a 8hL = 16hD photoperiod to influence lactation or
Varley, M.A.,R.E. Peaker, and T. Atkinson, 1984. Effect of
reproductive efficiency in sows. Can. J. Anim. Sci. 62:141-145.
lactation length of the sow on plasma progesterone, oestadiol-
17 and embryonicsurvival. Anim. Prod. 38:113-119.
Hacker, R.R. and M. Perera, 1981. Effect of light changes on
swine reproduction. University of Guelph. Annual Report.
1981. pp. 21-23. Varley, M.A., T. Atkinson, and L.N. Ross, 1981. The effect of
lactation length on the circulating concentrations of
Hemsworth, P.H., R.G. Beilharz, and W.J. Brown, 1978. The progesterone and oestradiol in the early-weaned sows.
importance of the courting on
behaviour of the boar the success Theriogenology16:179-183.
of natural and artificial matings. Appl. Anim. Ethol. 4:341-347.
Wetterman R.P. andF.W.Bazer, 1 9 8 5 . Influence of
Hemsworth, P.H., A. Brand, and P. Willems, 1981. The environmental temperature onprofilicacy of pigs..IN Control
behavioural response of sows to thepresence of human beings of Pig Reproduction II. Ed. Foxcroft G.R., D.J.A. Cole, and B.J.
and its relation productivity. Livest.Sci. 8,67-74. Weir, J. Reprod. Fert.:Supplement 33.
CIHEAM - Options Mediterraneennes
Figure 1 :Effect of weaning age oneconomic aspectsof pig production
S S MARQIH E/ 8 0 W -
RETURN ON CACltAL I -S
10 20 30 40
WEANINQ AGE (days)
Figure 2 :The effect of weaning age profitability in Great Britain
1975 .costs X. *
/-0 \ \
Current Feed Costs (C)
3 T9 8 5
I l * I I 1
14 21 28 35 42 49
Weaning Age (days)