Oestrous behaviour in relation to fertility and fecundity of gilts

Animal Reproduction Science, 5 (1982) 117--125

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Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

OESTROUS BEHAVIOUR IN RELATION TO FERTILITY AND FECUNDITY OF GILTS

G.M. CRONIN, P.H. HEMSWORTH and C.G. WINFIELD

Department of Agriculture, Animal Research Institute, Werribee, Vic. 3030 (Australia) (Accepted 19 April 1982)

ABSTRACT Cronin, G.M., Hemsworth, P.H. and Winfield, C.G., 1982. Oestrous behaviour in relation to fertility and fecundity of gilts. Anim. Reprod. ScL, 5: 117--125. The reproductive performance of 2484 gilts was recorded over a 12-month period at a large intensive piggery in southern Australia. Between 29 and 35 weeks of age, gilts were examined daily for response to the back-pressure test (BPT). Those subjectively assessed as showing a moderate or high response were taken to a boar for mating. Gilts that had showed a moderate response to the BPT on their first day of mating had lower average litter size than gilts showing a high BPT response (9.05 and 9.35 piglets, respectively; P < 0.05). A quantitative assessment of sexual receptivity was made while the gilt was with the boar, Gilts that were mated while showing low sexual receptivity on the first day of mating had poorer farrowing rate (78.1 vs. 83.1%, respectively; P < 0.05), as well as lower litter size (9.03 vs. 9.35 piglets, respectively; P < 0.05) than gilts that were mated when showing high sexual receptivity. A moderate BPT response was followed by either low sexual receptivity or failure to mate on 81.4% of occasions, compared with 12.8% for a high BIT response. Since 75% of gilts that showed a moderate BPT response on the first day of mating showed a high response on the following day, it was concluded that mating should only be attempted when grits exhibit a high response to the BPT. The mean farrowing rate and litter size for gilts at their first farrowing was 82.4% and 9.31 piglets (8.62 alive and 0.69 dead), respectively. INTRODUCTION

The importance of a high level of oestrous behaviour at the time of a controlled mating on reproductive efficiency in the gilt has been demonstrated in t w o studies. Both conception rate and litter size were positively associated with the level of positive response to the back-pressure test (BPT) at the time of insemination (Willemse and Boender, 1967; Alanko,:1974). Little is known of h o w either of these factors influence level of oestrous behaviour, particularly under Australian conditions, or the incidence of oestrus amongst gilts in Australian herds. This study was carried out to investigate the incidence of oestrus in gilts between 190 and 245 days of age at a large commercial piggery, and the effect of variability in the level o f oestrous behaviour on fertility and fecundity.

0378-4320/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company

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Oestrus is the period in the oestrous cycle when the gilt or sow is sexually receptive and during which ovulation occurs (Roberts, 1971). Sexual receptivity is defined in terms o f female responses necessary and sufficient for the male's success in achieving copulation (Beach, 1976). MATERIALS AND METHODS The study was c o n d u c t e d over a 12-month period at a large intensive piggery in Victoria. There were three breeds of gilts (Large White (LW), Landrace (LR) and a synthetic breed selected from LW X LR pigs on the basis of large litter size) and there were also crossbred gilts o f these three breeds. Groups of 40--71 gilts were selected for breeding at 21 weeks of age on the basis of growth rate and back-fat thickness. At 27 weeks of age t hey were moved to the dry sow house. Each day during the following week a y o u n g boar (7--11 m on th s o f age) was introduced into the group for 10 min. The gilts were transferred at 29 weeks of age t o an adjoining boar shed for mating over the subsequent 6-week period. Groups of five gilts were housed in 1.8 X 3.0 m pens 1.0 m from the boar pens. Gilts t h a t did n o t mate by 35 weeks of age were slaughtered at a local abattoir. One of three trained herdsmen tested each gilt daily from 29 to 35 weeks of age for the response to the BPT in the presence of a boar and recorded the responses as described in Table I. The condition of the vulva (reddened and swollen) was also considered when determining low responses. Signoret and Du Mesnil du Buisson (1961) have shown t hat 97% of oestrous gilts can be d e tected by this technique. Only gilts t hat showed a m o d e r a t e or high response were taken individually to a boar in a mating pen; those that showed a low BPT response were considered unlikely to be receptive and no action was taken. Any period of a minimum of 3 consecutive days in which a positive BPT response (low, m oder a t e or high) was recorded was termed a posiTABLE I Categories of response by gilts to the back-pressure test (BPT) in the presence of a boar Behaviour response to BPT

Level of response recorded

Vigorous avoidance Stands for approx. 10 s before running off Stands for 15--30 s before running off Stands for greater than 30 s, exhibits 'ear-play' (sideways movement and some retraction of the ears, Willemse and Boender, 1966; Schenk, 1967)

Negative Low Moderate positive High

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tive response period (PRP). If mating did not occur in this period, the next PRP was not recorded until at least 10 days had elapsed after the last PEP. All gilts that were mated, were mated twice on consecutive days. Matings were classed as either Type 1 or Type 2 on the basis of the sexual receptivity of the gilt to the boar. Gilts that stood immediately to the boar's first mounting attempt were recorded as having a Type 1 mating, while those that initially resisted the boar's mounting attempts before allowing copulation were recorded as having a Type 2 mating. The herdsman assisted the boar to gain intromission. At the end of each week, mated grits were returned to the dry sow shed and checked daily for returns to service. Only data relating to the gilts' first double-mating are included here. Air temperature records from inside the piggery were available for 8 months of the study period, which included 9 weeks of spring and all of summer and autumn. Farrowing data were available from the piggery's records, and associations between oestrous behaviour, mean maximum indoor temperature and fertility and fecundity were analysed using chi-squared tests on the proportion of gilts in various classes, and by analysis of variance. RESULTS

Of the 2484 gilts in the study 2224 (89.5%) mated, and 82.4% of these farrowed (Table II). The average total births and live births were 9.31 and 8.62 piglets per litter, respectively. Only data relating to the gilts that were mated are included.

TABLE II Reproductive performance of the gilts Parameter

Number of gilts

Percentage

Number of gilts at 29 weeks of age Not mated by 35 weeks of age Sales/culls/deaths pre-farrowing

2484 260 93

100.0 10.5 3.7

Farrowed Returns to service by 3 weeks Not-in-pig and not returned by 8 weeks Aborted after 8 weeks post-mating

1755 207 166 3

82.41 9.71 7.8 I 0.11

Piglets Average litter size -- total alive -- dead -

-

9.31 8.62 0.69

i Percentages of the number of mated gilts remaining after sales, culls and deaths prior to farrowing are excluded.

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Response to the back-pressure test and sexual receptivity The percentages of gilts that were mated at the first, second or third PRP were 81, 17 and 2%, respectively. A higher percentage of gilts failed to mate at their first PRP in summer and autumn than in winter and spring (21.0 and 17.4%, respectively; ×~ = 4.50, P < 0.05). In 14.2% of PRPs only a low BPT response was recorded; the incidence of this was lower in winter and higher in summer than in other seasons {10.7 and 15.2%, ×~ = 8.31, P < 0.01; and 16.5 and 13.2%, ×~ = 4.71, P < 0.05, respectively). In 3.6 and 82.2% of PRPs the maximum response to the BPT was moderate and high, respectively, and in these PRPs mating rate was 67.3 and 97.8%, respectively (×12 = 262, P < 0.001). Mating rate is defined as the percentage of PRPs in which mating occurs. On days when gilts showed either a moderate or high BPT response (1266 and 3701 observations, respectively), mating attempts resulted in 18.6 and 87.2% Type 1 matings, respectively, 59.2 and 6.3% Type 2 matings, respectively, and 22.2 and 6.5% failure to stand for the boar, resPectively (×~ = 2 , 1 9 6 . 4 , P < 0.001). For gilts which were mated, the mean duration of low, moderate and high BPT responses were 2.02 (pre-mating only), 0.54 and 1.64 days, respectively. The duration of the low response prior to mating was shorter in spring and longer in summer than in other seasons: spring 1.59 days, winter 1.92 days, autumn 2.03 days and summer'2.39 days (LSD = 0.28, P < 0.05). Within groups of gilts, mating tended to be synchronized with a peak incidence occurring between 5 and 10 days after entry to the boar shed (Fig. 1). 12

1c

6

c !lll/lI!II,IIIH! !ll ,I /

5

10

15

20

25

30

35

,40

D a y s a f t e r e n t r y t o b o a r shed

Fig. 1. P e r c e n t a g e of gilts m a t e d each day a f t e r e n t e r i n g b o a r shed.* E n t r y at d a y 1.

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Fertility and fecundity Excluding gilts that were culled or sold after mating (4.2% of those mated), 82.4% of the remaining gilts farrowed, with a mean litter size of 9.31 piglets born alive or dead (Table II). Mean litter size was significantly lower (P < 0.01) in gilts that mated at the first PRP compared with the second or third PRP (9.2, 9.7 and 10.5 piglets, respectively). The respective farrowing rates (82.4, 81.4 and 90.6%) did not differ significantly. Total piglets born to gilts, per 100 matings at the first, second or third PRP were 758, 791 and 947, respectively.

(i) Response to the BPT The level of response to the BPT prior to mating was not associated with the farrowing rate o f gilts (Table III). Mean litter size was significantly lower (9.05 vs. 9.35 piglets, respectively, P < 0.05) when the first of the gilt's double matings followed a moderate compared with a high BPT response (Table III). However, the level of response prior to the second mating was not significantly associated with mean litter size. Seventy-five percent of gilts that showed a moderate response on the first day of mating showed a high BPT response on the second day (Table III). T A B L E III Fertility and f e c u n d i t y o f gilts that showed high or m o d e r a t e responses to the BPT prior to mating ~

BFl~vesponse First

Gilts mated

Farrowing rate

Mean litter size

mating

Second mating

(n)

(%)

(piglets)

H H M M

H M H M

1253 590 213 72

82.1 83.2 80.8 87.5

9.42 b 9.21 ab 9.06 a 9.03 ab

I Ia I Ib

Pigletsfrom gilts per 100 matings

773 776 732 790

1 Excludes three gilts that aborted after 8 weeks post-mating. H: high BPP response. M: m o d e r a t e BPT response. a,b: p < 0.05. T r e a t m e n t s or c o m b i n a t i o n s of treatments followed by different letters differ significantly, P < 0.05.

(ii) Type of mating Gilts that experienced Type 1 matings at the first mating had a significantly higher farrowing rate (83.1 vs. 78.1%, respectively; ×3 = 4.20, P < 0.05) and mean litter size (9.35 vs. 9.03 piglets, respectively, P < 0.05) than gilts that experienced Type 2 matings at the first mating (Table IV). The percentages of gilts that returned to service after Type 1 or Type 2 matings at the

122 T A B L E IV Fertility and f e c u n d i t y o f gilts that had T y p e 1 or T y p e 2 matings ~ T y p e o f mating

Gilts mated

Farrowing rate

Mean litter size (piglets)

First mating

Second mating

(n)

(%)

T1 T1 T2 T2

T1 T2 T1 T2

1231 613 233 51

82.7 84.0 79.0 74.5

J I a J J b

9.44 a 9.20ab 8.96 b 9.00ab

a b

Piglets from gilts per 100 matings

781 773 7O8 671

Excludes three gilts that aborted after 8 weeks post-mating. T1 : T y p e 1 mating. T2 : T y p e 2 mating. a,b : p < 0-°05. T r e a t m e n t s or combinations of t r e a t m e n t s followed by different letters differ significantly, P < 0.05.

first mating were 9.3 and 12.3%, respectively, and the corresponding percentages of gilts which had not returned to service but which were n o t pregnant at 8 weeks were 7.5 and 9.5%, respectively. Eighty-two percent of gilts that experienced Type 2 matings on the first day of mating had Type 1 matings on the second day (Table IV).

(iii) Season Season of the year appeared to influence fertility and fecundity (Table V). Farrowing rate was significantly lower in gilts mated in summer than in other seasons, and was significantly higher in gilts mated in spring than in other seasons. However, mean litter size was significantly lower in gilts mated in spring than those mated in other seasons of the year. Nevertheless, in terms TABLE V Fertility and f e c u n d i t y of gilts m a t e d in different seasons of the year Season of mating

n

Farrowing rate (%)

Mean litter size

Piglets per 100 matings

Spring Summer Autumn Winter

476 498 648 509

88.5 73.7 85.0 81.7

9"04a 9.32 b 9.45 b 9.48 b

800 687 804 772

J x y

I Jp q J

x, y : x~ = 15.6, P < 0.01, for spring v. o t h e r seasons. P, q : x~ = 33.3, P < 0.01, for summer v. o t h e r seasons. a,b : p ~ 0.05. T r e a t m e n t s followed by the same letter do n o t differ significantly.

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of piglets born to gilts per 100 matings, reproductive performance was 13.3% lower in summer than at other times of the year. Farrowing rate, but not litter size, was associated with mean maximum indoor air temperature in the week of mating. When the weekly mean maximum indoor temperature (WMMIT) was 30°C or greater, the farrowing rate was significantly lower than when WMMIT was less than 30°C (72.9 amd 85.1%, respectively; X~ = 27.9, P < 0.001). The range of WMMITs recorded during the study was 20.1--35.7°C, while the lowest WMMIT during summer was 24.1°C. DISCUSSION

Since the management of this commercial piggery was typical of large intensive piggeries in southern Australia, the study probably provides widely applicable information on the reproductive efficiency of gilts in Australian intensive piggeries, and identifies areas where improvements in reproductive efficiency might be achieved. Factors that contributed to reduced reproductive efficiency were failure to mate by 35 weeks of age (10.5%), failure of mated gilts to achieve at least a moderate BPT response and thus be put to the boar at the first or second PRP (14.2% of PRPs), failure to mate at the first or second PRP although a moderate or high BPT response was displayed (3.6% of mated gilts}, and the failure of 17.6% of physically sound, mated gilts to farrow. The farrowing rate and litter size of gilts reported in this study are similar to those reported overseas (Brooks and Cole, 1973; Pay and Davies, 1973; MacPherson et al., 1977; MLC Survey, 1980), but are markedly higher than recent Australian estimates. Penny et al. (1971), in an abattoir survey of 25 culled gilts, reported a litter size of 7.2 piglets, while Paterson et al. (1980) reported an 85% farrowing rate and 8.0 piglets born per litter in one herd. As expected, there was a strong association between the response of the gilt to the BPT and her sexual receptivity. A moderate response to the BPT was followed by high sexual receptivity on 18.6% of occasions, compared to 87.2% of occasions following a high BPT response. Thus, since 75% of gilts showing a moderate BPT response on day 1 of mating showed a high response 24 h later, and similarly 82% of gilts showing low sexual receptivity on day 1 of mating showed a high response 24 h later, mating could be delayed until the next day. Furthermore, gilts mated when in low, compared with high, sexual receptivity at the first of the double matings had lower litter size and farrowing rate. Insemination occurring too early in relation to ovulation may be responsible for this reduction. However, the timing of mating would have improved on the second day of oestrus since sexual receptivity in 82% of these gilts improved from low to high levels between the first and second day of mating. A mating in which the gilt initially resists the boar's mounting attempts may be stressful to the extent where this interferes with the physiological mechanisms of fertilization. Evidence to support this suggestion comes from Liptrap (1970, 1973) who reported that administration of ACTH (which

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is likely to mimic a stress response) for several days prior to and during oestrus interferred with ovulation in the sow. Two hours of restraint stress at and after mating, so that maximal activation of adrenocortical secretion occurred, adversely affected embryo survival in the female rate (Euker and Reigle, 1973; Reigle, 1973). The study also confirms the important effect of season on the reproductive performance of the domestic pig. Reduced oestrous expression and farrowing rate occurred in summer. As in this study, Baharin and Beilharz (1977) working in the same herd reported that litter size was not significantly lower in gilts mated in summer, but was lower in spring-mated gilts. High temperatures during gestation may be responsible (Edwards et al., 1968; Omtvedt et al., 1971). ACKNOWLEDGEMENTS

We thank Mr. G.T. Hope, Manager of Mayfair Pig Farm, Bendigo for allowing us to conduct this study there, Messrs. Les Riddell, John Palmer and Jim Snudden for recording the oestrous behaviour data at the piggery and Mr. A.W. Makin for his technical assistance. We also wish to thank Dr. L. Jones for his assistance with the statistical analyses. The financial support of the Australian Pig Industry Research Committee is gratefully acknowledged.

REFERENCES Alanko, M., 1974. Fertilization and early development of ova in AI-gilts, with special reference to the role of tubal sperm concentration. A clinical and experimental study. College of Vet. Med., Helsinki, Finland. Baharin, K. and Beilharz, R.G., 1977. An analysis of reproductive performance in pigs based on records and performance of the boar. Aust. J. Exp. Agric. Anita. Husb., 17: 256--262. Beach, F.A., 1976. Sexual attractivity, proceptivity and receptivity in female mammals. Horm. Behav., 7: 105--138. Brooks, F.H. and Cole, D.J.A., 1973. Meat production from pigs which have farrowed 1. Reproductive performance and feed conversion efficiency. Anita. Prod., 17: 305--315. Edwards, R.L., Omtvedt, I.T., Turman, E.J., Stephens, D.F. and Mahoney, G.W.A., 1968. Reproductive performance of gilts following heat stress prior to breeding and in early gestation. J. Anita. Sci. 27: 1634--1637. Euker, J.S. and Riegle, G.C., 1973. Effects of stress on pregnancy in the rat. J. Reprod. Fertil., 34: 343--346. Liptrap, R.M., 1970. Effect of corticotrophin and corticosteroids on oestrus, ovulation and oestrogen excretion in the sow. J. Endocrinol., 47: 197--205. Liptrap, R.M., 1973. Oestrogen excretion by sows with induced cystic ovarian follicles. Res. Vet. Sci., 15: 215--219. MacPherson, R.M., Hovel, F.D. DeB. and Jones, A.S., 1977. Performance of sows first mated at puberty or second or third oestrus, and carcass assessment of once bred gilts. Anita. Prod., 24: 333--342. MLC Survey, 1980. Sow productivity. MLC Pig Improvement Service~ Newsletter, No. 14, March 1980.

125 Omtvedt, I.T.,Nelson, R.E., Edwards, R.L., Stephens, D.F. and Turman, E.J., 1971. Influence of heat stressduring early, mid and late pregnancy of gilts.J. Anim. Sci.,32: 312--317. Paterson, A.M., Barker, I. and Lindsay, D.R., 1980. Ovulation rate at firstmating and reproductive performance of gilts.Aust. Vet. J., 56: 442--443. Pay, M.G. and Davies, T.E., 1973. Growth, food consumption and litterproduction of female pigs mated at puberty and at low body weights. Anita. Prod., 17: 85--91. Penny, R.H.C., Edwards, M.J. and MuUey, R., 1971. The reproductive efficiency of pigs in Australia with particular reference to littersize.Aust. Vet. J., 47: 194--202. Riegle, G.D., 1973. Chronic stresseffects on adrenocortical responsiveness in young and aged rats. Neuroendocrinology, 11 : 1--10. Roberts, S.J., 1971. Veterinary Obstetrics and Genital Diseases. Ithaca, N e w York, 551 pp. (publ. bv author). Schenk, P.M., 1967. A n investigation into the oestrus symptoms and behaviour of sows. Z. Tierz. Z~ichtungsbiol.,83 : 86--140. Signoret, J.P. and D u Mesnil du Buisson, F., 1961. Study of the behaviour of the sow during oestrus. Proc. IV Int. Cong. on Anita. Reprod., Vol. If, The Hague, pp. 171--175. Willemse, A.H. and Boender, J., 1967. The relationship between the time of insemination and fertilityin gilts.Tijdschr. Diergeneeskd., 92: 18--34.