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Effects of parity, season and boar contact on the reproductive performance of weaned sows
Livestock Production Science 54 Ž1998. 151–157
Effects of parity, season and boar contact on the reproductive performance of weaned sows P.E. Hughes Department of Animal Production, Institute of Land and Food Resources, UniÕersity of Melbourne, ParkÕille 3052, Australia Received 12 May 1997; accepted 10 November 1997
Abstract Forty eight Large White= Landrace sows Ž12 from parity 1, 12 from parity 2 and 24 from parities 3–7. were allocated to each of 4 post-weaning boar contact treatments Ž0, 1, 2 or 3 exposures dayy1 . in each of the four seasons of the year. Litter size suckled was standardized at 10 piglets wherever possible Žrange 9–12 piglets. and lactation length was 24–35 days. Oestrus detection was performed twice-daily on all weaned sows and each sow was given 2 fertile matings 24 h apart. Data on anoestrus, conception rate and subsequent litter size were also collected. Sows being weaned from their first litter took significantly longer to return to oestrus post-weaning than did sows in parities 2–7 Ž5.9 " 0.38 vs. 5.1 " 0.21 days, P - 0.05.. There was no significant influence of boar contact post-weaning on the length of the rebreeding interval Ž5.5, 5.5, 5.4 and 4.9 days for sows receiving boar contact 0, 1, 2, or 3 times daily respectively.. Equally, season of the year did not significantly influence the length of the rebreeding interval Ž5.1, 5.2, 5.3 and 5.6 days for sows being weaned in spring, summer, autumn and winter respectively.. The size of the litter subsequently produced was significantly influenced by sow parity Ž12.1 " 0.46 vs. 13.1 " 0.28 piglets born to sows having either their second or third–eighth litter respectively. but was not significantly affected by either boar contact in the post-weaning period or season of the year. Subsequent litter size was also significantly affected by the litter size of the sow at the start of the experiment Ž r s 0.40, P - 0.001.. These results suggest that, with the exception of parity-1 sows, extended weaning-to-oestrus intervals are not a major problem in some sow genotypes. Furthermore, where the weaning-to-oestrus interval is extended, these results indicate that the provision of regular boar contact post-weaning is unlikely to stimulate an earlier return to oestrus. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Pigs; Boar contact; Season; Parity; Oestrus; Litter size
1. Introduction The length of the interval from weaning to oestrus is initially determined by the parity of the sow, season and herd ŽMartinat-Botte´ et al., 1985.. An early return to oestrus post-weaning may be stimulated by either partial- or split-weaning or the provision of regular boar contact Žsee Hughes and Hemsworth, 1994.. Conversely, return to oestrus
post-weaning may be delayed if early weaning is practiced, when sow nutrition is inadequate during lactation and, possibly, after-weaning ŽWhittemore, 1996. andror when sows are individually housed after weaning ŽHartmann and Hughes, 1996; den Hartog et al., 1994.. There is general agreement that the weaning-tooestrus interval decreases as sow parity increases ŽAumaitre et al., 1975; Martinat-Botte´ et al., 1985..
0301-6226r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 1 - 6 2 2 6 Ž 9 7 . 0 0 1 7 5 - 9
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P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
Similarly, the length of the weaning-to-oestrus interval appears to become more consistent Ži.e., less spread. as sow parity increases Žsee Hughes and Varley, 1980.. These effects of sow parity on the timing of the post-weaning oestrus appear to be primarily due to differences between sows in parities 1–2 and those in later parities. Season also influences the timing of post-weaning oestrus, sows weaned in the summer months taking longer to return to oestrus than sows weaned at other times of the year ŽBritt et al., 1983; Claus and Weiler, 1985.. This effect is probably due to long light duration and, more obviously, to high ambient temperature ŽBarb et al., 1991; Prunier et al., 1994, 1996.. However, the use of cooling systems does not prevent the extension of the weaning-to-oestrus interval in summer ŽHurtgen et al., 1980; Cox et al., 1983.. Boar contact Žthe boar effect. has been demonstrated to be effective in reducing the weaning-tooestrus interval with contacts starting either before or after weaning Že.g., Petchey and English, 1980; Hemsworth et al., 1982; Rowlinson and Bryant, 1982; Henderson and Hughes, 1984; Walton, 1986; Pearce and Pearce, 1992.. What is not known is how boar contact, parity and season interact to affect the length of the weaning to oestrus interval. The present study was conducted to evaluate the effects of these three factors, and their interactions, on the weaning to oestrus interval. In addition, since recent studies in the gilt strongly suggest that the efficacy of the boar effect may be enhanced with frequency of daily boar exposure ŽHughes, 1994a., the influence of the number of daily boar contacts during the post-weaning period was determined.
2. Materials and methods 2.1. Animals and treatments This study used 192 Large White = Landrace sows from the Mt. Derrimut herd of the University of Melbourne. Forty eight sows from each of parities 1 and 2 were used, the remaining 96 sows being from parities 3–7. In each season of the year 12 parity-1 sows, 12 parity-2 sows and 24 sows from parities 3–7 were allocated to the following post-weaning treatments: Control—no boar contact Once-daily boar contact Ž5 min dayy1 . Twice-daily boar contact Ž2 = 5 min dayy1 . Thrice-daily boar contact Ž3 = 5 min dayy1 . All sows were fed 6 kg dayy1 in lactation, 3.5 kg dayy1 from weaning to remating and 2.3 kg dayy1 during gestation. The diet fed during lactation and from weaning to remating contained 14.2 MJ of DE kgy1 and 188 g of crude protein kgy1 Ž0.44 g available lysine MJy1 of DE and other essential amino acids in a ratio to lysine of 0.5 methionineq cystine, 0.6 threonine, 0.15 tryptophan, 0.55 isoleucine and 1.0 leucine.. The gestation diet provided 12.5 MJ of DE kgy1 and 150 g of crude protein kgy1 Ž0.38 g available lysine MJy1 of DE and other amino acids in the same ratio to lysine as given above.. 2.2. Housing and management Sows were housed in farrowing pens fitted with farrowing crates for the duration of lactation Žmean s 29.1 " 0.33 days, range s 24–35 days.. At weaning, sows were transferred by treatment to group
Table 1 The effects of boar contact frequency on the timing of post-weaning oestrus Boar contact frequency Žno. exposures dayy1 .
No. of sows allocated Mean weaning-to-mating interval Ždays. SEM Proportion attaining oestrus within 7 days of weaning Proportion of anoestrus sows a a
Defined as failing to exhibit oestrus within 21 days of weaning.
0
1
2
3
48 5.5 0.34 0.85 0.04
48 5.5 0.43 0.87 0.04
48 5.4 0.45 0.81 0.06
48 4.9 0.24 0.94 0.00
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
pens Ž4 sows groupy1 . which were not adjacent to boars. All sows in boar contact treatments were taken to an outdoor pen Ž22 m2 . for a 5-min period of boar contact once, twice or three times dayy1 . Six boars were randomly used, these being at least 10 months of age and performing regular matings. Vulval reddening, vulval swelling, and response to a back pressure test were recorded for all sows twice daily. Once detected in oestrus each sow was given 2 fertile matings 24 h apart. Any sow failing to exhibit oestrus within 21 days of weaning was classified as anoestrus. During gestation sows were individually housed in tethered accommodation for the first 28 days post-mating and were then transferred to group housing until day 110 of the pregnancy when they were again moved to farrowing pens. 2.3. Litter performance Litter size Žtotal and born alive. was recorded for the initial litter. Cross-fostering was used to standardise the size of the litter being suckled, wherever possible, to 10 piglets littery 1 Žrange 9–12 piglets littery1 . within 48 h of birth. Creep feed Ž14.6 MJ of DE kgy1 and 202 g of crude protein kgy1 . was available ad libitum to all piglets from day 10 of lactation until weaning. The size of the subsequent litter Žtotal and born alive. was recorded for all sows that successfully conceived within 21 days of weaning the initial litter. 2.4. Statistical analysis Main treatment effects Ži.e., parity, season and boar contact. and their interactions were assessed Table 2 The effects of season on the timing of post-weaning oestrus in sows Season Spring Summer Autumn Winter No. of sows allocated 48 Mean weaning to mating 5.1 interval Ždays. SEM 0.28 Proportion attaining 0.94 oestrus within 7 days of weaning Proportion of 0.00 anoestrus sows a a
48 5.2
48 5.3
48 5.6
0.27 0.83
0.36 0.90
0.51 0.81
0.08
0.04
0.02
Defined as failing to exhibit oestrus within 21 days of weaning.
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Table 3 The effects of sow parity on the timing of post-weaning oestrus Parity
No. of sows allocated Mean weaning to mating interval Žd. SEM Proportion attaining oestrus within 7 days of weaning Proportion of anoestrus sows)
1
2–7
48 5.9a 0.38 0.73a
144 5.1b 0.21 0.92c
0.06
0.03
)Defined as failing to exhibit oestrus within 21 days of weaning. a vs. b: means are significantly different Ž P - 0.05.. a vs. c: means are significantly different Ž P - 0.01..
using the General Linear Model in the statistical package MINITAB 8.1. Treatment means were compared using Least Significant Difference Žmodified to analyse unequal numbers—Sokal and Rohlf, 1981.. Differences in farrowing rate were assessed using x 2 tests. 3. Results 3.1. InterÕal from weaning to oestrus A total of 185 sows returned to oestrus post-weaning out of the 192 sows weaned. While both the length of the weaning-to-oestrus interval and the proportion of anoestrus sows were lower for those sows given boar contact three times daily than for any other boar contact treatment neither of these differences was significant ŽTable 1.. Season also failed to significantly influence either the length of the weaning-to-oestrus interval or the proportion of Table 4 The effects of treatment on farrowing rate No. sows Farrowing rate Ž%. Boar contact frequency 0=daily 1=daily 2=daily 3=daily
46 46 45 48
95 95 98 89
Season
Spring Summer Autumn Winter
48 44 46 47
98 90 93 95
Parity
1 2 3–7
45 46 94
93 98 93
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
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Table 5 The effects of the parity of a weaned sow on the size of the subsequent litter Parity
No. of sows providing litter size data Litter size—total born SEM Litter size—born alive SEM
1
2–7
40 12.1a 0.46 11.1a 0.42
118 13.1b 0.28 12.3b 0.25
a vs. b: within a row means are significantly different Ž P - 0.05..
anoestrus sows ŽTable 2.. The weaning-to-oestrus interval was significantly longer for parity-1 sows compared with sows in parities 2–7 ŽTable 3.. No difference was apparent in this parameter between sows in parity 2 and sow in later parities Ž4.8 " 0.28 vs. 5.2 " 0.28 days respectively, P ) 0.05.. No significant two- or three-way interactions were observed between the imposed treatments for the length of the weaning-to-oestrus interval. 3.2. Gestation performance A total of 17 sows were removed from this study post-mating. The reasons for this culling were death Ž6 sows., leg weakness Ž5 sows., poor condition Ž4 sows., and aggression Ž2 sows.. Thus, farrowing rates were collected for 168 sows. The overall farrowing rate in this experiment was very high with 158 sows of the 168 mated sows Ž94.0%. giving birth to a subsequent litter. None of the imposed treatments significantly affected farrowing rate as measured by the successful birth of a litter 112–120
days after the initial mating ŽTable 4.. There was also no relationship between the length of the weaning to oestrus interval and subsequent conception rate Ž94.6% vs. 91.7% for sows with weaning to oestrus intervals of - 7 days and 7 q days respectively..
3.3. Subsequent litter size No significant interactions between season, parity and boar contact were detected for this parameter. There was no significant effect of boar contact postweaning on either total litter size at the subsequent parturition Ž13.3 " 0.45, 12.6 " 0.50, 12.6 " 0.44 and 13.0 " 0.53 for sows that were exposed after weaning to boar contact 0, 1, 2 and 3 times dayy1 respectively. or on the number of piglets born alive littery1 Ž12.6 " 0.43, 11.4 " 0.46, 11.8 " 0.39 and 12.2 " 0.46 for sows that were exposed postweaning to boar contact 0, 1, 2 and 3 times dayy1 respectively.. The season in which a sow was weaned also failed to influence subsequent litter size Ž11.9 " 0.45, 12.2 " 0.43, 11.4 " 0.47 and 12.3 " 0.38 piglets born alive littery1 for sows weaned in the spring, summer, autumn and winter respectively.. The size of the subsequent litter was significantly influenced by the parity of the sow. Both total litter size and the number of piglets born alive tended to increase with increasing sow parity Ž12.1 " 0.46 vs. 12.7 " 0.47 vs. 13.4 " 0.34 piglets born and 11.1 " 0.42 vs. 11.9 " 0.43 vs. 12.5 " 0.30 piglets born alive to sows giving birth to their second, third or fourth–eighth litter respectively., although these dif-
Table 6 The relationship between litter size at allocation to treatment and subsequent reproductive performance of the sow Initial litter size
No. sows
Mean weaning–oestrus interval Ždays.
No. sows giving subsequent litter size data
Subsequent litter size Žtotal born.
-8 8–9 10 11 12 13 14 ) 14
16 19 26 25 21 26 29 30
5.4 5.1 5.6 5.3 5.3 5.7 5.4 4.7
15 14 20 23 19 16 25 26
11.0 11.6 12.0 12.3 11.8 13.3 14.2 15.0
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
ferences were only significant when parity-1 sows were compared with sows in subsequent parities ŽTable 5.. Subsequent litter size was not influenced by the length of the weaning to oestrus interval Ž12.0 " 0.23 vs. 12.0 " 0.61 piglets born alive in the subsequent litters to sows that had weaning to oestrus intervals of - 7 days and 7 q days respectively.. Litter size at allocation to treatment was positively related to the subsequent litter size ŽTable 6. and correlation between farrowings was significant for the total number of piglets born Ž r s 0.40, P - 0.001. or born alive Ž r s 0.37, P - 0.001..
4. Discussion In the present experiment, sow parity influenced the length of the weaning-to-oestrus interval in full agreement with previous reports ŽAumaitre et al., 1975, 1976; Paterson et al., 1978; Martinat-Botte´ et al., 1985; Walton, 1986.. Present data show that this effect was primarily due to the difference between parity-1 sows and others. This has also been reported by other authors Že.g., Paterson et al., 1978; Martinat-Botte´ et al., 1985., although some reports have suggested that the weaning-to-oestrus interval continues to decrease as parity number increases Žsee Aumaitre et al., 1976.. It is interesting to note that, unlike the results of Walton Ž1986., the slight delay in return to oestrus post-weaning in parity-1 sows was not affected by boar exposure. The length of the weaning to oestrus interval was not significantly affected by the season of the year in which weaning occurred, even in primiparous sows. This finding contrasts with most reports in the literature, particularly in relation to the adverse seasonal effects of summerrearly autumn on the weaning-tooestrus interval in sows ŽAumaitre et al., 1976; Hurtgen et al., 1980; Hemsworth et al., 1982; Britt et al., 1983; Cox et al., 1983; Armstrong et al., 1986.. Similarly, in the present study boar contact after weaning failed to reduce the weaning to oestrus interval in either parity-1 or multiparous sows. These data are in agreement with those reported by Dyck Ž1988. but contrast with those from Walton Ž1986. and Pearce and Pearce Ž1992. showing that boar exposure reduces the duration of the weaning-tooestrus interval.
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It is unclear why no season or boar effects were seen in the present study. However, it should be noted that during the ‘worst’ season in this study Žwinter. the mean interval from weaning to oestrus was only 5.6 days and that 81% of all weaned sows had returned to oestrus within 7 days of weaning. These data suggest that, in this study, the majority of sows were reproductively fully competent postweaning—i.e., follicular growth, maturation and ovulation occurred at the maximum rate in these animals without the provision of additional stimuli. Indeed, it seems likely that some herds, such as the one used in this study and that studied by Clark et al. Ž1986., are genetically pre-disposed to return to oestrus readily after weaning Žsee ten Napel et al., 1995.. In contrast, the other cited reports in the literature indicate that the mean length of the weaning-to-oestrus interval is considerably greater than in the present study, being in the region of 8–17 days in the winter months and 17–28 days in the summer and early autumn. In these circumstances it is probable that removal of negative seasonal influences, such as high ambient temperatures or long daylength ŽHurtgen et al., 1980; Cox et al., 1983; Claus and Weiler, 1985., may reduce the duration of postweaning anoestrus. Similarly, it seems probable that a ‘boar effect’ should only be seen in weaned sows if delayed return to oestrus Ž) 7 days. occurs in a large proportion of control sows Že.g., Walton, 1986; Hemsworth et al., 1982; Pearce and Pearce, 1992.. Recent studies in the prepubertal gilt—where the ‘boar effect’ is most commonly seen to be stimulatory—have noted that frequent boar contact Ž2 or 3 times daily. is considerably more effective as a stimulus for oestrus than is a single daily period of boar contact ŽHughes, 1994a; Philip and Hughes, 1995.. It would, therefore, be of considerable interest to test similar boar exposure regimens in weaned sows. The results of the present study clearly show no advantage for frequent boar contact in sows that are returning to oestrus on average 5.5 days after weaning without provision of boar contact. However, it remains probable that a frequent boar contact regimen may reduce the duration of the weaning-to-oestrus interval in sows that would not otherwise readily return to oestrus post-weaning. Farrowing rate was extremely high in the present
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P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
study Ž94%. and was unaffected by boar contact after weaning, season, parity or the length of the weaning-to-oestrus interval. The lack of a seasonal effect on farrowing rate is somewhat surprising in view of the wealth of data suggesting that a seasonal pattern exists for this parameter, with maximum values occurring in the winterrspring and minimum values being seen in summer and early autumn Žfor review see Love et al., 1993.. The reasonŽs. for these between-study differences are unknown, although it is possible that aspects of matingrgestation management, such as housing conditions, ameliorated potential problems Žsee Martinat-Botte´ et al., 1985.. Present results are in contrast with others showing that farrowing rate is lower for parity-1 sows than for those in later parities ŽBritt et al., 1983; Martinat-Botte´ et al., 1984., although there is no evidence to suggest that farrowing rate varies in later parities Žsee Martinat-Botte´ et al., 1985.. Where parity differences in farrowing rate have been reported it has been suggested that the relationship is actually between the length of the weaning-to-oestrus interval and farrowing rate since parity-1 sows tend to take longer to return to oestrus post-weaning than do their older counterparts Žsee Tomes and Nielsen, 1982; Martinat-Botte´ et al., 1985.. No such relationship was observed in the current study. Litter size was significantly influenced by both sow parity and size of the previous litter, but was not affected by either boar contact post-weaning or season. Seasonal variations in litter size have been observed in some studies but not in others, as pointed out by Love et al. Ž1993.. The relationship between parity and litter size is well documented Žsee Hughes and Varley, 1980.. The number of piglets produced in a litter usually increases from first to second litter, and from second to third litter, but then plateaus until approximately the seventh or eighth litter ŽHughes and Varley, 1980; Hughes, 1994b.. Our results provide further support for the existence of this relationship. Moreover, our data show a good repeatability of litter size between two successive parities. It should be noted that the square of the coefficient of variation Žaround 0.16. is very close to the heritability of litter size Ž0.15. which was reported by Haley et al. Ž1988.. In conclusion, the present results confirm the effect of sow parity on the length of the weaning-to-
oestrus interval. They also indicate that, under some circumstances, neither season nor boar contact influences the timing of the post-weaning oestrus. It is suggested that this finding reflects the relatively short duration of the weaning-to-oestrus interval in nearly all sows in the current study.
Acknowledgements The author thanks the Australian Pig Research and Development Corporation for their financial support and Mr. J. Ferlazzo for his technical help.
References Armstrong, J.D., Britt, J.H., Kraeling, R.R., 1986. Effect of restriction of energy during lactation on body condition, energy metabolism, endocrine changes and reproductive performance in primiparous sows. J. Anim. Sci. 53, 1915–1925. Aumaitre, A., Dagorn, J., Legault, C., le Denmat, M., 1976. Influence of farm management and breed type on sow’s conception–weaning interval and productivity in France. Livest. Prod. Sci. 3, 75–83. Aumaitre, A., Perez, J.M., Chauvel, J., 1975. Effet de l’habitat et de l’age au sevrage sur les composentres de la productivite des truies en France. J. Rech. Porcine France 7, 52–67. Barb, C.R., Estienne, M.J., Kraeling, R.R., Marple, D.N., Rampacek, P.B., Rahe, C.H., Sartin, J.L., 1991. Endocrine changes in sows exposed to elevated ambient temperature during lactation. Dom. An. Endo. 8, 117–127. Britt, J.H., Szarek, V.E., Levis, D.G., 1983. Characterization of summer infertility of sows in large confinement units. Theriogenology 20, 133–140. Clark, J.R., Komkov, A., Tribble, L.F., 1986. Effects of parity, season, gonadotropin releasing hormone and altered suckling intensity on the interval to rebreeding in sows. Theriogenology 26, 299–308. Claus, R., Weiler, U., 1985. Influence of light and photoperiodicity on pig prolificacy. J. Reprod. Fert. 33, 185–197, Suppl. Cox, N.M., Britt, J.H., Armstrong, W.D., Alhusen, H.D., 1983. Effect of feeding fat and altered weaning schedule on rebreeding in primiparous sows. J. Anim. Sci. 56, 21–29. den Hartog, L.A., Vesseur, P.C., Kemp, B., 1994. Nutrition-reproduction interactions in the sow. In: Cole, D.J.A., Wiseman, J., Varley, M.A. ŽEds.., Principles of Pig Science, Nottingham Univ. Press, UK. Dyck, G.W., 1988. The effect of housing facilities and boar exposure after weaning on the incidence of postlactational anestrus in primiparous sows. Can. J. Anim. Sci. 68, 983–985. Haley, C.S., Avalos, E., Smith, C., 1988. Selection for litter size in the pig. Anim. Br. 56, 317–332, Abstr. Hartmann, P.E., Hughes, P.E., 1996. Lactation. In: Dunkin, A.C.,
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157 Taverner, M.R. ŽEds.., World Animal Science, C. ProductionSystem Approach. 10. Pig Production. Elsevier, Amsterdam. Hemsworth, P.H., Salden, N.T.C.J., Hoogerbrugge, A., 1982. The influence of the post-weaning social environment on the weaning to mating interval of the sow. Anim. Prod. 35, 41–48. Henderson, R., Hughes, P.E., 1984. The effects of partial weaning, movement and boar contact on the subsequent reproductive performance of lactating sows. Anim. Prod. 39, 131–136. Hughes, P.E., 1994a. The role of contact frequency in modifying the efficacy of the boar effect. Anim. Reprod. Sci. 35, 273– 280. Hughes, P.E., 1994b. Nutrition of the replacement gilt and breeding sow. In: Proc. Aust. Assoc. Pig Vet., Canberra, 1994, pp. 35–40. Hughes, P.E., Hemsworth, P.H., 1994. Mating management and A.I. In: Cole, D.J.A., Wiseman, J., Varley, M.A. ŽEds.., Principles of Pig Science. Nottingham Univ. Press, UK. Hughes, P.E., Varley, M.A., 1980. Reproduction in the Pig. Butterworths, London. Hurtgen, J.P., Leman, A.D., Crabo, B., 1980. Seasonal influence on oestrous activity in sows and gilts. J. Am. Vet. Med. Assoc. 176, 119–123. Love, R.J., Evans, G., Klupiec, C., 1993. Seasonal effects on fertility in gilts and sows. J. Reprod. Fert. 48, 191–206, Suppl. Martinat-Botte, ´ F., Bariteau, F., Badouard, B., Terqui, M., 1985. Control of pig reproduction in a breeding programme. J. Reprod. Fert. 33, 211–228, Suppl. Martinat-Botte, ´ F., Dagorn, J., Terqui, M., Dando, P., 1984. Effect of confinement, climatic conditions and litter parity on the seasonal variations of the fertility rate and prolificacy. Ann. Rech. Vet. 15, 165–172. Paterson, A.M., Barker, I., Lindsay, D.R., 1978. Summer infertility in pigs: its incidence and characteristics in an Australian commercial piggery. Aust. J. Exp. Agric. Anim. Husb. 18, 698–701.
157
Pearce, G.P., Pearce, A.N., 1992. Contact with a sow in oestrus or a mature boar stimulates the onset of oestrus in weaned sows. Vet. Rec. 130, 5–9. Petchey, A.M., English, P.R., 1980. A note on the effects of boar presence on the performance of sows and their litters when penned as groups in late lactation. Anim. Prod. 31, 107–109. Philip, G., Hughes, P.E., 1995. The effects of contact frequency and season on the efficacy of the boar effect. Anim. Reprod. Sci. 40, 143–150. Prunier, A., Dourmad, J.Y., Etienne, M., 1994. Effect of light regimen under various ambient temperatures on sow and litter performance. J. Anim. Sci. 72, 1461–1466. Prunier, A., Quesnel, H., Messias de Braganca, M., Kermabon, A.Y., 1996. Environmental and seasonal influences on the return-to-oestrus after weaning in primiparous sows: a review. Livest. Prod. Sci. 45, 103–110. Rowlinson, P., Bryant, M.J., 1982. Lactational oestrus in the sow: 2. The influence of group housing, boar presence and feeding level upon the occurrence of oestrus in lactating sows. Anim. Prod. 34, 283–290. Sokal, R.R., Rohlf, F.J., 1981. Biometry, 2nd edn. Freeman, San Francisco, CA. ten Napel, J., Kemp, B., Luiting, P., de Vries, A.G., 1995. A biological approach to examine genetic variation in weaningto-oestrus interval in first-litter sows. Livest. Prod. Sci. 41, 81–93. Tomes, G.J., Nielsen, H.E., 1982. Factors affecting reproductive efficiency of the breeding herd. In: Cole, D.J.A., Foxcroft, G.R. ŽEds.., Control of Pig Reproduction. Butterworths, London. Walton, J.S., 1986. Effect of boar presence before and after weaning on oestrus and ovulation in sows. J. Anim. Sci. 62, 9–15. Whittemore, C.T., 1996. Nutrition reproduction interactions in primiparous sows. Livest. Prod. Sci. 46, 65–83.
Effects of parity, season and boar contact on the reproductive performance of weaned sows P.E. Hughes Department of Animal Production, Institute of Land and Food Resources, UniÕersity of Melbourne, ParkÕille 3052, Australia Received 12 May 1997; accepted 10 November 1997
Abstract Forty eight Large White= Landrace sows Ž12 from parity 1, 12 from parity 2 and 24 from parities 3–7. were allocated to each of 4 post-weaning boar contact treatments Ž0, 1, 2 or 3 exposures dayy1 . in each of the four seasons of the year. Litter size suckled was standardized at 10 piglets wherever possible Žrange 9–12 piglets. and lactation length was 24–35 days. Oestrus detection was performed twice-daily on all weaned sows and each sow was given 2 fertile matings 24 h apart. Data on anoestrus, conception rate and subsequent litter size were also collected. Sows being weaned from their first litter took significantly longer to return to oestrus post-weaning than did sows in parities 2–7 Ž5.9 " 0.38 vs. 5.1 " 0.21 days, P - 0.05.. There was no significant influence of boar contact post-weaning on the length of the rebreeding interval Ž5.5, 5.5, 5.4 and 4.9 days for sows receiving boar contact 0, 1, 2, or 3 times daily respectively.. Equally, season of the year did not significantly influence the length of the rebreeding interval Ž5.1, 5.2, 5.3 and 5.6 days for sows being weaned in spring, summer, autumn and winter respectively.. The size of the litter subsequently produced was significantly influenced by sow parity Ž12.1 " 0.46 vs. 13.1 " 0.28 piglets born to sows having either their second or third–eighth litter respectively. but was not significantly affected by either boar contact in the post-weaning period or season of the year. Subsequent litter size was also significantly affected by the litter size of the sow at the start of the experiment Ž r s 0.40, P - 0.001.. These results suggest that, with the exception of parity-1 sows, extended weaning-to-oestrus intervals are not a major problem in some sow genotypes. Furthermore, where the weaning-to-oestrus interval is extended, these results indicate that the provision of regular boar contact post-weaning is unlikely to stimulate an earlier return to oestrus. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Pigs; Boar contact; Season; Parity; Oestrus; Litter size
1. Introduction The length of the interval from weaning to oestrus is initially determined by the parity of the sow, season and herd ŽMartinat-Botte´ et al., 1985.. An early return to oestrus post-weaning may be stimulated by either partial- or split-weaning or the provision of regular boar contact Žsee Hughes and Hemsworth, 1994.. Conversely, return to oestrus
post-weaning may be delayed if early weaning is practiced, when sow nutrition is inadequate during lactation and, possibly, after-weaning ŽWhittemore, 1996. andror when sows are individually housed after weaning ŽHartmann and Hughes, 1996; den Hartog et al., 1994.. There is general agreement that the weaning-tooestrus interval decreases as sow parity increases ŽAumaitre et al., 1975; Martinat-Botte´ et al., 1985..
0301-6226r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 1 - 6 2 2 6 Ž 9 7 . 0 0 1 7 5 - 9
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Similarly, the length of the weaning-to-oestrus interval appears to become more consistent Ži.e., less spread. as sow parity increases Žsee Hughes and Varley, 1980.. These effects of sow parity on the timing of the post-weaning oestrus appear to be primarily due to differences between sows in parities 1–2 and those in later parities. Season also influences the timing of post-weaning oestrus, sows weaned in the summer months taking longer to return to oestrus than sows weaned at other times of the year ŽBritt et al., 1983; Claus and Weiler, 1985.. This effect is probably due to long light duration and, more obviously, to high ambient temperature ŽBarb et al., 1991; Prunier et al., 1994, 1996.. However, the use of cooling systems does not prevent the extension of the weaning-to-oestrus interval in summer ŽHurtgen et al., 1980; Cox et al., 1983.. Boar contact Žthe boar effect. has been demonstrated to be effective in reducing the weaning-tooestrus interval with contacts starting either before or after weaning Že.g., Petchey and English, 1980; Hemsworth et al., 1982; Rowlinson and Bryant, 1982; Henderson and Hughes, 1984; Walton, 1986; Pearce and Pearce, 1992.. What is not known is how boar contact, parity and season interact to affect the length of the weaning to oestrus interval. The present study was conducted to evaluate the effects of these three factors, and their interactions, on the weaning to oestrus interval. In addition, since recent studies in the gilt strongly suggest that the efficacy of the boar effect may be enhanced with frequency of daily boar exposure ŽHughes, 1994a., the influence of the number of daily boar contacts during the post-weaning period was determined.
2. Materials and methods 2.1. Animals and treatments This study used 192 Large White = Landrace sows from the Mt. Derrimut herd of the University of Melbourne. Forty eight sows from each of parities 1 and 2 were used, the remaining 96 sows being from parities 3–7. In each season of the year 12 parity-1 sows, 12 parity-2 sows and 24 sows from parities 3–7 were allocated to the following post-weaning treatments: Control—no boar contact Once-daily boar contact Ž5 min dayy1 . Twice-daily boar contact Ž2 = 5 min dayy1 . Thrice-daily boar contact Ž3 = 5 min dayy1 . All sows were fed 6 kg dayy1 in lactation, 3.5 kg dayy1 from weaning to remating and 2.3 kg dayy1 during gestation. The diet fed during lactation and from weaning to remating contained 14.2 MJ of DE kgy1 and 188 g of crude protein kgy1 Ž0.44 g available lysine MJy1 of DE and other essential amino acids in a ratio to lysine of 0.5 methionineq cystine, 0.6 threonine, 0.15 tryptophan, 0.55 isoleucine and 1.0 leucine.. The gestation diet provided 12.5 MJ of DE kgy1 and 150 g of crude protein kgy1 Ž0.38 g available lysine MJy1 of DE and other amino acids in the same ratio to lysine as given above.. 2.2. Housing and management Sows were housed in farrowing pens fitted with farrowing crates for the duration of lactation Žmean s 29.1 " 0.33 days, range s 24–35 days.. At weaning, sows were transferred by treatment to group
Table 1 The effects of boar contact frequency on the timing of post-weaning oestrus Boar contact frequency Žno. exposures dayy1 .
No. of sows allocated Mean weaning-to-mating interval Ždays. SEM Proportion attaining oestrus within 7 days of weaning Proportion of anoestrus sows a a
Defined as failing to exhibit oestrus within 21 days of weaning.
0
1
2
3
48 5.5 0.34 0.85 0.04
48 5.5 0.43 0.87 0.04
48 5.4 0.45 0.81 0.06
48 4.9 0.24 0.94 0.00
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
pens Ž4 sows groupy1 . which were not adjacent to boars. All sows in boar contact treatments were taken to an outdoor pen Ž22 m2 . for a 5-min period of boar contact once, twice or three times dayy1 . Six boars were randomly used, these being at least 10 months of age and performing regular matings. Vulval reddening, vulval swelling, and response to a back pressure test were recorded for all sows twice daily. Once detected in oestrus each sow was given 2 fertile matings 24 h apart. Any sow failing to exhibit oestrus within 21 days of weaning was classified as anoestrus. During gestation sows were individually housed in tethered accommodation for the first 28 days post-mating and were then transferred to group housing until day 110 of the pregnancy when they were again moved to farrowing pens. 2.3. Litter performance Litter size Žtotal and born alive. was recorded for the initial litter. Cross-fostering was used to standardise the size of the litter being suckled, wherever possible, to 10 piglets littery 1 Žrange 9–12 piglets littery1 . within 48 h of birth. Creep feed Ž14.6 MJ of DE kgy1 and 202 g of crude protein kgy1 . was available ad libitum to all piglets from day 10 of lactation until weaning. The size of the subsequent litter Žtotal and born alive. was recorded for all sows that successfully conceived within 21 days of weaning the initial litter. 2.4. Statistical analysis Main treatment effects Ži.e., parity, season and boar contact. and their interactions were assessed Table 2 The effects of season on the timing of post-weaning oestrus in sows Season Spring Summer Autumn Winter No. of sows allocated 48 Mean weaning to mating 5.1 interval Ždays. SEM 0.28 Proportion attaining 0.94 oestrus within 7 days of weaning Proportion of 0.00 anoestrus sows a a
48 5.2
48 5.3
48 5.6
0.27 0.83
0.36 0.90
0.51 0.81
0.08
0.04
0.02
Defined as failing to exhibit oestrus within 21 days of weaning.
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Table 3 The effects of sow parity on the timing of post-weaning oestrus Parity
No. of sows allocated Mean weaning to mating interval Žd. SEM Proportion attaining oestrus within 7 days of weaning Proportion of anoestrus sows)
1
2–7
48 5.9a 0.38 0.73a
144 5.1b 0.21 0.92c
0.06
0.03
)Defined as failing to exhibit oestrus within 21 days of weaning. a vs. b: means are significantly different Ž P - 0.05.. a vs. c: means are significantly different Ž P - 0.01..
using the General Linear Model in the statistical package MINITAB 8.1. Treatment means were compared using Least Significant Difference Žmodified to analyse unequal numbers—Sokal and Rohlf, 1981.. Differences in farrowing rate were assessed using x 2 tests. 3. Results 3.1. InterÕal from weaning to oestrus A total of 185 sows returned to oestrus post-weaning out of the 192 sows weaned. While both the length of the weaning-to-oestrus interval and the proportion of anoestrus sows were lower for those sows given boar contact three times daily than for any other boar contact treatment neither of these differences was significant ŽTable 1.. Season also failed to significantly influence either the length of the weaning-to-oestrus interval or the proportion of Table 4 The effects of treatment on farrowing rate No. sows Farrowing rate Ž%. Boar contact frequency 0=daily 1=daily 2=daily 3=daily
46 46 45 48
95 95 98 89
Season
Spring Summer Autumn Winter
48 44 46 47
98 90 93 95
Parity
1 2 3–7
45 46 94
93 98 93
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157
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Table 5 The effects of the parity of a weaned sow on the size of the subsequent litter Parity
No. of sows providing litter size data Litter size—total born SEM Litter size—born alive SEM
1
2–7
40 12.1a 0.46 11.1a 0.42
118 13.1b 0.28 12.3b 0.25
a vs. b: within a row means are significantly different Ž P - 0.05..
anoestrus sows ŽTable 2.. The weaning-to-oestrus interval was significantly longer for parity-1 sows compared with sows in parities 2–7 ŽTable 3.. No difference was apparent in this parameter between sows in parity 2 and sow in later parities Ž4.8 " 0.28 vs. 5.2 " 0.28 days respectively, P ) 0.05.. No significant two- or three-way interactions were observed between the imposed treatments for the length of the weaning-to-oestrus interval. 3.2. Gestation performance A total of 17 sows were removed from this study post-mating. The reasons for this culling were death Ž6 sows., leg weakness Ž5 sows., poor condition Ž4 sows., and aggression Ž2 sows.. Thus, farrowing rates were collected for 168 sows. The overall farrowing rate in this experiment was very high with 158 sows of the 168 mated sows Ž94.0%. giving birth to a subsequent litter. None of the imposed treatments significantly affected farrowing rate as measured by the successful birth of a litter 112–120
days after the initial mating ŽTable 4.. There was also no relationship between the length of the weaning to oestrus interval and subsequent conception rate Ž94.6% vs. 91.7% for sows with weaning to oestrus intervals of - 7 days and 7 q days respectively..
3.3. Subsequent litter size No significant interactions between season, parity and boar contact were detected for this parameter. There was no significant effect of boar contact postweaning on either total litter size at the subsequent parturition Ž13.3 " 0.45, 12.6 " 0.50, 12.6 " 0.44 and 13.0 " 0.53 for sows that were exposed after weaning to boar contact 0, 1, 2 and 3 times dayy1 respectively. or on the number of piglets born alive littery1 Ž12.6 " 0.43, 11.4 " 0.46, 11.8 " 0.39 and 12.2 " 0.46 for sows that were exposed postweaning to boar contact 0, 1, 2 and 3 times dayy1 respectively.. The season in which a sow was weaned also failed to influence subsequent litter size Ž11.9 " 0.45, 12.2 " 0.43, 11.4 " 0.47 and 12.3 " 0.38 piglets born alive littery1 for sows weaned in the spring, summer, autumn and winter respectively.. The size of the subsequent litter was significantly influenced by the parity of the sow. Both total litter size and the number of piglets born alive tended to increase with increasing sow parity Ž12.1 " 0.46 vs. 12.7 " 0.47 vs. 13.4 " 0.34 piglets born and 11.1 " 0.42 vs. 11.9 " 0.43 vs. 12.5 " 0.30 piglets born alive to sows giving birth to their second, third or fourth–eighth litter respectively., although these dif-
Table 6 The relationship between litter size at allocation to treatment and subsequent reproductive performance of the sow Initial litter size
No. sows
Mean weaning–oestrus interval Ždays.
No. sows giving subsequent litter size data
Subsequent litter size Žtotal born.
-8 8–9 10 11 12 13 14 ) 14
16 19 26 25 21 26 29 30
5.4 5.1 5.6 5.3 5.3 5.7 5.4 4.7
15 14 20 23 19 16 25 26
11.0 11.6 12.0 12.3 11.8 13.3 14.2 15.0
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ferences were only significant when parity-1 sows were compared with sows in subsequent parities ŽTable 5.. Subsequent litter size was not influenced by the length of the weaning to oestrus interval Ž12.0 " 0.23 vs. 12.0 " 0.61 piglets born alive in the subsequent litters to sows that had weaning to oestrus intervals of - 7 days and 7 q days respectively.. Litter size at allocation to treatment was positively related to the subsequent litter size ŽTable 6. and correlation between farrowings was significant for the total number of piglets born Ž r s 0.40, P - 0.001. or born alive Ž r s 0.37, P - 0.001..
4. Discussion In the present experiment, sow parity influenced the length of the weaning-to-oestrus interval in full agreement with previous reports ŽAumaitre et al., 1975, 1976; Paterson et al., 1978; Martinat-Botte´ et al., 1985; Walton, 1986.. Present data show that this effect was primarily due to the difference between parity-1 sows and others. This has also been reported by other authors Že.g., Paterson et al., 1978; Martinat-Botte´ et al., 1985., although some reports have suggested that the weaning-to-oestrus interval continues to decrease as parity number increases Žsee Aumaitre et al., 1976.. It is interesting to note that, unlike the results of Walton Ž1986., the slight delay in return to oestrus post-weaning in parity-1 sows was not affected by boar exposure. The length of the weaning to oestrus interval was not significantly affected by the season of the year in which weaning occurred, even in primiparous sows. This finding contrasts with most reports in the literature, particularly in relation to the adverse seasonal effects of summerrearly autumn on the weaning-tooestrus interval in sows ŽAumaitre et al., 1976; Hurtgen et al., 1980; Hemsworth et al., 1982; Britt et al., 1983; Cox et al., 1983; Armstrong et al., 1986.. Similarly, in the present study boar contact after weaning failed to reduce the weaning to oestrus interval in either parity-1 or multiparous sows. These data are in agreement with those reported by Dyck Ž1988. but contrast with those from Walton Ž1986. and Pearce and Pearce Ž1992. showing that boar exposure reduces the duration of the weaning-tooestrus interval.
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It is unclear why no season or boar effects were seen in the present study. However, it should be noted that during the ‘worst’ season in this study Žwinter. the mean interval from weaning to oestrus was only 5.6 days and that 81% of all weaned sows had returned to oestrus within 7 days of weaning. These data suggest that, in this study, the majority of sows were reproductively fully competent postweaning—i.e., follicular growth, maturation and ovulation occurred at the maximum rate in these animals without the provision of additional stimuli. Indeed, it seems likely that some herds, such as the one used in this study and that studied by Clark et al. Ž1986., are genetically pre-disposed to return to oestrus readily after weaning Žsee ten Napel et al., 1995.. In contrast, the other cited reports in the literature indicate that the mean length of the weaning-to-oestrus interval is considerably greater than in the present study, being in the region of 8–17 days in the winter months and 17–28 days in the summer and early autumn. In these circumstances it is probable that removal of negative seasonal influences, such as high ambient temperatures or long daylength ŽHurtgen et al., 1980; Cox et al., 1983; Claus and Weiler, 1985., may reduce the duration of postweaning anoestrus. Similarly, it seems probable that a ‘boar effect’ should only be seen in weaned sows if delayed return to oestrus Ž) 7 days. occurs in a large proportion of control sows Že.g., Walton, 1986; Hemsworth et al., 1982; Pearce and Pearce, 1992.. Recent studies in the prepubertal gilt—where the ‘boar effect’ is most commonly seen to be stimulatory—have noted that frequent boar contact Ž2 or 3 times daily. is considerably more effective as a stimulus for oestrus than is a single daily period of boar contact ŽHughes, 1994a; Philip and Hughes, 1995.. It would, therefore, be of considerable interest to test similar boar exposure regimens in weaned sows. The results of the present study clearly show no advantage for frequent boar contact in sows that are returning to oestrus on average 5.5 days after weaning without provision of boar contact. However, it remains probable that a frequent boar contact regimen may reduce the duration of the weaning-to-oestrus interval in sows that would not otherwise readily return to oestrus post-weaning. Farrowing rate was extremely high in the present
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study Ž94%. and was unaffected by boar contact after weaning, season, parity or the length of the weaning-to-oestrus interval. The lack of a seasonal effect on farrowing rate is somewhat surprising in view of the wealth of data suggesting that a seasonal pattern exists for this parameter, with maximum values occurring in the winterrspring and minimum values being seen in summer and early autumn Žfor review see Love et al., 1993.. The reasonŽs. for these between-study differences are unknown, although it is possible that aspects of matingrgestation management, such as housing conditions, ameliorated potential problems Žsee Martinat-Botte´ et al., 1985.. Present results are in contrast with others showing that farrowing rate is lower for parity-1 sows than for those in later parities ŽBritt et al., 1983; Martinat-Botte´ et al., 1984., although there is no evidence to suggest that farrowing rate varies in later parities Žsee Martinat-Botte´ et al., 1985.. Where parity differences in farrowing rate have been reported it has been suggested that the relationship is actually between the length of the weaning-to-oestrus interval and farrowing rate since parity-1 sows tend to take longer to return to oestrus post-weaning than do their older counterparts Žsee Tomes and Nielsen, 1982; Martinat-Botte´ et al., 1985.. No such relationship was observed in the current study. Litter size was significantly influenced by both sow parity and size of the previous litter, but was not affected by either boar contact post-weaning or season. Seasonal variations in litter size have been observed in some studies but not in others, as pointed out by Love et al. Ž1993.. The relationship between parity and litter size is well documented Žsee Hughes and Varley, 1980.. The number of piglets produced in a litter usually increases from first to second litter, and from second to third litter, but then plateaus until approximately the seventh or eighth litter ŽHughes and Varley, 1980; Hughes, 1994b.. Our results provide further support for the existence of this relationship. Moreover, our data show a good repeatability of litter size between two successive parities. It should be noted that the square of the coefficient of variation Žaround 0.16. is very close to the heritability of litter size Ž0.15. which was reported by Haley et al. Ž1988.. In conclusion, the present results confirm the effect of sow parity on the length of the weaning-to-
oestrus interval. They also indicate that, under some circumstances, neither season nor boar contact influences the timing of the post-weaning oestrus. It is suggested that this finding reflects the relatively short duration of the weaning-to-oestrus interval in nearly all sows in the current study.
Acknowledgements The author thanks the Australian Pig Research and Development Corporation for their financial support and Mr. J. Ferlazzo for his technical help.
References Armstrong, J.D., Britt, J.H., Kraeling, R.R., 1986. Effect of restriction of energy during lactation on body condition, energy metabolism, endocrine changes and reproductive performance in primiparous sows. J. Anim. Sci. 53, 1915–1925. Aumaitre, A., Dagorn, J., Legault, C., le Denmat, M., 1976. Influence of farm management and breed type on sow’s conception–weaning interval and productivity in France. Livest. Prod. Sci. 3, 75–83. Aumaitre, A., Perez, J.M., Chauvel, J., 1975. Effet de l’habitat et de l’age au sevrage sur les composentres de la productivite des truies en France. J. Rech. Porcine France 7, 52–67. Barb, C.R., Estienne, M.J., Kraeling, R.R., Marple, D.N., Rampacek, P.B., Rahe, C.H., Sartin, J.L., 1991. Endocrine changes in sows exposed to elevated ambient temperature during lactation. Dom. An. Endo. 8, 117–127. Britt, J.H., Szarek, V.E., Levis, D.G., 1983. Characterization of summer infertility of sows in large confinement units. Theriogenology 20, 133–140. Clark, J.R., Komkov, A., Tribble, L.F., 1986. Effects of parity, season, gonadotropin releasing hormone and altered suckling intensity on the interval to rebreeding in sows. Theriogenology 26, 299–308. Claus, R., Weiler, U., 1985. Influence of light and photoperiodicity on pig prolificacy. J. Reprod. Fert. 33, 185–197, Suppl. Cox, N.M., Britt, J.H., Armstrong, W.D., Alhusen, H.D., 1983. Effect of feeding fat and altered weaning schedule on rebreeding in primiparous sows. J. Anim. Sci. 56, 21–29. den Hartog, L.A., Vesseur, P.C., Kemp, B., 1994. Nutrition-reproduction interactions in the sow. In: Cole, D.J.A., Wiseman, J., Varley, M.A. ŽEds.., Principles of Pig Science, Nottingham Univ. Press, UK. Dyck, G.W., 1988. The effect of housing facilities and boar exposure after weaning on the incidence of postlactational anestrus in primiparous sows. Can. J. Anim. Sci. 68, 983–985. Haley, C.S., Avalos, E., Smith, C., 1988. Selection for litter size in the pig. Anim. Br. 56, 317–332, Abstr. Hartmann, P.E., Hughes, P.E., 1996. Lactation. In: Dunkin, A.C.,
P.E. Hughesr LiÕestock Production Science 54 (1998) 151–157 Taverner, M.R. ŽEds.., World Animal Science, C. ProductionSystem Approach. 10. Pig Production. Elsevier, Amsterdam. Hemsworth, P.H., Salden, N.T.C.J., Hoogerbrugge, A., 1982. The influence of the post-weaning social environment on the weaning to mating interval of the sow. Anim. Prod. 35, 41–48. Henderson, R., Hughes, P.E., 1984. The effects of partial weaning, movement and boar contact on the subsequent reproductive performance of lactating sows. Anim. Prod. 39, 131–136. Hughes, P.E., 1994a. The role of contact frequency in modifying the efficacy of the boar effect. Anim. Reprod. Sci. 35, 273– 280. Hughes, P.E., 1994b. Nutrition of the replacement gilt and breeding sow. In: Proc. Aust. Assoc. Pig Vet., Canberra, 1994, pp. 35–40. Hughes, P.E., Hemsworth, P.H., 1994. Mating management and A.I. In: Cole, D.J.A., Wiseman, J., Varley, M.A. ŽEds.., Principles of Pig Science. Nottingham Univ. Press, UK. Hughes, P.E., Varley, M.A., 1980. Reproduction in the Pig. Butterworths, London. Hurtgen, J.P., Leman, A.D., Crabo, B., 1980. Seasonal influence on oestrous activity in sows and gilts. J. Am. Vet. Med. Assoc. 176, 119–123. Love, R.J., Evans, G., Klupiec, C., 1993. Seasonal effects on fertility in gilts and sows. J. Reprod. Fert. 48, 191–206, Suppl. Martinat-Botte, ´ F., Bariteau, F., Badouard, B., Terqui, M., 1985. Control of pig reproduction in a breeding programme. J. Reprod. Fert. 33, 211–228, Suppl. Martinat-Botte, ´ F., Dagorn, J., Terqui, M., Dando, P., 1984. Effect of confinement, climatic conditions and litter parity on the seasonal variations of the fertility rate and prolificacy. Ann. Rech. Vet. 15, 165–172. Paterson, A.M., Barker, I., Lindsay, D.R., 1978. Summer infertility in pigs: its incidence and characteristics in an Australian commercial piggery. Aust. J. Exp. Agric. Anim. Husb. 18, 698–701.
157
Pearce, G.P., Pearce, A.N., 1992. Contact with a sow in oestrus or a mature boar stimulates the onset of oestrus in weaned sows. Vet. Rec. 130, 5–9. Petchey, A.M., English, P.R., 1980. A note on the effects of boar presence on the performance of sows and their litters when penned as groups in late lactation. Anim. Prod. 31, 107–109. Philip, G., Hughes, P.E., 1995. The effects of contact frequency and season on the efficacy of the boar effect. Anim. Reprod. Sci. 40, 143–150. Prunier, A., Dourmad, J.Y., Etienne, M., 1994. Effect of light regimen under various ambient temperatures on sow and litter performance. J. Anim. Sci. 72, 1461–1466. Prunier, A., Quesnel, H., Messias de Braganca, M., Kermabon, A.Y., 1996. Environmental and seasonal influences on the return-to-oestrus after weaning in primiparous sows: a review. Livest. Prod. Sci. 45, 103–110. Rowlinson, P., Bryant, M.J., 1982. Lactational oestrus in the sow: 2. The influence of group housing, boar presence and feeding level upon the occurrence of oestrus in lactating sows. Anim. Prod. 34, 283–290. Sokal, R.R., Rohlf, F.J., 1981. Biometry, 2nd edn. Freeman, San Francisco, CA. ten Napel, J., Kemp, B., Luiting, P., de Vries, A.G., 1995. A biological approach to examine genetic variation in weaningto-oestrus interval in first-litter sows. Livest. Prod. Sci. 41, 81–93. Tomes, G.J., Nielsen, H.E., 1982. Factors affecting reproductive efficiency of the breeding herd. In: Cole, D.J.A., Foxcroft, G.R. ŽEds.., Control of Pig Reproduction. Butterworths, London. Walton, J.S., 1986. Effect of boar presence before and after weaning on oestrus and ovulation in sows. J. Anim. Sci. 62, 9–15. Whittemore, C.T., 1996. Nutrition reproduction interactions in primiparous sows. Livest. Prod. Sci. 46, 65–83.