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The effect of age at stimulation by relocation and first mature boar contact on the attainment of puberty in the gilt
Animal Reproduction Science, 12 (1986) 31--38
31
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
THE EFFECT OF AGE AT STIMULATION BY RELOCATION AND FIRST MATURE BOAR CONTACT ON THE ATTAINMENT OF PUBERTY IN THE GILT PHILIPPA R. EASTHAM 1, G.W. DYCK 2 and D~I.A. COLE
Department o f Agricultur e and Horticulture, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough, Leics, LE12 5 RD (Great Britain) (Accepted 24 April 1986)
ABSTRACT
Eastham, P.R., Dyck, G.W. and Cole, D.J.A., 1986. The effect of age at stimulation b y relocation and first mature boar contact on the attainment of p u b e r t y in the gilt. Anim. Reprod. Sci., 12: 31--38. Thirty-four Landrace × (Landrace × Large White) gilts were randomly allocated at a mean age o f 70 days to one of three treatments. The treatments involved gilts being relocated and housed adjacent to a mature boar (their first boar contact) in addition to having full contact with a boar for 30 rain each day at a mean age of 160, 180 or 200 days. The gilts were served twice at the pubertal oestrus and the reproductive tracts were examined at slaughter 21 days later to determine ovulation rate and embryo survival. Delaying the application of a p u b e r t y stimulus b e y o n d a mean gilt age of 160 days resulted in gilts being significantly (P < 0.001) older and heavier at puberty. The mean time taken from first stimulation to p u b e r t y was similar for gilts in the 160-days-of-age and 180-days-of-age groups but was significantly (P < 0.05) shorter for gilts in the 200-daysof-age group and this result was not due to extreme animals. The three treatment groups had a similar pattern of p u b e r t y attainment. Age at first stimulation had no significant effects on the early reproductive performance of the gilts.
INTRODUCTION The introduction of a mature boar to prepubertal gilts stimulates the attainment of puberty with the greatest reliability in terms of the induction interval, synchrony of puberty onset and age at puberty when gilts have first boar contact between 150 and 170 days of age and more specifically at 160--165 days of age (Brooks and Cole, 1970; Shearer and Adam, 1973; Bourn et al., 1974; Bourn et al., 1975; Hughes and Cole, 1976; Kirkwood a n d H u g h e s , 1 9 7 9 ; B r o o k s a n d S m i t h , 1 9 8 0 ; K i r k w o o d e t al., 1 9 8 1 ; C o l e e t
Present addresses: 1 Edinburgh School of Agriculture, West Mains Road, Edinburgh EH9 3JG (Great Britain) 2Agriculture Canada Research Station, Brandon, Man. R 7 A 5Z7 (Canada) R e p r i n t requests should be sent to Dr. D.J.A. Cole. 0378-4320/86/$03.50
© 1986 Elsevier Science Publishers B.V.
32 al., 1982; Deligeorgis et al., 1984). The interval from first boar contact to p u b e r t y and hence age at p u b e r t y differs between herds, possibly as a result o f genotype and management differences, and also variations have been recorded between trials within the same herd. Data on 268 gilts stimulated to attain p u b e r t y in the University of Nottingham herd showed a mean induction interval of 11.6 days with the highest frequencies of gilts reaching p u b e r t y on days 6, 7 and 8 after boar exposure (Brooks, 1970; Pattinson, 1970; Hughes, 1976; P.R. Eastham and D.J.A. Cole, unpublished data, 1981). This experiment was designed to further investigate the consistency o f p u b e r t y induction at three different ages of relocation and first mature boar contact. MATERIALS AND METHODS Animals and treatments One hundred and two Landrace X (Landrace X Large White) gilts were used in a randomised block design to give 34 gilts per treatment. The experim e n t was arranged as three blocks o f animals using gilts born in October, February and September. At a mean age of 70 days, gilts were randomly allocated to treatment. There were three treatments in which gilts were moved from the experimental rearing house to straw-bedded pens in partly covered outside yards where t h e y were housed adjacent to a mature boar and thus received first boar c o n t a c t at a mean age of 160 (Treatment 1), 180 (Treatment 2) or 200 (Treatment 3) days. Feeding F r o m 70 to 159 days of age, gilts were group fed a standard grower diet twice daily according to the ARC (1967) scale of feeding (for diet composition see Eastham et al., 1984). From 160 days of age, gilts were each fed once daily 2.25 kg of a sow diet until mating and thereafter they received 1.8 kg/day (for diet composition see Eastham et al., 1984). Gilts were group fed the sow diet whilst in the rearing accommodation, b u t following relocation, gilts were individually fed. Water was available ad libitum throughout the trial. Oestrus detection and mating F r o m 120 days of age until p u b e r t y stimulation (160, 180 or 200 days of age), gilts were visually checked each day for any signs of oestrous activity. Following relocation, all gilts were tested for oestrus once daily by introducing a fertile, mature boar into the pen for 30 min. Oestrus was determined b y a standing heat reflex and the acceptance of intromission by the
33 boar. Gilts were m a t e d twice at the pubertal oestrus and weighed on the first day o f the oestrus period.
Slaughter Gilts were slaughtered 21 days after the first day o f mating. A n y gilt failing to reach p u b e r t y b y 50 days after relocation and first boar contact was slaughtered and the reproductive tracts examined to determine its reproductive status. The reproductive tracts were removed at slaughter and subsequently examined using the procedure described by Cole et al. (1982).
Statistical analysis Data from the interval from relocation and first boar contact to p u b e r t y (induction interval) and the age at p u b e r t y were firstly transformed logarithmically and then analysed by a censored analysis o f variance. This analysis estimates the values for those gilts which were prepubertal at slaughter b y the m e t h o d given in Taylor (1-973) such that the value m u s t be greater than the 'cut-off' point which was an i n d u c t i o n interval of 50 days in this experiment. Data for the weight at p u b e r t y assumed a normal distribution and were analysed by analysis of variance. Conception rate and e m b r y o survival data were analysed by analysis o f deviance assuming a binomial error, while ovulation rate data and the n u m b e r o f viable e m b r y o s at 21 days of pregnancy were analysed b y analysis of deviance assuming Poisson errors. RESULTS
Puberty attainment The effects of gilt age at relocation and first boar contact on the attainm e n t o f p u b e r t y are given in Table 1 and Fig. 1. Twenty-one, 28 and 26 gilts reached p u b e r t y on Treatments 1, 2 and 3, respectively. The younger gilts at relocation and first boar contact were younger and lighter at p u b e r t y with these differences between the treatment groups all being significant at the P < 0.001 level (Table 1). All three treatment groups showed a fairly synchronous pattern for the onset o f p u b e r t y (Fig. 1). However, the mean interval from the start o f stimulation to p u b e r t y was shorter (P < 0.05) for the 200-days-of-age group (Table 1) and in confirmation that this result was n o t biased b y extreme animals with extended response periods~ it was f o u n d that this difference was maintained when the 'cut-off' point for t h e experiment was artificially applied at day 10 after the imposition of the p u b e r t y stimulus.
2.2831 d (191.9) 83.0 d
0.973 a (9.40)
1.055 *a (11.35) 2.2486 ***c (177.3) 68.9 ***c
34 28 *+
34 21 ÷
180 days of age
2.3155 e (206.8) 92.5 e
0.7745 (5.94)
34 26 ÷+*
200 days of age
2.47 (72)
0.00834 (79)
0.0999(79)
Standard errors o f a difference b e t w e e n means (d.f.)
Values with different superscripts in the same row are significantly different *P< 0.05; * * * P < 0.001. + Three gilts were r e m o v e d due to inadequate growth; three gilts died; six gilts were prepubertal at slaughter; one intersex pig was removed. ++ F o u r gilts were r e m o v e d due to inadequate g r o w t h ; one gilt was prepubertal at slaughter; one gilt had previously o v u l a t e d with showing oestrus. +++ One gilt was removed due to inadequate g r o w t h ; f o u r gilts died; one intersex pig was r e m o v e d ; t w o gilts had previously ovulated without showing oestrus.
No. of gilts allocated No. of gilts reaching puberty Mean time f r o m relocation and boar contact to p u b e r t y (log days) (Days) Mean age at p u b e r t y (log days) (Days) Mean weight at p u b e r t y (kg)
160 days o f age
R e l o c a t i o n and first boar c o n t a c t at
Treatments
The effect of gilt age at relocation and first boar c o n t a c t o n the a t t a i n m e n t of p u b e r t y
TABLE 1
O9
35 10C
8C
.~
6c 5c
~
i
4c 3c 2C 1C
10
20
30
40
50
Days from relocation and boar exposure to puberty
Fig. 1. Cumulative attainment of puberty of gilts following initiation o f stimulation at varying gilt ages.(A *) Relocation and boar contact at 160 days of age; (o o) relocation and boar contact at 180 days of age; ( = - - = ) relocation and boar contact at 200 days o f age.
Reproductive performance Conception rate, ovulation rate and the number of viable embryos at 21 days o f p r e g n a n c y w e r e n o t significantly a f f e c t e d b y t r e a t m e n t s (Table 2).
TABLE 2 The effect of gilt age at relocation and first boar contact on early reproductive performance Treatments Relocation and first boar contact at
Mean number of corpora lutea Mean number o f embryos at 21 days of pregnancy Conception rate
160 days of age
180 days o f age
200 days Standard of age error +
Significance of difference between treatments
11.3
10.3
10.6
0.605
NS
9.2 16/19 ++
9.0 24/25 *++
8.7 24/26
0.612
NS NS
+ Standard errors are approximate and vary due to replication and therefore the lowest is quoted. ++ Two gilts were not mated due to leg or back problems. *++ Three gilts were not mated due to leg or back problems.
36
DISCUSSION
These results confirm the earlier reports o f Brooks and Cole (1970), Hughes and Cole (1976) and Kirkwood and Hughes (1979) which suggested t h a t delaying the stimulation o f p u b e r t y after a gilt age of about 160 days is unnecessary since the reproductive mechanisms o f the gilt are capable o f responding to a puberty stimulus at this age and developmental state. There was ~o significant difference in the interval from the start of stimulation to puberty following relocation and first boar contact at 160 days o f age or 180 days o f age and hence gilts which were exposed to the puberty stimulus at 180 days of age were significantly older and heavier at puberty t h a n those first stimulated at 160 days o f age. Similarly, gilts first stimulated at 200 days of age were significantly older and heavier than those exposed to the puberty stimulus at 180 days of age and they also showed a significantly shorter induction interval than the 160-days and 180-days age groups. The mean interval of about 11 days from relocation and first boar contact at 160 days o f age to p u b e r t y attainment is in agreement with the value calculated from 268 gilts in the Nottingham herd which were first stimulated at a similar age. In contrast to Kirkwood and Hughes (1979) who suggested t h a t the induction interval tended to increase (although not significantly) in gilts having first boar contact at 174 or 181 days of age, these results showed a similar induction interval for both the 160-days and 180days-of-age groups. There was a tendency for the induction interval to decrease with increasing age with the 200-days group showing a significantly shorter interval. This is in agreement with Hughes (1976) who suggested t h a t the induction interval was reduced in gilts first stimulated at 190 days of age compared with those stimulated at 160 days o f age. The short puberty induction interval and highly synchronised puberty onset seen in the 200-days group probably arose because all gilts in this group reached puberty during the experimental period, whereas some gilts in both the 160-days and 180days-of-age groups were prepubertal (most being in the replicate using September-born gilts in the former treatment group) and in the analysis an induction interval greater than 50 days was estimated for these gilts. All three t r e a t m e n t groups showed a synchronised onset of oestrus and this is in conflict with other workers where the degree of synchronisation decreased in the older age group gilts (Hughes and Cole, 1976; Kirkwood and Hughes, 1979). It has been suggested t h a t this loss of synchrony m a y be due to some gilts reaching puberty prior to first boar contact and thus being unaffected by the introduction of a mature boar (Hughes and Cole, 1976). No visual signs of oestrous activity prior to boar exposure were seen by these workers or in this study, which as shown by Hughes and Cole (1975) and in the experiment reported here does not always mean t h a t gilts have not yet ovulated. The highly synchronous response together with the shorter induction interval observed when gilts were relocated and exposed to a mature boar at 200 days o f age may be due to puberty stimulation occurring at a
37
similar time to the natural attainment o f p u b e r t y in this herd and therefore eliciting such a precipitous response. The results obtained in this experiment implied that gilt age at rMocation and first mature boar contact did not influence the subsequent reproductive performance which was measured in terms of conception rate, ovulation rate and the n u m b e r o f e m b r y o s at 21 days o f gestation and this is in agreement with other reports (Brooks, 1970; Aherne et al., 1976; Hughes and Cole, 1976; Kirkwood and Hughes, 1979). The chronological age o f the gilt at the time of first boar contact has been shown to be of paramount importance in determining the efficacy o f the pubertal response as assessed in terms o f the induction interval, age at puberty and the synchrony of the pubertal oestrus (see Hughes, 1982; Eastham, 1985). In conclusion, the results from this study show that gilts in this herd are capable of responding well to a p u b e r t y stimulus at a b o u t 160 days o f age and that delaying initiation of the stimulus to an older gilt age merely results in a similar or possibly slightly reduced induction interval, b u t obviously an increased age and weight at puberty. ACKNOWLEDGEMENTS
The authors w o u l d like to thank the Agricultural and F o o d Research Council for supporting this study, Mr. E.G. Clent and Mr. A.B. Messham for their assistance with the care o f the animals, Mr. J. Corbett for slaughtering the animals, and Mr. J. Craigon for his statistical advice.
REFERENCES Agricultural Research Council (ARC), 1967. Summary of requirements for energy. In: The Nutrient Requirements of Farm Livestock, No. 3, Pigs. Agricultural Research Council, London, p. 82. Aherne, F.X., Christopherson, R.J., Thompson, J.R. and Hardin, R.T., 1976. Factors affecting the onset of puberty, post-weaning oestrus and blood hormone levels of Lacombe gilts. Can. J. Anim. Sci., 56: 681--692. Bourn, P., Carlson, R., Lantz, B. and Zimmerman, D.R., 1974. Age at puberty in gilts as influenced by age at boar exposure and transport. J. Anita. Sci., 39 : 987 (Abstract). Bourn, P., Kinsey, R., Carlson, R. and Zimmerman, D.R., 1975. Puberty in gilts as influenced by boar exposure and "transport p h e n o m e n o n " J. Anita. Sci., 4 1 : 3 4 4 (Abstract). Brooks, P.H., 1970. Short-term nutrition effects o n fecundity of sows and gilts. Ph.D. Thesis, University of Nottingham. Brooks, P.H. and Cole, D.J.A., 1970. The effect of the presence of a boar on the attainment of puberty in gilts. J. Reprod. Fertil., 23 : 435--440. Brooks, P.H. and Smith, D.A., 1980. The effect of mating age o n the reproductive performance, food utilisation and liveweight change of the female pig. Livestock Prod. Sci., 7: 67--78. Cole, D.J.A., Dyck, G.W. and Nathan, S., 1982. Reproduction in the gilt. 4. The effect of rearing gilts with contemporary castrated males or intact males on the attainment of puberty. Anim. Prod., 35: 171--175.
38 Deligeorgis, S.G., Lunney, D.C. and English, P.R., 1984. A note on the efficacy of complete v. partial boar exposure on puberty attainment in the gilt. Anita. Prod., 39: 145--147. Eastham, P . R , 1985. Induction of puberty in the gilt. Ph.D. Thesis, University of Nottingham, pp. 78--84. Eastham, P.R., Dyck, G.W. and Cole, D.J.A., 1984. Reproduction in the gilt. 5. The effect of the presence of the mature male during rearing on puberty attainment. Anita. Prod., 39: 277--282. Hughes, P.E., 1976. Puberty and reproduction in the gilt. Ph.D. Thesis, University of Nottingham. Hughes, P.E., 1982. Factors affecting the natural attainment of puberty in the gilt. In: D.J.A. Cole and G.R. Foxcroft (Editors), Control of Pig Reproduction. Butterworths, London, pp. 117--137. Hughes P.E. and Cole, D.J.A., 1975. Reproduction in the gilt. 1. The influence of age and weight at puberty o n ovulation rate and embryo survival in the gilt. Anita. Prod., 21 : 183--189. Hughes, P.E. and Cole, D.J.A., 1976. Reproduction in the gilt. 2. The influence of gilt age at boar introduction on the attainment of puberty. Anita. Prod., 23 : 89--94. Kirkwood, R.N. and Hughes, P.E., 1979. The influence Of age at first boar contact on puberty attainment in the gilt. Anita. Prod., 29: 231--238. Kirkwood, R.N., Forbes, J.M. and Hughes, P.E., 1981. Influence of boar contact o n attainment of puberty in gilts after removal of the olfactory bulbs. J. Reprod. FertU., 61 : 193--196. Pattinson, M.A., 1970. Studies on puberty in the gilt. B. Sc. Thesis, University of Nottingham. Shearer, I.J. and Adam, J.L., 1973. Nutritional and physiological developments in reproduction of pigs. Proc. N.Z. Soc. Anita. Prod., 33 : 62--86. Taylor, J., 1973. The analysis of designed experiments with censored observations. Biometrics, 29: 35--43.
31
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
THE EFFECT OF AGE AT STIMULATION BY RELOCATION AND FIRST MATURE BOAR CONTACT ON THE ATTAINMENT OF PUBERTY IN THE GILT PHILIPPA R. EASTHAM 1, G.W. DYCK 2 and D~I.A. COLE
Department o f Agricultur e and Horticulture, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough, Leics, LE12 5 RD (Great Britain) (Accepted 24 April 1986)
ABSTRACT
Eastham, P.R., Dyck, G.W. and Cole, D.J.A., 1986. The effect of age at stimulation b y relocation and first mature boar contact on the attainment of p u b e r t y in the gilt. Anim. Reprod. Sci., 12: 31--38. Thirty-four Landrace × (Landrace × Large White) gilts were randomly allocated at a mean age o f 70 days to one of three treatments. The treatments involved gilts being relocated and housed adjacent to a mature boar (their first boar contact) in addition to having full contact with a boar for 30 rain each day at a mean age of 160, 180 or 200 days. The gilts were served twice at the pubertal oestrus and the reproductive tracts were examined at slaughter 21 days later to determine ovulation rate and embryo survival. Delaying the application of a p u b e r t y stimulus b e y o n d a mean gilt age of 160 days resulted in gilts being significantly (P < 0.001) older and heavier at puberty. The mean time taken from first stimulation to p u b e r t y was similar for gilts in the 160-days-of-age and 180-days-of-age groups but was significantly (P < 0.05) shorter for gilts in the 200-daysof-age group and this result was not due to extreme animals. The three treatment groups had a similar pattern of p u b e r t y attainment. Age at first stimulation had no significant effects on the early reproductive performance of the gilts.
INTRODUCTION The introduction of a mature boar to prepubertal gilts stimulates the attainment of puberty with the greatest reliability in terms of the induction interval, synchrony of puberty onset and age at puberty when gilts have first boar contact between 150 and 170 days of age and more specifically at 160--165 days of age (Brooks and Cole, 1970; Shearer and Adam, 1973; Bourn et al., 1974; Bourn et al., 1975; Hughes and Cole, 1976; Kirkwood a n d H u g h e s , 1 9 7 9 ; B r o o k s a n d S m i t h , 1 9 8 0 ; K i r k w o o d e t al., 1 9 8 1 ; C o l e e t
Present addresses: 1 Edinburgh School of Agriculture, West Mains Road, Edinburgh EH9 3JG (Great Britain) 2Agriculture Canada Research Station, Brandon, Man. R 7 A 5Z7 (Canada) R e p r i n t requests should be sent to Dr. D.J.A. Cole. 0378-4320/86/$03.50
© 1986 Elsevier Science Publishers B.V.
32 al., 1982; Deligeorgis et al., 1984). The interval from first boar contact to p u b e r t y and hence age at p u b e r t y differs between herds, possibly as a result o f genotype and management differences, and also variations have been recorded between trials within the same herd. Data on 268 gilts stimulated to attain p u b e r t y in the University of Nottingham herd showed a mean induction interval of 11.6 days with the highest frequencies of gilts reaching p u b e r t y on days 6, 7 and 8 after boar exposure (Brooks, 1970; Pattinson, 1970; Hughes, 1976; P.R. Eastham and D.J.A. Cole, unpublished data, 1981). This experiment was designed to further investigate the consistency o f p u b e r t y induction at three different ages of relocation and first mature boar contact. MATERIALS AND METHODS Animals and treatments One hundred and two Landrace X (Landrace X Large White) gilts were used in a randomised block design to give 34 gilts per treatment. The experim e n t was arranged as three blocks o f animals using gilts born in October, February and September. At a mean age of 70 days, gilts were randomly allocated to treatment. There were three treatments in which gilts were moved from the experimental rearing house to straw-bedded pens in partly covered outside yards where t h e y were housed adjacent to a mature boar and thus received first boar c o n t a c t at a mean age of 160 (Treatment 1), 180 (Treatment 2) or 200 (Treatment 3) days. Feeding F r o m 70 to 159 days of age, gilts were group fed a standard grower diet twice daily according to the ARC (1967) scale of feeding (for diet composition see Eastham et al., 1984). From 160 days of age, gilts were each fed once daily 2.25 kg of a sow diet until mating and thereafter they received 1.8 kg/day (for diet composition see Eastham et al., 1984). Gilts were group fed the sow diet whilst in the rearing accommodation, b u t following relocation, gilts were individually fed. Water was available ad libitum throughout the trial. Oestrus detection and mating F r o m 120 days of age until p u b e r t y stimulation (160, 180 or 200 days of age), gilts were visually checked each day for any signs of oestrous activity. Following relocation, all gilts were tested for oestrus once daily by introducing a fertile, mature boar into the pen for 30 min. Oestrus was determined b y a standing heat reflex and the acceptance of intromission by the
33 boar. Gilts were m a t e d twice at the pubertal oestrus and weighed on the first day o f the oestrus period.
Slaughter Gilts were slaughtered 21 days after the first day o f mating. A n y gilt failing to reach p u b e r t y b y 50 days after relocation and first boar contact was slaughtered and the reproductive tracts examined to determine its reproductive status. The reproductive tracts were removed at slaughter and subsequently examined using the procedure described by Cole et al. (1982).
Statistical analysis Data from the interval from relocation and first boar contact to p u b e r t y (induction interval) and the age at p u b e r t y were firstly transformed logarithmically and then analysed by a censored analysis o f variance. This analysis estimates the values for those gilts which were prepubertal at slaughter b y the m e t h o d given in Taylor (1-973) such that the value m u s t be greater than the 'cut-off' point which was an i n d u c t i o n interval of 50 days in this experiment. Data for the weight at p u b e r t y assumed a normal distribution and were analysed by analysis of variance. Conception rate and e m b r y o survival data were analysed by analysis o f deviance assuming a binomial error, while ovulation rate data and the n u m b e r o f viable e m b r y o s at 21 days of pregnancy were analysed b y analysis of deviance assuming Poisson errors. RESULTS
Puberty attainment The effects of gilt age at relocation and first boar contact on the attainm e n t o f p u b e r t y are given in Table 1 and Fig. 1. Twenty-one, 28 and 26 gilts reached p u b e r t y on Treatments 1, 2 and 3, respectively. The younger gilts at relocation and first boar contact were younger and lighter at p u b e r t y with these differences between the treatment groups all being significant at the P < 0.001 level (Table 1). All three treatment groups showed a fairly synchronous pattern for the onset o f p u b e r t y (Fig. 1). However, the mean interval from the start o f stimulation to p u b e r t y was shorter (P < 0.05) for the 200-days-of-age group (Table 1) and in confirmation that this result was n o t biased b y extreme animals with extended response periods~ it was f o u n d that this difference was maintained when the 'cut-off' point for t h e experiment was artificially applied at day 10 after the imposition of the p u b e r t y stimulus.
2.2831 d (191.9) 83.0 d
0.973 a (9.40)
1.055 *a (11.35) 2.2486 ***c (177.3) 68.9 ***c
34 28 *+
34 21 ÷
180 days of age
2.3155 e (206.8) 92.5 e
0.7745 (5.94)
34 26 ÷+*
200 days of age
2.47 (72)
0.00834 (79)
0.0999(79)
Standard errors o f a difference b e t w e e n means (d.f.)
Values with different superscripts in the same row are significantly different *P< 0.05; * * * P < 0.001. + Three gilts were r e m o v e d due to inadequate growth; three gilts died; six gilts were prepubertal at slaughter; one intersex pig was removed. ++ F o u r gilts were r e m o v e d due to inadequate g r o w t h ; one gilt was prepubertal at slaughter; one gilt had previously o v u l a t e d with showing oestrus. +++ One gilt was removed due to inadequate g r o w t h ; f o u r gilts died; one intersex pig was r e m o v e d ; t w o gilts had previously ovulated without showing oestrus.
No. of gilts allocated No. of gilts reaching puberty Mean time f r o m relocation and boar contact to p u b e r t y (log days) (Days) Mean age at p u b e r t y (log days) (Days) Mean weight at p u b e r t y (kg)
160 days o f age
R e l o c a t i o n and first boar c o n t a c t at
Treatments
The effect of gilt age at relocation and first boar c o n t a c t o n the a t t a i n m e n t of p u b e r t y
TABLE 1
O9
35 10C
8C
.~
6c 5c
~
i
4c 3c 2C 1C
10
20
30
40
50
Days from relocation and boar exposure to puberty
Fig. 1. Cumulative attainment of puberty of gilts following initiation o f stimulation at varying gilt ages.(A *) Relocation and boar contact at 160 days of age; (o o) relocation and boar contact at 180 days of age; ( = - - = ) relocation and boar contact at 200 days o f age.
Reproductive performance Conception rate, ovulation rate and the number of viable embryos at 21 days o f p r e g n a n c y w e r e n o t significantly a f f e c t e d b y t r e a t m e n t s (Table 2).
TABLE 2 The effect of gilt age at relocation and first boar contact on early reproductive performance Treatments Relocation and first boar contact at
Mean number of corpora lutea Mean number o f embryos at 21 days of pregnancy Conception rate
160 days of age
180 days o f age
200 days Standard of age error +
Significance of difference between treatments
11.3
10.3
10.6
0.605
NS
9.2 16/19 ++
9.0 24/25 *++
8.7 24/26
0.612
NS NS
+ Standard errors are approximate and vary due to replication and therefore the lowest is quoted. ++ Two gilts were not mated due to leg or back problems. *++ Three gilts were not mated due to leg or back problems.
36
DISCUSSION
These results confirm the earlier reports o f Brooks and Cole (1970), Hughes and Cole (1976) and Kirkwood and Hughes (1979) which suggested t h a t delaying the stimulation o f p u b e r t y after a gilt age of about 160 days is unnecessary since the reproductive mechanisms o f the gilt are capable o f responding to a puberty stimulus at this age and developmental state. There was ~o significant difference in the interval from the start of stimulation to puberty following relocation and first boar contact at 160 days o f age or 180 days o f age and hence gilts which were exposed to the puberty stimulus at 180 days of age were significantly older and heavier at puberty t h a n those first stimulated at 160 days o f age. Similarly, gilts first stimulated at 200 days of age were significantly older and heavier than those exposed to the puberty stimulus at 180 days of age and they also showed a significantly shorter induction interval than the 160-days and 180-days age groups. The mean interval of about 11 days from relocation and first boar contact at 160 days o f age to p u b e r t y attainment is in agreement with the value calculated from 268 gilts in the Nottingham herd which were first stimulated at a similar age. In contrast to Kirkwood and Hughes (1979) who suggested t h a t the induction interval tended to increase (although not significantly) in gilts having first boar contact at 174 or 181 days of age, these results showed a similar induction interval for both the 160-days and 180days-of-age groups. There was a tendency for the induction interval to decrease with increasing age with the 200-days group showing a significantly shorter interval. This is in agreement with Hughes (1976) who suggested t h a t the induction interval was reduced in gilts first stimulated at 190 days of age compared with those stimulated at 160 days o f age. The short puberty induction interval and highly synchronised puberty onset seen in the 200-days group probably arose because all gilts in this group reached puberty during the experimental period, whereas some gilts in both the 160-days and 180days-of-age groups were prepubertal (most being in the replicate using September-born gilts in the former treatment group) and in the analysis an induction interval greater than 50 days was estimated for these gilts. All three t r e a t m e n t groups showed a synchronised onset of oestrus and this is in conflict with other workers where the degree of synchronisation decreased in the older age group gilts (Hughes and Cole, 1976; Kirkwood and Hughes, 1979). It has been suggested t h a t this loss of synchrony m a y be due to some gilts reaching puberty prior to first boar contact and thus being unaffected by the introduction of a mature boar (Hughes and Cole, 1976). No visual signs of oestrous activity prior to boar exposure were seen by these workers or in this study, which as shown by Hughes and Cole (1975) and in the experiment reported here does not always mean t h a t gilts have not yet ovulated. The highly synchronous response together with the shorter induction interval observed when gilts were relocated and exposed to a mature boar at 200 days o f age may be due to puberty stimulation occurring at a
37
similar time to the natural attainment o f p u b e r t y in this herd and therefore eliciting such a precipitous response. The results obtained in this experiment implied that gilt age at rMocation and first mature boar contact did not influence the subsequent reproductive performance which was measured in terms of conception rate, ovulation rate and the n u m b e r o f e m b r y o s at 21 days o f gestation and this is in agreement with other reports (Brooks, 1970; Aherne et al., 1976; Hughes and Cole, 1976; Kirkwood and Hughes, 1979). The chronological age o f the gilt at the time of first boar contact has been shown to be of paramount importance in determining the efficacy o f the pubertal response as assessed in terms o f the induction interval, age at puberty and the synchrony of the pubertal oestrus (see Hughes, 1982; Eastham, 1985). In conclusion, the results from this study show that gilts in this herd are capable of responding well to a p u b e r t y stimulus at a b o u t 160 days o f age and that delaying initiation of the stimulus to an older gilt age merely results in a similar or possibly slightly reduced induction interval, b u t obviously an increased age and weight at puberty. ACKNOWLEDGEMENTS
The authors w o u l d like to thank the Agricultural and F o o d Research Council for supporting this study, Mr. E.G. Clent and Mr. A.B. Messham for their assistance with the care o f the animals, Mr. J. Corbett for slaughtering the animals, and Mr. J. Craigon for his statistical advice.
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38 Deligeorgis, S.G., Lunney, D.C. and English, P.R., 1984. A note on the efficacy of complete v. partial boar exposure on puberty attainment in the gilt. Anita. Prod., 39: 145--147. Eastham, P . R , 1985. Induction of puberty in the gilt. Ph.D. Thesis, University of Nottingham, pp. 78--84. Eastham, P.R., Dyck, G.W. and Cole, D.J.A., 1984. Reproduction in the gilt. 5. The effect of the presence of the mature male during rearing on puberty attainment. Anita. Prod., 39: 277--282. Hughes, P.E., 1976. Puberty and reproduction in the gilt. Ph.D. Thesis, University of Nottingham. Hughes, P.E., 1982. Factors affecting the natural attainment of puberty in the gilt. In: D.J.A. Cole and G.R. Foxcroft (Editors), Control of Pig Reproduction. Butterworths, London, pp. 117--137. Hughes P.E. and Cole, D.J.A., 1975. Reproduction in the gilt. 1. The influence of age and weight at puberty o n ovulation rate and embryo survival in the gilt. Anita. Prod., 21 : 183--189. Hughes, P.E. and Cole, D.J.A., 1976. Reproduction in the gilt. 2. The influence of gilt age at boar introduction on the attainment of puberty. Anita. Prod., 23 : 89--94. Kirkwood, R.N. and Hughes, P.E., 1979. The influence Of age at first boar contact on puberty attainment in the gilt. Anita. Prod., 29: 231--238. Kirkwood, R.N., Forbes, J.M. and Hughes, P.E., 1981. Influence of boar contact o n attainment of puberty in gilts after removal of the olfactory bulbs. J. Reprod. FertU., 61 : 193--196. Pattinson, M.A., 1970. Studies on puberty in the gilt. B. Sc. Thesis, University of Nottingham. Shearer, I.J. and Adam, J.L., 1973. Nutritional and physiological developments in reproduction of pigs. Proc. N.Z. Soc. Anita. Prod., 33 : 62--86. Taylor, J., 1973. The analysis of designed experiments with censored observations. Biometrics, 29: 35--43.