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Attainment of puberty in peripubertal gilts provided daily boar exposure: enhanced response following addition of prepubertal gilts to the breeding facility
Animal Reproduction Scisrce, 27 ( 1992) 257-262 Elsevier Science F’ublishm B.V., Amsterdam
257
Short Commmication Attainment of puberty in peripubertal gilts provided daily boar exposure: enhanced response following addition of prepubertal gilts to the breeding facility K.A. Bryan and D.R. Hagen’
Department ofDairy
and Animal Science. The fenmylvonia PA 16802, USA (Accepled l2June
State University. University Psk
1991)
ABSTRACT
Bryan. K.A. and Hagen, D.R.. 1992. Attainment of puberty in peripubertal gills provided daily boar erpOSure: enhanced response following addition of prepuberlal gills 10 rhe breeding facility. Anim. ReprodSci..27: 251-262.
Two experiments were conducwd to examine further the attainment of puberty in gilts provided daily boar enporure. Of particular interesr was an investigation of the proposed habitualion effect of sibs to the influence of mature boar presence. Thirty (Experiment 1) and 24 (Experiment 2) peripubertal Dumc gills (88 k& 164 days of age) were fed either ad libitum (F) or 1.81 kg (L) of a complete diet daily from allotment to atrus. Gilts and mature active boars ‘IIere housed in the same breeding facility. and gilts were observed foi estrus twice daily through 245 Iays of age. In both experiments, then was no difference due (0 the level of feed intake for any reproductive Wait measured. Cumulative pmportionsofsubjecl gill. mhibilingeswus following relocation, mixing with unfamiliar pen maxsand initizuionofboarexposureweresimilarfor both experiments, with approximately 50% of subject gilts attaining puberly within 42 days of Ihe slart of each experimenl. Funhemmre, cumulative proponions of subject gilts attaining puberty tended 10 plateau following Day 42 in both experimenls. In Experiment 2.36 novel prepubetial purebred gilts (Yorkshire and Dumc, 80 kg, 159 days of age) were inlroduced inlo the breeding facility on Day 73 following initiation of boar exposure. These novel prepubertal gilts were not co-mingled with the original subject gills and a significant proportion (29%) of the subject gills war observed to be in estruuswithin 10 days. Thus the introduction of novel prepubertal gilts in:o the breeding facility appeared lo increase the incidence of estms observed in peripubtrial gilrs, regardless of nutritional status. This linding could be attributable 10 increased levels of in mature boars, thereby increasing the efficiency ofestrus detection and/ or by enhancing the male pheromonal induction of esuus, both afwhich require funher investigation.
activity
‘Auihor to whom reprint requests should be addressed.
8 i 992 Elsevier Science Publishers B.V. All rights reserved 0378-4320/92/$05.00
KA. BRYAN AND D.R. HAGEN
258 INTRODUCTION
Although the vast majority of gilts will attain puberty by 245 days of age (Christenson and Ford, 1979), puberty may occur considerably earlier (Aheme et al.. I976 ). There has been considerable interest in mating silts at hghter weights and younger ages in order to improve the total efficiency of the breeding herd (Kirkwood and Hughes. 1979: Brooks and Smith, 1980: Knott et al.,-1984; Walton, 1984). The presence of boars substantially reduces the age and weight at puberty (Bourn et al., 1974), and increases the accuracy of estrus detection in gilts (Walton, 1984). However, gilts may become ‘conditioned’ to boar presence and reach puberty at about the same age as gilts reared in isolation from boars (Brooks and Cole, 1973). Furthermore, confinement rearing of swine reduces the percentage of gilts showing reguiar cstrous cycles from 5 to 9 months of age (Christenson, 1981). Therefore, the present experiments were conducted to compare the effects of ad libitum and restricted feeding on the number of days from initiation of the feeding regimen to estrus in gilts reared ia confinement and provided boar exposure. Of particular interest was an investigation of the proposed habituation effect of gilts to stimuli from mature boars. MATERIALS
AND METHOD3
Purebred Duroc gilts were used in two experiments conducted in the same building during consecutive summers. At the initiatioa of each experiment, gilts were moved from the grower facility to the breeding barn, weighed, mixed with unfamiliar pen mates and housed in total confinement. Briefly, the building contained 20 pens measuring 1.52 mx4.5? m, with a center alley 1.37 m wide. The floor was solid concrete except for 1.22m of reinforced concrete slotted flooring at the rear of each pen. A supplemented photoperiod of 14 h (OtiOO-2O:OO)was provided. Gilts were randomly allotted to two treatments: ad libitum feed intake (F) or daily provision of I .81 kg (L) of a diet based on corn and soybean meal ( 150 g crude protein kg-’ dry matter). Gilts were examined for estrus twice daily with a mature active boar. During observation for estrus, gilts were allowed physical contact with a boar for 20 min in the center alley. Observation for estrus continued through 245 days of age. In Experiment I, 30 peripubertal gilts (88 kg; 162 days of age) were randomly allotted to treatment and housed five per pen. In Experiment 2, 24 peripubertal gilts (87 ; 167 days of age) were randomly allotted to treatment and housed four per pen. On Day 73 of boar exposure and estrus deter
259
tion, 36 novel prepubertal purebred gilts (Yorkshire and Duroc, 80 kg, 159 days of age) were introduced into the breeding facility. The novel gilts were housed four per pen across the alley from subject boars and gilts. In both experiments, boars were used in rotation, in that no boar was used during two consecutive estrus detection periods. At the first observed estrus, gilts were weighed and the date was recorded. To confirm estrus, gilts were mated at either the first or second observed estms, and slaughtered from Day 42 to 49 for inciusion in another study (Bryan and Hagen, 1991) . Individual observations were analyzed using least-square means with the General Linear Models procedure of the Statistical Analysis System (1985) because of the unequal number of estrual gilts in each treatment. For all dependent variables associated with gilt, the term in the model was treatment (level of feeding). The proportion of gilts exhibiting estrus was analyzed by x2 (CochranandCox. lc573. RESULTS AND DISCUSSION
There was no difference due to treatment for any reproductive trait measured in either Experiment 1 or Experiment 2 (all R-0.25; Table I). The cumulative percentages of gilts observed in estrus over time for Experiments I and 2 were similar (data not shown). In Experiment 2, the incidence of estrus increased following Day 73 ofboar exposure. Of the 54 gilts utilized in the present experiments, 32 (59%) exhibited estrus. This is a lower percentage of estrual gilts than that reported by Knott et al. ( 1984), who mated at least 76% of Yorkshire gilts utilized in each of three groups. Pearce and Hughes ( 1984) reported that 80% of crossbred gilts (huge WhitexLandrace) exposed to boars exhibited estrus by 240 days of age. The reasons for this low percentage of gilts exhibiting estnts are not readily apparent, but in the present experiments the gilts were purebred Duroc and this may have been a contributing factor. In a more recent study, 85% ofgilts were observed in estrus after being transported for 160 km and provided boar exposure (Signoret et al., 1990). However, in the present study transportationinduced stress was probably not as dramatic as in the work of Signoret et al. ( 1990). Thus, slowly acting (boar presence) vs. rapidly acting (transportation, change of environment and boar presence) stressors may facilitate differing proportions of gilts to exhibit estrus. Also, the Season of year may have influenced the attainment of puberty or the effectiveness of boar exposure. Hughes ( 1982) concluded that the high environmental temperatures to which spring-born gilts may be exposed may inhibit their attainment of puberty. All gilts utilized in the present experiments were born in the spring and environmental temperatures (inside the building) during both experiments were similar and ranged from 12 to 34°C (data not shown). Pearce and Hughes ( 1984) concluded that environmental temperatures of 20-25°C for the ini-
K.*. BRYAN AND D.R HAGEN
260 TABLE I EfTectofthe fcedmgregimenon thecharscteristinafperipubcMlgiltsateslrus, with (Experimerr 2). theaddilion ofprepubetigiltstotbc bmdingfacilityon
No. ofgjbs
.Mean use8, SIUI(days)’ Wan weight al wn (kg)
before Day 73 Mean a&xat esbu~ (days) Mean weiehtatestrus (kg) lnwval 10 esbus (days) Proponion ofpilts oborvcd in CSINS afier Day 73 Mean a*e at cstruus I da% 1 Mean v&t at at&siki) Inrerval10 estrus Idays)
Experiment
I
Experiment
2
F
L
F
L
I5
161Cl.l 88.2+1.6
185f5.4 108.8zk4.3 22.725.4
I5
162+1.1 88.2f1.6
l82k5.7 95.lk4.5 IP.9?5.7
116’
l/7’
241 122 76
239 I23 76
:2 169t2.8 81.5t2.2
199f5.6 108.0~5.4 24.525.3 416’
242k6.8 139.926.6 79.8t6.5
I)
without (Experiment and Day 73 afestrus defection overall
Expcfiment 1 Experiment 2 30 I2 166k2.8 162fCI.8 87.Wz2.2 88.2+1.1
196f6.1 lOl.9f5.9 28.6tS.8 317‘
233f7.9 123.5k7.6 77.Of7.5
183zk3.7 lO2.4t3.5 20.923.7
24 168f2.0 &7.2? 1.5
198k4.0 105.2f4.1 26.4t3.7
Z/13’
71135
240 122.5 76.0
238 132.9k5.2 18.6t4.7
‘Leant-square means without superscripts are not significantly ditferent (P,O.25). 2Proparlions ofgilts obxrved in ertrus before Day 73 arc not signiiimnlly dilBrent (P>O.25) between feeding levels wi!hin experiment. ‘Pmponionl of Bib obwved in eILrui before Day 73 arc not rigni&antly diffwem (Pz-0.25) between expwimenrr. *Prownionsnf$ts observed in ewus after Day 73 are not significantI) different IP> 0.25) between fcedmg levels within experiment. ‘Proptvtionsofgilts in ntrus&r Day 73 are signilicanlly ddlerent (P=O. 164) between experiments.
tial30 days of boar exposure inhibited the sexual maturation of gilts and that gilts responded to boar exposure only when temperatures began to fall. Of particular interest was the increased attainment of puberty in gilts after Day 73 in Experiment 2. In Experiment I, only two out of 13 gilts exhibited first estrus after 73 days of boar exposure (approximately 230 days of age), compared with seven out of I3 gilts in Experiment 2 (P=O. 164). Although normally considered not to be statistically significant (P=O.164), failure to reject the null hypothesis that ‘proportions of gilts exhibiting estrus following Day 73 were similar between experiments’ overlooks the biology of the experiment in favor of classical acceptance of statistical significance by the scientific community. The difference in the proportions of gilts exhibiting estrus following Day 73 of boar exposure in both experiments is of biological and economic significance. Brooks and Cole ( 1973) proposed that gins tend ir, become ‘conditioned’ to a particular boar. After a few days of exposure to a single boar, the boar becomes iess effective in stimulating gilts into estrus. Although in both the present experiments boars were used in rotation to de-
BOAR EXPOS”REAND
P”BEtlTv
IN 0,LTS
264
tect estrus, there was a 3 week period during which no gilts were observed in estrus. Gilts which had not attained puberty prior to this time were regarded as being habituated’ or ‘conditioned’ to stimuli associated with boar presence. Numerous studies have examined the effect of boar exposure on the age and weight of gilts at puberty (Hughes and Cole, 1976;Kirkwood and Hughes, 1979, 1981; Pearce and Hughes, 1984, Walton, 1984,1985a,b). There apparently is no previous report that prepubertal gilts (not co-mingled witb subject peripubertal gilts) can provide sufftcient stimulus for the attainment of puberty in subject gilts provided daily boar exposure. A similar finding has been reported for the effect of the introdltction of novel estrual cows on the incidence of estrus in subject cows (Alexander et al., 1984). However, in the present Experiment 2, gilts moved to the breeding facility on Day 73 were immature and prepubertal. Therefore, if during the production cycle prep&&al gilts are periodically added to the group of peripubertal replacement gilts to be mated, this could serve to enhance their responsiveness to stimuli from boars or other gilts, thus reducing the interval to estrus. Alternatively, when novel gilts are introduced to the group of replacement gilts, boars in the same building may be stimulated to increased levels of activity and, thus, are either more effective in stimulating estrus or are more efficient in detecting estrual females. Furthermore, ‘habituation’ ofgilts to boar presence is not likely to be observed. However, further studies are needed to investigate the mechanisms by which the introduction of unfamiliar prepubcrtal gilts, either to the replacement pool of peripubertal gilts or to the breeding barn, facilitates an increased proportion of gilts to exhibit pubertal es&us. ACKNOWLEDGEMENTS
Appreciation is expressed to V.E. Hazlett and D.J.E. Hosterman for assistance in the care of animals, and to A.M. Clark and T.C. Perry for assistance in the detection of e&us. REFERENCES Aheme, F.X., Christopherson, R.J.. Thompson, J.R. and Hardin, R.T., 1976. Factorsaffecting the onset of puberty, post-weaning estrus and blood hormone levels of Lacombe gilts. Can. J. Anim. Sci., 56: 681-692. Alexander, T.J., Sager, P.L. Roseoberger, J.L. and Hagen, D.R., 1984. The influence of the stage of the estmus cycle and novel cows upon mounting activity of dairy cattle, J. Anim. Sci., 59: 1430-1439. Bourn. P., Carlson. R., Lantz, B. and Zimmerman, D.R., 1974. Age at puberty in gilts as intloenccd by age at boar exposure and tmospon. J. Anim. Sci., 39: 987 (Abstract). Brooks, P.H. and Colt. D.J.A., 1973. Meat production from pigs which have farmwed. I. Rcproductive performace and food convenion effkiency. Anim. Prod., 17: 305-3 15.
262
K.4 BRYAN ANDD.R “*czR
Brooks, F.H. and Smith, D.A., 1980. The effect of mating age on the reproductive performanu food utilization and livewei&t change of the female pig Live% Prod. Sci., 7: 67-78. Bryan, K_A. and Hagen, D.R.. 1991. Effects of nutrient intake and sexual age of the dam t mating on fetal development in swine. Growth Dev. Aging, 55: 27-33. Christenson, RX., J98i. Influence of conlinement and -II of the year on puberty and e! trous activity of gilts. J. Anim. Sci., 52: 821-1330. Christenson, R.K. and Ford, J.J., 1979. Puberty aad estrus incontincmont-rcarcdgilts. J. Anin sti.,49: 743-‘151. Cochran, W.G. and Cox, GM., 1957. Experimental Designs. Wiley, New York. PP. 103-104. H&es, P.E., 1982. Factors alfecting the natural attainment of pubcfl~ in the gilt. lo: D.J.! Cole and 6.1. Foxcroft (Editors), Control of Pig Reproduction, Buttenvonh, London, pl 117-138. Hughes, P.E. and Cole, D.J.A., 1976. Reproduction in the gilt. 2. The irfluence of gilt age i boarintroduction 00 the attainment of puberty. Anim. Prod., 23: 89-94. Kirkwood, R.N. and Hughes, P-E.. 1979. The inlluence of nge at tint boar contact oa pubcr atlainment in the gilt. Aaim. Prod., 29: 231-238. Kirkwood, R.N. and Hughes, P.E.. 1981. A note on the influence of boar age on its ability I advancepabertyin thegilt.Anim.Prod., 32: 211-213. Knott, R.E., Et&and, D.C. and Kennick. W.H., 1984. Estrus, ovulation, concePtion and en bryo survival in coatinement-managed gilts of three weight groops. J. Anim. Sei., 5Sz 281 284. Pearce, G.?. and Hughes, P.E., 1984. The innueaee of tily movement of gilts aad the envirol mrnt in which hoar exposure occurs cm the elficacy of boar-iaduccd precocious puberty I thegilt. Anim. Prod., 40: 161-167. Signoret, J.P., Martinat-Botte, F., Elariteru,F., Forge&, Y., Macar, C,, Moreau. A. and Tequ M., 1990. Control of oestrus in gilts. 1. ManaSetnent-induced puberty. Anim. Reprod. SC. 22: 221-225. Statistical Anaiysis Systems Institute, 1985. SAS User’s Guide. SAS Institute Inc.. Gary, Nl pp. 139-l 99. Walton. J.S., : 984. A note on the effect of exposure to a boat on the development of the repn ductive system of immature Sills. Anim. Prod., 39: 4833086. Walton, J.S.. I985a. A note on the e&t of cxposina gilts to a matum boar at I40 days of ag Anim. Prod.. 41: 123-126. Walton. J.S., 1985b. A note on the effect on puberty in gilts ofexposure to a bcw bctwccn IA and 160dsysofage. Anim. Prod.,r)l: !27-129.
257
Short Commmication Attainment of puberty in peripubertal gilts provided daily boar exposure: enhanced response following addition of prepubertal gilts to the breeding facility K.A. Bryan and D.R. Hagen’
Department ofDairy
and Animal Science. The fenmylvonia PA 16802, USA (Accepled l2June
State University. University Psk
1991)
ABSTRACT
Bryan. K.A. and Hagen, D.R.. 1992. Attainment of puberty in peripubertal gills provided daily boar erpOSure: enhanced response following addition of prepuberlal gills 10 rhe breeding facility. Anim. ReprodSci..27: 251-262.
Two experiments were conducwd to examine further the attainment of puberty in gilts provided daily boar enporure. Of particular interesr was an investigation of the proposed habitualion effect of sibs to the influence of mature boar presence. Thirty (Experiment 1) and 24 (Experiment 2) peripubertal Dumc gills (88 k& 164 days of age) were fed either ad libitum (F) or 1.81 kg (L) of a complete diet daily from allotment to atrus. Gilts and mature active boars ‘IIere housed in the same breeding facility. and gilts were observed foi estrus twice daily through 245 Iays of age. In both experiments, then was no difference due (0 the level of feed intake for any reproductive Wait measured. Cumulative pmportionsofsubjecl gill. mhibilingeswus following relocation, mixing with unfamiliar pen maxsand initizuionofboarexposureweresimilarfor both experiments, with approximately 50% of subject gilts attaining puberly within 42 days of Ihe slart of each experimenl. Funhemmre, cumulative proponions of subject gilts attaining puberty tended 10 plateau following Day 42 in both experimenls. In Experiment 2.36 novel prepubetial purebred gilts (Yorkshire and Dumc, 80 kg, 159 days of age) were inlroduced inlo the breeding facility on Day 73 following initiation of boar exposure. These novel prepubertal gilts were not co-mingled with the original subject gills and a significant proportion (29%) of the subject gills war observed to be in estruuswithin 10 days. Thus the introduction of novel prepubertal gilts in:o the breeding facility appeared lo increase the incidence of estms observed in peripubtrial gilrs, regardless of nutritional status. This linding could be attributable 10 increased levels of in mature boars, thereby increasing the efficiency ofestrus detection and/ or by enhancing the male pheromonal induction of esuus, both afwhich require funher investigation.
activity
‘Auihor to whom reprint requests should be addressed.
8 i 992 Elsevier Science Publishers B.V. All rights reserved 0378-4320/92/$05.00
KA. BRYAN AND D.R. HAGEN
258 INTRODUCTION
Although the vast majority of gilts will attain puberty by 245 days of age (Christenson and Ford, 1979), puberty may occur considerably earlier (Aheme et al.. I976 ). There has been considerable interest in mating silts at hghter weights and younger ages in order to improve the total efficiency of the breeding herd (Kirkwood and Hughes. 1979: Brooks and Smith, 1980: Knott et al.,-1984; Walton, 1984). The presence of boars substantially reduces the age and weight at puberty (Bourn et al., 1974), and increases the accuracy of estrus detection in gilts (Walton, 1984). However, gilts may become ‘conditioned’ to boar presence and reach puberty at about the same age as gilts reared in isolation from boars (Brooks and Cole, 1973). Furthermore, confinement rearing of swine reduces the percentage of gilts showing reguiar cstrous cycles from 5 to 9 months of age (Christenson, 1981). Therefore, the present experiments were conducted to compare the effects of ad libitum and restricted feeding on the number of days from initiation of the feeding regimen to estrus in gilts reared ia confinement and provided boar exposure. Of particular interest was an investigation of the proposed habituation effect of gilts to stimuli from mature boars. MATERIALS
AND METHOD3
Purebred Duroc gilts were used in two experiments conducted in the same building during consecutive summers. At the initiatioa of each experiment, gilts were moved from the grower facility to the breeding barn, weighed, mixed with unfamiliar pen mates and housed in total confinement. Briefly, the building contained 20 pens measuring 1.52 mx4.5? m, with a center alley 1.37 m wide. The floor was solid concrete except for 1.22m of reinforced concrete slotted flooring at the rear of each pen. A supplemented photoperiod of 14 h (OtiOO-2O:OO)was provided. Gilts were randomly allotted to two treatments: ad libitum feed intake (F) or daily provision of I .81 kg (L) of a diet based on corn and soybean meal ( 150 g crude protein kg-’ dry matter). Gilts were examined for estrus twice daily with a mature active boar. During observation for estrus, gilts were allowed physical contact with a boar for 20 min in the center alley. Observation for estrus continued through 245 days of age. In Experiment I, 30 peripubertal gilts (88 kg; 162 days of age) were randomly allotted to treatment and housed five per pen. In Experiment 2, 24 peripubertal gilts (87 ; 167 days of age) were randomly allotted to treatment and housed four per pen. On Day 73 of boar exposure and estrus deter
259
tion, 36 novel prepubertal purebred gilts (Yorkshire and Duroc, 80 kg, 159 days of age) were introduced into the breeding facility. The novel gilts were housed four per pen across the alley from subject boars and gilts. In both experiments, boars were used in rotation, in that no boar was used during two consecutive estrus detection periods. At the first observed estrus, gilts were weighed and the date was recorded. To confirm estrus, gilts were mated at either the first or second observed estms, and slaughtered from Day 42 to 49 for inciusion in another study (Bryan and Hagen, 1991) . Individual observations were analyzed using least-square means with the General Linear Models procedure of the Statistical Analysis System (1985) because of the unequal number of estrual gilts in each treatment. For all dependent variables associated with gilt, the term in the model was treatment (level of feeding). The proportion of gilts exhibiting estrus was analyzed by x2 (CochranandCox. lc573. RESULTS AND DISCUSSION
There was no difference due to treatment for any reproductive trait measured in either Experiment 1 or Experiment 2 (all R-0.25; Table I). The cumulative percentages of gilts observed in estrus over time for Experiments I and 2 were similar (data not shown). In Experiment 2, the incidence of estrus increased following Day 73 ofboar exposure. Of the 54 gilts utilized in the present experiments, 32 (59%) exhibited estrus. This is a lower percentage of estrual gilts than that reported by Knott et al. ( 1984), who mated at least 76% of Yorkshire gilts utilized in each of three groups. Pearce and Hughes ( 1984) reported that 80% of crossbred gilts (huge WhitexLandrace) exposed to boars exhibited estrus by 240 days of age. The reasons for this low percentage of gilts exhibiting estnts are not readily apparent, but in the present experiments the gilts were purebred Duroc and this may have been a contributing factor. In a more recent study, 85% ofgilts were observed in estrus after being transported for 160 km and provided boar exposure (Signoret et al., 1990). However, in the present study transportationinduced stress was probably not as dramatic as in the work of Signoret et al. ( 1990). Thus, slowly acting (boar presence) vs. rapidly acting (transportation, change of environment and boar presence) stressors may facilitate differing proportions of gilts to exhibit estrus. Also, the Season of year may have influenced the attainment of puberty or the effectiveness of boar exposure. Hughes ( 1982) concluded that the high environmental temperatures to which spring-born gilts may be exposed may inhibit their attainment of puberty. All gilts utilized in the present experiments were born in the spring and environmental temperatures (inside the building) during both experiments were similar and ranged from 12 to 34°C (data not shown). Pearce and Hughes ( 1984) concluded that environmental temperatures of 20-25°C for the ini-
K.*. BRYAN AND D.R HAGEN
260 TABLE I EfTectofthe fcedmgregimenon thecharscteristinafperipubcMlgiltsateslrus, with (Experimerr 2). theaddilion ofprepubetigiltstotbc bmdingfacilityon
No. ofgjbs
.Mean use8, SIUI(days)’ Wan weight al wn (kg)
before Day 73 Mean a&xat esbu~ (days) Mean weiehtatestrus (kg) lnwval 10 esbus (days) Proponion ofpilts oborvcd in CSINS afier Day 73 Mean a*e at cstruus I da% 1 Mean v&t at at&siki) Inrerval10 estrus Idays)
Experiment
I
Experiment
2
F
L
F
L
I5
161Cl.l 88.2+1.6
185f5.4 108.8zk4.3 22.725.4
I5
162+1.1 88.2f1.6
l82k5.7 95.lk4.5 IP.9?5.7
116’
l/7’
241 122 76
239 I23 76
:2 169t2.8 81.5t2.2
199f5.6 108.0~5.4 24.525.3 416’
242k6.8 139.926.6 79.8t6.5
I)
without (Experiment and Day 73 afestrus defection overall
Expcfiment 1 Experiment 2 30 I2 166k2.8 162fCI.8 87.Wz2.2 88.2+1.1
196f6.1 lOl.9f5.9 28.6tS.8 317‘
233f7.9 123.5k7.6 77.Of7.5
183zk3.7 lO2.4t3.5 20.923.7
24 168f2.0 &7.2? 1.5
198k4.0 105.2f4.1 26.4t3.7
Z/13’
71135
240 122.5 76.0
238 132.9k5.2 18.6t4.7
‘Leant-square means without superscripts are not significantly ditferent (P,O.25). 2Proparlions ofgilts obxrved in ertrus before Day 73 arc not signiiimnlly dilBrent (P>O.25) between feeding levels wi!hin experiment. ‘Pmponionl of Bib obwved in eILrui before Day 73 arc not rigni&antly diffwem (Pz-0.25) between expwimenrr. *Prownionsnf$ts observed in ewus after Day 73 are not significantI) different IP> 0.25) between fcedmg levels within experiment. ‘Proptvtionsofgilts in ntrus&r Day 73 are signilicanlly ddlerent (P=O. 164) between experiments.
tial30 days of boar exposure inhibited the sexual maturation of gilts and that gilts responded to boar exposure only when temperatures began to fall. Of particular interest was the increased attainment of puberty in gilts after Day 73 in Experiment 2. In Experiment I, only two out of 13 gilts exhibited first estrus after 73 days of boar exposure (approximately 230 days of age), compared with seven out of I3 gilts in Experiment 2 (P=O. 164). Although normally considered not to be statistically significant (P=O.164), failure to reject the null hypothesis that ‘proportions of gilts exhibiting estrus following Day 73 were similar between experiments’ overlooks the biology of the experiment in favor of classical acceptance of statistical significance by the scientific community. The difference in the proportions of gilts exhibiting estrus following Day 73 of boar exposure in both experiments is of biological and economic significance. Brooks and Cole ( 1973) proposed that gins tend ir, become ‘conditioned’ to a particular boar. After a few days of exposure to a single boar, the boar becomes iess effective in stimulating gilts into estrus. Although in both the present experiments boars were used in rotation to de-
BOAR EXPOS”REAND
P”BEtlTv
IN 0,LTS
264
tect estrus, there was a 3 week period during which no gilts were observed in estrus. Gilts which had not attained puberty prior to this time were regarded as being habituated’ or ‘conditioned’ to stimuli associated with boar presence. Numerous studies have examined the effect of boar exposure on the age and weight of gilts at puberty (Hughes and Cole, 1976;Kirkwood and Hughes, 1979, 1981; Pearce and Hughes, 1984, Walton, 1984,1985a,b). There apparently is no previous report that prepubertal gilts (not co-mingled witb subject peripubertal gilts) can provide sufftcient stimulus for the attainment of puberty in subject gilts provided daily boar exposure. A similar finding has been reported for the effect of the introdltction of novel estrual cows on the incidence of estrus in subject cows (Alexander et al., 1984). However, in the present Experiment 2, gilts moved to the breeding facility on Day 73 were immature and prepubertal. Therefore, if during the production cycle prep&&al gilts are periodically added to the group of peripubertal replacement gilts to be mated, this could serve to enhance their responsiveness to stimuli from boars or other gilts, thus reducing the interval to estrus. Alternatively, when novel gilts are introduced to the group of replacement gilts, boars in the same building may be stimulated to increased levels of activity and, thus, are either more effective in stimulating estrus or are more efficient in detecting estrual females. Furthermore, ‘habituation’ ofgilts to boar presence is not likely to be observed. However, further studies are needed to investigate the mechanisms by which the introduction of unfamiliar prepubcrtal gilts, either to the replacement pool of peripubertal gilts or to the breeding barn, facilitates an increased proportion of gilts to exhibit pubertal es&us. ACKNOWLEDGEMENTS
Appreciation is expressed to V.E. Hazlett and D.J.E. Hosterman for assistance in the care of animals, and to A.M. Clark and T.C. Perry for assistance in the detection of e&us. REFERENCES Aheme, F.X., Christopherson, R.J.. Thompson, J.R. and Hardin, R.T., 1976. Factorsaffecting the onset of puberty, post-weaning estrus and blood hormone levels of Lacombe gilts. Can. J. Anim. Sci., 56: 681-692. Alexander, T.J., Sager, P.L. Roseoberger, J.L. and Hagen, D.R., 1984. The influence of the stage of the estmus cycle and novel cows upon mounting activity of dairy cattle, J. Anim. Sci., 59: 1430-1439. Bourn. P., Carlson. R., Lantz, B. and Zimmerman, D.R., 1974. Age at puberty in gilts as intloenccd by age at boar exposure and tmospon. J. Anim. Sci., 39: 987 (Abstract). Brooks, P.H. and Colt. D.J.A., 1973. Meat production from pigs which have farmwed. I. Rcproductive performace and food convenion effkiency. Anim. Prod., 17: 305-3 15.
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Brooks, F.H. and Smith, D.A., 1980. The effect of mating age on the reproductive performanu food utilization and livewei&t change of the female pig Live% Prod. Sci., 7: 67-78. Bryan, K_A. and Hagen, D.R.. 1991. Effects of nutrient intake and sexual age of the dam t mating on fetal development in swine. Growth Dev. Aging, 55: 27-33. Christenson, RX., J98i. Influence of conlinement and -II of the year on puberty and e! trous activity of gilts. J. Anim. Sci., 52: 821-1330. Christenson, R.K. and Ford, J.J., 1979. Puberty aad estrus incontincmont-rcarcdgilts. J. Anin sti.,49: 743-‘151. Cochran, W.G. and Cox, GM., 1957. Experimental Designs. Wiley, New York. PP. 103-104. H&es, P.E., 1982. Factors alfecting the natural attainment of pubcfl~ in the gilt. lo: D.J.! Cole and 6.1. Foxcroft (Editors), Control of Pig Reproduction, Buttenvonh, London, pl 117-138. Hughes, P.E. and Cole, D.J.A., 1976. Reproduction in the gilt. 2. The irfluence of gilt age i boarintroduction 00 the attainment of puberty. Anim. Prod., 23: 89-94. Kirkwood, R.N. and Hughes, P-E.. 1979. The inlluence of nge at tint boar contact oa pubcr atlainment in the gilt. Aaim. Prod., 29: 231-238. Kirkwood, R.N. and Hughes, P.E.. 1981. A note on the influence of boar age on its ability I advancepabertyin thegilt.Anim.Prod., 32: 211-213. Knott, R.E., Et&and, D.C. and Kennick. W.H., 1984. Estrus, ovulation, concePtion and en bryo survival in coatinement-managed gilts of three weight groops. J. Anim. Sei., 5Sz 281 284. Pearce, G.?. and Hughes, P.E., 1984. The innueaee of tily movement of gilts aad the envirol mrnt in which hoar exposure occurs cm the elficacy of boar-iaduccd precocious puberty I thegilt. Anim. Prod., 40: 161-167. Signoret, J.P., Martinat-Botte, F., Elariteru,F., Forge&, Y., Macar, C,, Moreau. A. and Tequ M., 1990. Control of oestrus in gilts. 1. ManaSetnent-induced puberty. Anim. Reprod. SC. 22: 221-225. Statistical Anaiysis Systems Institute, 1985. SAS User’s Guide. SAS Institute Inc.. Gary, Nl pp. 139-l 99. Walton. J.S., : 984. A note on the effect of exposure to a boat on the development of the repn ductive system of immature Sills. Anim. Prod., 39: 4833086. Walton, J.S.. I985a. A note on the e&t of cxposina gilts to a matum boar at I40 days of ag Anim. Prod.. 41: 123-126. Walton. J.S., 1985b. A note on the effect on puberty in gilts ofexposure to a bcw bctwccn IA and 160dsysofage. Anim. Prod.,r)l: !27-129.