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Age at puberty and estrous activity of straightbred and reciprocal crossbred gilts
Animal Reproduction Science, 8 (1985) 2 8 1 - - 2 8 6
281
Elsevier Science Publishers B.V., A m s t e r d a m -- Printed in The Netherlands
AGE AT PUBERTY A N D ESTROUS ACTIVITY OF STRAIGHTBRED AND RECIPROCAL CROSSBRED GILTS
R.D. A L L R I C H 1, R.K. C H R I S T E N S O N 2 and J.J. F O R D
Roman L. Hruska U.S. Meat Animal Research Center, U.S. Department o f Agriculture, P.O. Box 166, Clay Center, NE 68933 (U.S.A.) IPresent address: D e p a r t m e n t of Animal Sciences, Lilly Hall, Purdue University, West Lafayette, IN 4 7 9 0 7 (U.S.A.) 2To w h o m reprint requests should be addressed. ( A c c e p t e d 17 April 1984)
ABSTRACT Allrich, R.D., Christenson, R.K. and Ford, J.J., 1985. Age at p u b e r t y and estrous activity o f straightbred and reciprocal crossbred gilts. Anim. Reprod. Sci., 8: 281- 286. Age at p u b e r t y , estrous activity and g r o w t h were evaluated in 294 straightbred and reciprocal crossbred gilts maintained in c o n f i n e m e n t conditions. Trial 1 used straightbred Landrace (L), Yorkshire (Y) and reciprocal crossbred (LY, YL) gilts. Trial 2 used LY and YL gilts, and Trial 3 used L and Duroc (D) reciprocal crossbred gilts (LD, DL). Daily observations for estrous activity with a m a t u r e boar were initiated at 150 days of age and c o n t i n u e d until gilts reached 255 days of age. Gilts not exhibiting estrus by 255 days of age were e x a m i n e d by laparoscopy to determine r e p r o d u c t i v e status. In Trial 1, age at p u b e r t y was greater for Y gilts c o m p a r e d to L and reciprocal crossbred gilts. Differences b e t w e e n reciprocal crosses for age at p u b e r t y were n o t significant in any trial. In Trial 1, the percentage of gilts exhibiting regular estrous cycles at 195 days of age was lower for Y gilts than for the o t h e r three groups of gilts; however, by 225 days of age, this difference was n o t significant. In all trials, reciprocal crossbred gilts did n o t differ with respect to percentage exhibiting regular estrous cycles or in percentage prepubertal. In Trial 1, Y gilts had a higher percentage prepubertal at 255 days of age than the reciprocal crossbred gilts. The percentage of gilts exhibiting behavioral anestrus at 255 days of age did n o t differ a m o n g breed groups within any trial. Based on these observations, we concluded the breed maternal effects were small or n o n e x i s t e n t relative to direct additive and nonadditive genetic effects in the breed c o m b i n a t i o n s that were investigated.
INTRODUCTION
The maternal environment during gestation and lactation are known to influence growth rate, food conversion and carcass traits of swine (Pani et al., 1963; Ahlsehwede and Robison, 1971a,b; Robison, 1972; Young et al., 1976; Johnson, 1981). The extent to which reproductive characteristics are Mention o f trade names or companies does n o t constitute an implied warranty o r endorsem e n t by the U S D A or the authors.
282 affected by the maternal environment is less certain. Johnson et al. (1978) reported no differences in ovulation rate and embryo development between reciprocal crosses. Theoretically, reciprocal crossbred animals are genetically equal {assuming sires and dams of each parent breed are of equal average genetic merit) but have experienced different maternal environments during their prenatal and early postnatal existence. Utilizing reciprocal crossbred animals is therefore a technique that can be employed to investigate breed maternal effects. Several researchers (Reutzel and Sumption, 1968; Legault, 1973; Hutchens et al., 1981) have implied the existence of breed maternal effects based on expectations of variance components. Also, Foote et al. (1956) found a difference in age at puberty between Yorkshire (Y) and Duroc (D) reciprocal crossbred gilts. However, Short (1963) using the same breeds and Clark et al. {1970) using Y and Poland China breeds, found no reciprocal differences with respect to age at puberty. Hutchens et al. {1982) found no reciprocal differences in age or weight at puberty using a four-breed diallel design involving D, Y, Landrace (L) and Spotted breeds. The objectives of the present study were to evaluate several reproductive traits in reciprocal crossbred gilts and to further characterize these traits for straightbred and reciprocal crossbred gilts maintained in confinement. MATERIALS AND METHODS Trial 1 utilized 116 July-born gilts of straightbred L 1 (four sires, eleven litters) and Y (five sires, thirteen litters) breeding as well as the reciprocal crosses (LY, five sires, twelve litters; YL, four sires, eleven litters). Trial 2 involved 80 December-born gilts of LY (four sires, fourteen l i t t e r s ) a n d YL (seven sires, sixteen litters) breeding. In Trial 2, approximately 50% of the dams and 100% of the sires were also utilized in Trial 1. Trial 3 involved 98 June-born gilts of LD (six sires, 22 litters) and DL {seven sires, seventeen litters) breeding. Gilts were weaned at 4 weeks of age, maintained in a nursery as groups of females (irrespective of breed) until 10 weeks of age, and then moved to a modified open-front finishing building and penned in groups of ten to twelve for the duration of the study. A corn and soybean meal based ration containing 18.5% protein was fed ad libitum to gilts in the nursery. Thereafter, gilts were fed ad libitum, a diet with 16% protein until 100 kg body weight when a 14% protein diet was fed at a rate of 1.82 kg per head daily. Daily observations for estrous activity were initiated at 150 days of age and continued until gilts were 255 days of age. Estrus was evaluated by moving gilts from their pen and placing them for 15 min each day into a pen with a mature male. Puberty was defined as the age that a gilt first 1Foundation Landraee animals were purchased from Pig Improvement Co., Spring Green, WI.
283
showed the immobilization response in the presence of a mature boar. Gilts not reaching p u b e r t y did not contribute to pubertal data calculated for each subclass. Gilts not exhibiting regular estrous cycles b y 255 days of age were examined by laparoscopy to determine whether they were behaviorally anestrous (ovaries with corpora lutea, preovulatory follicles or corpora albicantia and uterus typical of cyclic gilts) or prepubertal (no evidence of ovulation and small uterus). B o d y weight was recorded every 30 days during the study. Inconsistency in n values of tables are a result of: (1) cessation of regular estrous cycle and (2) lameness or death. The data were analyzed by least-squares fixed-model procedures (General Linear Models Procedure; SAS, 1979). The model for analysis of all traits (trials analyzed separately) included fixed effects of breed. In comparisons of reciprocal crosses between Trials 1 and 2, fixed effects of season and breed X season interaction were included in the model. Proportional data were analyzed by chi-square procedures (Steel and Torrie, 1960). Differences between breed group means in Trial 1 were determined by the NewmanKeuls test (Steel and Torrie, 1960). RESULTS
In all three trials, differences among reciprocal crosses were not significant for age at p u b e r t y (Table I). In Trial 1, age at puberty was greater (P < 0.05) for Y gilts in comparison to L, LY, and YL gilts. Heterosis estimate (-5.65 days) for age at puberty was not significant. Reciprocal crosses did not differ with respect to percentage exhibiting regular estrous cycle at any age evaluated (Table II) within any trial. In Trial 1, Y gilts had the lowest (P < 0.01) percentage exhibiting regular estrous cycles at 195 days; however, this difference was not significant at either 225 or 255 days of age. The percentage of gilts that showed behavioral anestrus did not differ between reciprocal crossbred gilts in any trial (Table III); however, the overall TABLE
I
Age (days) of gilts at first estrus a Trial
1 2
Breed L
Y
LY
YL
1 8 4 . 7 -+ 4 . 0 b (26/29)
199.8 + 4.2 c (23/29)
1 8 7 . 2 -+ 4 . 0 b (26127)
186.0 + 4.0 b (27/31)
1 8 0 . 0 -+ 4 . 0 (36/38)
183.6 ± 3.9 (38142)
3
aData presented a r e l e a s t - s q u ~ x e s m e a n s + S E M ; p r o p o r t i o n
~, gC Mt oe amn es a wn /ittoht adl i f fneur emnbt e rs u op fe r gs ci lrtisp ti sn gwr iotuhpi n) . s a m e
LD
DL
197.3 + 3.8 (55/62)
2 0 0 . 0 -+ 3 . 7 (34/36)
in parenthesis
row differ, P < 0.05.
= (number
of gilts contribut-
284
T A B L E II
P e r c e n t a g e o f gilts e x h i b i t i n g r e g u l a r estrous c y c l e s at 1 9 5 , 2 2 5 a n d 2 5 5 d a y s o f age Age (days)
Trial
Breed L
Y
LY
YL
195
1 2 3
72(21/29) a
38(11/29) b
74(20/27) a 71(27/38)
68(21]31) a 62(26]42)
225
1 2 3
86(25/29)
69(20]29)
85(23/27) 79(30/38)
84(26/31) 71(30/42)
255
1 2 3
90(26/29)
76(22]29)
89(24/27) 82(31/38)
77(24/31) 79(33/42)
LD
DL
44(27/62)
39(15/38)
76(47/62)
67(24]36)
77(48/62)
75(27/36)
a'bvalues with different supereripts within same row differ, P ~ 0.01. F o r p r o p o r t i o n i n p a r e n t h e s e s see f o o t n o t e T a b l e I. T A B L E III P e r c e n t a g e o f gilts b e h a v i o r a l l y a . n e s t r o u s ( B A ) o r p r e p u b e r t a l (PP) a t 2 5 5 d a y s o f age Parameter
(%)
Trial
Breed L
Y
BA
1 2 3
0
(0/29)
3.5(1/29)
PP
1 2 3
3.5(1/29) a,b 17.0(5129) a
LY
YL
7.4(2/27) 13.2(5/38)
9.7(3/31) 14.3(6/42)
0 (0]27) b 5.3(2/38)
LD
DL
17.7(11/62)
16.7(6/36)
0 (0/31) b 4.8(2/42) 0
(0/62)
5.5(2/36)
a'bvalues with different superscripts within same row differ, P ~ 0.05. F o r p r o p o r t i o n i n p a r e n t h e s i s see f o o t n o t e T a b l e I.
percentage of gilts that were behaviorally anestrous was greater in Trials 2 and 3. Reciprocal crossbred gilts in Trials 1, 2 and 3 did not differ in percentage of prepubertal gilts (Table III). In Trial 1, a greater (P < 0.05) percentage of Y gilts were prepubertal at 255 days of age than the LY and YL gilts (Table III). In Trial 1, the reciprocal crossbred gilts had greater ( P < 0 . 0 5 ) b o d y weights at all ages evaluated compared to the straightbred gilts and the heterosis estimate for b o d y weight averaged 5.3% (P < 0.01). In comparisons of parameters for reciprocal crossbred gilt between Trials 1 and 2, no significant influence of season or season × breed interaction was detected. In Trial 3, the most pronounced reciprocal difference was noted with DL gilts being consistently heavier (P < 0.01) at all ages evaluated than LD gilts. DISCUSSION
A difference in age at puberty for reciprocal cross YD and DY gilts was reported by Foote et al. (1956). Subsequent studies with different breed
285 combinations (Short, 1963; Clark et al., 1970; Christenson, 1981; Hutchens et al., 1982) and results of the present study did n o t show a reciprocal difference, and thus we suggest that breed maternal effects do not have a major influence on age at puberty in gilts. The difference in age at puberty for L and Y straightbred gilts in Trial 1 is in agreement with that reported by Christenson and Ford (1979b) using the same genetic population. Both reciprocal crosses (LY, YL) were similar to the L gilts in age at puberty suggesting the presence of nonadditive gene action. The percentage of gilts exhibiting regular estrous cycles at or near breeding age varies with breed (Christenson and Ford, 1979b; Christenson, 1981). Reciprocal differences in the percentage of gilts exhibiting regular estrous cycles and the percentage prepubertal were negligible in all three trials indicating that breed maternal effects have little influence on these traits. This is in contrast to a report by Christenson (1981) where a difference in percentage of gilts exhibiting regular estrous cycles for L and Large White (LW) reciprocal crossbred gilts was detected. The large difference in percentage of gilts exhibiting regular estrous cycles for L and LW reciprocal crossbred gilts was a result of a high percentage (16.4%) of LW X L gilts with behavioral anestrus as compared to a low (1.4%) percentage of L Z LW gilts. An explanation for the difference in the two studies may be due to the breeds used in producing the reciprocal crosses. The L breed was c o m m o n to all reciprocal crosses in both studies, but the other breeds contributing to the reciprocal crosses differed. Gilts that show behavioral anestrus can represent a considerable proportion of the gilts intended as breeding stock and breeds differ as to incidence of behavioral anestrus (Einarsson and Linde, 1974; Christenson and Ford, 1979a,b; Christenson, 1981; Cronin et al., 1983). No more than 90% (mean = 81%) of the gilts of any breed combination were consistently exhibiting regular estrous cycles by 255 days of age. The percentage of gilts which show regular estrous cycles at a younger age requires more attention in research relating to confinement swine production. At 195 days of age, in the breed groups with the youngest age at puberty (184 days; L, LY and YL), 69% of the gilts were showing estrous cycles compared to the three breed groups with the oldest age at puberty (199 days; Y, LD and DL) in which only 40% were showing estrous cycles. Thus, this reduction in age at puberty by 15 days resulted in 29% more gilts available for selection as replacements. This allows for selection of replacement gilts at an age nearer to standard market age, thereby decreasing production costs. Tess et al. (1983) have summarized the benefit of decreasing age at puberty in gilts relative to biological and economic efficiency of pork production. ACKNOWLEDGEMENTS The authors express their appreciation to Mark Anderson, Robert Byrkit, Jenell Dague, Jean Gray and Toni Tolles for their invaluable expertise and to Kathy Leising for her secretarial assistance.
286
Published as paper number 7278, Journal Series, Nebraska Agricultural Experiment Station. Research was supported in part by U S D A Cooperative State Research Service Grant 701-15-42.
REFERENCES Ahlschwede, W.T. and Robison, O.W., 1971a. Prenatal and postnatal influences on growth and backfat in swine. J. Anita. Sci., 32: 10--16. Ahlschwede, W.T. and Robison, O.W., 1971b. Maternal effects on weights and backfat of swine. J. Anita. Sci., 33: 1206--1211. Christenson, R.K., 1981. Influence of confinement and seasons of the year on puberty and estrous activity of gilts. J. Anim. Sci., 52: 821--830. Christenson, R.K. and Ford, J.J., 1979a. Effect of methallibure on estrous response of anestrous gilts reared in confinement. J. Anita. Sci., 48: 87--91. Christenson, R.K. and Ford, J.J., 1979b. Puberty and estrus in confinement-reared gilts. J. Anim. Sci., 49: 743--751. Clark, J.R., First, N.L., Chapman, A.B. and Casida, L.E., 1970. Age at puberty in four genetic groups of swine. J. Anim. Sci., 3 1 : 1 0 3 2 (Abstract). Cronin, G.M., Hemsworth, P.H., Winfield, C.G., Muller, B. and Chamley, W.A., 1983. The incidence of, and factors associated with, failure to mate by 245 days of age in the gilt. Anita. Reprod. Sci., 5: 199--205. Einarsson, S. and Linde, C., 1974. Studies on the reproductive tract of anoestrous gilts. In: Proc. 3rd Int. Pig Vet. Soc. Congress, 12--14 June, 1974, Lyon, France, pp. J. 10.1--10.4. Foote, W.C., Waldorf, D.P., Chapman, A.B., Self, H.L., Grummer, R.H. and Casida, L.E., 1956. Age at puberty of gilts produced by different systems of mating. J. Anita. Sci., 15: 959--969. Hutchens, L.K., Hintz, R.L. and Johnson, R.K., 1981. Genetic and phenotypic relationships between pubertal and growth characteristics in gilts. J. Anim. Sci., 53: 946--951. Hutchens, L.K., Hintz, R.L. and Johnson, R.K., 1982. Breed comparisons for age and weight at puberty in gilts. J. Anim. Sci., 55: 60--66. Johnson, R.K., 1981. Crossbreeding in swine. Experimental results. J. Anita. Sci., 52: 906--923. Johnson, R.K., Omtvedt, I.T. and Walters, L.E., 1978. Comparison of productivity and performance for two-breed and three-breed crosses in swine. J. Anita. Sci., 46: 69--82. Legault, C., 1973. Genetic analysis of sexual precocity, ovulation and number of embryos in the sow: heritability, effect of heterosis. Journ. Rech. Porc. Fr., 5: 147--154. Pani, S.N., Day, B.N., Tribble, L.F. and Lasley, J.F., 1963. Maternal influence in swine as reflected by differences in reciprocal crosses. Missouri Agric. Exp. Sta., Bull. 830, 19 pp. Reutzel, L.F. and Sumption, L.J., 1968. Genetic and phenotypic relationships involving age at puberty and growth rate of gilts. J. Anim. Sci., 27: 27--30. Robison, O.W., 1972. The role of maternal effects in animal breeding. V. Maternal effects in swine. J. Anim. Sci., 35: 1303--1315. SAS, 1979. SAS User's Guide. Statistical Analysis System Institute, Cary, NC, 494 pp. Short, R.E., 1963. Influence of heterosis and plane of nutrition on reproductive phenomena in gilts. M.S. Thesis, University of Nebraska, Lincoln, NE, 54 pp. Steel, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., New York, NY, 481 pp. Tess, M.W., Bennett, G.L. and Dickerson, G.E., 1983. Simulation of genetic changes in life cycle efficiency of pork production. I. A bioeconomic model. J. Anim. Sci., 56: 336--353. Young, L.D., Johnson, R.K., Omtvedt, I.T. and Walters, L.E., 1976. Postweaning performance and carcass merit of purebred and two-breed cross pigs. J. Anita. Sci., 42: 1124--1132.
281
Elsevier Science Publishers B.V., A m s t e r d a m -- Printed in The Netherlands
AGE AT PUBERTY A N D ESTROUS ACTIVITY OF STRAIGHTBRED AND RECIPROCAL CROSSBRED GILTS
R.D. A L L R I C H 1, R.K. C H R I S T E N S O N 2 and J.J. F O R D
Roman L. Hruska U.S. Meat Animal Research Center, U.S. Department o f Agriculture, P.O. Box 166, Clay Center, NE 68933 (U.S.A.) IPresent address: D e p a r t m e n t of Animal Sciences, Lilly Hall, Purdue University, West Lafayette, IN 4 7 9 0 7 (U.S.A.) 2To w h o m reprint requests should be addressed. ( A c c e p t e d 17 April 1984)
ABSTRACT Allrich, R.D., Christenson, R.K. and Ford, J.J., 1985. Age at p u b e r t y and estrous activity o f straightbred and reciprocal crossbred gilts. Anim. Reprod. Sci., 8: 281- 286. Age at p u b e r t y , estrous activity and g r o w t h were evaluated in 294 straightbred and reciprocal crossbred gilts maintained in c o n f i n e m e n t conditions. Trial 1 used straightbred Landrace (L), Yorkshire (Y) and reciprocal crossbred (LY, YL) gilts. Trial 2 used LY and YL gilts, and Trial 3 used L and Duroc (D) reciprocal crossbred gilts (LD, DL). Daily observations for estrous activity with a m a t u r e boar were initiated at 150 days of age and c o n t i n u e d until gilts reached 255 days of age. Gilts not exhibiting estrus by 255 days of age were e x a m i n e d by laparoscopy to determine r e p r o d u c t i v e status. In Trial 1, age at p u b e r t y was greater for Y gilts c o m p a r e d to L and reciprocal crossbred gilts. Differences b e t w e e n reciprocal crosses for age at p u b e r t y were n o t significant in any trial. In Trial 1, the percentage of gilts exhibiting regular estrous cycles at 195 days of age was lower for Y gilts than for the o t h e r three groups of gilts; however, by 225 days of age, this difference was n o t significant. In all trials, reciprocal crossbred gilts did n o t differ with respect to percentage exhibiting regular estrous cycles or in percentage prepubertal. In Trial 1, Y gilts had a higher percentage prepubertal at 255 days of age than the reciprocal crossbred gilts. The percentage of gilts exhibiting behavioral anestrus at 255 days of age did n o t differ a m o n g breed groups within any trial. Based on these observations, we concluded the breed maternal effects were small or n o n e x i s t e n t relative to direct additive and nonadditive genetic effects in the breed c o m b i n a t i o n s that were investigated.
INTRODUCTION
The maternal environment during gestation and lactation are known to influence growth rate, food conversion and carcass traits of swine (Pani et al., 1963; Ahlsehwede and Robison, 1971a,b; Robison, 1972; Young et al., 1976; Johnson, 1981). The extent to which reproductive characteristics are Mention o f trade names or companies does n o t constitute an implied warranty o r endorsem e n t by the U S D A or the authors.
282 affected by the maternal environment is less certain. Johnson et al. (1978) reported no differences in ovulation rate and embryo development between reciprocal crosses. Theoretically, reciprocal crossbred animals are genetically equal {assuming sires and dams of each parent breed are of equal average genetic merit) but have experienced different maternal environments during their prenatal and early postnatal existence. Utilizing reciprocal crossbred animals is therefore a technique that can be employed to investigate breed maternal effects. Several researchers (Reutzel and Sumption, 1968; Legault, 1973; Hutchens et al., 1981) have implied the existence of breed maternal effects based on expectations of variance components. Also, Foote et al. (1956) found a difference in age at puberty between Yorkshire (Y) and Duroc (D) reciprocal crossbred gilts. However, Short (1963) using the same breeds and Clark et al. {1970) using Y and Poland China breeds, found no reciprocal differences with respect to age at puberty. Hutchens et al. {1982) found no reciprocal differences in age or weight at puberty using a four-breed diallel design involving D, Y, Landrace (L) and Spotted breeds. The objectives of the present study were to evaluate several reproductive traits in reciprocal crossbred gilts and to further characterize these traits for straightbred and reciprocal crossbred gilts maintained in confinement. MATERIALS AND METHODS Trial 1 utilized 116 July-born gilts of straightbred L 1 (four sires, eleven litters) and Y (five sires, thirteen litters) breeding as well as the reciprocal crosses (LY, five sires, twelve litters; YL, four sires, eleven litters). Trial 2 involved 80 December-born gilts of LY (four sires, fourteen l i t t e r s ) a n d YL (seven sires, sixteen litters) breeding. In Trial 2, approximately 50% of the dams and 100% of the sires were also utilized in Trial 1. Trial 3 involved 98 June-born gilts of LD (six sires, 22 litters) and DL {seven sires, seventeen litters) breeding. Gilts were weaned at 4 weeks of age, maintained in a nursery as groups of females (irrespective of breed) until 10 weeks of age, and then moved to a modified open-front finishing building and penned in groups of ten to twelve for the duration of the study. A corn and soybean meal based ration containing 18.5% protein was fed ad libitum to gilts in the nursery. Thereafter, gilts were fed ad libitum, a diet with 16% protein until 100 kg body weight when a 14% protein diet was fed at a rate of 1.82 kg per head daily. Daily observations for estrous activity were initiated at 150 days of age and continued until gilts were 255 days of age. Estrus was evaluated by moving gilts from their pen and placing them for 15 min each day into a pen with a mature male. Puberty was defined as the age that a gilt first 1Foundation Landraee animals were purchased from Pig Improvement Co., Spring Green, WI.
283
showed the immobilization response in the presence of a mature boar. Gilts not reaching p u b e r t y did not contribute to pubertal data calculated for each subclass. Gilts not exhibiting regular estrous cycles b y 255 days of age were examined by laparoscopy to determine whether they were behaviorally anestrous (ovaries with corpora lutea, preovulatory follicles or corpora albicantia and uterus typical of cyclic gilts) or prepubertal (no evidence of ovulation and small uterus). B o d y weight was recorded every 30 days during the study. Inconsistency in n values of tables are a result of: (1) cessation of regular estrous cycle and (2) lameness or death. The data were analyzed by least-squares fixed-model procedures (General Linear Models Procedure; SAS, 1979). The model for analysis of all traits (trials analyzed separately) included fixed effects of breed. In comparisons of reciprocal crosses between Trials 1 and 2, fixed effects of season and breed X season interaction were included in the model. Proportional data were analyzed by chi-square procedures (Steel and Torrie, 1960). Differences between breed group means in Trial 1 were determined by the NewmanKeuls test (Steel and Torrie, 1960). RESULTS
In all three trials, differences among reciprocal crosses were not significant for age at p u b e r t y (Table I). In Trial 1, age at puberty was greater (P < 0.05) for Y gilts in comparison to L, LY, and YL gilts. Heterosis estimate (-5.65 days) for age at puberty was not significant. Reciprocal crosses did not differ with respect to percentage exhibiting regular estrous cycle at any age evaluated (Table II) within any trial. In Trial 1, Y gilts had the lowest (P < 0.01) percentage exhibiting regular estrous cycles at 195 days; however, this difference was not significant at either 225 or 255 days of age. The percentage of gilts that showed behavioral anestrus did not differ between reciprocal crossbred gilts in any trial (Table III); however, the overall TABLE
I
Age (days) of gilts at first estrus a Trial
1 2
Breed L
Y
LY
YL
1 8 4 . 7 -+ 4 . 0 b (26/29)
199.8 + 4.2 c (23/29)
1 8 7 . 2 -+ 4 . 0 b (26127)
186.0 + 4.0 b (27/31)
1 8 0 . 0 -+ 4 . 0 (36/38)
183.6 ± 3.9 (38142)
3
aData presented a r e l e a s t - s q u ~ x e s m e a n s + S E M ; p r o p o r t i o n
~, gC Mt oe amn es a wn /ittoht adl i f fneur emnbt e rs u op fe r gs ci lrtisp ti sn gwr iotuhpi n) . s a m e
LD
DL
197.3 + 3.8 (55/62)
2 0 0 . 0 -+ 3 . 7 (34/36)
in parenthesis
row differ, P < 0.05.
= (number
of gilts contribut-
284
T A B L E II
P e r c e n t a g e o f gilts e x h i b i t i n g r e g u l a r estrous c y c l e s at 1 9 5 , 2 2 5 a n d 2 5 5 d a y s o f age Age (days)
Trial
Breed L
Y
LY
YL
195
1 2 3
72(21/29) a
38(11/29) b
74(20/27) a 71(27/38)
68(21]31) a 62(26]42)
225
1 2 3
86(25/29)
69(20]29)
85(23/27) 79(30/38)
84(26/31) 71(30/42)
255
1 2 3
90(26/29)
76(22]29)
89(24/27) 82(31/38)
77(24/31) 79(33/42)
LD
DL
44(27/62)
39(15/38)
76(47/62)
67(24]36)
77(48/62)
75(27/36)
a'bvalues with different supereripts within same row differ, P ~ 0.01. F o r p r o p o r t i o n i n p a r e n t h e s e s see f o o t n o t e T a b l e I. T A B L E III P e r c e n t a g e o f gilts b e h a v i o r a l l y a . n e s t r o u s ( B A ) o r p r e p u b e r t a l (PP) a t 2 5 5 d a y s o f age Parameter
(%)
Trial
Breed L
Y
BA
1 2 3
0
(0/29)
3.5(1/29)
PP
1 2 3
3.5(1/29) a,b 17.0(5129) a
LY
YL
7.4(2/27) 13.2(5/38)
9.7(3/31) 14.3(6/42)
0 (0]27) b 5.3(2/38)
LD
DL
17.7(11/62)
16.7(6/36)
0 (0/31) b 4.8(2/42) 0
(0/62)
5.5(2/36)
a'bvalues with different superscripts within same row differ, P ~ 0.05. F o r p r o p o r t i o n i n p a r e n t h e s i s see f o o t n o t e T a b l e I.
percentage of gilts that were behaviorally anestrous was greater in Trials 2 and 3. Reciprocal crossbred gilts in Trials 1, 2 and 3 did not differ in percentage of prepubertal gilts (Table III). In Trial 1, a greater (P < 0.05) percentage of Y gilts were prepubertal at 255 days of age than the LY and YL gilts (Table III). In Trial 1, the reciprocal crossbred gilts had greater ( P < 0 . 0 5 ) b o d y weights at all ages evaluated compared to the straightbred gilts and the heterosis estimate for b o d y weight averaged 5.3% (P < 0.01). In comparisons of parameters for reciprocal crossbred gilt between Trials 1 and 2, no significant influence of season or season × breed interaction was detected. In Trial 3, the most pronounced reciprocal difference was noted with DL gilts being consistently heavier (P < 0.01) at all ages evaluated than LD gilts. DISCUSSION
A difference in age at puberty for reciprocal cross YD and DY gilts was reported by Foote et al. (1956). Subsequent studies with different breed
285 combinations (Short, 1963; Clark et al., 1970; Christenson, 1981; Hutchens et al., 1982) and results of the present study did n o t show a reciprocal difference, and thus we suggest that breed maternal effects do not have a major influence on age at puberty in gilts. The difference in age at puberty for L and Y straightbred gilts in Trial 1 is in agreement with that reported by Christenson and Ford (1979b) using the same genetic population. Both reciprocal crosses (LY, YL) were similar to the L gilts in age at puberty suggesting the presence of nonadditive gene action. The percentage of gilts exhibiting regular estrous cycles at or near breeding age varies with breed (Christenson and Ford, 1979b; Christenson, 1981). Reciprocal differences in the percentage of gilts exhibiting regular estrous cycles and the percentage prepubertal were negligible in all three trials indicating that breed maternal effects have little influence on these traits. This is in contrast to a report by Christenson (1981) where a difference in percentage of gilts exhibiting regular estrous cycles for L and Large White (LW) reciprocal crossbred gilts was detected. The large difference in percentage of gilts exhibiting regular estrous cycles for L and LW reciprocal crossbred gilts was a result of a high percentage (16.4%) of LW X L gilts with behavioral anestrus as compared to a low (1.4%) percentage of L Z LW gilts. An explanation for the difference in the two studies may be due to the breeds used in producing the reciprocal crosses. The L breed was c o m m o n to all reciprocal crosses in both studies, but the other breeds contributing to the reciprocal crosses differed. Gilts that show behavioral anestrus can represent a considerable proportion of the gilts intended as breeding stock and breeds differ as to incidence of behavioral anestrus (Einarsson and Linde, 1974; Christenson and Ford, 1979a,b; Christenson, 1981; Cronin et al., 1983). No more than 90% (mean = 81%) of the gilts of any breed combination were consistently exhibiting regular estrous cycles by 255 days of age. The percentage of gilts which show regular estrous cycles at a younger age requires more attention in research relating to confinement swine production. At 195 days of age, in the breed groups with the youngest age at puberty (184 days; L, LY and YL), 69% of the gilts were showing estrous cycles compared to the three breed groups with the oldest age at puberty (199 days; Y, LD and DL) in which only 40% were showing estrous cycles. Thus, this reduction in age at puberty by 15 days resulted in 29% more gilts available for selection as replacements. This allows for selection of replacement gilts at an age nearer to standard market age, thereby decreasing production costs. Tess et al. (1983) have summarized the benefit of decreasing age at puberty in gilts relative to biological and economic efficiency of pork production. ACKNOWLEDGEMENTS The authors express their appreciation to Mark Anderson, Robert Byrkit, Jenell Dague, Jean Gray and Toni Tolles for their invaluable expertise and to Kathy Leising for her secretarial assistance.
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Published as paper number 7278, Journal Series, Nebraska Agricultural Experiment Station. Research was supported in part by U S D A Cooperative State Research Service Grant 701-15-42.
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