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Effect of chlortetracycline supplementation during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival and fetal development in gilts
THERIOGENOLOGY
EFFECT OF CHLORTETRACYCLINE SUPPLEMENTATION DURING PREBREEDING AND EARLY GESTATION ON AGE AT PUBERTY, OWLATION RATE, EMBRYO SURVIVAL AND FETAL DEVELOPMENT IN GILTS R.R. Grandhi,
1
Virginia
Received
E.T. Kornegay, M.D. Lindemann and J.W. Knight Department of Animal Science Polytechnic Institute and State University Blacksburg, VA 24061 for publication: Decembyr 3, 2986 Accepted: May 27, 1987 ABSTRACT
A total of 166 crossbred gilts weighing approximately 87 5 1 kg was limit-fed (2.5 kg/d) a corn-soybean meal gestation diet containing either 0 or 220 ppm of chlortetracycline (CTC) from 157 2 1 d of age until 15 d after These gilts were slaughtered at 31 + 1 or 71 d f 1 d of gestation breeding. Age (190 + 3 d vs 195 + 3 d) and for evaluation of reproductive performance. body weights (106 + 2 kg vs 106 t 2 kg) at puberty were similar for control and CTC-fed gilts, respectively. Although not significant (P > 0.05), ovulation rate was higher in CTC-fed than in control gilts as assessed at both 31 d (14.2 t 0.7 vs 12.9 zh 0.9, P = 0.31) and 71 d (13.9 zt 0.6 vs 12.4 5 0.5, P = 0.10) There was an increase (P = 0.04) in the number of live embryos of gestation. for CTC-fed gilts at 31 d (12.1 f 0.7 vs 9.7 f 0.7) but not at 71 d (10.0 f 1.1 vs 9.6 + 1.0) of gestation. The mean uterine length, placental length, placental weight, fetal length, fetal weight, and allantoic fluid volumes were similar between the control and CTC-fed gilts. Results indicated that feeding GTG during prebreeding and early gestation did not influence the proportion or However, CTC feeding may have influenced a trend toage of gilts at puberty. ward an increased ovulation rate and increased number of live embryos in gilts. Key words:
gilts, chlortetracycline,
ovulation
rate, embryo survival
Acknowledgements: We thank Gene Ball and his staff for care of animals; Cynthia Strader and Ed Bonnette for data collection; and Dr. R. F. Kelly, Department of Food Science, for slaughtering gilts. Mention of trade names or proprietary products does not constitute a guarantee or warranty of the product and does not imply its approval $0 the exclusion of other products that may also substitute. Present address: Agriculture Canada Research Station, Box 610. Brandon, Manitoba, Canada. R7A 527.
NOVEMBER
1987 VOL. 28 NO. 5
661
THERIOGENOLOGY
INTRODUCTION It has long been recognized that feeding antibiotics at low levels as a nonnutrient feed additive benefits growth performance of pigs (1,Z). However, informationas to the effect of antibioticson female reproductiveefficiency of swine is limited. Dean and Tribble (3) reported a significant increase in litter size of sows fed 0.54 g of CTCa daily in the breeding ration. Myers and Speer (4) and Langlois et al. (5) also observed an increase in litter size in sows fed CTC during breeding and early gestation. However, Messersmith et al. (6) and Soma and Speer (7) did not observe such an increase in litter size of gilts or sows fed CTC. Since the litter size in swine is largely determined by ovulation rate and prenatal survival, an increase in litter size in CTC-fed gilts and sows was probably due to a positive influence on these two reproductive functions. Hays et al. (8) repyrted that sows fed SP-250b from weaning to 3 d after mating had a larger number (P > 0.05) of fertilizedova than did the control group, however, such information is not available in gilts. The objective of this study was to determine the influence of feeding CTC during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival, and fetal development in gilts. MATERIALS
AND METHODS
Data were collected from six trials conducted from November 1984 to May 1985 at Blacksburg and Suffolk,Virginia. A total of 166 crossbred gilts (Large White x Yorkshire or Large White x Duroc) housed in total confinementor in open front pens with concrete floors was used. Gilts were weighed at 157 + 1 d of age and randomly assigned, on the basis of body weight and litter origin, to the following two treatment diets: 1) a corn-soybeanmeal gestation diet containing 14% crude protein, 3400 kcal digestible energy/kg, and minerals and vitamins to meet or exceed the National Research Council (9) recommendedlevels (control),or 2) 220 mg/kg CTC added to the control diet. The experimental diets were fed as mash at a level of 2.5 kg/d until breeding and at 2.0 kg/d from breeding to 15 d of gestation. Then all gilts were switched to the control diet and fed 2.0 kg/d for the remainder of gestation. Gilts were checked daily for estrus using mature boars and bred at second estrus by natural mating. A total of 31 gilts from both treatment groups was randomly selected for slaughter at 31 f.1 or 71 zt1 d of gestationto record various uterine and fetal data. Each fetus and placenta were separated; placental length and weight, fetal crown-rump length and weight, and allantoic fluid volume were determined for each conceptus unit. The data for each gestation phase were analyzed separatelyusing the General Linear Models procedure of the StatisticalAnalysis System (10). The
'.AureomycinChlortetsacycline,American Cyanamid Co., Princeton, NJ. b'Chlortetracycline , 40%; sulfamethazine,40%; and penicillin, 20%. American Cyanamid Co., Princeton, NJ.
662
NOVEMBER
1987 VOL. 28 NO. 5
THERIOGENOLOGY
breeding weight was used as a covariate for ovulation rate, number of live fetuses and embryo survival, whereas the body weights at slaughter and day of gestation were used as covariates for the uterine and fetal measurements. RESULTS AND DISCUSSION
The number of gilts that were detected in first estrus during the 1%wk period of feeding experimental diets and the mean age and body weight at first detested estrus were similar between control and CTC-fed groups (Table l), indicating that CTC had very little influence on these traits. A lack of difference in weight gains until puberty or breeding between CTC-fed and control gilts was probably due to limit-feeding of diets during the experiment. Table 1.
Effect of chl.ortetracycline supplementation weights at puberty and breedinga
No. of gilts allotted No. of gilts in estrusb Age at start (d) Body weight at start (kg) Age at puberty (d)c Body weight at puberty (kg) Body weight at breeding (kg)
on age and body
Control
Chlortetracycline
83 44 156.8 + 0.8 88.3 + 2.0 190.3 dz 2.8 106.5 It:2.1 118.9 zt 2.9
83 44 156.9 zt 0.9 86.5 + 1.9 195.6 zt 2.8 106.1 zt 2.1 114.1 zt 2.9
a Least squares means + SEM. A Gilts in first detected estrus within approximately c Puberty defined as first detected estrus.
12 wk after starting test.
The ovulation rate of CTC-fed gilts was higher but not significantly (P > 0.05) different than that of the control gilts either at 31 (P = 0.31) or 71 (P = 0.10) d of gestation (Table 2). The increase in live embryos (fetuses) for CTC-fed gilts, compared with the control gilts, was significant (P = 0.04) at 31 but not at 71 d (P = 0.83) of gestation. Feeding CTC also seemed to have a positive influence on reducing the incidence of embryonic mortality during the first 31 d of gestation as indicated by a lower (P = 0.13) number of dead embryos in CTC-fed gilts than in control gilts. Etienne et al. (11) showed that the prenatal mortality continues up to 105 d of gestation, although the highest proportion of it generally occurs before 30 d of gestation. Webel and Dzuik (12) reported that uterine space may be a limiting factor for late embryonic mortality after day 30 of gestation. Knight et al. (13) established that limited placental surface area is the major cause of prenatal mortality after approximately 60 d of gestation.
A reduction in the number of live fetuses observed at 71 d of gestation, in CTC-fed gilts was probably due to limitation of uterine space or placental insufficiency. Uterine length, placental length, and placental weights were not significantly (P > 0.05) different between control and CTC-fed gilts either at 31 or 71 d of gestation. This finding indicates that CTC had very little influence on uterine and placental development, which may be required to ac-
NOVEMBER 1987 VOL. 28 NO. 5
663
THERIOGENOLOGY
commodate increased number of f&uses. The fetal length, distribution of fetuses in right and left uterine horns, fetal sex at 71 d of age, and allantoic fluid volumes were also similar between the control and CTC-fed gilts. In agreement with previous reports (3,6) our results suggest that feeding CTC during prebreeding and early gestation may benefit ovulation rate and number of live f&uses in gilts. Table 2.
Effect of chlortetracycline (CTC) supplementation on ovulation rate, embryo survival, and uterine and fetal measurementsa
Gestation: Diets:
31+ld Control
No. of gilts No. of CL No. of live fetuses No. of dead fetuses Embryo survival (%) Uterine length (cm) Placental length (cm) Placental weight (g) Fetal length (cm) Fetal weight (g) Fetal position scored Allantoic fluid (ml) Fetal sex scoree
6 12.9 * 0.9 9.7 + 0.76 0.6 -Ir0.2 75.4 f 6.2 318 + 17 55 * 1 41 f 3 2.1 f 0.1 22 +- 2 1.5 + 0.1 186 + 27 -_-
71+ld Control
CTC 9 14.2 * 0.7 12.1 + 0.7c 0.2 rf:0.2 85.5 f 5.7 300 + 14 49 II:1 36 + 2 2.3 + 0.1 19 ?r 2 1.5 + 0.1 la2 + 22 ---
a Least squares means zt SEM. b,c Within gestation, means followed by different (P < 0.05) d 1 = right uterine horn; 2 = left uterine horn. e 1 = male; 2 = female.
12.4 9.6 0.4 76.8 399 74 255 16.4 299 1.5 355 1.6
9 + 0.5 + 1.0 + 0.2 z!z6.6 * 17 + 5 t 19 + 0.3 +- 15 * 0.1 * 33 + 0.1
CTC
13.9 10.0 0.3 71.7 366 79 266 16.3 285 1.5 449 1.6
7 + 0.6 * 0.1 * 0.3 + 7.7 1 19 + 6 zb 21 ?r 0.4 iz 17 zb 0.1 * 38 + 0.1
letters differ significantly
REFERENCES
664
1.
Jukes, T.H. 22~526-534
Antibiotics (1972).
in animal feeds and animal production/
2.
Hays, V.W. (1985).
Antibiotics
3.
Dean, B.T. and Tribble, L.F. Effect of feeding therapeutic level of antibiotic at breeding on reproductive performance of swine. J. Anim. Sci. =:207-209 (1962).
4.
Myers, D.J. and Speer, V.C. Effects of an antibiotic performance of sows with short farrowing intervals. 36:1125-1128 (1973).
5.
Influence of Langlois, B. E., Cromwell, G.L. and Hays, V.W. chlortetracycline in swine feed on reproductive performance and on incidence and persistence of antibiotic resistant enteric bacteria. J. Anim. Sci. a:1369-1382 (1978).
for animals.
Sci. of Food and Agric.
NOVEMBER
Bioscience
3:17-16
and flushing on J. Anim. Sci.
1987 VOL. 28 NO. 5
THERIOGENOLOGY
6.
Messersmith, R.E., Johnson, D.D., Elliott, R.F. and Drain, J.J. Value of chlortetracycline in breeding rations for sows. J. Anim. Sci. Z:752-755 (1966).
7.
Soma, J.A. and Speer, V.C. Effect of pregnant mare serum and chlortetracycline on the reproductive efficiency of sows. J. Anim. Sci. 41:100-105 (1975).
a.
Hays, V.W., King, J.L., Cromwell, G.L., Dutt, R.H. and Kratzer, D.D. Effect of lactation length and dietary antibiotics on reproductive performance of sows. J. Anim. Sci. 46:884-a91 (1978).
9.
National No. 2. 22-25.
Research Nutrient
Council. Nutrient Requirements of Domestic Animals. requirements of swine. Washington, DC. .1979, PP.
10.
Statistical Institute,
Analysis System. Cary, NC, 1982;
11.
Etienne, M., Comous, S. and Cuvillier, M. during growth on puberty and reproductive Nutr. Develop. 23:309-319 (1983).
12.
Webel, S.K. and Dzuik, P.J. Effect of stage of gestation and uterine space on prenatal survival in the pig. J. Anim. Sci. =:960-963 (1974).
13.
Knight, J.W., Bazer, F.W., Thatcher, W.W., Franke, D.E. and Wallace, H.D. Conceptus development in intact and unilaterally hysterectomizedovariectomized gilts: interrelationships among hormonal status, placental development, fetal fluids and fetal growth. .I. Anim. Sci. &:620-637 (1977).
NOVEMBER
User's Guide, Statistical pp. 139-199.
1987 VOL. 28 NO. 5
Analysis
System
Effect of feed restriction performance in gilts. Reprod.
665
EFFECT OF CHLORTETRACYCLINE SUPPLEMENTATION DURING PREBREEDING AND EARLY GESTATION ON AGE AT PUBERTY, OWLATION RATE, EMBRYO SURVIVAL AND FETAL DEVELOPMENT IN GILTS R.R. Grandhi,
1
Virginia
Received
E.T. Kornegay, M.D. Lindemann and J.W. Knight Department of Animal Science Polytechnic Institute and State University Blacksburg, VA 24061 for publication: Decembyr 3, 2986 Accepted: May 27, 1987 ABSTRACT
A total of 166 crossbred gilts weighing approximately 87 5 1 kg was limit-fed (2.5 kg/d) a corn-soybean meal gestation diet containing either 0 or 220 ppm of chlortetracycline (CTC) from 157 2 1 d of age until 15 d after These gilts were slaughtered at 31 + 1 or 71 d f 1 d of gestation breeding. Age (190 + 3 d vs 195 + 3 d) and for evaluation of reproductive performance. body weights (106 + 2 kg vs 106 t 2 kg) at puberty were similar for control and CTC-fed gilts, respectively. Although not significant (P > 0.05), ovulation rate was higher in CTC-fed than in control gilts as assessed at both 31 d (14.2 t 0.7 vs 12.9 zh 0.9, P = 0.31) and 71 d (13.9 zt 0.6 vs 12.4 5 0.5, P = 0.10) There was an increase (P = 0.04) in the number of live embryos of gestation. for CTC-fed gilts at 31 d (12.1 f 0.7 vs 9.7 f 0.7) but not at 71 d (10.0 f 1.1 vs 9.6 + 1.0) of gestation. The mean uterine length, placental length, placental weight, fetal length, fetal weight, and allantoic fluid volumes were similar between the control and CTC-fed gilts. Results indicated that feeding GTG during prebreeding and early gestation did not influence the proportion or However, CTC feeding may have influenced a trend toage of gilts at puberty. ward an increased ovulation rate and increased number of live embryos in gilts. Key words:
gilts, chlortetracycline,
ovulation
rate, embryo survival
Acknowledgements: We thank Gene Ball and his staff for care of animals; Cynthia Strader and Ed Bonnette for data collection; and Dr. R. F. Kelly, Department of Food Science, for slaughtering gilts. Mention of trade names or proprietary products does not constitute a guarantee or warranty of the product and does not imply its approval $0 the exclusion of other products that may also substitute. Present address: Agriculture Canada Research Station, Box 610. Brandon, Manitoba, Canada. R7A 527.
NOVEMBER
1987 VOL. 28 NO. 5
661
THERIOGENOLOGY
INTRODUCTION It has long been recognized that feeding antibiotics at low levels as a nonnutrient feed additive benefits growth performance of pigs (1,Z). However, informationas to the effect of antibioticson female reproductiveefficiency of swine is limited. Dean and Tribble (3) reported a significant increase in litter size of sows fed 0.54 g of CTCa daily in the breeding ration. Myers and Speer (4) and Langlois et al. (5) also observed an increase in litter size in sows fed CTC during breeding and early gestation. However, Messersmith et al. (6) and Soma and Speer (7) did not observe such an increase in litter size of gilts or sows fed CTC. Since the litter size in swine is largely determined by ovulation rate and prenatal survival, an increase in litter size in CTC-fed gilts and sows was probably due to a positive influence on these two reproductive functions. Hays et al. (8) repyrted that sows fed SP-250b from weaning to 3 d after mating had a larger number (P > 0.05) of fertilizedova than did the control group, however, such information is not available in gilts. The objective of this study was to determine the influence of feeding CTC during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival, and fetal development in gilts. MATERIALS
AND METHODS
Data were collected from six trials conducted from November 1984 to May 1985 at Blacksburg and Suffolk,Virginia. A total of 166 crossbred gilts (Large White x Yorkshire or Large White x Duroc) housed in total confinementor in open front pens with concrete floors was used. Gilts were weighed at 157 + 1 d of age and randomly assigned, on the basis of body weight and litter origin, to the following two treatment diets: 1) a corn-soybeanmeal gestation diet containing 14% crude protein, 3400 kcal digestible energy/kg, and minerals and vitamins to meet or exceed the National Research Council (9) recommendedlevels (control),or 2) 220 mg/kg CTC added to the control diet. The experimental diets were fed as mash at a level of 2.5 kg/d until breeding and at 2.0 kg/d from breeding to 15 d of gestation. Then all gilts were switched to the control diet and fed 2.0 kg/d for the remainder of gestation. Gilts were checked daily for estrus using mature boars and bred at second estrus by natural mating. A total of 31 gilts from both treatment groups was randomly selected for slaughter at 31 f.1 or 71 zt1 d of gestationto record various uterine and fetal data. Each fetus and placenta were separated; placental length and weight, fetal crown-rump length and weight, and allantoic fluid volume were determined for each conceptus unit. The data for each gestation phase were analyzed separatelyusing the General Linear Models procedure of the StatisticalAnalysis System (10). The
'.AureomycinChlortetsacycline,American Cyanamid Co., Princeton, NJ. b'Chlortetracycline , 40%; sulfamethazine,40%; and penicillin, 20%. American Cyanamid Co., Princeton, NJ.
662
NOVEMBER
1987 VOL. 28 NO. 5
THERIOGENOLOGY
breeding weight was used as a covariate for ovulation rate, number of live fetuses and embryo survival, whereas the body weights at slaughter and day of gestation were used as covariates for the uterine and fetal measurements. RESULTS AND DISCUSSION
The number of gilts that were detected in first estrus during the 1%wk period of feeding experimental diets and the mean age and body weight at first detested estrus were similar between control and CTC-fed groups (Table l), indicating that CTC had very little influence on these traits. A lack of difference in weight gains until puberty or breeding between CTC-fed and control gilts was probably due to limit-feeding of diets during the experiment. Table 1.
Effect of chl.ortetracycline supplementation weights at puberty and breedinga
No. of gilts allotted No. of gilts in estrusb Age at start (d) Body weight at start (kg) Age at puberty (d)c Body weight at puberty (kg) Body weight at breeding (kg)
on age and body
Control
Chlortetracycline
83 44 156.8 + 0.8 88.3 + 2.0 190.3 dz 2.8 106.5 It:2.1 118.9 zt 2.9
83 44 156.9 zt 0.9 86.5 + 1.9 195.6 zt 2.8 106.1 zt 2.1 114.1 zt 2.9
a Least squares means + SEM. A Gilts in first detected estrus within approximately c Puberty defined as first detected estrus.
12 wk after starting test.
The ovulation rate of CTC-fed gilts was higher but not significantly (P > 0.05) different than that of the control gilts either at 31 (P = 0.31) or 71 (P = 0.10) d of gestation (Table 2). The increase in live embryos (fetuses) for CTC-fed gilts, compared with the control gilts, was significant (P = 0.04) at 31 but not at 71 d (P = 0.83) of gestation. Feeding CTC also seemed to have a positive influence on reducing the incidence of embryonic mortality during the first 31 d of gestation as indicated by a lower (P = 0.13) number of dead embryos in CTC-fed gilts than in control gilts. Etienne et al. (11) showed that the prenatal mortality continues up to 105 d of gestation, although the highest proportion of it generally occurs before 30 d of gestation. Webel and Dzuik (12) reported that uterine space may be a limiting factor for late embryonic mortality after day 30 of gestation. Knight et al. (13) established that limited placental surface area is the major cause of prenatal mortality after approximately 60 d of gestation.
A reduction in the number of live fetuses observed at 71 d of gestation, in CTC-fed gilts was probably due to limitation of uterine space or placental insufficiency. Uterine length, placental length, and placental weights were not significantly (P > 0.05) different between control and CTC-fed gilts either at 31 or 71 d of gestation. This finding indicates that CTC had very little influence on uterine and placental development, which may be required to ac-
NOVEMBER 1987 VOL. 28 NO. 5
663
THERIOGENOLOGY
commodate increased number of f&uses. The fetal length, distribution of fetuses in right and left uterine horns, fetal sex at 71 d of age, and allantoic fluid volumes were also similar between the control and CTC-fed gilts. In agreement with previous reports (3,6) our results suggest that feeding CTC during prebreeding and early gestation may benefit ovulation rate and number of live f&uses in gilts. Table 2.
Effect of chlortetracycline (CTC) supplementation on ovulation rate, embryo survival, and uterine and fetal measurementsa
Gestation: Diets:
31+ld Control
No. of gilts No. of CL No. of live fetuses No. of dead fetuses Embryo survival (%) Uterine length (cm) Placental length (cm) Placental weight (g) Fetal length (cm) Fetal weight (g) Fetal position scored Allantoic fluid (ml) Fetal sex scoree
6 12.9 * 0.9 9.7 + 0.76 0.6 -Ir0.2 75.4 f 6.2 318 + 17 55 * 1 41 f 3 2.1 f 0.1 22 +- 2 1.5 + 0.1 186 + 27 -_-
71+ld Control
CTC 9 14.2 * 0.7 12.1 + 0.7c 0.2 rf:0.2 85.5 f 5.7 300 + 14 49 II:1 36 + 2 2.3 + 0.1 19 ?r 2 1.5 + 0.1 la2 + 22 ---
a Least squares means zt SEM. b,c Within gestation, means followed by different (P < 0.05) d 1 = right uterine horn; 2 = left uterine horn. e 1 = male; 2 = female.
12.4 9.6 0.4 76.8 399 74 255 16.4 299 1.5 355 1.6
9 + 0.5 + 1.0 + 0.2 z!z6.6 * 17 + 5 t 19 + 0.3 +- 15 * 0.1 * 33 + 0.1
CTC
13.9 10.0 0.3 71.7 366 79 266 16.3 285 1.5 449 1.6
7 + 0.6 * 0.1 * 0.3 + 7.7 1 19 + 6 zb 21 ?r 0.4 iz 17 zb 0.1 * 38 + 0.1
letters differ significantly
REFERENCES
664
1.
Jukes, T.H. 22~526-534
Antibiotics (1972).
in animal feeds and animal production/
2.
Hays, V.W. (1985).
Antibiotics
3.
Dean, B.T. and Tribble, L.F. Effect of feeding therapeutic level of antibiotic at breeding on reproductive performance of swine. J. Anim. Sci. =:207-209 (1962).
4.
Myers, D.J. and Speer, V.C. Effects of an antibiotic performance of sows with short farrowing intervals. 36:1125-1128 (1973).
5.
Influence of Langlois, B. E., Cromwell, G.L. and Hays, V.W. chlortetracycline in swine feed on reproductive performance and on incidence and persistence of antibiotic resistant enteric bacteria. J. Anim. Sci. a:1369-1382 (1978).
for animals.
Sci. of Food and Agric.
NOVEMBER
Bioscience
3:17-16
and flushing on J. Anim. Sci.
1987 VOL. 28 NO. 5
THERIOGENOLOGY
6.
Messersmith, R.E., Johnson, D.D., Elliott, R.F. and Drain, J.J. Value of chlortetracycline in breeding rations for sows. J. Anim. Sci. Z:752-755 (1966).
7.
Soma, J.A. and Speer, V.C. Effect of pregnant mare serum and chlortetracycline on the reproductive efficiency of sows. J. Anim. Sci. 41:100-105 (1975).
a.
Hays, V.W., King, J.L., Cromwell, G.L., Dutt, R.H. and Kratzer, D.D. Effect of lactation length and dietary antibiotics on reproductive performance of sows. J. Anim. Sci. 46:884-a91 (1978).
9.
National No. 2. 22-25.
Research Nutrient
Council. Nutrient Requirements of Domestic Animals. requirements of swine. Washington, DC. .1979, PP.
10.
Statistical Institute,
Analysis System. Cary, NC, 1982;
11.
Etienne, M., Comous, S. and Cuvillier, M. during growth on puberty and reproductive Nutr. Develop. 23:309-319 (1983).
12.
Webel, S.K. and Dzuik, P.J. Effect of stage of gestation and uterine space on prenatal survival in the pig. J. Anim. Sci. =:960-963 (1974).
13.
Knight, J.W., Bazer, F.W., Thatcher, W.W., Franke, D.E. and Wallace, H.D. Conceptus development in intact and unilaterally hysterectomizedovariectomized gilts: interrelationships among hormonal status, placental development, fetal fluids and fetal growth. .I. Anim. Sci. &:620-637 (1977).
NOVEMBER
User's Guide, Statistical pp. 139-199.
1987 VOL. 28 NO. 5
Analysis
System
Effect of feed restriction performance in gilts. Reprod.
665