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The effect of exogenous estradiol on litter size in a typical swine herd
THERIOGENOLOGY
THE EFFECT OF EXOGENOUS ESTRADIOL ON LITTER SIZE IN A TYPICAL SWINE HERD W. F. Pope, M. S. Lawyer and N. L. First Department of Meat and Animal Science University of Wisconsin Madison, WI 53706 Received for publication: November> 2, 1985 Accepted: Mau 19, 1987 ABSTRACT Fifty-six female pigs (12 gilts, 26 primiparous and 18 multiparous sows) were bred and assigned to receive either corn oil (vehicle; n=28) or estradiol-17g (2 mg/day; i.m.; n-28) on Days 12 and 13 (Day 0 = first day of estrus) to determine if exogenous estradiol could improve litter size in swine. Though litter size of the females farrowing was not increased with estradiol treatment (vehicle versus estradiol, 9.7 + 0.8 versus 10.1 + 1.8 live pigs born, respectively), more females in-this group remaina pregnant (vehicle versus estradiol, 6 versus 1 recycled, respectively; Pf these estrad'iol- treated females produced smaller (pCO.05) litters and this may be of concern in herds experiencing low fertilization/conception rates. Overall 60 more pigs were born alive to females in the estradiol-treated group than to the control group females. This experiment demonstrated that supplemental estradiol treatment on Days 12 and 13 assisted in maintenance of pregnancy and thereby increased litter size on a per-female-bred basis. INTRODUCTION Litter size is the most important biological variable affecting profitable swine production (1). Tess and coworkers (1) demonstrated that the expected costs of production were reduced more by increasing the number born alive than by improving rate of gain, feed conversion or age at puberty. Unfortunately, factors affecting litter size are complicated and not well understood. Selection for litter size, for example, has resulted in little gain because components of litter size (ovulation rate, embryo survival or uterine capacity) being selected for or against remain unknown. Furthermore, these components are interrelated so that sows with high ovulation rates may not have increased litter size due to prenatal losses after 30 d of gestation (2). Treatment of mated sows with exogenous estradiol increased embryo survival (3) and induced uterine elongation (4) and therefore could be
Key words:
litter size, porcine, estradiol-17g
Acknowledgements: Dept. of Meat and Anim. Sci. Paper No. 952. Research was supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison and a grant from the W. R. Grace Company.
JULY
1987 VOL. 28 NO. 1
9
THERIOGENOLOGY
beneficial throughout the periods of embryo loss and establishment of uterine capacity. Previous attempts to increase litter size with exogenous progesterone therapy have produced mixed results (5-7). However, inclusion of estrogen with progesterone has increased embryo survival (8,9), placental development (10) and litter size (11). The present experiment examined the ability of exogenous estradiol alone to improve litter size in a typical Wisconsin herd. MATERIALS AND METHODS Fifty-six females (12 gilts, 26 primiparous and 18 multiparous sows) were used from a herd that typically experienced an 87% conception rate and a litter size of 9.5 to 10.5 pigs per farrowing. The management of this herd assisted with natural hand mating of each female on each day of detected estrus. Females were assigned to receive either corn oil (vehicle) or estradiol-175 (2 mg/day) in the order they were bred. Injections were given on Days 12 and 13 (Day 0 = first day of estrus) into the muscle of the neck (1 ml/day). This dosage of estradiol-17D was determined to be embryotrophic and to induce uterine elongation (4) in a preliminary trial. Estrous activity was monitored subsequent to the injections and farrowing dates corresponded to the mating under investigation. The number of live, mummified and dead piglets were noted at farrowing. Frequency of females mated only once and/or returning to estrus following mating were compared by use of a contingency test for independence (12). The distribution of litter size in the two treatment groups was partitioned into the frequency of females having O-5, 6-10, 11-15 and greater than 15 piglets born alive and compared by use of a contingency test of independence. Actual litter size was compared by use of an independent t-test.
Table 1. Number of vehicle and estradiol-treated females returning to estrus and those bred only once
Vehicle
Number of females bred
Estradiol
28
28
Number of females bred only once
9
10
Number of females returning to estrus
6a
lb
Number of females returning to estrus following only one breeding
5
1
a,bRows with different superscripts are different (BO.05).
10
JULY 1987 VOL. 28 NO. 1
THERIOGENOLOGY
RFSULTS
Significantly more (P~0.05) females returned to estrus (Table 1) when treated with vehicle versus estradiol-17g. While the number of females mated only once was not different, five of the nine vehicle and only one of the ten estradiol-treated females (RO.08) bred only once returned to estrus. These data suggest estradiol-treatment rescued poorly mated females (bred only once) from recycling. Treatment of bred females with estradiol broadened the distribution of litter size (Table 2), with smaller and larger litters occurring more frequently (litter size x treatment interaction, P
Table 2. Distribution of litter size by sows treated with vehicle or estradiol-17Ba
Litter Size
O-5
Number of females Vehicle Estradiol
0
2
6-10
16
13
xl-15
6
11
a15
0
1
acolumned numbers represent number of sows farrowing a particular litter size.
Table 3. Frequency of vehicle and estradiol-treated females having small litters (number born alive/female farrowing)
Litter Size
1 2 3 4 5
JULY
No. born alive/female farrowing Vehicle Estradiol
0 0 0 0 0
1987 VOL. 28 NO. 1
0 1 0 0 1
THERIOGENOLOGY
When litter size was expressed as number born per female farrowing, estradiol exposure had no effect (Table 4). Correcting for the number of females recycling, litter size (per female bred) was increased (P
Table 4.
Litter size of vehicle and estradiol treated females expressed relative to number farrowing and number breda
Vehicle
Mean of females farrowing (SEW (Range) Mean of females bred (SEW Number of live piglets
Live Born
Total Born
(Z (6-15)
10.2 (1.2) (6-16)
Estradiol Live Born
Total Born
10.1 (1.8) (2-18)
10.7 (1.9) (2-18)
b
1O.F (0.7)
b (Z,
(G, 214
274
aResults of 28 vehicle- and 28 estradiol-treated females. bRows with the same superscript are different (PcO.05). CROWS with the same superscript are different (PcO.10).
DISCUSSION Results from this experiment suggested that estradiol treatment did not increase litter size of the females farrowing. However, fewer females exposed to estradiol returned to estrus after mating, suggesting this treatment was beneficial in maintaining some events of early pregnancy. Correspondingly, estradiol-treated females experienced higher conception rates and an increased number of pigs born per bred female. Successful mating of female swine, as reflected by conception rates and litter size, has been demonstrated to be highly dependent on proper timing of gamete interactions. These physiological events are limited by accurate heat detection, mating procedures, genetic variation, health and boar utilization. Females mated only once were primarily associated with inaccurate heat detection, a problem considered typical of the swine industry. Since at least four blastocysts are required to maintain pregnancy (131, the high incidence of females bred only once returning to estrus, in the vehicle-treated group, was probably related
12
JULY 1987 VOL. 28 NO. 1
THERIOGENOLOGY
to a reduced number of fertilized oocytes and a reduced number of blastocysts present. Likewise, the ten mated females in the estradiol group, which were bred only once, were assumed to have less blastocysts present in early gestation. However, pregnancy was maintained in estradiol-treated females, perhaps through augmentation of luteal function (14) on Days 12 and 13, a sensitive stage of luteal maintenance (15). Supplemental estradiol therapy, at the time period of maternal recognition of pregnancy, appeared to support the endogenous signal and maintain pregnancy in females with abnormally small litters. Such a treatment may b? detrimental to producers by not allowing these females to normally recycle and breed again. A higher and more embryotrophic dosage of est:tadiolon Days 12 and 13 (3) may prove valuable to better managed herds, as an increase in litter size on a pre-farrowing-basis may be possible. Likewise reducing the injections regime to one injection would also reduce labor cost associated with this therapy. REFERENCES 1. Tess, M. W., Bennett, G. L. and Dickerson, G. E. Simulation of genetic changes in life cycle efficiency of pork production. II. Effects of components on efficiency. J. Anim. Sci. -56:354-368 (1983). 2. Johnson, R. K., Zimmerman, D. R., Lamberson, W. R. and Sasaki, S. Influencing prolificacy by selection for physiological factors, In: G. R. Foxcroft, D. J. A. Cole and B. J. Weir (eds.) Control of zg Reproduction II. Dorset Press, Dorchester 1985, pp. 139-149. 3. Pope, W. F., Lawyer, M. S., Butler, W. R., Foote, R. H. and First, N. L. Dose-response shift in the ability of gilts to remain pregnant following exogenous estradiol-17B exposure. .I.Anim. Sci. (in press) (1986). 4. Pope, W. F. and First, N. L. Factors affecting the survival of pig embryos. Theriogenology -23:91-105 (1985). 5. Spies, H. G., Zimmerman, D. R., Self, H. L. and Casida, L. E. The effect of exogenous progesterone on formation and maintenance of the corpora lutea and on early embryo survival in pregnant swine. J. Anim. Sci. 18:163-172 (1959). 6. Sammelwitz, P. H., Dziuk, P. J. and Nalbandov, A. V. Effect of progesterone on embryo mortality of rats and swine. J. Anim. Sci. 15:1211 Abstr. (1956). 7. Halnes, C. E., Warnick, A. C., Wallace, H. D. and Edwards, G. M. The effect of level of feeding and progesterone injections on reproductive performance in gilts. J. Anim. Sci. -16:1099 Abstr. (1957).
JULY
1987 VOL. 28 NO. I
13
l-HERIOGENOLOGY
8. Reddy, V. B., Mayer, D. T. and Lasley, J. F. Hormonal modification of the intra-uterine environment in swine and its effect on embryonic viability. MO. Agri. Exp. Stn. Bull. 667, Boxeman, MT (1958). 9. Day, B. N., Anderson, L. L., Emmerson, M. A., Hazel, L. N. and Effect of estrogen and progesterone on early Melempy, R. M. embryonic mortality in ovariectomized gilts. J. Anim. sci. 18:607-613 (1959). progesterone 10. Dalton, D. L. and Knight, J. W. Effects of exogenous and estrone on conceptus development in swine. J. Anim. Sci. -56:1354-1361 (1983). 11. Wildt, D. E., Culver, A. A., Morcom, C. B. and Dukelow, W. R. Effect of administration of progesterone and oestrogen on litter size in pigs. J. Reprod. Fertil. 48:209-211 (1976). The principles and practice of 12. Sokal, R. R. and Rohlf, F. J. statistics in biological research. In: R. Emerson, D. Kennedy and R. B. Park (eds.). Biometry, Freman?%blishers, San Francisco,l969, pp. 71-129. 13. Polge, C., Rowson, L. E. A. and Chang, M. C. The effect of reducing the number of embryos during early stages of gestation on the maintenance of pregnancy in the pig. J. Reprod. Fertil. 12:395-397 (1966). 14. Gardner, M. L., First, N. L. and Casida, L. E. Effect of exogenous estrogen on corpus luteum maintenance in gilts. J. Anim. Sci. -22:132-134 (1963). 15. Dhindsa, D. S. and Dxiuk, P. J. Effect on pregnancy in the pig after killing embryos or fetuses in one uterine horn in early gestation. J. Anim. Sci. 27:122-126. 16. Bazer, F. W. and Thatcher, W. W. Theory of maternal recognition of pregnancy in swine based on estrogen controlled endocrine versus uterine secretion of prostaglandin F2o the exocrine by endometrium. Prostaglandins -14:397-401 (1977).
14
JULY
1987 VOL. 28 NO. I
THE EFFECT OF EXOGENOUS ESTRADIOL ON LITTER SIZE IN A TYPICAL SWINE HERD W. F. Pope, M. S. Lawyer and N. L. First Department of Meat and Animal Science University of Wisconsin Madison, WI 53706 Received for publication: November> 2, 1985 Accepted: Mau 19, 1987 ABSTRACT Fifty-six female pigs (12 gilts, 26 primiparous and 18 multiparous sows) were bred and assigned to receive either corn oil (vehicle; n=28) or estradiol-17g (2 mg/day; i.m.; n-28) on Days 12 and 13 (Day 0 = first day of estrus) to determine if exogenous estradiol could improve litter size in swine. Though litter size of the females farrowing was not increased with estradiol treatment (vehicle versus estradiol, 9.7 + 0.8 versus 10.1 + 1.8 live pigs born, respectively), more females in-this group remaina pregnant (vehicle versus estradiol, 6 versus 1 recycled, respectively; P
Key words:
litter size, porcine, estradiol-17g
Acknowledgements: Dept. of Meat and Anim. Sci. Paper No. 952. Research was supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison and a grant from the W. R. Grace Company.
JULY
1987 VOL. 28 NO. 1
9
THERIOGENOLOGY
beneficial throughout the periods of embryo loss and establishment of uterine capacity. Previous attempts to increase litter size with exogenous progesterone therapy have produced mixed results (5-7). However, inclusion of estrogen with progesterone has increased embryo survival (8,9), placental development (10) and litter size (11). The present experiment examined the ability of exogenous estradiol alone to improve litter size in a typical Wisconsin herd. MATERIALS AND METHODS Fifty-six females (12 gilts, 26 primiparous and 18 multiparous sows) were used from a herd that typically experienced an 87% conception rate and a litter size of 9.5 to 10.5 pigs per farrowing. The management of this herd assisted with natural hand mating of each female on each day of detected estrus. Females were assigned to receive either corn oil (vehicle) or estradiol-175 (2 mg/day) in the order they were bred. Injections were given on Days 12 and 13 (Day 0 = first day of estrus) into the muscle of the neck (1 ml/day). This dosage of estradiol-17D was determined to be embryotrophic and to induce uterine elongation (4) in a preliminary trial. Estrous activity was monitored subsequent to the injections and farrowing dates corresponded to the mating under investigation. The number of live, mummified and dead piglets were noted at farrowing. Frequency of females mated only once and/or returning to estrus following mating were compared by use of a contingency test for independence (12). The distribution of litter size in the two treatment groups was partitioned into the frequency of females having O-5, 6-10, 11-15 and greater than 15 piglets born alive and compared by use of a contingency test of independence. Actual litter size was compared by use of an independent t-test.
Table 1. Number of vehicle and estradiol-treated females returning to estrus and those bred only once
Vehicle
Number of females bred
Estradiol
28
28
Number of females bred only once
9
10
Number of females returning to estrus
6a
lb
Number of females returning to estrus following only one breeding
5
1
a,bRows with different superscripts are different (BO.05).
10
JULY 1987 VOL. 28 NO. 1
THERIOGENOLOGY
RFSULTS
Significantly more (P~0.05) females returned to estrus (Table 1) when treated with vehicle versus estradiol-17g. While the number of females mated only once was not different, five of the nine vehicle and only one of the ten estradiol-treated females (RO.08) bred only once returned to estrus. These data suggest estradiol-treatment rescued poorly mated females (bred only once) from recycling. Treatment of bred females with estradiol broadened the distribution of litter size (Table 2), with smaller and larger litters occurring more frequently (litter size x treatment interaction, P
Table 2. Distribution of litter size by sows treated with vehicle or estradiol-17Ba
Litter Size
O-5
Number of females Vehicle Estradiol
0
2
6-10
16
13
xl-15
6
11
a15
0
1
acolumned numbers represent number of sows farrowing a particular litter size.
Table 3. Frequency of vehicle and estradiol-treated females having small litters (number born alive/female farrowing)
Litter Size
1 2 3 4 5
JULY
No. born alive/female farrowing Vehicle Estradiol
0 0 0 0 0
1987 VOL. 28 NO. 1
0 1 0 0 1
THERIOGENOLOGY
When litter size was expressed as number born per female farrowing, estradiol exposure had no effect (Table 4). Correcting for the number of females recycling, litter size (per female bred) was increased (P
Table 4.
Litter size of vehicle and estradiol treated females expressed relative to number farrowing and number breda
Vehicle
Mean of females farrowing (SEW (Range) Mean of females bred (SEW Number of live piglets
Live Born
Total Born
(Z (6-15)
10.2 (1.2) (6-16)
Estradiol Live Born
Total Born
10.1 (1.8) (2-18)
10.7 (1.9) (2-18)
b
1O.F (0.7)
b (Z,
(G, 214
274
aResults of 28 vehicle- and 28 estradiol-treated females. bRows with the same superscript are different (PcO.05). CROWS with the same superscript are different (PcO.10).
DISCUSSION Results from this experiment suggested that estradiol treatment did not increase litter size of the females farrowing. However, fewer females exposed to estradiol returned to estrus after mating, suggesting this treatment was beneficial in maintaining some events of early pregnancy. Correspondingly, estradiol-treated females experienced higher conception rates and an increased number of pigs born per bred female. Successful mating of female swine, as reflected by conception rates and litter size, has been demonstrated to be highly dependent on proper timing of gamete interactions. These physiological events are limited by accurate heat detection, mating procedures, genetic variation, health and boar utilization. Females mated only once were primarily associated with inaccurate heat detection, a problem considered typical of the swine industry. Since at least four blastocysts are required to maintain pregnancy (131, the high incidence of females bred only once returning to estrus, in the vehicle-treated group, was probably related
12
JULY 1987 VOL. 28 NO. 1
THERIOGENOLOGY
to a reduced number of fertilized oocytes and a reduced number of blastocysts present. Likewise, the ten mated females in the estradiol group, which were bred only once, were assumed to have less blastocysts present in early gestation. However, pregnancy was maintained in estradiol-treated females, perhaps through augmentation of luteal function (14) on Days 12 and 13, a sensitive stage of luteal maintenance (15). Supplemental estradiol therapy, at the time period of maternal recognition of pregnancy, appeared to support the endogenous signal and maintain pregnancy in females with abnormally small litters. Such a treatment may b? detrimental to producers by not allowing these females to normally recycle and breed again. A higher and more embryotrophic dosage of est:tadiolon Days 12 and 13 (3) may prove valuable to better managed herds, as an increase in litter size on a pre-farrowing-basis may be possible. Likewise reducing the injections regime to one injection would also reduce labor cost associated with this therapy. REFERENCES 1. Tess, M. W., Bennett, G. L. and Dickerson, G. E. Simulation of genetic changes in life cycle efficiency of pork production. II. Effects of components on efficiency. J. Anim. Sci. -56:354-368 (1983). 2. Johnson, R. K., Zimmerman, D. R., Lamberson, W. R. and Sasaki, S. Influencing prolificacy by selection for physiological factors, In: G. R. Foxcroft, D. J. A. Cole and B. J. Weir (eds.) Control of zg Reproduction II. Dorset Press, Dorchester 1985, pp. 139-149. 3. Pope, W. F., Lawyer, M. S., Butler, W. R., Foote, R. H. and First, N. L. Dose-response shift in the ability of gilts to remain pregnant following exogenous estradiol-17B exposure. .I.Anim. Sci. (in press) (1986). 4. Pope, W. F. and First, N. L. Factors affecting the survival of pig embryos. Theriogenology -23:91-105 (1985). 5. Spies, H. G., Zimmerman, D. R., Self, H. L. and Casida, L. E. The effect of exogenous progesterone on formation and maintenance of the corpora lutea and on early embryo survival in pregnant swine. J. Anim. Sci. 18:163-172 (1959). 6. Sammelwitz, P. H., Dziuk, P. J. and Nalbandov, A. V. Effect of progesterone on embryo mortality of rats and swine. J. Anim. Sci. 15:1211 Abstr. (1956). 7. Halnes, C. E., Warnick, A. C., Wallace, H. D. and Edwards, G. M. The effect of level of feeding and progesterone injections on reproductive performance in gilts. J. Anim. Sci. -16:1099 Abstr. (1957).
JULY
1987 VOL. 28 NO. I
13
l-HERIOGENOLOGY
8. Reddy, V. B., Mayer, D. T. and Lasley, J. F. Hormonal modification of the intra-uterine environment in swine and its effect on embryonic viability. MO. Agri. Exp. Stn. Bull. 667, Boxeman, MT (1958). 9. Day, B. N., Anderson, L. L., Emmerson, M. A., Hazel, L. N. and Effect of estrogen and progesterone on early Melempy, R. M. embryonic mortality in ovariectomized gilts. J. Anim. sci. 18:607-613 (1959). progesterone 10. Dalton, D. L. and Knight, J. W. Effects of exogenous and estrone on conceptus development in swine. J. Anim. Sci. -56:1354-1361 (1983). 11. Wildt, D. E., Culver, A. A., Morcom, C. B. and Dukelow, W. R. Effect of administration of progesterone and oestrogen on litter size in pigs. J. Reprod. Fertil. 48:209-211 (1976). The principles and practice of 12. Sokal, R. R. and Rohlf, F. J. statistics in biological research. In: R. Emerson, D. Kennedy and R. B. Park (eds.). Biometry, Freman?%blishers, San Francisco,l969, pp. 71-129. 13. Polge, C., Rowson, L. E. A. and Chang, M. C. The effect of reducing the number of embryos during early stages of gestation on the maintenance of pregnancy in the pig. J. Reprod. Fertil. 12:395-397 (1966). 14. Gardner, M. L., First, N. L. and Casida, L. E. Effect of exogenous estrogen on corpus luteum maintenance in gilts. J. Anim. Sci. -22:132-134 (1963). 15. Dhindsa, D. S. and Dxiuk, P. J. Effect on pregnancy in the pig after killing embryos or fetuses in one uterine horn in early gestation. J. Anim. Sci. 27:122-126. 16. Bazer, F. W. and Thatcher, W. W. Theory of maternal recognition of pregnancy in swine based on estrogen controlled endocrine versus uterine secretion of prostaglandin F2o the exocrine by endometrium. Prostaglandins -14:397-401 (1977).
14
JULY
1987 VOL. 28 NO. I