The effect of exogenous estradiol on litter size in a typical swine herd.

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-17beta (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 remained pregnant (vehicle versus estradiol, 6 versus 1 recycled, respectively; P<0.05). Litter size, expressed as the number of pigs born per-female-bred, was therefore increased with exogenous estradiol (vehicle versus estradiol, 7.6+/-0.8 versus 9.8+/-0.7 live pigs born, respectively; P<0.05). Some of these estradiol- treated females produced smaller (P<0.05) 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.

Intrauterine migration of the porcine embryo: coordination of bead migration with estradiol.

Forty crossbred gilts were used in three experiments to examine the effects of estradiol on embryo migration. Small, spherical beads of Silastic glue containing either cholesterol or estradiol-17 beta were used to mimic embryo migration. In the first experiment, 10 cholesterol- and 10 estradiol-impregnated beads were injected into the tip of the uterine horns, either on the same side (n = 5) or opposite from each other (n = 5). The second experiment consisted of a localized release of cholesterol or estradiol and observing migration of cholesterol-containing beads inserted 10 cm anterior and posterior to this site (n = 5). In the third experiment, 10 cholesterol-impregnated beads were injected into either the tip or base of one uterine horn. Additionally, these gilts were exposed to vehicle or exogenous estradiol in a 2 X 2 factorial arrangement of treatments (n = 5). Results of these experiments indicated that cholesterol-impregnated beads migrated further (P less than .05) when adjacent to estradiol-containing beads than when in an opposite uterine horn. Localized release of estradiol failed to induce movement of beads away from the site of steroid release. Finally, beads inserted at the base of the uterus moved anteriorly following treatment of gilts with estradiol. We suggest from these experiments that the porcine uterine horn cannot discriminate between estradiol- and cholesterol-releasing beads and, further, lacks a coordinated ability to displace adjacent beads. A site-dose dependent mechanism(s) of estrogenic induction of migration may exist such that porcine embryos become bilaterally intermixed following posterior, then anterior, waves of uterine contractions.

Dose-response shift in the ability of gilts to remain pregnant following exogenous estradiol-17 beta exposure.

Sixty mated gilts were assigned to a 2 X 6 factorial arrangement (n = 5) of day of injection (d 9 and 10 vs 12 and 13; d 0 = first day of estrus) and dose of estradiol-17 beta (0, .125, .5, 2, 8 and 32 mg X gilt-1 X d-1). Gilts were subsequently slaughtered on d 30; pregnancy was verified and percent embryonic survival calculated. A 64-fold shift in the dose-response curve for percent embryonic survival illustrated that the adverse effects of exogenous estradiol-17 beta were less when administered on d 12 and 13 as compared with d 9 and 10 (day X dose, P less than .01). This experiment demonstrated that the uterine-embryonic environment of d 12 and 13 pregnant gilts was more tolerant of exogenous estrogen alterations than that of d 9 and 10 pregnant gilts.

Role of the adrenals in the maintenance of pregnancy in cows.

On Day 215 of gestation, cows were treated as controls (Group 1), bilaterally ovariectomized (Group 2), bilaterally adrenalectomized (Group 3) or bilaterally adrenalectomized and ovariectomized (Group 4). The mean +/- s.e.m. lengths of gestation (days) were 278 +/- 3 (N = 5), 270 +/- 2 (N = 7), 277 +/- 1 (N = 5) and 219 +/- 1 (N = 3) in Groups 1, 2, 3 and 4 respectively. In Group 4, serum progesterone concentrations declined to undetectable levels within 24 h after surgery and all the cows aborted 3-6 days later. All the cows in Groups 1, 2 and 3, except 1 cow in Group 2, completed gestation and delivered live calves. Progesterone concentrations in Group 2, cows declined to approximately one-third those of cows in Groups 1 or 3. All 3 cows in Group 4 and 7/8 in Group 2 had a retained placenta. At 1 and 2 days after surgery there were no significant differences in plasma levels of oestradiol-17 beta, but by the third day this difference was significant (P less than 0.01). Oestrogen levels were high before parturition in cows in Groups 1 and 3 but were not noticeably elevated in those in Groups 2 and 4. The abrupt termination of pregnancy and negligible concentrations of progesterone in adrenalectomized-ovariectomized cows indicate that the bovine adrenals contribute to progesterone production and are capable of maintaining pregnancy after ovariectomy at 215 days of gestation.

Effect of asynchronous superinduction on embryo survival and range of blastocyst development in swine.

The importance of uniform development of blastocysts was examined by comparing the effects of asynchronous superinduction (Day 6 embryos into Day 7 pregnant recipients and Day 7 embryos into Day 6 pregnant recipients) on the range of embryo development at Days 12 and 13 to subsequent survival to Day 30. Twenty gilts were used to produce five Day 7 recipients that received Day 6 embryos and five Day 6 recipients that received Day 7 embryos. Embryos from the Day 7 and Day 6 recipients were examined 6 days later. Recovered embryos ranged morphologically from spherical to filamentous blastocysts. This range of embryos was within the limits of that previously observed for naturally mated sows. However, recovered blastocysts from the Day 6 embryos transferred into Day 7 recipients were morphologically more variable and proportionately less developed than the blastocysts from the Day 7 embryos transferred into Day 6 recipients. Forty additional gilts were subsequently utilized to generate 20 recipients (10 recipients per transfer group) that were examined on Day 30. More Day 7 embryos transferred into Day 6 recipients survived (p less than 0.05) than Day 6 embryos transferred into Day 7 recipients. These experiments suggested that greater variation in early development of embryos, within litters, subsequently resulted in greater mortality of embryos.