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I. Revah and W. R. Butler

Prolonging the lifespan of bovine follicles is known to result in reduced fertility after ovulation and insemination. In this study, the effect of prolonged development of follicles on oocyte viability was examined. In Expt 1, six cows in the aspirated-prolonged-follicle group received a vaginal progesterone releasing device on day 4 of the oestrous cycle (day 1 = ovulation) and prostaglandin F (40 mg) on day 6. Ultrasound-guided follicular aspiration was performed on day 13. Six cows in the aspirated-growing-follicle group received prostaglandin F on day 6, and follicular aspiration on day 7. In Expt 2, all cows were stimulated with 36 mg FSH-P to develop multiple large follicles for study. Three cows in the prolonged-multiple-follicle group received the same treatment as did cows in Expt 1, but were ovariectomized on day 13. Three cows in the growing-multiple-follicle group received prostaglandin F on day 6 and were ovariectomized on day 7. Oocytes recovered in both experiments were stained to reveal the stage of nuclear development. All oocytes from aspirated-prolonged and prolonged-multiple follicles showed expanded cumulus cells and condensed chromatin dispersed in the ooplasm, with possible germinal vesicle breakdown. Oocytes from aspirated-growing and growing-multiple follicles showed compact cumulus cells and an intact germinal vesicle. Plasma concentrations of oestradiol in both growing follicle groups increased until oocyte recovery. Oestradiol in the aspiratedprolonged-follicle group increased after luteolysis on day 6 and remained high until follicular aspiration. In contrast, in the FSH-stimulated prolonged-multiple-follicle group, oestradiol fell to trace amounts on day 8 and remained low. Oestradiol concentrations in follicular fluid were consistent with plasma concentrations for all groups. Bovine oocytes from prolonged dominant follicles undergo premature maturation in vivo, which perhaps accounts for the poor fertility observed in other studies when oestrous synchronization with progestins prolongs follicle lifespan.

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S T Butler, S H Pelton and W R Butler

Prolonged anovulation following parturition has a negative impact on fertility in dairy cows. Insulin plays an important role in ovarian function in many species, and is profoundly depressed in dairy cows during early lactation. We hypothesized that hypoinsulinemia during early lactation represents a key indicator of nutritional status, resulting in delayed ovulation. Holstein cows (n = 10) were subjected to either a hyperinsulinemic–euglycemic clamp (INS) or saline infusion (CTL) for 96 h, beginning on day 10 after parturition during the first postpartum follicular wave. Insulin was infused continuously (0.3 μg/kg body weight per h) via a jugular catheter, and euglycemia was maintained by infusion of glucose. Circulating insulin concentrations were elevated 2.6-fold in INS cows compared with CTL cows (0.73 ± 0.026 vs 0.28 ± 0.026 ng/ml; P < 0.001). Insulin treatment did not affect (P > 0.05) luteinizing hormone (LH) pulse frequency, pulse amplitude or mean circulating LH. Circulating estradiol was elevated in INS cows (P < 0.01) and circulating testosterone also tended to be higher. The ratio of testosterone to estradiol was not different between treatments for the initial 30 h of infusion, but was significantly reduced thereafter in response to insulin (P < 0.01), suggesting that hyperinsulinemia increased follicular aromatase activity. Insulin treatment also resulted in reduced circulating nonesterified fatty acids, and increased circulating total and free insulin-like growth factor-I concentrations. Insulin infusion increased estradiol secretion by the dominant follicle of the first postpartum follicular wave in dairy cows, and this effect appears not to be mediated through changes in pulsatile LH release.

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W. R. BUTLER, A. D. JOHNSON and W. R. GOMES

In 1933, Mason reported that long-term vitamin A deficiency caused sloughing of seminiferous tubular elements of the rat testis. Since that time, several workers have reported testicular lesions caused by deficiency of the vitamin (Beaver, 1961; Coward, McHowell, Pitt & Thompson, 1966; Gamball, 1966). Gamball (1966) found changes in testicular phospholipid associated with sterility following vitamin A deficiency. Since other treatments which result in sterility also cause lipid changes in the testis (Fleeger, Bishop, Gomes & VanDemark, 1968; Johnson, VanDemark, Gomes, Butler & Hodgen, 1967), it is possible that testicular lipids reflect the status of the testis, even during early stages of degeneration following deleterious treatments. The present study was undertaken to determine whether testicular lipid levels are affected by short-term vitamin A deficiency and, if so,

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S. L. Fu, G. D. Dial, D. M. Keister and W. R. Butler

Summary. In Phase I of this study to enhance ovulation rate and hence litter size, gilts received 0 (sham control), 0·625, 1·25, 2·5 or 5·0 mg epostane/kg body weight on Days 10, 11 and 12 of the oestrous cycle (5 gilts/group). After epostane treatment, plasma progesterone concentrations were reduced (P < 0·01) in a dose-related manner, % progesterone decline = 21·30 × √(dose) + 10·45, R2 = 0·70, but recovered to pretreatment levels by 24 h. In Phase II the effects of epostane on ovulation rate and litter size were tested at two study centres. At each centre 108 gilts were treated with the same doses of epostane as used in Phase I and the doses were given for 7 days (Days 15–21) or 12 days (Days 10–21) during the first oestrous cycle. Gilts were inseminated twice during the oestrus after treatment and were slaughtered 30 days later. Mean (± s.d.) ovulation rate was 16 ± 2·7 (N = 8) and 21 ± 4·0 (N = 61) for control and epostane-treated gilts in Centre A and 12 ± 2·4 (N = 5) and 17 ± 3·8 (N = 55) respectively in Centre B (P < 0·01 for both) and was dose related (ovulation rate = 3·38 × √(dose) + 16·17, R2 = 0·31). The effects of 7- or 12-day epostane treatment on ovulation rate were not different (P > 0·05), indicating that effects of treatment after Day 14 of the oestrous cycle are most important to subsequent ovulation frequency. The number of viable embryos was not significantly increased after epostane treatment (P > 0·05). We conclude that treatment with epostane, 3β-hydroxysteroid dehydrogenase inhibitor, late in the oestrous cycle increases ovulation rate in gilts.

Keywords: gilt; epostane; ovulation rate; progesterone; corpora lutea