No abstract

Primiparous sows that farrowed on a commercial farm during late summer in 1980 (n = 65) or late winter in 1981 (n = 62) and lactated 3 to 4 wk were used. Sows were assigned in a factorial experiment to one of two lactation diets (control or 10% fat-supplemented) and one of three periods (0, 2 or 5 d) of early weaning of the heaviest one-half of the litter. Days from weaning to estrus averaged 16.7 +/- 1.5 and 8.7 +/- 1.6 in summer and winter, respectively, and the season X diet interaction was significant for days from weaning to estrus and percentage of sows that exhibited estrus after weaning. In summer, supplementing diets with fat reduced the weaning-to-estrus interval from 20.9 +/- 2.1 to 12.6 +/- 2.1 d and increased percentage of sows in estrus by 10 d postweaning from 34 to 59. In winter, days from weaning to estrus tended to be greater and percentage of sows in estrus by 10 d postweaning tended to be less in sows fed fat-supplemented diets (10.3 +/- 2.5, 74%) than in sows fed control diets (7.1 +/- 2.9, 82%). Over both seasons, weaning one-half the litter 2 d early (2-d group) increased the percentage of sows in estrus by 10 d after weaning (77%) compared with 5-d (58%) or 0-d (51%) groups. Total litter weight at weaning was not affected by season, diet or days with one-half litter. However, piglets of lightest weight remaining on sows two or five extra days gained .09 +/- .03 kg/d more than lightest weight pigs in control (0-d) litters over the same interval. Early weaning of heaviest pigs may improve reproductive performance of primiparous sows in summer and winter, while supplementing lactation diets with fat may improve performance in summer, when weaning-to-estrus interval is longer than in winter.

The objective was to determine whether exogenous insulin and dietary energy interact to affect follicular development in gilts. In a 2 x 2 x 2 completely randomized design, main effects were level of dietary energy (5771 or 9960 kcal metabolizable energy/day beginning on Day 12 of the estrous cycle), insulin dosage (0 or 0.4 IU/kg twice daily beginning on Day 15 of the cycle), and day of cycle at ovary removal (Day 17 or Day 19). Percentage of follicles designated small (less than or equal to 3 mm diameter) decreased from Day 17 to Day 19 of the cycle, and the percentage of large follicles (greater than or equal to 7 mm) increased (p less than 0.05). Insulin interacted with day of the cycle (p less than 0.05) to affect distribution of medium (4-6 mm) and macroscopically atretic follicles. Percentage of atretic follicles increased from Day 17 to Day 19 in saline-treated (from 15.5% to 38.2%) but not in insulin-treated animals (6.3% to 10.7%). Percentage of medium (4-6 mm) follicles decreased from Day 17 to Day 19 in saline-treated gilts (from 41.7 to 16.6%) but not in insulin-treated gilts (39.8% to 35.1%). Intrafollicular testosterone and progesterone concentrations were not affected by treatments. In medium follicles, the ratio of estradiol to progesterone was greater (p less than 0.05) for insulin-treated gilts on Day 17 than for the other treatment combinations.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of bromocryptine (CB-154) on prolactin (PRL) and luteinizing hormone (LH) secretion were studied in lactating sows and ovariectomized (OVX) gilts. In Exp]. 1, the litters of four sows were standardized to four pigs each at 20 to 30 d of lactation and a cannula was placed nonsurgically into the jugular vein of each sow. Twenty-four hours later (0800 h) blood samples were taken and two sows each were injected subcutaneously with 120 mg CB-154 or vehicle. Blood samples were then taken every 30 min for the next 23.5 h. An additional six sows whose litters were standardized to six pigs each at 28 to 30 d of lactation comprised EXp. 2. In Exp. 3, five puberal gilts were OVX. Forty-eight hours after OVX a cannula was placed into the jugular vein. The day after cannulation blood samples were drawn every 30 min from 0800 to 2400 h. Immediately after the sampling at 1200 h, two gilts were injected subcutaneously with 120 mg CB-154 and three were injected subcutaneously with vehicle. Exp. 4 was a repetition of Exp. 3 except that six gilts were OVX 10 d before the experiment and three each were treated with CB-154 of vehicle. Serum PRL concentrations were consistently depressed after CB-154 treatment in both the lactating sows (Exp. 1, from 35 to 5 ng/ml, and Exp. 2, from 45 to 7 ng/ml) and the OVX gilts (Exp. 3, from 20 to 13 ng/ml, and ?Exp. 4, from 9 to 2 ng/ml), but changes in serum LH concentrations after CB-154 treatment were not consistent among the four experimental groups. Therefore, we conclude that CB-154 depressed PRL secretion in the lactating sows and OVX gilts. In addition, CB-154 depressed LH secretion in the lactating sows, but the data are inconclusive as to whether or not BC-154 influenced LH secretion in the OVX gilts.

Two experiments were conducted to determine whether pulsatile administration of gonadotropin releasing hormone (GnRH) would induce estrus and ovulation in lactating, anestrous sows. In each experiment, six lactating sows received GnRH, i.v. (2.5 micrograms every 2 h, Exp. 1; 1.5 micrograms every h, Exp. 2) until 24 h after estrus or 7 days, whichever came first. In Experiment 1, three of six GnRH-treated lactating sows exhibited estrus 4.0 +/- 0.0 days after GnRH treatment began. All three GnRH-treated sows conceived at the estrus induced during lactation. Patterns of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum around estrus were similar between GnRH-treated sows that exhibited estrus during lactation and weaned control sows. However, in GnRH-treated sows that did not show estrus, a preovulatory-like surge in FSH, but not in LH, occurred on Day 4 of GnRH treatment. Prolactin concentrations in serum dropped from 25.6 +/- 2.4 ng/ml during lactation to less than 6 ng/ml within 12 h after weaning (Exp. 1). In Experiment 2, all six GnRH-treated sows exhibited estrus 3.8 +/- 0.3 days after initiation of GnRH treatment, and five sows conceived. Patterns of LH and FSH during lactation were similar between GnRH-treated and lactating control sows during the first 3 days of GnRH treatment. During 3 days before estrus, LH concentrations were lower (P less than 0.05) and FSH concentrations tended to be higher (P less than 0.20) in lactating GnRH-treated sows than in control sows whose litters had been weaned. Concentrations of estradiol in GnRH-treated sows were greater than those in controls during lactation but were similar in both groups on the day of estrus. In both experiments, concentrations of progesterone were greater in GnRH-treated than in control sows prior to and during estrus. We conclude that, despite some differences in hormone secretion between GnRH-treated lactating sows and sows with litters weaned, pulsatile administration of GnRH caused requisite endocrine changes for fertile estrus during lactation.