It has been suggested previously that the increased litter size of the prolific Chinese Meishan pig may result from an increased littermate embryonic synchrony. This study compared embryonic diversity in Meishan and domestic (white line crossbred) sows. Third-parity Meishan sows (n = 14) and second-parity domestic sows (n = 15) were observed for estrus every 6 h and were hand-mated at 24 and 30 h after first observed estrus (d 0) to boars of the same breed. The sows were slaughtered on d 11.9 +/- .1 (mean +/- SEM). Embryos were flushed from each uterine horn and were individually sonicated, lyophilized, and frozen (-86 degrees C) until they were assayed for estradiol-17 beta (E2 beta), DNA, and protein content. Ovulation rate was higher (P < .001) in Meishan (24.9 +/- 1.1) than in domestic sows (15.2 +/- .7). The average littermate embryonic diameter was smaller (P < .001) for Meishan than for domestic sows, although morphological embryonic diversity (standard deviation for diameter) did not differ (P > .10) between the two breeds. In addition, for embryos of the same diameter, no differences (P > .10) in number of embryonic cells (micrograms of DNA/embryo) or in cell size (protein:DNA ratio) were observed for either breed. The more advanced (> 6 mm) embryos from Meishan sows contained less (P < .001) E2 beta (picograms/embryo) than did embryos of the same size from domestic sows. The prolificacy of the Meishan sow may result from both an increased ovulation rate and reduced E2 beta production by Meishan embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Three experiments investigated ovarian follicular development in sows whose litters were weaned at 28 to 31 d of lactation. Unilateral ovariectomy near the time of weaning was used to assess early follicular characteristics and to identify those sows that would not return to estrus within 10 d after weaning. This allowed segregation of and exclusion from the study those sows that had a prolonged interval from weaning to first estrus. In Exp. 1, 82 and 72% of the large follicles that were marked at 48 or 72 h after weaning (10 sows per time point) were subsequently identified as corpora lutea. In Exp. 2, sows (seven to nine per time point) were unilaterally ovariectomized at 0, 6, 12, 18, 24, or 48 h after weaning, and follicular fluid was evaluated for changes in steroid concentrations. Progesterone concentrations in fluid from medium-sized (4 to 6 mm) follicles increased by 6 h after weaning and then declined through 24 h concomitant with increases in testosterone and estradiol. For Exp. 3, follicular fluid and granulosa cells from individual follicles were obtained from sows (seven to nine per time point) at 0, 6, and 24 h after weaning. In follicular fluid, insulin-like growth factor I (IGF-I) concentrations were not correlated (P greater than .05) with concentrations of progesterone, testosterone, or estradiol, or with granulosa cell production of estradiol during culture in androstenedione-supplemented medium.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

No abstract