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Conceptus development in Large White and prolific Chinese Meishan pigs

Summary. Large White (LW) and Meishan (MS) gilts were killed on Days 8, 10, 11, 12, 14 and 30 of gestation. Mean diameters (mm) for MS and LW conceptuses, respectively, were: Day 8, 0·45 and 0·69; Day 10, 2·7 and 1·9; Day 11, 5·3 and 2·7, with the differences among days being affected by breed (P < 0·01). Variation in diameter among conceptuses from LW gilts was greater (P < 0·01) than that for MS gilts on Days 8–11, respectively: Day 8, 20 and 46%; Day 10, 29 and 38%; and Day 11, 22 and 44%. Conceptuses had elongated in 3 of 5 MS and 1 of 4 LW gilts on Day 11, 6 and 6 MS and 2 of 4 LW gilts on Day 12 and all gilts of both breeds on Day 14. These results indicate that conceptuses of MS gilts develop more rapidly and more uniformly between Days 8 and 14 of gestation. Overall, embryonic survival for Days 8–12 for gilts not having elongated conceptuses was 90·2% for MS and 73·2% for LW gilts (P < 0·01). On Day 30 of gestation, embryonic survival was also higher (P < 0·01) for MS (89%) than LW (55%) gilts. However, embryonic weight, crown–rump length, placental length, allantoic fluid volume, amniotic fluid volume, as well as total glucose, fructose and protein in allantoic fluid were not affected by breed. Placental weight was greater (P < 0·01) for LW gilts. Uterine development at Day 30 of gestation, based on total length and weight of uterine horns, width of uterine horns, total endometrial surface area and total endometrial weight was greater (P < 0·01) for LW gilts. Ovulation rates on Days 8–14 and on Day 30 were also higher (P < 0·05) for LW gilts. These results indicate that: (1) ovulation rates were lower and uteri were smaller for prolific MS gilts; (2) faster and more uniform conceptus development between Days 8 and 14 of gestation for MS gilts was associated with higher embryonic survival; and (3) embryos and placentae surviving to Day 30 had similar weights and lengths, but embryonic survival to Day 30 of gestation was higher for MS gilts. Factors regulating rate and uniformity of conceptus development in swine may be primary determinants of prolificacy.

Keywords: pig; conceptus; Chinese; uterus; pregnancy

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