Follicle development and timing of ovulation are indicators of the reproductive performance of sows. The present study aimed to determine factors influencing pre‐ovulatory follicle diameter and weaning‐to‐ovulation interval (WOI) in spontaneously ovulating sows in tropical climates with special emphasis on breed, parity and backfat thickness at weaning. In total, 80 sows were included in the study. Follicle development was determined by using transrectal real‐time B‐mode ultrasonography every 6 hr after standing oestrus. Weaning‐to‐oestrous interval (WEI), oestrous‐to‐ovulation interval (EOI), WOI and the diameter of graafian follicles were investigated in relation to breed, parity number (1, 2–3 and 4–7) and backfat thickness (low, moderate and high) of sows. Overall, WEI, EOI, WOI and the pre‐ovulatory follicle diameter were 92.5 ± 21.6 hr, 64.3 ± 19.3 hr, 156.3 ± 29.1 hr and 10.3 ± 2.0 mm, respectively. Pre‐ovulatory follicle size was smaller in primiparous sows compared with sows of greater parity, 4–7 (9.7 ± 0.51 and 11.7 ± 0.52 mm, respectively, p < .05). Weaning‐to‐ovulation interval was positively correlated with WEI (r = 0.75, p < .001) and EOI (r = 0.66, p < .001), but negatively correlated with size of the graafian follicle (r = –0.34, p < .01). Sows with a shorter WEI had a larger pre‐ovulatory follicle diameter (at 64 hr after oestrus) (r = –0.37, p < .01). Sows with low backfat thickness had a WOI 23.4 hr longer than those with moderate backfat thickness (p < .05) and 17.6 hr longer than sows with a high backfat thickness (p = .140). The follicle diameter in primiparous sows with high backfat thickness (11.7 ± 1.1 mm) was higher than in those with low (8.9 ± 0.7 mm, p < .05) or moderate (8.6 ± 0.8, p < .05) backfat thickness. In conclusion, factors influencing follicle diameter and WOI in sows included parity number and backfat thickness at weaning. The impact of backfat thickness on follicle diameter, WEI and WOI was most pronounced in primiparous sows.

中文翻译：

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影响热带环境中自发排卵母猪排卵前卵泡直径和断奶至排卵间隔的因素

卵泡发育和排卵时间是母猪生殖性能的指标。本研究旨在确定影响热带气候下自发排卵母猪排卵前卵泡直径和断奶至排卵间隔（WOI）的因素，并特别着重于断奶时的品种，胎次和背脂厚度。该研究总共包括80头母猪。发情后每隔6小时使用经直肠实时B型超声检查来确定卵泡发育。研究了断奶至发情间隔（WEI），发情至排卵间隔（EOI），WOI和卵泡卵的直径与品种，胎次数（1、2–3和4–7）和背脂厚度的关系（低，中，高）母猪。总体而言，WEI，EOI，WOI和排卵前卵泡直径为92.5±21.6小时64。3±19.3小时，156.3±29.1小时和10.3±2.0毫米。初产母猪的排卵前卵泡大小较小，而同胎母猪的排卵前卵泡大小较小，为4–7（分别为9.7±0.51和11.7±0.52 mm，p  <.05）。断奶至排卵间隔与WEI（r  = 0.75，p  <.001）和EOI（r  = 0.66，p  <.001）呈正相关，但与黑手卵泡大小呈负相关（r  = –0.34，p  <.01）。WEI较短的母猪的排卵前卵泡直径较大（发情后64小时）（r  = –0.37，p  <.01）。低背膘厚度母猪具有一个WOI 23.4小时比那些中度背膘厚度（较长p  <.05）和比具有高背膘厚度母猪17.6小时更长（p = .140）。高背脂厚度（11.7±1.1 mm）的初生母猪的卵泡直径大于低背脂厚度（8.9±0.7 mm，p  <.05）或中度 背肥厚度（8.6±0.8，p <.05）的母猪的卵泡直径。总之，影响母猪卵泡直径和WOI的因素包括断奶时的胎次数和后脂肪厚度。初生母猪背脂厚度对卵泡直径，WEI和WOI的影响最为明显。