Department of Animal Sciences, University of Illinois, Urbana-Champaign, IL.
J Anim Sci. 2019 Apr 3;97(4):1433-1445. doi: 10.1093/jas/skz036.
Factors that affect follicle health and growth can influence estrus, ovulation, conception, and litter size. Since the majority of the breeding herd is composed of sows, production schedules are established based on synchronized follicle growth following weaning. Insemination of sows over a 3- to 4-d period after weaning facilitates farrowing over fewer days and helps improve the uniformity of pigs at weaning. Synchronized inseminations of the group are reduced when disturbance to the follicular phase results in delayed estrus. The failure of >15 follicles to uniformly progress beyond the 6.0 mm size within 4 d during the follicular phase is associated with delayed estrus and ovulation, reduced ovulation rate, and reduced farrowing rate. In sows, the follicular phase is initiated at weaning by removal of the suckling inhibition, whereas in cycling gilts, luteolysis and clearance of progesterone begins the process. The timing and patterns of follicle-stimulating hormone and luteinizing hormone stimulation to the ovary determine follicle health and selection for ovulation. Interestingly, abnormal wean-to-estrus intervals in sows and deviations from a 19- to 22-d estrous cycle in gilts are associated with reduced fertility. However, in both cases, it is not entirely clear whether the abnormal intervals are a direct result of problems occurring prior to or only during the follicular phase. In prepubertal gilts, the signal for initiating the follicular phase remains elusive, but could reside in differential sensitivity and response to hormone signals at the level of the ovary and brain. Although the mechanisms are not clear, factors such as boar exposure, stress, feed intake, growth rate, and birthweight have been shown to stimulate an early follicular phase. In contrast, inhibitors to follicle growth have been associated with season, heat stress, photoperiod, negative energy balance, poor body condition, slow growth, fewer parities, and short lactation length. Hormonal aids for inducing and delaying the follicular phase, as well as for inducing ovulation are available to aid in synchronized breeding schedules.
影响卵泡健康和生长的因素会影响发情、排卵、受孕和产仔数。由于大多数繁殖猪群由母猪组成，因此生产计划是根据断奶后卵泡的同步生长制定的。在断奶后 3-4 天内对母猪进行配种，可以减少产仔天数，并有助于提高断奶猪的均匀度。如果卵泡期受到干扰导致发情延迟，会减少同步配种的母猪数量。在卵泡期的 4 天内，>15 个卵泡未能均匀地长到 6.0 毫米以上，这与发情和排卵延迟、排卵率降低以及产仔率降低有关。在母猪中，断奶时通过去除哺乳抑制来启动卵泡期，而在循环后备母猪中，黄体溶解和孕酮清除开始这个过程。对卵巢的促卵泡激素和促黄体生成素刺激的时间和模式决定了卵泡的健康和排卵的选择。有趣的是，母猪的断奶至发情间隔异常和后备母猪的发情周期从 19-22 天偏离与生育力降低有关。然而，在这两种情况下，尚不清楚异常间隔是否是卵泡期之前或仅在卵泡期期间发生的问题的直接结果。在未成熟的后备母猪中，启动卵泡期的信号仍然难以捉摸，但可能存在于卵巢和大脑水平对激素信号的敏感性和反应的差异。尽管机制尚不清楚，但已经证明，公猪接触、应激、采食量、生长速度和初生重等因素会刺激早期卵泡期。相反，抑制卵泡生长的因素与季节、热应激、光照周期、负能平衡、身体状况不佳、生长缓慢、产次较少以及泌乳期较短有关。诱导和延迟卵泡期以及诱导排卵的激素辅助剂可用于辅助同步配种计划。
