Claus R, Weiler U
J Reprod Fertil Suppl. 1985;33:185-97.
In the wild pig mating activity is seasonal. The main breeding period is in late autumn but a second period may occur around April. It is known from other species that seasonal variations in breeding activity are mainly regulated by photoperiod. In the domestic pig seasonal influences on prolificacy still exist: for example, AI boars not only show decreased steroid synthesis, sperm counts and libido in summer compared with the optima which occur in winter but also a biphasic pattern with a transient increase in spring. In cyclic sows ovarian function may be affected with anoestrus mainly in summer and occasionally in February/March. Additionally ovulation rate may be lower in summer and the duration of oestrus prolonged compared with that in late autumn and winter. In consequence the interval from weaning to oestrus is prolonged in summer and mating during this season leads to lower conception rates and slightly smaller litters. Light programmes which extend the daily light period to a constant 15-16 h seem to be ineffective in improving reproductive characteristics of the sow but stimulate the sucking frequency of piglets and increase survival of piglets with a low birthweight. Simulation, in summer, of the decreasing photoperiod (naturally occurring in autumn) stimulates the reproductive characteristics of AI boars, optimizing testicular steroid production, libido and semen composition. Similarly, a programme of decreasing light (20 min decrease/week) from May to August removed the seasonal increase (June-August) of the weaning-to-oestrus interval which was 5.7 days (compared with 23.6 days for the controls). An interaction between photoperiod and puberty attainment seems to exist for male and female pigs. Further experiments with appropriate light programmes, however, are necessary to clarify this interaction.
在野猪中，交配活动具有季节性。主要繁殖期在深秋，但第二个繁殖期可能在4月左右出现。从其他物种可知，繁殖活动的季节性变化主要受光周期调节。在家猪中，季节性对繁殖力的影响仍然存在：例如，人工授精公猪在夏季不仅与冬季的最佳状态相比，类固醇合成、精子数量和性欲会下降，而且还呈现出一种双相模式，春季会短暂增加。在发情周期的母猪中，卵巢功能可能会受到影响，主要在夏季出现发情停止，偶尔在2月/3月也会出现。此外，与深秋和冬季相比，夏季的排卵率可能较低，发情持续时间会延长。因此，夏季从断奶到发情的间隔会延长，在此季节交配会导致受孕率降低和产仔数略少。将每日光照时间延长至恒定的15 - 16小时的光照程序似乎对改善母猪的繁殖特性无效，但会刺激仔猪的吸吮频率，并提高低出生体重仔猪的存活率。在夏季模拟秋季自然发生的光照周期缩短，会刺激人工授精公猪的繁殖特性，优化睾丸类固醇的产生、性欲和精液成分。同样，从5月到8月实施光照递减程序（每周减少20分钟）消除了断奶至发情间隔的季节性增加（6月至8月），该间隔为5.7天（对照组为23.6天）。公猪和母猪在光周期与性成熟之间似乎存在相互作用。然而，需要进一步进行适当光照程序的实验来阐明这种相互作用。
