The Thai Journal of Veterinary Medicine


Although the domestic pig is not a true seasonal breeder, a seasonal effect on reproductive performance exists. A reduction in reproductive performance during some periods of the year is most pronounced in primiparous sows and is manifested in various ways such as, delayed puberty, prolonged weaning-to-first-service interval (WSI), increased number of sows returning to oestrus after mating, decreased conception rate, decreased farrowing rate (FR), decreased litter size and an increased incidence of abortion. Both high ambient temperatures and/or changes in photoperiod have been reported to be the cause of these problems. The pig is considered to be a short-day seasonal breeder and variations in day-length have been demonstrated to be an important factor that controls the pattern of seasonal reproduction in pigs. Pigs are susceptible to heat stress because of their limited ability to decrease body temperature, through either evaporation or sweating. A number of additional factors such as parity, housing and ventilation, feed intake and boar effects have been shown to contribute to seasonal variations in sow reproductive performance. A number of management practices are suggested to reduce seasonal effects on sow reproductive performance.

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