Nutrition and sow prolificacy.

Prolificacy has been defined as the number of viable piglets produced per year or per breeding lifetime. Prolificacy is influenced by age at first successful mating, ovulation rate and embryo survival at each mating, number of live born, viable pigs and the sow's ability to be successfully remated at regular intervals. It is concluded that under normal conditions of feeding and management nutrition will have a minimal influence on gilt prolificacy. However, to gain the advantages of a slightly younger age at puberty, maximal ovulation rate and an adequate fat cover (if only to ensure against subsequent poor management), gilts should be fed ad libitum up to the time of mating. Long-term performance is best served by minimizing fluctuations in live weight and fat reserves, so avoiding extremes of body condition and subsequent poor performance. This is achieved by small controlled increases in sow body weight during pregnancy and feeding to appetite for restricted periods each day during lactation. Assuming the sow has not achieved a very poor condition during lactation, feeding level during pregnancy will have little effect on numbers of piglets born, and only a limited influence on piglet birthweights. The conclusion that piglet birth weights will be influenced more by total pregnancy feed intake than pattern of feed distribution is unchallenged. Lactation feed intake is shown to have marked effects on the post-weaning performance, low-level feeding leading to an extension of the remating interval and possibly increasing embryo mortality. No benefit of high-level feeding after weaning is demonstrable, except possibly in primiparous sows or sows having suffered an extreme loss of liveweight and body condition during the previous lactation.