EFFECTS OF NUTRITION ON PREGNANT AND LACTATING SOWS

It has been suggested that the long-term reproduction of the sow is be st served by minimizing weight and fat loss in lactation. Such a strat egy would require only a minimal restoration of weight in the followin g pregnancy, which would be beneficial, since the greater feed intake and weight gain in pregnancy, the greater the weight loss in lactation . Feeding ad libitum should be practised during lactation while gestat ion feed intake must be held low. A relationship between feed intake a nd embryo survival has been demonstrated in several studies, but the d ata are sometimes difficult to interpret. High energy feeding during t he premating period and during early pregnancy, however, are often ass ociated with increased embryo mortality. A short-term starvation in la ctation decreased prolactin to post-weaning concentrations, and insuli n and glucose to very low concentrations. Prolactin increased very rap idly after refeeding indicating that a neural mechanism might be invol ved. The increasing levels of cholecystokinin after refeeding and the neural reflex triggered might be related to this increase in prolactin . No changes in LH release were observed during the periods of starvat ion or refeeding. The catabolic rate during the first week of lactatio n is higher in sows with higher backfat thickness than in late gestati on. As lactation progresses a more balanced metabolism is achieved reg ardless of backfat thickness before parturition. High-weight-loss prim iparous sows need a longer recovery period from their negative energy balance during lactation than do low-weight-loss primiparous sows or m ultiparous sows. Several investigations have demonstrated that sows lo sing excessive amounts of body weight have extended weaning to oestrou s intervals and an increase in anoestrus. Sows with low body-weight lo ss during lactation have higher plasma insulin and lower cortisol arou nd weaning than do sows with high body-weight loss. What remains undef ined is the degree of weight or condition loss below which an extensio n in the remating interval will occur and the level of dietary energy intake required to prevent this extension.