High food intake in early pregnancy resulted in increased prenatal mortality and reduced subsequent litter size in many studies using gilts (den Hartog and Van Kempen, 1980). With multiparous sows there is generally no difference in the rate of embryo survival or litter size with high feeding in early pregnancy (Toplis et al, 1983, Dyck & Cole, 1986).
Limited evidence suggests that sows fed low levels in lactation and then a high level early in the following pregnancy may show increased rates of embryo mortality (Pike and Boaz, 1972; Hughes et al, 1984). The effect of high feeding may be due to low plasma progesterone concentrations (Hughes et al 1984; Dyck et al, 1980) in early pregnancy which may be associated with reduced embryo survival and litter size.
This study was designed to investigate the effects of high or low feed intake in lactation and early pregnancy on plasma progesterone concentrations in early pregnancy and subsequent litter size using multiparous sows.