Reproductive performance of modern lean genotypes of pig has been shown to be particularly sensitive to dietary protein (Sinclair et al. 1996, Cia et al. 1998). This experiment examined the effect of modifying body protein : lipid ratio at different absolute protein mass on ovarian function in lactating gilts. A partial weaning technique was used to increase the potential sensitivity of the reproductive axis to differing lactational dietary protein levels.

A 3x2 factorial experiment involving 60 first parity sows compared 3 different pregnancy feeding strategies and 2 lactation diets. During pregnancy, sows were fed from day 42 either a set quantity (mean of 2.27 kg/day) of basal diet (5 g lysine, 13 MJ DE/kg[C]), or basal diet + energy (maize starch + soya oil in 3:1 ratio [E]), or additional basal diet supplying both protein and energy [P]. Lactation diets provided either high (180 g CP/kg, 9g lysine/kg [H]) or low lysine (120 g CP/kg, 6g lysine/kg [L]) and were formulated to be isoenergetic (14.5 MJ DE/kg) and fed to appetite. From day 21 of lactation, sows were separated from their litters and housed next to a boar for 8 hours each day; final weaning occurred on day 31.