Response to dietary protein during lactation of Meishan synthetic, Large White and Landrace gilts given food to achieve the same target backfat level at farrowing

Abstract

AbstractA 3 × 2 factorial experiment was used to investigate the influence of the breed type of gilts (Meishan synthetic 50% (M), purebred Large White (LW) and purebred Landrace (LR)) on response to insoenergetic diets of differing protein levels (180 g crude protein (CP) per kg, 9 g lysine per kg; or 240 g CP per kg, 12 g lysine per kg) offered to appetite over a 28-day lactation. Body fat reserves were adjusted during pregnancy by supplementing a set quantity of basal diet (131 g CP per kg, 12·7 MJ digestible energy (DE) per kg) with an energy source (maize starch + soya oil), to attain a backfat at P2 (6·5 mm off midline at last rib) of 25 mm at farrowing for all breeds. There were no significant diet effects or breed ×diet interactions on lactational performance. On day 1 of lactation, backfat was: M = 25·9, LW = 24·9, LR = 23·9 mm (P < 0·005). M gilts were lighter at farrowing (M = 173, LW = 192, LR = 182 kg; P < 0·001) and had more piglets than LW and LR. LR gilts had heavier piglets at birth (M = 1·13, LW = 1·18, LR = 1·38 kg, P < 0·001) than M and LW gilts. M gilts had a higher food intake (M = 6·4, LW = 5·2, LR = 5·1 kg/day; P < 0·001) but higher fat (M = 4·1, LW = 2·2, LR = 2·9 mm; P < 0·05) and weight (M = 15·9, LW = 1·0, LR = 4·7 kg; P < 0·001) loss over lactation than LW and LR gilts. LW gilts had a lower lactation output as reflected by lower litter weights at weaning than M and LR gilts (M = 73·7, LW = 59·3, LR = 75·2 kg; P < 0·002). It is concluded that lactation of gilts is not improved by provision of a very high protein diet (240 g CP per kg) and that performance still differs between breeds when backfat levels are standardized.