A 3 X 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 P 2 (6-5 mm off midline at last rib) of 25 mm at farrowing for all breeds. There were no significant diet effects or breed Xdiet 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.

This experiment measured the consequences of manipulating body fat reserves at farrowing by nutritional means in three sow breed types. A 3 ×2× 2 factorial experiment involving 83 second parity sows (previously given food to achieve a standard backfat measurement of 25 mm at first farrowing) was used to investigate the influence of breed type (Meishan synthetic 50% (M) or purebred European Landrace (LR) and Large White (LW) on response to isoenergetic 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 the preceding pregnancy by supplementing a set quantity of basal diet (131 g CP per kg, 12·7 MJ digestible energy per kg) with an energy source (maize starch + soya oil), to attain a backfat at P2 of either 23 mm (T) or 28 mm (F) at farrowing. No lactation diet effects on performance were observed. There were no significant breed or diet differences in backfat at farrowing. M sows were lighter at farrowing than LW and LR (M = 19·4, LW = 22·3, LR = 21·4 kg, P < 0·001). M consumed more food throughout lactation than LR and LW (M = 7·02, LW = 5·02, LR = 5·86 kg/day, P < 0·01) but weight loss was higher for M than for LW and LR sows (M = 11·7, LW = 5·4, LR = 6·1 kg, P < 0·05). Fat loss also showed a breed effect (M = 3·6, LW = 2·1, LR = 2·7 mm P2, P < 0·05), as did litter growth rates (M = 2·33, LW = 1·74, LR = 2·07 kg/day, P < 0·01). However, the breed effect disappeared when litter size was added as a covariate. The proportion of sows that was served within 5 days of weaning was higher for M than for the White breed types (W) (M = 0·74 , W = 0·51 , P < 0·05). The Meishan synthetics still mobilized more body tissue and produced greater milk yields than the W sows when backfat levels were standardized between breeds. The use of a very high protein food did not offer any advantage for the sow in terms of milk production or conservation of maternal body reserves.