Meishan synthetic sows and gilts have been shown to produce higher litter weights at weaning than White breed type sows and gilts. To investigate the factors contributing to this, 64 multiparous sows were used in a 2 × 2 × 2 factorial experiment to assess the influence of maternal breed type (0·50 Meishan synthetic (M) or purebred European Landrace and Large White (W)), litter size (eight (L) or 12 (H) piglets) and breed of piglet (0·25 Meishan hybrid (m) or white hybrid (w)) on sow and litter production and behaviour over a 28-day lactation. All litters were formed by cross-fostering to standardized litter rearing size 24 h after farrowing. Sows were given food twice daily to appetite. When there were no treatment interactions, main effects are presented. M sows were lighter (M = 215, W = 241 (s.e. 3·61) kg, P < 0·001) and fatter (M = 31·5, W = 21·7 (s.e. 0·72) mm, P < 0·001) at farrowing than W and had higher maternal weight loss (M = 24·7, W = 5·9 (s.e. 0·85) kg, P < 0·001) and higher back fat loss (M = 5·6, W = 2·0 (s.e. 0.28) mm, P < 0·001) in lactation. High litter size resulted in higher maternal weight loss (L = 7·4, H = 13·2 (s.e. 0·85) kg, P < 0·001) and fat loss (L = 2·9, H = 4·7 (s.e. 0·28) mm, P < 0·002) than low litter size. Litter growth rate was higher for M than for W (M = 27·0, W = 14·5 (s.e. 0·42) kg/week, P < 0·002) and for high litter size than for low litter size (L = 24·3, H = 17·3 (s.e. 0·42 kg/week, P < 0·001). The m piglets had lower litter growth rates than w piglets (m = 15·1, w – 16·5 (s.e. 0·42) kg/week, P < 0·001). There were no breed differences in the length of suckling periods but M had shorter suckling intervals than W (M = 38·1, W = 48·7 (s.e. 1·08) min, P < 0·001). It is concluded that the higher litter weights produced by M sows are due solely to maternal effects and not litter size or piglet genotype.