SCHMEISEROVÁ M., ZEMAN L. (2000): The effect of amino acid supplement in lactation on reproductive performance of first parity sows. EAAP - 51 th Annual Meeting, The Hague 2000: 145. ABSTRACT: Eighty – five first parity sows of LW breed were used in experiment to determine the effect of amino acids supplement in lactation on their reproductive performance. In gestation sows were housed in groups of 25 and fed individually by an electronic feeder with a basal wheat-barley diet (12.9 MJ ME). Sows were fed once a day and consumed 2.2 kg of mixture a day. In lactation sows were housed individually and fed with basal barley – wheat – corn diet (13.1 MJ ME, 7.56 g/kg of lysine, 2.57 g/kg of methionine, 4.93 g/kg of threonine). – control group (C) which was for experimental group (E) supplemented with lysine, methionine and threonin (13.1 MJ ME, 8.70 g/kg of lysine, 2.80 g/kg of methionine, 5.10 g/kg of threonin) Sows were fed twice a day according to number of piglets (10 piglets – 6.2 kg, ± 0.4 kg per piglet). Sows of group E gained more from mating to weaning at 30 days of lactation (22,74 kg vs. 23,50 kg). Number of piglets born alive was lower for E group (9.52 vs. 9.08) but number of piglets at 21 days of age and at weaning was higher for treated sows (8.38 vs. 8.41 at 21 days of age, 8.11 vs. 8.51 at weaning resp.). Piglets of treated sows were heavier through whole lactation and gained more from birth to weaning (5.38 kg vs. 5.53 kg per piglet). Results were not significantly different.