Body weight loss during lactation and its influence on weaning-to-service interval and ovulation rate in Landrace and Yorkshire sows in the tropical environment of Thailand

The aim of this study was to investigate the ovulation rate and the weaning -to-service interval (WSI) of sows in relation to their body weight loss du ring lactation in tropical climatic conditions. Effect of lactation length (LL), number of total born piglets, number of live bom piglets, litter birt h weight, average piglet birth weight, number of pigs weaned, litter weanin g weight and average pig weaned weight on sow weight loss during lactation were also studied. This study was conducted in two commercial purebred sow herds (A, B) in the central part of Thailand from August to December 1997. The herds had both Landrace (L) and Yorkshire (Y) sows. The 123 sows (55 L and 68 Y) in herd A and 153 sows (95 L and 58 Y) in herd B, parity 1-4, wer e weighed within 4 days after farrowing and at weaning. Lactation length, l itter size at birth and at weaning, litter weight at birth and at weaning, and WSI were recorded for each of these sows. In herd A, 52 sows (20 L and 32 Y) were examined once by laparoscopy between days 8 and 14 after AI-serv ice. These sows had farrowed at least seven piglets in the previous parturi tion. The numbers of corpora lutea (CL) in both ovaries were counted, and w ere assumed to equal the ovulation rate. L-sows had significantly (P < 0.05 ) higher relative weight loss during lactation (RWL) than Y-sows. The RWL i ncreased by 0.7% for each extra pig weaned. When LL increased by I day, wit hin the interval of 17-34 days, RWL decreased by 0.6%. Sows with a high wei ght loss had significantly (P < 0.05) longer WSI than sows with medium or l ow weight loss. Weight loss had a significant (P < 0.05) effect on WSI in p arity 1 and 2 sows. Y-sows had more CL than L-sows (15.7 versus 14.0) (P < 0.05). RWL, parity and regression on lactation length had no significant ef fect on number of CL. In conclusion, sows with higher number of pigs weaned lose more weight. Under the restricted feeding regime applied, high weight loss during lactation prolongs WSI in parity I and 2 sows, but has no infl uence on the ovulation rate at first oestrus after weaning. The ovulation r ate is higher in Yorkshire than in Landrace sows. The ovulation rate is ind ependent of parity. (C) 2001 Elsevier Science B.V. All rights reserved.