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The aims of this thesis were to study causes of variation in reproductive performance in sows under tropical conditions. The influences o f climate, breed, parity, lactation length, weight loss during lactation and weaning-to-service interval were studied. In total, data from 7 purebred herds and 14 crossbred herds were included. Data were recorded in PigCHAMP® (version 2.0, Univ. of Minnesota) software. Both Landrace and Yorkshire sows were present in all purebred herds. Sows that were exposed to high ambient temperature during lactation, around mating and during early pregnancy had the lowest reproductive performance. Farrowing rate and number o f total bom piglets decreased significantly with increasing temperature and heat index (combining temperature and humidity) during the first four weeks after mating. Farrowing rate decreased by 1.8% and number of total bom piglets decreased by 0.07 piglets for each 1°C increase within the range 26° to 38°C. An increase in maximum temperature by 1°C led to an increase in weaning-to-service interval (WSI) by 0.17 days Landrace sows had, in general, better reproductive performance than Yorkshire sows. However Yorkshire sows had a shorter WSI, a higher percentage mated within 7 days after weaning and a higher ovulation rate compared with Landrace sows. The seasonal pattern did not differ between Landrace and Yorkshire sows. Crossbred primiparous sows had a shorter WSI and a higher percent mated within 5 days after weaning compared with purebred sows. Reproductive performance changed with parity number. Parity 2 sows lost more weight during lactation than sows o f other parities. There was no significant difference in ovulation rate among first to fourth parity sows. Lactation length within the range o f 17-35 days had no significant effect on WSI, ovulation rate, subsequent farrowing rate or subsequent litter size. Relative weight loss during lactation had a significant effect on WSI in parity 1 and 2 sows, but not in older sows. Sows with high weight loss had significantly longer WSI than sows with medium or low weight loss. Relative weight loss during lactation had no effect on ovulation rate. Sows with WSi 7-10 days had significantly lower farrowing rate in subsequent reproductive cycles than sows with WSI 30 days had the lowest lifetime piglet production. Sows with WSI > 30 days had 1.7 times higher risk o f culling compared with sows with WSI 0-4 days. |
