INTERRELATIONSHIPS AMONG AGE, BODY-WEIGHT, BACKFAT AND LACTATION FEED-INTAKE WITH REPRODUCTIVE-PERFORMANCE AND LONGEVITY OF SOWS

Data from an experiment involving gilts mated at first, second or third observed estrus and feeding of three levels of gestation energy throughout four parities were used to evaluate the effects of age, body weight, backfat thickness and changes in them on various measures of reproductive performance. Regression equations were estimated by using a stepwise regression analysis. Data were available for 304 initial sows that farrowed a first litter of which 115 farrowed to initial assigned breeding within gestation dietary energy level and completed four parities. Age, weight, backfat thickness or ratios between them at initial mating did not account for an appreciable amount of the variation (R2 < 0.08) in number of pigs born alive in the first litter or total number of pigs born alive per initial sow. Feed intake in lactation, age at first estrus as gilts or age at breeding of sows and the ratio of backfat to weight at farrowing accounted for a small proportion of the variation in weaning to estrus interval. There was an increased culling rate of sows with less than 12 mm P2 backfat at weaning after parities 2 and 3.