Effect of season of birth and sex on heart weight and body weight and their interrelationship in pigs reared in the tropics

Abstract

ABSTRACTA total of 142 pigs, born at four different times of the year, were slaughtered between 1 and 9 months of age to study the effects of season of birth and sex on heart weight and body weight in the equatorial climate of southern Nigeria.Analysis of loge heart or body weight showed that season of birth influenced heart and body growth (P < 0·001). The differences occurred largely during the phase of rapid growth, with smaller differences at weaning and at 9 months. Pigs born during the high-rainfall period (May to September) showed stunted body and heart growth during the subsequent dry and warmer seasons. Those born during the dry seasons (November to March), but which passed their rapid-growth phase through the rainy, cooler seasons, were attaining market weights and adult heart weights earlier in life. However, all pigs with early growth reductions recovered, at least partially, later in life. The males had larger hearts at later ages than the females although the differences were not significant (P > 0·05). Allometric regression analyses for heart and body weight showed no seasonal effects but there was a small but significant sex effect (P < 0·001). The males had a smaller intercept and a larger slope when log, heart weight was fitted to log, body weight.Pigs reared in this equatorial climate appeared to have higher heart weights relative to body weights than those reared in temperate regions. The highest recorded proportional value of 0·0032 is outside the range of 0·0023 to 00028 recorded in temperate regions. This suggests a probable physiological adaptation to increased work load on the heart under warm tropical conditions.