Effect of sex and season of birth on Gompertz growth curve parameters in "Nero di Parma" pigs

The growth curves of "Nero di Parma" pigs were studied by applying the Gompertz equation to 1069 body weight (BW) records from 285 pigs (156 females, 129 castrated males) born in 11 outdoor and 5 indoor herds; pigs were fed commercial complete feeds offered ad libitum and, on a limited basis in the outdoor system, diets were integrated with pasture. The parameters of the Gompertz equation were compared with reference to sex and season of birth.Mature BW for castrated males (229.0 kg) was 3.5% greater than that for females (221.3 kg) (P<0.05), but growth rate was 7.6% lower (7.38*10-3 vs 7.99*10-3, respectively) (P<0.05) and age at maturity (205.7 vs 189.6 d, respectively) was 16.1 d greater (P<0.05). Summer and winter born pigs showed a lower mature BW (P<0.05) than those born in other seasons. Summer born pigs grew slower than those born in spring (9.57%), winter (9.58%) and autumn (21.47%) (P<0.05). Earlier maturing pigs were those born in autumn, followed by those born in winter, spring and summer, respectively. Regardless of sex and season of birth, pigs showed their maximum ADG (ADGmax) of 635 g/d at 82.6 kg BW. Castrated males have a lower ADGmax than females (622 vs 650 g/d) at a heavier weight (84.2 vs 81.4 kg). Autumn born pigs showed the highest ADGmax (695 g/d), reached at 84.9 kg BW.The growth performance of "Nero di Parma" pigs is greater than those reported for Italian domestic pig breeds. The significant effect of the studied environmental factors on the growth curve in this genetic type will make it possible to choose the best rearing conditions in relation to its usual weight at slaughter (>180 kg).