Comparing the growth curves of females and immuno castrated males in commercial conditions
Concerning pigs, intact males grow faster than females; inversely, surgically castrated males perform worse than females. Immuno castration appears as an alternative to surgical castration in pigs, since it features less detrimental effects on growth and guarantees the full preservation of animal welfare conditions. The objective was to compare the growth curve parameters obtained from females and immuno castrated males, reared in commercial conditions. The experiment lasted 105 d and 168 piglets from 6 commercial white genetic lines (28 piglets each) were selected at the end of the nursery period (24.8 kg ± 5.10 kg BW). Animals were allocated to a growing-finishing facility and segregated by sex (males and females). Pigs were fed with up to 6 consecutive different corn-soybean diets in a controlled ad libitum way and ractopamine (10 ppm) was added as a feed additive 28 d before slaughtering. A total of 166 animals finished the experiment (124.4 kg ± 6.20 kg BW). Males were immuno castrated by giving them 2 doses of vaccine Vivax (Zoetis®) around 56 and 28 d before slaughtering. Pigs were weighed weekly individually (up to 15 times) and data was adjusted using the double exponential Gompertz model (Live Weight = A*exp(-exp(b-(c*t))); the resulting growth parameters were statistically analyzed by ANOVA. Immuno castrated males had greater ADG (mean values of 1,070 vs 997 g/d, P < 0.001) and tended to have a better G:F (441 vs 428 g of growth/kg feed, P = 0.076) than females. Immuno castrated males, compared with females, had greater values for mature live weight (A) (334.3 vs 272.9 kg; P < 0.001), and also maximum growth rate ((A*c)/e) (1,249 vs 1,099 g/d, P < 0.001), age ((b/c) (155 vs 141 d, P<0.001) and live weight (118.5 vs 103.6 kg, P < 0.001) at the inflection point (which corresponds to the maximum growth rate with age). In contrast, specific growth rate (c) was higher for females (0.0111 vs 0.0105, P < 0.025) compared to immuno castrated males. It is concluded that Gompertz model was a useful tool to demonstrate that Immuno castrated male pigs grow faster and more efficiently than females.
Immuno castrated pigs, growth curve, Gompertz approach