Australian researchers set up an experiment to determine interactive effects of sex (castrated vs. intact) and a ractopamine feeding program on growth performance, carcass composition and pork quality.
Sixty entire male pigs (Large White × Landrace × Duroc crossbred) were individually reared from 45 to 114 kg liveweight. They were put in a 2 by 3 factorial experiment to determine the interactive effects of sex and a ractopamine feeding program.
Pigs were immunologically castrated using Improvac with vaccinations administered at 13 weeks of age and 5 weeks before slaughter.
The pigs were constantly fed 0 or 5 ppm ractopamine for 26 days before slaughter v. a step-up program where 5 ppm of ractopamine was fed for 14 days followed by 10 ppm ractopamine for the final 12 days before slaughter.
Following the second vaccination, immunocastrated pigs ate more (P < 0.001) and grew faster (P < 0.05) than entire male pigs without affecting feed conversion efficiency. Dietary ractopamine supplementation for the last 26 days before slaughter improved feed conversion ratio (P = 0.024) and daily gain (P = 0.046).
Dietary ractopamine supplementation also increased carcass total tissue (P = 0.023) and total lean (P = 0.027) content without affecting the objective meat quality (P > 0.05) in both entire and immunocastrated male pigs.
The effects of dietary ractopamine and immunocastration were additive, such that pigs that were immunocastrated and received ractopamine grew 18% faster than control entire males.
However, a step-up program of ractopamine supplementation did not provide further improvements in growth performance and carcass composition when compared with constant 5 ppm ractopamine supplementation.
These findings indicate that ractopamine supplementation improved growth performance in entire and immunocastrated male pigs, thereby offering a means of improving growth performance of entire males without detrimental effects on pork quality.
The full text article is available from Animal Production Science:
Ractopamine supplementation increases lean deposition in entire and immunocastrated male pigs. Moore et.al.