Effect of gender (gilt and surgically and immunocastrated male) and ractopamine hydrochloride supplementation on growth performance, carcass, and pork quality characteristics of finishing pigs under commercial conditions

This study evaluated the effects of gender and feeding of ractopamine on growth performance, carcass, and meat quality characteristics of pigs reared under commercial conditions. The study was performed as a randomized complete block design (blocking factor date of start on test) with a 3 x 2 factorial arrangement of treatments: 1) gender [gilt vs. surgical castrate vs. intact males immunocastrated] and 2) ractopamine level (0 vs. 5 g/ton). The study was conducted out over a fixed duration (126 d) from 1 wk after weaning (28 d of age; 8.04 +/- 1.31 kg BW) to 154 d of age (111.44 +/- 4.67 kg BW) in 3 growth periods: nursery (d 0 to 35 of the study), growing (d 35 to 70), and finishing (d 70 to 126). Ractopamine was fed for the final 28 d of the study (d 98 to 126). Pigs were kept in groups of 10 or 11 in the nursery phase and then moved to the growing- finishing facility where they were kept in groups of 22 to the end of the study. At the end of the growth study, pigs were harvested and carcass and pork quality were evaluated, including consumer evaluation of eating quality. During the nursery, there was no effect of gender (P > 0.05) on G: F, but surgical castrates grew faster (P < 0.05) than intact males and gilts and had greater (P < 0.05) ADFI than intact males. There was no effect of gender (P > 0.05) on ADG in the growing period; however, immunocastrated males had lower ADFI than surgical castrates and greater G:F than surgical castrates and gilts. In finishing, immunocastrated males and surgical castrates had similar ADG but grew faster than gilts; G:F was greater for immunocastrated males than the other genders. Feeding 5 compared to 0 g/ton ractopamine increased ADG and G: F but had no effect (P > 0.05) on carcass yield or fresh meat quality. Carcass yield was lower but percentage lean cut yield was greater for immunocastrated males than for surgical castrates. Longissimus muscle drip loss was greater (P = 0.05) for immunocastrated males than surgical castrates. Gender had no effect (P > 0.05) on consumer panel evaluation. Feeding ractopamine had no effect on pork flavor and tenderness but improved juiciness scores. Odor scores were similar (P > 0.05) for surgical castrates and immunocastrated males that were fed ractopamine. Consumers gave lower liking scores for odor for immunocastrated males than surgical castrates that were not fed ractopamine. This study highlights the feed efficiency and lean cut yield advantage for immunocastrated males compared to surgical castrates and suggests a similar growth response to feeding ractopamine in these genders. Although immunocastrated males had a lower carcass yield and higher drip loss, panelists were not able to detect differences in pork juiciness, flavor, and tenderness when compared to surgical castrate pigs.