Entire male (EM) pigs (152; ∼30 kg body weight) were used to examine immunocastration using Improvest and feeding ractopamine on growth performance, carcass and meat quality, and fatty acid composition. Timing for administering second dose of Improvest compared dosing at 4 and 8 wk pre-slaughter. A factorial arrangement evaluated two genotypes [Large Whites and Duroc crossbreds (Durocs)] by five management regimens (EM fed control diet, EM fed ractopamine, second dose Improvest 4 wk pre-slaughter, second dose Improvest 8 wk pre-slaughter, second dose Improvest 4 wk pre-slaughter plus ractopamine). Average daily gain and gain to feed (G:F) were generally greater (P ≤ 0.01) in Durocs. Immunocastration increased (P < 0.01) dry matter intake (DMI); feeding ractopamine decreased (P < 0.02) DMI and increased (P < 0.03) G:F. Immunocastration decreased (P < 0.04) carcass and lean yields; feeding ractopamine increased (P < 0.04) carcass weights, lean yield, muscling, and longissimus shear force while decreasing (P < 0.01) backfats. Immunocastration did not affect loin pH, color, drip loss, and shear force. Timing for second Improvest dose did not affect most growth performance, carcass, and meat quality traits except for greater (P < 0.02) backfats when administering dose 8 wk pre-slaughter. Effects of immunocastration and (or) feeding ractopamine were relatively consistent in both genotypes evaluated.
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