The study was carried out to evaluate the performance and carcass traits of surgically castrated entire male and immunocastrated pigs fed diets containing different levels of amino acids and energy with or without ractopamine.
Seventy-two pigs with average initial weight of 20 kg were used. Pigs were assigned to 4 treatments, surgically castrated pigs fed control diet, entire male pigs fed control diet, entire male pigs fed control diet+3% amino acids and energy, or entire male pigs fed control diet+5% amino acids and energy with 6 pens and 3 pigs per pen in a completely randomized design. The first dose of immunocastration vaccine was administered when the entire male pigs reached average live weight of 65 kg. The second dose of immunocastration vaccine was administered 28 d before slaughter, and 5 ppm of ractopamine was added to the diet of half of the pens for each treatment at that time. Twenty-four pigs (1 per pen) were selected based on the average pen weight and slaughtered. Entire male pigs had 11% lower (P<0.05) feed intake and improved (P<0.05) feed efficiency by 15% compared to surgically castrated pigs. Supplementation with 3% and 5% of amino acids and energy did not change the daily feed intake and feed efficiency of entire male pigs. Surgically castrated pigs fed with control diet without ractopamine reached the slaughter age 5.5 kg lighter (P<0.05) than those fed the diet with ractopamine.
Compared to immunocastrated pigs fed diets with different nutritional levels and with or without ractopamine, they were, on average, 13 kg lighter (P<0.05). Unlike growth performance, diets did not influence the carcass characteristics of surgically castrated and immunocastrated pigs. The addition of ractopamine to the diet increased (P<0.05) initial and final body weights, hot carcass dressing percentage, and muscle thickness of surgically castrated and immunocastrated pigs.
The addition of amino acids and energy improved the growth performance of immunocastrated pigs, and ractopamine increased body weight, carcass dressing percentage, and muscle thickness of surgically castrated and immunocastrated pigs.
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