Effect of a ractopamine feeding program on growth performance and carcass composition in finishing pigs.
Barrows and gilts (n = 100 per gender) were used to determine the effects of an increasing, decreasing, or constant ractopamine (RAC) dietary concentration on growth performance and carcass characteristics. Pigs, within a gender, were assigned randomly to pens (five pigs per pen and 10 pens per treatment). Pens were assigned randomly to one of four dietary treatments at a starting weight of 71.2 kg, to target an average ending weight of 109 kg. The four dietary treatments (as-fed basis) were 1) control = 0 ppm RAC, wk 0 to 6; 2) RAC step-up = 5.0 ppm, wk 1 to 2; 10.0 ppm, wk 3 to 4; and 20.0 ppm, wk 5 to 6; 3) RAC step-down = 20.0 ppm, wk 1 to 2; 10.0 ppm, wk 3 to 4; and 5.0 ppm, wk 5 to 6; and 4) RAC constant = 11.7 ppm, wk 0 to 6. Feed allocation was recorded daily, and pigs were weighed and feed was weighed back every 2 wk. Jugular blood samples were obtained from two randomly selected pigs per pen on d -3, 7, 21, 35, and 41 for determination of plasma urea nitrogen (PUN) concentrations. Two pigs were selected randomly per pen and sent to a commercial slaughter facility at the end of the 6-wk experimental period. Carcass data were evaluated on an equal time basis and on an equal weight basis by using hot carcass weight (HCW) as a covariate. Overall, ADG and G:F were improved (P < 0.05) for pigs fed RAC compared with control, with no differences among RAC feeding programs. In wk 3 and 4, improvements (P < 0.05) in ADG and G:F were realized with the implementation of a RAC step-up program compared with control pigs. The concentrations of PUN were decreased (P < 0.05) at d 7 and 21 with RAC feeding, and a RAC step-up program maintained the decrease (P < 0.05) in PUN through d 35 and 41. A RAC step-up and constant program increased (P < 0.05) HCW and percent yield. Loin muscle area and percentage of fat-free lean increased (P < 0.05) and backfat thickness decreased (P < 0.05) in pigs fed RAC. If pigs were considered to be on feed for an equal time period, advantages (P < 0.05) were observed for weight of boneless trimmed ham, shoulder and loin for the step-up and constant RAC treatments compared with the controls. Feeding a RAC step-up or constant feeding program resulted in favorable responses in growth performance and yielded more lean pork.
See
M T
MT
Department of Animal Science, North Carolina State University, Raleigh 27695-7621, USA. todd_see@ncsu.edu
Armstrong
T A
TA
Weldon
W C
WC
D000318:Adrenergic beta-Agonists / Q000008:administration & dosage* / Q000494:pharmacology; D000818:Animals; D001806:Blood Urea Nitrogen; D001823:Body Composition / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004435:Eating / Q000187:drug effects; D005260:Female; D008297:Male; D008460:Meat / Q000592:standards; D010627:Phenethylamines / Q000008:administration & dosage* / Q000494:pharmacology; D011897:Random Allocation; D013552:Swine / Q000033:anatomy & histology / Q000254:growth & development*; D015430:Weight Gain / Q000187:drug effects
D000318:Adrenergic beta-Agonists; D010627:Phenethylamines; C060897:ractopamine