Effects of ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers1
- 1 October 2006
- journal article
- Published by Oxford University Press (OUP) in Journal of Animal Science
- Vol. 84 (10), 2795-2800
- https://doi.org/10.2527/jas.2005-614
Abstract
An experiment was conducted to determine the relationship between feeding ractopamine and different amounts of MP on growth and carcass characteristics of feedlot heifers. Seventy-two crossbred heifers (475 kg of initial BW) were fed individually a diet based on steam-flaked corn for ad libitum intake for 29 d. Heifers were implanted with 140 mg of trenbolone acetate and 14 mg of estradiol-17β 60 d before the experiment. Treatments were arranged as a 2 × 3 factorial and included 0 or 200 mg of ractopamine-HCl (23 ppm)/ d, and urea, solvent soybean meal, or expeller soybean meal (ESBM) as the predominant protein supplement. The amounts of MP supplied by the urea, solvent soybean meal, and ESBM diets were 688, 761, and 808 g/ d, respectively, calculated according to level 1 of the NRC model. Body weights were obtained 1 d before ractopamine feeding and at slaughter. Blood samples were obtained 1 d before starting the experiment and 13 d later. Ractopamine improved ADG, efficiency of gain, carcass-adjusted ADG, and carcass-adjusted efficiency of gain (P < 0.01). For ADG, heifers demonstrated a ractopamine × protein source interaction (P < 0.05); heifers not fed ractopamine had greater ADG when fed ESBM than when fed urea, whereas for heifers fed ractopamine there were no differences (P ≥ 0.10) among protein supplements. This interaction was not observed for carcass-adjusted ADG (P = 0.60). Final live weights (P = 0.02) and carcass weights (P = 0.01) were greater with ractopamine feeding. Carcass marbling scores and yield grades were not affected by ractopamine or protein source (P ≥ 0.39). Plasma total α-amino N and glucose concentrations decreased more from pretreatment concentrations when heifers were fed ractopamine (P < 0.05). Feeding ractopamine to heifers for 28 d before slaughter improved ADG and efficiency of gain without any large effects on carcass characteristics. The MP supply does not need to be increased from that provided by finishing diets based on steam-flaked corn with urea as the primary N supplement to allow the maximal response to ractopamine by finishing heifers. Copyright © 2006. . Copyright 2006 Journal of Animal ScienceKeywords
This publication has 12 references indexed in Scilit:
- Effects of crude protein concentration and degradability on performance, carcass characteristics, and serum urea nitrogen concentrations in finishing beef steersJournal of Animal Science, 2004
- Effects of ractopamine at different dietary protein levels on growth performance and carcass characteristics in finishing pigsAnimal Feed Science and Technology, 1999
- Effect of energy source and escape protein on receiving and finishing performance and health of calves.Journal of Animal Science, 1998
- The feeding value of dry-rolled and steam-flaked corn in finishing diets for feedlot cattle: influence of protein supplementation.Journal of Animal Science, 1998
- Protein levels in beef cattle finishing diets: industry application, university research, and systems results.Journal of Animal Science, 1996
- Effects of anabolic steroids on nitrogen metabolism and growth of steers fed corn silage and corn-based diets supplemented with urea or combinations of soybean meal and feathermeal2Journal of Animal Science, 1994
- A net carbohydrate and protein system for evaluating cattle diets: I. Ruminal fermentationJournal of Animal Science, 1992
- A net carbohydrate and protein system for evaluating cattle diets: III. Cattle requirements and diet adequacyJournal of Animal Science, 1992
- A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availabilityJournal of Animal Science, 1992
- Influence of level of dietary protein or energy on effects of ractopamine in finishing swine2Journal of Animal Science, 1991