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Effect of pre-harvest feeding and ractopamine hydrochloride supplementation on growth performance, carcass characteristics, and end product quality in market dairy cows

J. D. Allen^*, J. K. Ahola, M. Chahine, J. I. Szasz^*, C. W. Hunt^*, C. S. Schneider^*, G. K. Murdoch^* and R. A. Hill^*

^* Department of Animal and Veterinary Science, University of Idaho, Moscow 83844 , Department of Animal and Veterinary Science, Caldwell Research and Extension Center, University of Idaho, Caldwell 83605 Department of Animal and Veterinary Science, Twin Falls Research and Extension Center, University of Idaho, Twin Falls 83303

jahola{at}uidaho.edu

Abstract

An experiment was conducted in market dairy cows to determine the effect of feeding time and ractopamine hydrochloride on growth performance, carcass characteristics, and end product quality. In 3 replicates, 9 Holstein cows per replicate (n = 27; 659 ± 25.3 kg initial BW) culled from 3 dairies were randomly assigned to 3 treatments: 1) harvest immediately (control), 2) feed for 90 d (NoR), or 3) feed for 90 d with ractopamine hydrochloride (312 mg·cow^-1·d^-1) for the final 32 d (RAC). On d 0, NoR and RAC cows were placed in individual pens and fed a high concentrate diet (86% concentrate, DM basis) for 90 d before harvest. All cows were subjectively scored for BCS and locomotion score on d 0, and NoR and RAC cows were evaluated again after 90 d. Individual DMI was recorded daily throughout the trial, and BW was collected every 14 d. Age and age x treatment did not affect (P > 0.05) any of the traits evaluated in this study. When cows fed for 90 d (NoR and RAC combined) were compared to non-fed controls, fed cows had greater (P < 0.001) final BCS, BW and HCW, lower (P < 0.001) final locomotion score, and greater (P < 0.03) dressing percentage, external fat thickness, and marbling score. Fed cows also tended to have more desirable yield grade (P = 0.08), ribeye area (P = 0.11), fat color (P = 0.09), lean maturity (P = 0.06), and quality grade (P = 0.09) compared to control cows. Warner-Bratzler shear force was not affected (P = 0.23) by feeding. However, a 12-member trained sensory panel revealed that fed cow carcasses had more desirable (P < 0.04) tenderness, juiciness and overall acceptability than control cow carcasses. Flavor intensity also tended (P = 0.10) to be more desirable for fed vs. control cows. No difference (P > 0.10) in off-flavor was detected among treatments. Finally, there was no effect (P > 0.10) of ractopamine hydrochloride on growth performance, carcass characteristics, or end product quality. In conclusion, feeding a high concentrate diet for 90 d improved important live animal, carcass, and end-product characteristics related to the quality and palatability of beef from market dairy cows; however, no effect of ractopamine supplementation was observed.

Key Words: carcass quality • end product • growth performance • market dairy cow • pre-harvest feeding • ractopamine hydrochloride