Carcass characteristics of Nellore steers fed whole corn diets containing feed antibiotics

Abstract Text: The objective was to investigate the effects of feed antibiotics on carcass characteristics of feedlot steers fed whole corn diets. Ninety-seven Nellore steers (302 ± 47 kg of BW and 24 months of age) were assigned to a randomized complete block design experiment with 4 blocks (based on initial BW) and 5 treatments (Mon30: monensin 30 ppm; Virg25: virginiamycin 25 ppm; Mon20+Virg25: monensin 20 ppm + virginiamycin 25 ppm; Fla40: flavomycin 40 ppm; Mon20+Fla20: monensin 20 ppm + flavomycin 20 ppm). Pen was the experimental unit. The steers were slaughtered after a 100-d period of feeding. Steers were fed TMR (88.2% DM, 12.5% CP, 71.5% TDN) with 85% whole grain corn and 15% pelleted protein concentrate on a DM basis. Feed was supplied ad libitum. Steers were weighed after a 16-h fast on d 100 of the experimental period to determine final body weight. Hot carcass weight was determined after skinning and evisceration. Hot carcass yield was obtained at the time of slaughter. Subcutaneous fat thickness (FT) was measurement in Longissumus dorsimuscle at 12th rib. No carcass characteristic measures of feedlot Nellore steers fed whole corn diets were affected by the different feed antibiotics (Table 1). Carcass characteristic values were higher than data reported previously for Nellore steers fed high-concentrate diets based on corn (267.0 kg HCW, 54.6% HCY), except by FT (3.9 mm) (Silva, 2009).  A relatively short number of animals (n= 97) was used in this experiment. It is not known if a higher number would have affected the variables studied.

Table 1. Final body weight (BWf), hot carcass weight (HCW), hot carcass yield (HCY) and subcutaneous fat thickness (FT) of Nellore steers fed whole corn diets containing feed antibiotics
Variable	Feed antibiotics					SEM	P Value
	Mon30	Virg25	Mon20+Virg25	Fla40	Mon20+Fla20
No. of pens (steers)	4 (19)	4 (20)	4 (19)	4 (19)	4 (20)	-	-
BWf (kg)	539	534	537	544	539	4.38	0.618
HCW (kg)	309.1	306.1	309.5	309.5	303.7	2.62	0.455
HCY (%)	57.4	57.3	57.6	56.9	56.2	0.45	0.267
FT (mm)	3.2	3.4	2.9	3.4	3.5	0.18	0.158

Keywords: beef cattle, feedlot, finishing