Two trials were conducted to study the effects of feeding a mixture of ammonium salts of isovaleric, 2-methylbutyric, isobutyric and valeric acids (AS-VFA) on feedlot performance and carcass characteristics of growing and finishing Angus, Hereford and Angus X Hereford steers. In trial 1,192 steers (8 steers/pen, 6 pen/treatment) averaging 251 kg body weight and in trial 2, 240 steers (8 steer/pen, 7 pens/treatment, 9 pens/control treatment) averaging 216 kg body weight were randomly assigned to four anhydrous ammonium salt-volatile fatty acid (AS-VFA) treatment levels: 0 (control), .14, .28 and .42% of the diet dry matter (DM). In each trial, the growing and finishing diets were isocaloric, isonitrogenous and supplemented with monensin (26 mg/kg diet). In both trials, steers received implants of 200 mg progesterone and 20 mg estradiol benzoate. Combined data from the trials confirmed the absence of average daily gain and feed conversion responses during the growing period. During the finishing period, the combined data for gain and feed conversion for the control steers and the steers fed .14, .28 and .42% AS-VFA were 1.43, 7.09; 1.43, 6.99; 1.48, 6.67 and 1.45, 6.80, respectively. Gains increased 3.5% (P less than .10) and feed conversion improved 5.9% (P less than .07) in steers fed .28% AS-VFA compared with gain and feed conversion of the control steers. At the end of the growing period in the first trial, a urea dilution technique was used to estimate the body composition of 12 steers from each treatment. Estimates of percent body fat and percent body protein were similar (P greater than .20) for all steers, irrespective of treatment. At the end of the trials, carcass yield grades for the combined data were 2.6 and 2.8 (P less than .10) for steers fed .28% AS-VFA and for the control steers, respectively. Carcass weight, dressing percentage and marbling score were lower (P less than .10) in steers fed AS-VFA than for steers fed the control. However, in general, carcass characteristics were not greatly influenced by AS-VFA. A possible use for a supplement containing branched-chain fatty acids and valeric acid in finishing steer diets is suggested by the improvement in feedlot performance and by the slight increase in carcass yield.
Animals Body Composition