Effects of Hand-Fed Versus Self-Fed Fat Supplementation on Growth and Reproductive Performance of Developing Beef Heifers

Growth and digestion trials were conducted to determine the efficacy of supplemental fat for developing beef heifers consuming a bromegrass hay-based diet. In Exp. 1, Angus × Gelbvieh heifers were allotted to one of three treatments in a randomized complete block design experiment for 2 consecutive yr (yr 1: n = 88, BW = 263.6 ± 0.6 kg; yr 2: n = 56, BW = 276.8 ± 3.1 kg). Supplemental treatments included a hand-fed corn- and soybean meal-based supplement (CRN), a hand-fed corn- and soybean meal-based supplement containing 15% soybean oil (OIL), or a self-fed tub supplement containing 16.7% (as fed) soapstocks (TUB). Heifers were inseminated and diagnosed for pregnancy following the conclusion of the feeding period. For Exp. 2, IVDMD and volatile fatty acids (VFA) were determined using the proportions of hay and supplement that heifers consumed in Exp.1, yr 1. Treatment differences for Exp. 1 and 2 were evaluated using the single degree of freedom orthogonal contrasts, CRN + OIL vs TUB and OIL vs TUB. Total feed intake tended to be less (P=0.09) for heifers on the TUB treatment in Exp. 1, yr 1; however, hay intake was greater (P=0.02) for heifers on the TUB treatment than for hand-fed heifers. In both years, hand-fed heifers had greater ADG (P≤0.02) and BW gain efficiencies (P≤0.005) than did heifers on the TUB treatment. Average daily gain and gain efficiency were also greater (P≤0.02) for heifers on the OIL treatment than for heifers on the TUB treatment in yr 1 and 2. Overall pregnancy rate was greater (P≤0.03) for heifers on CRN and OIL than for heifers on the TUB treatment (93.2% vs 72.4%) in yr 1. In yr 2, however, overall pregnancy rates were similar (P=0.30) among all treatment groups. In Exp. 2, IVDMD was greater (P=0.002) for hand-fed diets than for the TUB diet. Total VFA were not different (P=0.34) among supplement treatments; however, the acetate:propionate ratio was less (P=0.0001) for the CRN and OIL treatments compared with the TUB treatment. Less than projected intake of TUB supplement and, thus, an overall lower plane of nutrition contributed to decreased growth in both years and poorer reproductive performance in yr 1 for heifers on the TUB treatment compared with heifers that were hand-fed a supplement.