Influence of Fish Meal and Supplemental Fat on Performance of Finishing Steers Exposed to Moderate or High Ambient Temperatures

Source: T. W. White, L. D. Bunting, L. S. Sticker, F. G. Hembry, and A. M. Saxton
Ninety-six Hereford x Angus steers E initial BW = 295 kgl were used in two growth experiments conducted at moderate and high ambient temperatures (AT), 48 steers per AT. Within each AT, calves were assigned to six dietary treatments consisting of a basal diet (approximately 60% corn and 20% grass hay) supplemented with either 0, 2.5, or 5% fat and with either soybean meal (SBM1 or Menhaden fish meal (FMI included at levels such that a ratio of 16.3 kcal of NEm per kilogram of CP was maintained. Blood and ruminal fluid were collected 40 d before slaughter. During the final 28 d of the moderate AT experiment, apparent digestibility of dietary components was measured in four individually fed steers from each dietary treatment. Steer ADG was not affected by fat, and DMI and efficiency of gain were not affected (P > .lo1 by treatment. Average daily gain was lower for steers fed FM than for those fed SBM at moderate AT but higher at high AT (CP source x AT interaction; P .05). Ruminal ratio of acetate to propionate declined linearly with increasing fat at moderate AT but was not affected by fat at high AT (fat x AT interaction trend; P = .08). Plasma urea N concentration increased linearly (P < .051 with increasing fat and was higher (P .051 in steers kept at high than in those kept at moderate AT. Although apparent digestibility was not altered in steers fed FM, DM and NDF (P < .051 and ADF P = .07) digestibility decreased with increasing fat in steers fed SBM (CP source x fat interaction). Even though there was little benefit from feeding fat, FM increased gain of steers, but only when fed at high AT.