Effects of sodium bentonite supplements on growth performance of feedlot steers fed direct-cut or wilted grass silage based diets

Forty crossbred steers (initial liveweight: 339 ± 41 kg) were assigned to four equal groups in a 98-d feeding experiment to determine the effects of sodium bentonite supplements (2% of dietary dry matter) on their growth performance. The steers were fed ad libitum a total mixed ration based on direct-cut (two groups) or wilted (two groups) grass silage. One group of steers fed the same silage received the diet without supplementation (control), while the second group received the diet with the sodium bentonite supplement. The steers were housed in pens with electronic headgates in an unheated enclosed feedlot. Feed intake was recorded throughout the experiment and weighing conducted every 2 wk. Apparent digestibilities of dietary components were determined with four steers in a parallel 4 × 4 Latin square experiment. Feed intake, average daily gain (ADG) and the efficiency of feed utilization were higher (P < 0.05) in steers fed wilted than in those fed the poorly fermented direct-cut grass silage. Bentonite increased (P = 0.04) ADG in steers fed the direct-cut grass silage, but in those fed the wilted grass silage ADG was virtually the same for both the control or the bentonite-supplemented steers. Except for energy, digestibility of nutrients was superior (P ≤ 0.05) in the wilted than in the direct-cut grass silage, but there were no effects (P > 0.05) of bentonite. It was concluded that it may be useful to supplement poorly fermented direct-cut silage diets with sodium bentonite, but not those based on wilted grass silage. Key words: Feedlot steers, sodium bentonite, grass silage, growth performance