| dc.description.abstract | End products of ruminal fermentation differ based on availability of structural (fiber) and nonstructural (starch) carbohydrates. Two experiments were conducted to evaluate the effect of dietary components (starch and fiber) on energy metabolism, nutrient digestibility, growing and finishing phase performance, and carcass composition. In an initial metabolism experiment, 10 yearling steers were used in a 5 × 5 replicated Latin square. Experimental diets were formulated to contain an increasing proportion of concentrate with a concomitant decrease in forage resulting in diets of disparate forage-to-concentrate (F:C) ratios. Fecal and urinary energy loss decreased (P < 0.04) while methane energy loss responded quadratically (P < 0.01), increasing and then decreasing, as the F:C decreased. As a result, the efficiency of the conversion of digestible energy to metabolizable energy increased quadratically (P < 0.01) as the F:C decreased. In a follow up feedlot experiment, light-weight (initial BW = 175.59 ± 1.3 kg) steer calves (n = 970) were fed diets of disparate starch content for a 119 d growing period and then finished on a common diet. Growing diets were formulated to contain 1 of 3 levels of starch on a dry matter basis. The concentration of starch in the growing diet did not affect ADG or DMI during the growing (P ≥ 0.15) or finishing period. (P ≥ 0.20) At the end of the growing period, 12th rib fat linearly decreased (P = 0.04) as starch level increased while marbling score was not affected (P = 0.57). Final HCW and 12th rib fat were not different (P ≥ 0.66).
An evaluation of cattle source and season of arrival on feedlot on performance and animal health outcomes was also performed. A commercial feedlot database of 230 lots representing 15,659 cattle was used. The cattle were classified as originating from Mexico or the United States and date of arrival to the feedlot was used to assign season of arrival. Average daily gain exclusive of deads was greater in native sourced compared to Mexican sourced cattle for all seasons of arrival (P = 0.01). Total death loss was greater in native compared to Mexican origin cattle in the Summer and Fall (P < 0.01), but were similar among cattle country of origin during the Spring and Winter (P ≥ 0.28). | en |
