Abstract A large portion of U.S. feedlot cattle are produced in the High Plains region. The Ogallala Aquifer lies beneath much of the High Plains region, and provides water for livestock production and crop irrigation. Irrigation within the region has led to significant decreases in aquifer levels, underscoring the need for alternative production practices that consume less water. Planting sorghum in place of corn is one such alternative. Sorghum generally has been regarded as being nutritionally inferior to corn, owing in part to the extensive intermingling of starch and protein within the endosperm, which can interfere with digestion. This study aimed to evaluate exogenous enzymes as a means of improving sorghum digestion through disruption of the starch-protein matrix. A blend of exogenous carbohydrase and protease enzymes (Pyramid PowerGrow Ruminant; Scott City, KS) was incorporated into finishing diets to evaluate impact on nutrient digestibility, feedlot performance, and carcass characteristics of steers fed sorghum-based finishing diets. Yearling steers (n = 280; 441.74 kg ± 15.19 kg initial body weight) were randomly assigned to one of 36 feedlot pens with 7 or 8 steers per pen. Pens were randomly assigned to a dietary treatment within a block (18 blocks, based on order of processing). Treatments (control and enzyme) were randomly assigned to pens within each block. Cattle were vaccinated against viral (Pyramid 5 + Presponse SQ; Boehringer Ingelheim, Duluth, GA) and clostridial pathogens (Bovilis Covexin 8; Merck Animal Health, Rahway, NJ); treated with an injectable antiparasitic internal (Cydectin; Elanco Animal Health, Indianapolis, IN); administered an prophylactic dose of injectable antibiotic (Draxxin, Zoetis Animal Health, Florham Park, NJ); implanted with a long-acting estradiol/trenbolone acetate implant (Synovex One Feedlot; Zoetis Animal Health) and administered an oral dose of Megasphaera elsdenii (Lactipro; Axiota Animal Health; Fort Collins, CO). Steers were then transitioned to finishing diets using three step-up diets, each fed for 7 days. Cattle were fed once daily in the morning, ad libitum, and daily feed bunk scores were taken to determine feed allocation. On day 67, fresh fecal pats were collected from pen surfaces and analyzed for concentrations of protein, starch, neutral detergent fiber, ash, organic matter, and acid detergent insoluble ash. On day 148, steers were harvested at a commercial abattoir and carcass data were collected following 96 hours of refrigeration. Response variables include nutrient digestion; DM intake; average daily gain; feed efficiency; hot carcass weight; USDA yield and quality grades, and incidence of abscessed livers. Data were analyzed as mixed models with diet as the fixed effect, pen as the experimental unit, and block as the random effect. Modest but non-significant differences (P 0.10) were observed between treatment for nutrient digestibility, feedlot performance, and carcass characteristics.
Kiselewski et al. (Wed,) studied this question.