Energy costs of feeding excess protein from corn-based byproducts to finishing cattle

Authors: JENNINGS, JENNY - Texas Agrilife Research; Meyer, Beverly; GUIROY, PABLE - Cargill, Incorporated; COLE, NOEL - Retired ARS Employee

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2018
Publication Date: 3/6/2018
Citation: Jennings, J.S., Meyer, B.E., Guiroy, P.J., Cole, N.A. 2018. Energy costs of feeding excess protein from corn-based byproducts to finishing cattle. Journal of Animal Science. 96:653-669. doi:10.1093/jas/sky021.
DOI: https://doi.org/10.1093/jas/sky021

Interpretive Summary: Feedlot tends to use byproducts because they tend to be cheaper than grains. However, large quantities of high protein distillers grains and corn gluten feed in beef cattle finishing diets leads to diets that contain greater concentrations of protein than are required by the animal, and may change cattle’s energy balance. Therefore, scientists from Texas A&M AgriLife Research, Cargill, Inc. and ARS (Bushland, TX) conducted two experiments to determine the effects of feeding excess protein on the efficiency of energy utilization by beef calves. We found that the maintenance energy were 4 to 6% greater for the high protein diet. The results suggest that feeding excess protein will increase the maintenance energy requirements of finishing steers, and thus decrease the feed efficiency.

Technical Abstract: The increased use of byproducts in finishing diets leads to diets that contain greater concentrations of CP and MP than required by cattle. The hypothesis was that excess dietary CP and MP would increase maintenance energy requirments due to the energy costs of removing excess N as urea in urine. To evaluate the potential efficiency lost, two experiments were performed to determine the effects of feeding excess CP and MP to calves fed a finishing diet at 1 x maintenance energy intake (Exp. 1) and at 2 x maintenance intake (Exp. 2). In each experiment, 8 crossbred Angus-based steers were assigned to two dietary treatments in a switch back design with three periods. Treatments were steam-flaked corn-based finishing diets with two dietary CP concentrations, 13.8% CP/9.63% MP (CON) or 19.5% CP/14.14% MP (DM basis; ECP) containing corn gluten meal to reflect a diet with excess CP and MP from corn by-products. Each period was 27-d in length with a 19-d dietary adaptation period in outdoor individual pens followed by a 4-d sample collection in one of four open circuit respiration chambers, 2-d fast in outdoor pen, and 2-d fast in one of four respiration chambers. Energy metabolism, diet digestibility, C and nitrogen (N) balance, oxygen consumption, and carbon dioxide, and methane production were measured. At both levels of intake, DE as a proportion of GE tended to be greater (P < 0.06) in ECP than CON steers. Metabolizable energy as a proportion of GE tended to be greater (P = 0.08) in the ECP steers than the CON steers at 2 x maintenance intake. At 1 x and 2 x maintenance intake, urinary N excretion (g/d) was greater (P < 0.01) in the ECP steers than the CON steers. Heat production as a proportion of ME intake at 1 x maintenance tended (P = 0.06) to be greater for CON than ECP (90.0 vs 87.0% for CON and ECP, respectively). At 1 x maintenance intake, fasting heat production (FHP) was similar (P=0.45) for both treatment; whereas, at 2 x maintenance intake, FHP tended to be greater (P = 0.09) by 6% in ECP than CON steers. Maintenance energy requirements estimated from linear and quadratic regression of energy retention on ME intake were 4 to 6% greater for ECP than CON. Results of these studies suggest that feeding excess CP and MP from a protein source that is high in RUP and low in protein quality will increase maintenance energy requirements of finishing steers.