Cattle are a significant source of agricultural greenhouse gas (GHG) emissions; with enteric methane being the major GHG produced under most management systems. Decreasing enteric methane production of grazing cattle presents the greatest opportunity to reduce beef cattle GHG emissions because 1) enteric methane release is greater on forage-based than concentrate-based diets; 2) cattle fed high-fiber diets have lower rates of gain and thus require more time to reach market weight than cattle fed concentrate-based diets and 3) the vast majority of feed used to produce beef from conception to plate is forage-based. Throughout the world cattle frequently graze low-quality forages that are deficient in protein. While research has studied the effects of protein supplementation of low-quality forages on weight gain, feed intake and digestibility, effects on GHG emissions are lacking. Therefore, the objective of this study was to identify the effects of protein supplementation to low-quality forage diets on GHG emissions.
Twenty-three British-cross steers were utilized in a three-period crossover design. Steers were provided ad libitum access to a low quality grass hay (4.9% crude protein) and assigned to one of three supplemental treatments: 1) no supplement (control), 2) cottonseed meal (CSM 0.29% of body weight), or ) dried distillers grain (DDGS 0.41% of body weight). Supplemental protein intake was similar for the CSM and DDGS treatments. Enteric CH4 and metabolic CO2 emissions were measured using a GreenFeed system (C-Lock Inc., Rapid City, SD). Steers were offered supplement at 0800h each day in Calan headgates and hay was delivered after steers had consumed the supplement. Data were analyzed using a mixed model (SAS,2013).
Supplementation with CSM or DDGS increased hay intake (P < 0.01) by an average of 53% compared to control. Supplementation also increased (P < 0.01) total CO2 and total CH4 emissions compared to control, but no difference was noted between CSM and DDGS. The increases in total production of CO2 and CH4 are attributed to the large increase in hay intake. However, supplementing with CSM or DDGS decreased (P < 0.05) methane loss as a proportion of gross energy (GE) intake, compared to control steers. Steers supplemented with DDGS tended (P < 0.10) to have a lower methane loss as a percentage of GE intake (Ym) than steers supplemented with CSM; probably because of the higher fat intake in cattle fed the DDGS. Collectively, these data suggest that protein supplementation decreases the carbon footprint of beef cattle by decreasing methane emissions per unit of energy intake and per unit of production.
Additional studies will attempt to further define the effects of supplement composition and intake level on GHG emissions.
N. Andy Cole, Supervisory Research Animal Scientist and Lab Director, USDA-ARS-Conservation & Production Research Laboratory, Bushland, TX Andy.firstname.lastname@example.org
Adam Shreck, ORISE Fellow sponsored by USDA-ARS-CPRL, Bushland, TX;
Jenny Jennings, Animal Nutritionist, Texas A&M AgriLife Research; Amarillo;
Richard Todd, Research Soil Scientist, USDA-ARS-CPRL, Bushland, TX.
For more information contact Andy Cole, 806-356-5748
This research was partially funded by a USDA-NIFA-CAP Grant titled “Resilience and vulnerability of beef cattle production in the Southern Great Plains under changing climate, land use and markets”.
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