Location: Forage and Livestock Production ResearchTitle: Effect of frame size on estimated dry matter intake, and enteric methane (CH4) and carbon dioxide (CO2) production in lactating angus cows grazing native tall-grass prairie in central Oklahoma, USA I: Summer season Author
|Neel, James - Jim|
|Turner, Kenneth - Ken|
|Coleman, Samuel - Retired Ars Employee|
|Brown, Michael - Retired Ars Employee|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2018
Publication Date: N/A
Interpretive Summary: Methane gas has been suggested as a major contributor to global warming. Within the USA, all agriculture (livestock, agricultural soils, and rice production) contributed about 9% to total greenhouse gas emissions in 2015. In ruminants, enteric methane (CH4) is a necessary byproduct of fermentation within the symbiotic relationship between rumen microbes and the ruminant host. Rumen microbial fermentation provides the animal with both maintenance and production energy. The continual flow of microbes out of the rumen into the lower tract also provides a source of high quality protein to the animal. To ensure the availability of energy and protein, the host provides the microbial population with a safe and controlled anaerobic environment, a continual source of fermentation substrate, and the removal of fermentation end-products. The most efficient cow size for use in grazing systems has long been debated. It is often suggested that the primary U.S. beef production model has led to the selection of an animal type which is efficient for beef production within a feedlot finishing system, but has resulted in sacrificed production efficiency within the cow-calf sector due to increased cow size. Since increased rumen CH4 production is inversely related to energy availability and production efficiency for the host animal, the goal of our research was to determine the relationship between cow frame size, enteric methane production, and cow productivity for lactating Angus cows grazing native tall-grass prairie during the summer season in central Oklahoma, USA. Large-frame cows weighed 128 kg more than medium-framed cows, they produced a 39 kg heavier calf at weaning, and there was no difference in estimated dry matter intake between cow types. The results indicate that large-frame cows: 1) Are more efficient at converting native prairie into saleable product; 2) Large-frame have superior energy use efficiency; and 3) Have improved rumen fermentation efficiency. There was no difference in amount of cow CH4 or carbon dioxide produced per kg of calf. Further research is needed to evaluate the impact of cow frame type on enteric gas production during other seasons of the year.
Technical Abstract: Methane (CH4) gas has been suggested as a major contributor to global warming. In the USA, all agriculture (livestock, agricultural soils, and rice production) contributed about 9% to total greenhouse gas (GHG) emissions in 2015 (www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions). In ruminants, enteric methane is a necessary byproduct of fermentation within the symbiotic relationship between rumen microbes and the ruminant host. Since increased rumen CH4 production is inversely related to energy availability and production efficiency for the host animal, the goal of our research was to determine the relationship between cow frame size (FS), enteric methane production, and cow productivity. Twenty eight lactating Angus cows (BW: 545 ± 49 kg) of either medium FS (n=14) or large FS (n=14) were utilized in this study. Each cow type was bred to bulls of similar type. All animals grazed simultaneously within a native tall-grass prairie pasture in central Oklahoma, USA during the summer season (SS). Throughout the study period, daily estimates of individual animal enteric CH4 and carbon dioxide production were taken via a commercially available breath analyzer, with two GreenFeed (C-Lock, Inc., Rapid City, SD) systems deployed in the pasture. Medium-frame cows had a lower (P<0.001) body weight (BW) and frame score than large-frame cows (481 versus 609 kg, and 4.6 versus 6.8, respectively). Estimated dry matter intake (DMI) did not differ between cow types. Large-frame cows required less (P<0.05) herbage DM per unit of 205 day weaning weight (WW) than medium (8.4 versus 9.4 kg DM kg-1 WW). Large-frame cows produced greater (P<0.001) daily CH4 (315 versus 270 g d-1) compared to medium-frame cows, and greater (P<0.01) CH4 per unit of DMI (13.6 versus 12.2 g-1 kg). When expressed as CH4 per unit of cow BW for the total SS DMI, large frame cows produced less (P<0.05) CH4 (48.3 versus 52.6 g-1 kg BW). There was no difference in SS enteric CH4 per unit of adjusted WW (0.11 kg kg-1). Results indicate that large-frame cows may have improved rumen fermentation efficiency, and are more efficient at converting native prairie into saleable product. Further research is needed to evaluate the impact of cow frame type on enteric gas production during other seasons of the year.