Mitigating enteric methane production and nitrogen excretion from forage-fed ruminants

Abstract

Sustainability of animal agriculture requires efficient use of energy and nitrogen (N) by ruminants fed high forage diets. Therefore, there is a need to decrease enteric methane (CH4) emissions and prevent excessive N release from beef cattle into the environment. Thus, this thesis focused on quantification and mitigation of CH4 emissions and N excretion from beef cattle fed corn silage (CS) and alfalfa based diets. In western Canada, production of corn with short growing season (≤ 2600 corn heat unit, CHU) for silage is increasing due to its potentially high nutritive value, while alfalfa is a forage of choice because of its high crude protein (CP) and total digestible nutrient contents. The objective of the first study was to determine the variability in nutrient content, degradability of dry matter (DM) and neutral detergent fiber (NDF), and CH4 production of short-season whole plant corn hybrids grown and adapted in two locations of Alberta (AB; central or southern) and harvested before or after a light frost (-1.5ºC). Harvesting southern AB hybrids after frost did not affect starch content but NDF degradability increased. Harvesting central AB hybrids after frost increased starch content and reduced CH4 emissions, but had limited effects on DM and NDF degradabilities. The objective of the second study was to determine the long term effects of hydrolyzable tannin (HT) alone and in combination with condensed tannin (CT) at low [0.25%; chestnut (CN) or CN and quebracho mix (CNQ)] and high (1.5%; CN or CNQ) doses on N use and CH4 emissions in growing beef steers fed an alfalfa silage-based diet. Tannin, irrespective of type or dose, decreased ruminal ammonia-N concentration. Tannin type and dose did not affect daily CH4 production but 1.5% CNQ tended to decrease CH4 yield (CH4 per kilogram of DM intake) compared with control. The objective of the third experiment was to determine the effects of different forms of HT, including 2% CN, 1.5% tannic acid (TA), or a sub-unit (gallic acid, GA)] on CH4 production, N utilization, and diet digestibility in beef cattle fed a diet mainly containing alfalfa silage. Both TA and CN decreased CP digestibility and shifted N excretion from urine to feces, while GA decreased CH4 production and decreased the proportion of urea N in urinary N. In conclusion, for short-season CS, it is possible to select hybrids adapted for their use in central AB based on their CHU rating to reduce the carbon footprint of animal agriculture without affecting animal performance. Also for alfalfa silage based diets supplemented with tannin, the simplest unit or metabolite of the tannin has the potential to lower CH4 emissions and N excretion from beef cattle.