Effect of tannin-containing hays on enteric methane emissions and nitrogen partitioning in beef cattle

Authors: STEWART, ELIZABETH - Utah State University; BEAUCHEMIN, KAREN - Agri Food - Canada; DAI, XIN - Utah State University; Christensen, Rachael; MACADAM, JENNIFER - Utah State University; VILLALBA, JUAN - Utah State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2019
Publication Date: 7/12/2019
Citation: Stewart, E., Beauchemin, K., Dai, X., Christensen, R., MacAdam, J.W., Villalba, J.J. 2019. Effect of tannin-containing hays on enteric methane emissions and nitrogen partitioning in beef cattle. Journal of Animal Science. 97:3286-3299. https://doi.org/10.1093/jas/skz206.
DOI: https://doi.org/10.1093/jas/skz206

Interpretive Summary: Tannins have been shown to improve nitrogen use efficiency and reduce methane emissions in growing cattle. They are contained in several commonly used forages, but it is not known if they are effective in forages harvested as hay, and whether a reduction in methane can occur in growing cattle or dry beef cows fed tannin-containing hay. Therefore, a study was conducted to test whether tannins in hay are as effective as other reported forms of feeding tannins on reduction of methane emissions and N excretion routes. Mature beef cows and heifers were individually fed diets that consisted only of a single hay that either contained tannins (sanfoin, birdsfoot trefoil, small burnet) or did not contain tannins (cicer milkvetch, alfalfa, meadow brome grass). Cows were fed for 14 d and then measurements of intake, full collection of urine and feces, blood sampling, and enteric methane emissions using a tracer gas technique were conducted for 5 d. Cows and heifers that consumed tannin-containing hays excreted less urea in their urine. Enteric methane as estimated using the tracer gas technique was greatest for meadow brome grass, which does not contain tannin, and least for small burnet which had the highest concentration of tannin (4.5% hydrolyzable tannin). Cicer milkvetch showed intermediate results, similar to those of tannin-containing legumes, suggesting it has secondary compound properties similar to tannins. The results affirmed that tannin-containing hays have the potential to reduce environmental excretion of urinary urea, increase N retention and reduce enteric methane.

Technical Abstract: The objective of this study was to determine whether feeding tannin-containing hays to heifers and mature beef cows influences enteric methane (CH4) emissions and nitrogen (N) excretion relative to feeding traditional legume and grass hays. Fifteen mature beef cows (Exp. 1) and 9 yearling heifers (Exp. 2) were each randomly assigned to treatment groups in an incomplete bock design with 2 periods and 6 types of hays with 3 hays fed each period (n = 5 cows and 3 heifers per treatment). Groups were fed tannin-containing [birdsfoot trefoil (BFT), sainfoin (SAN), small burnet (SML)], or non-tannin containing [alfalfa (ALF), cicer milkvetch (CMV), meadow bromegrass (MB)] hays. Each period consisted of 14 d of adjustment followed by 5 d of sample collection. Nine cows and 9 heifers were selected for the measurement of enteric CH4 emissions (sulfur hexafluoride tracer gas technique), and excretion of feces and urine, while dry matter intake (DMI) was measured for all animals. The concentration of condensed tannins in SAN and BFT was 2.5 ± 0.50% and 0.6 ± 0.09% of dry matter (DM), respectively, while SML contained hydrolyzable tannins (4.5 ± 0.55% of DM). Cows and heifers fed tannin-containing hays excreted less urinary urea N (g/d; P < 0.001) and showed lower concentrations of blood urea N (mg/dL; P < 0.001) than animals fed ALF or CMV, indicating that tannins led to a shift in route of N excretion from urine to feces. Additionally, cows fed either BFT or CMV showed the greatest percentage of retained N (P < 0.001). Enteric CH4 yield (g/kg of DMI) from heifers (P = 0.089) was greatest for MB, while daily CH4 production (g/d) from heifers (P = 0.054) was least for SML. However, digestibility of crude protein was reduced for cows (P < 0.001) and heifers (P < 0.001) consuming SML. The results suggest that tannin-containing hays have the potential to reduce urinary urea N excretion, increase N retention, and reduce enteric CH4 emissions from beef cattle. The non-bloating tannin-free legume CMV, may also reduce environmental impacts relative to ALF and MB hays by reducing N excretion in urine and increasing N retention.