Isoflavone supplementation, via red clover hay, alters the rumen microbial community and promotes weight gain of steers grazing mixed grass pastures

Authors: Harlow, Brittany; Flythe, Michael; Kagan, Isabelle; GOODMAN, JACK - University Of Kentucky; Klotz, James; Aiken, Glen

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2020
Publication Date: 3/13/2020
Citation: Harlow, B.E., Flythe, M.D., Kagan, I., Goodman, J.P., Klotz, J.L., Aiken, G.E. 2020. Isoflavone supplementation, via red clover hay, alters the rumen microbial community and promotes weight gain of steers grazing mixed grass pastures. PLoS One. 15(3): e0229200. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0229200.
DOI: https://doi.org/10.1371/journal.pone.0229200

Interpretive Summary: Dietary protein supplementation is often used to improve the performance of grazing cattle. For this reason, the forage legume red clover (Trifolium pretense) can be interseeded in pastures to increase protein availability and overall digestibility of the diet. In addition to red clover’s nutritional benefits, the legume also produces isoflavones (e.g. biochanin A) that are believed to improve protein utilization by inhibiting hyper-ammonia-producing bacteria that waste protein in the rumen and promote fiber-utilization. Consequently, supplementation with purified biochanin A (representative of a 30% red clover diet) to grazing steers has been shown to improve average daily gain. Purified biochanin A is prohibitively expensive for supplementation in grazing systems, but whole red clover supplementation could be a viable alternative to achieve the same microbiological and performance benefits. The following experiment was initiated to determine the microbiological and animal growth benefits of two levels of supplemental red clover hay representing a 30% and 15% red clover diet on grazing steers. Over two spring grazing seasons, Angus cross steers were supplemented with two levels of red clover hay balanced for protein with dried distiller’s grain (DDG) on endophyte-free cool season grass pasture. A rumen-fistulated Holstein steer was included in each pasture as a microbiological tester. Rumen contents were sampled from testers to determine both the number and fermentation of different bacterial functional groups (protein, fiber, sugar-degrading bacteria). The hypotheses were that red clover hay supplementation would 1) increase average daily gain in a dose-dependent manner; 2) suppress HAB and protein fermentation; and 3) promote fiber fermentation. All supplementation strategies (DDG ± red clover hay) increased steer growth in comparison to pasture-only controls with the 15% red clover hay treatment having the greatest benefit. Similarly, the 15% red clover hay supplemented steers had the greatest inhibition of HAB and promotion of fiber fermentation in the rumen. In conclusion, lower levels of red clover supplementation may be optimal for maximizing animal performance in grazing steers. The impact of this research is that red clover could be interseeded in pastures or utilized as a supplemental protein source to improve grazing cattle performance and overall rumen function at 15% of the total diet or potentially at even lower levels.

Technical Abstract: Biochanin A, an isoflavone present in the pasture legume red clover (Trifloium pratense L.), alters fermentation in the rumen of cattle and other ruminants. Biochanin A inhibits hyper-ammonia-producing bacteria and promotes cellulolytic bacteria and fiber catalysis in vitro and ex vivo. Consequently, biochanin A supplementation improves weight gain in grazing steers. Red clover contains biologically active isoflavones that may act synergistically. Therefore, the objective was to evaluate the effect of two levels of red clover hay on growth performance and the microbial community in growing steers grazing mixed grass pastures. A grazing experiment was conducted over 2 early growing seasons (2016 and 2017) with 36 cross-bred steers and twelve rumen-fistulated, growing Holstein steers for evaluation of average daily gain and rumen microflora, respectively. Steers were blocked by body weight and assigned to pastures with one of four treatments: 1) pasture only, 2) pasture + dry distillers’ grains (DDG), 3) pasture + DDG + low level of red clover hay (~15% red clover diet), or 4) pasture + DDG + high level of red clover hay (~30% red clover diet). DDG were added to treatments to meet protein requirements and to balance total protein supplementation between treatments. All supplementation strategies (DDG ± red clover hay) increased average daily gains in comparison to pasture-only controls (P < 0.05), with a low level of red clover supplementation being the most effective (+0.17 kg d-1 > DDG only controls; P < 0.05). Similarly, hyper-ammonia-producing bacteria inhibition (10 – 100-fold; P < 0.05), fiber catalysis (+10 – 25%; P < 0.05) and short chain fatty acid concentrations were greatest with the low red clover supplement (+~25%; P < 0.05). These results provide evidence that lower levels or red clover supplementation may be optimal for maximizing overall microbial community function and animal performance in grazing steers.