Effect of biochanin A on the rumen microbial community of Holstein steers consuming a high fiber diet and subjected to a subacute acidosis challenge.

Subacute rumen acidosis (SARA) occurs when highly fermentable carbohydrates are introduced into the diet, decreasing pH and disturbing the microbial ecology of the rumen. Rumen amylolytic bacteria rapidly catabolize starch, fermentation acids accumulate in the rumen and reduce environmental pH. Historically, antibiotics (e.g., monensin, MON) have been used in the prevention and treatment of SARA. Biochanin A (BCA), an isoflavone produced by red clover (Trifolium pratense), mitigates changes associated with starch fermentation ex vivo. The objective of the study was to determine the effect of BCA on amylolytic bacteria and rumen pH during a SARA challenge. Twelve rumen fistulated steers were assigned to 1 of 4 treatments: HF CON (high fiber control), SARA CON, MON (200 mg d-1), or BCA (6 g d-1). The basal diet consisted of corn silage and dried distiller's grains ad libitum. The study consisted of a 2-wk adaptation, a 1-wk HF period, and an 8-d SARA challenge (d 1-4: 40% corn; d 5-8: 70% cracked corn). Samples for pH and enumeration were taken on the last day of each period (4 h). Amylolytic, cellulolytic, and amino acid/peptide-fermenting bacteria (APB) were enumerated. Enumeration data were normalized by log transformation and data were analyzed by repeated measures ANOVA using the MIXED procedure of SAS. The SARA challenge increased total amylolytics and APB, but decreased pH, cellulolytics, and in situ DMD of hay (P < 0.05). BCA treatment counteracted the pH, microbiological, and fermentative changes associated with SARA challenge (P < 0.05). Similar results were also observed with MON (P < 0.05). These results indicate that BCA may be an effective alternative to antibiotics for mitigating SARA in cattle production systems.

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

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 microbiota, 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.

Effects of grazing different ergovaline concentrations on vasoactivity of bovine lateral saphenous vein.

Previous research has demonstrated that exposure to ergot alkaloids reduces vasoactivity of serotonin (5HT) receptors. Chemical suppression of tall fescue seedhead production is a tool to reduce the level of exposure to ergot alkaloids by a grazing animal. Therefore, the objective was to evaluate contractility of lateral saphenous veins biopsied from mixed breed steers following a 87- to 101-d grazing period on 3-ha pastures of bermudagrass (Cynodon dactylon; n = 5 steers; BW = 340 ± 9 kg), or toxic endophyte-infected tall fescue (Lolium arundinaceum) that was not treated (n = 5 steers; BW = 300 ± 6; 0.56 ppm ergovaline) or was treated (n = 5 steers; BW = 294 ± 9 kg; 0.24 ppm ergovaline) with herbicide containing aminopyralid and metsulfuron-methyl. To evaluate contractility, biopsied veins were mounted in a multimyograph and exposed to increasing concentrations of a tall fescue seed extract (EXT; ergovaline source) and 5HT1B (CP 93129), 5HT1D (L-694,247), and 5HT2A (TCB2) agonists. All contractility data were normalized to a maximal response of 1 × 10-4 M norepinephrine and were analyzed as a split plot treatment design using SAS for effects of pasture treatment, agonist concentration, and the interaction. There was no contractile response to any concentration of 5HT1B agonist in any of the pasture treatments. There were pasture × concentration interactions for contractile responses to 5HT2A agonist (P < 0.01) and EXT (P < 0.01). For both EXT and TCB2, veins from bermudagrass steers were more vasoactive to the higher concentrations of these compounds (P < 0.05), and there were no differences between veins collected from the unsuppressed or seedhead-suppressed treatments (P = 0.66). There was also a pasture × concentration interaction for the contractile responses to 5HT1D agonist (P < 0.01). However, these responses were not sigmoidal and reached a zenith at 5 × 10-7 and 1 × 10-6 M. At these concentrations, the response was greatest for veins from the unsuppressed treatment (P < 0.05) and did not differ between veins from suppressed and bermudagrass treatments (P = 0.41). Although reduced levels of ergovaline in seedhead-suppressed pastures did not alter vasoactivity of 5HT2A or 5HT1B receptors in the lateral saphenous vein, elevated vasoactivity of 5HT1D in veins from unsuppressed tall fescue pasture treatment suggests that lower ergovaline levels in seedhead-suppressed pastures can influence the vascular effects of ergot alkaloids.