Biochanin a Mitigates Rumen Microbial Changes Associated with a Sub-Acute Ruminal Acidosis Challenge

Ruminal acidosis is a common digestive disorder in cattle that has significant implications on both health and performance. Sub-acute ruminal acidosis (SARA; pH 5.5 – 5.0), specifically, occurs when highly fermentable carbohydrate (e.g., starch) is introduced into the diet disturbing the microbial ecology of the rumen. Resident starch-utilizing bacteria (e.g., Streptococcus bovis, Lactobacilli) rapidly catabolize starch, causing fermentation acids to accumulate in the rumen, reducing 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 starch-utilizing 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). Diets consisted of corn silage and dried distiller’s grains ± cracked corn ad libitum. The study consisted of a 2-wk adaptation, a 1-wk HF period, and an 8-d SARA step-up challenge (d 1 – 4: 40% corn; d 5 – 8: 70% corn). Samples for pH and enumeration were taken on the last day of each period (4 h). Total starch-utilizing bacteria including, Lancefield group D Gram-positive cocci (GPC; S. bovis, enterococci) and lactobacilli, were enumerated. Enumeration data were normalized by log transformation and data were analyzed by repeated measures ANOVA using the MIXED procedure of SAS. During the HF period, pH, and starch-utilizing bacteria were unaffected by MON and BCA treatment (P > 0.05). The SARA challenge increased total starch-utilizing bacteria, including GPC, and Lactobacilli (P < 0.05). Although BCA had minimal effects on starch-utilizing bacteria during the 40% SARA challenge (inhibited Lactobacilli; P < 0.05), BCA decreased total starch-utilizing bacteria, including lactobacilli and GPC, when steers were fed a 70% corn diet (P < 0.05). Similar results were observed with MON (excluding Lactobacilli). The SARA challenge decreased pH during both the 40% (pH 5.48) and 70% (pH 5.28) periods in comparison to HF CON (pH 6.11; P < 0.01). However, BCA and MON were able to partially mitigate the pH decline (BCA 40%: 5.92, 70%: 5.59; MON 40%: 5.76, 70%: 5.43; P < 0.01). These results indicate that BCA may be an effective antibiotic alternative for mitigating SARA in cattle production systems.