PSV-6 Isoflavones in forage diets of steers consuming ‘KY31’ tall fescue with differing inclusion rates of red clover.

Abstract Tall fescue (Schedonorus arundinaceus) toxicosis has an estimated annual economic impact of $2 billion on the U.S. beef industry. Biochanin A, an isoflavone present in legumes such as red clover (Trifolium pratense), exhibits phytoestrogenic properties that mitigate the vasoconstriction associated with fescue toxicosis. The objective of this study was to quantify isoflavone concentrations in red clover and evaluate their potential correlation with digestibility in steers consuming ‘KY31’ tall fescue with varying levels of red clover inclusion. A metabolism study was conducted using a 4 × 4 Latin square design, with individual steer (average 493.4 kg BW ± 21.0 kg) as the row factor and period as the column factor. The four dietary treatments included: (1) 100% tall fescue hay (Control), (2) 90% tall fescue hay + 10% red clover hay, (3) 80% tall fescue hay + 20% red clover hay, and (4) 70% tall fescue hay + 30% red clover hay. Isoflavone concentrations in the forage were analyzed using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to quantify biochanin A, formononetin, genistein, and daidzein. The total aglycone concentration in the diet increased with red clover inclusion compared to the control (P < 0.001). Total isoflavone content also differed significantly between the 10% and 30% red clover inclusion rates (P = 0.029). Similar trends were observed for formononetin (P = 0.025), genistein (P = 0.024), and daidzein (P = 0.027). Biochanin A concentrations differed significantly between red clover treatments and the control (P < 0.001); however, no significant differences were detected among the red clover treatments. A regression analysis was conducted to evaluate the relationship between crude protein digestibility (CPD) and isoflavone intake. The linear regression model yielded an R² value of 0.52 for total isoflavones, indicating a moderate correlation with CPD. Similar correlations were observed for biochanin A (R² = 0.50), formononetin (R² = 0.52), genistein (R² = 0.50), and daidzein (R² = 0.52). These findings are indicative of potential fescue toxicosis mitigation and greater forage intake potential and digestibility with the inclusion of red clover in tall fescue diets.