Evaluation of the Effects of Grass-Legume Mixtures on Beef Cattle in the Deep South

Abstract

Forage systems in the Deep South, USA, present seasonal limitations that reduce cattle productivity, particularly due to suboptimal summer forage quality and the prevalence of toxic tall fescue (Schedonorus arundinaceus). This dissertation evaluated the integration of leguminous species — alfalfa (Medicago sativa L.) and red clover (Trifolium pratense) — into perennial grass systems to enhance nutritive value, reduce fescue toxicosis, and improve beef cattle performance under regional production constraints. Three studies were conducted to address complementary objectives. First, a digestibility trial using four ruminally fistulated steers assessed microbial responses and nutrient digestibility of conserved forages — bermudagrass (Cynodon dactylon) hay, alfalfa baleage, and alfalfa-bermudagrass baleage — in a completely randomized design. Second, a metabolism trial utilizing a Latin square design examined the effects of increasing red clover hay inclusion (0%, 10%, 20%, and 30%) in ‘KY31’ tall fescue diets on digestive kinetics and fescue toxicosis indicators. Third, a grazing study, utilizing a completely randomized block design on tall fescue pastures, each grazed by stocker steers (267 ± 35.8 kg body weight (BW)), evaluated red clover interseeding and supplementation with a 50:50 soybean hull/corn gluten feed blend at 0.5% and 1.0% of body weight as strategies to maintain growth and mitigate fescue toxicosis. Inclusion of alfalfa in conserved forages significantly increased crude protein (CP) concentration (P < 0.01) and dry matter digestibility (DMD; P < 0.01), with corresponding shifts in microbial communities (P < 0.01). Increasing red clover inclusion in tall fescue diets reduced rumen temperature (P < 0.01), suggesting attenuation of vasoconstriction associated with fescue toxicosis. Clover inclusion also elevated DMD (P < 0.04) and CP concentration (P < 0.01). The grazing trial demonstrated that red clover inclusion improved average daily gain (ADG) relative to non-supplemented controls and was comparable to the 0.5% supplementation group (P < 0.05); gain per hectare followed a similar pattern (P = 0.03). Collectively, these findings highlight the potential benefits of incorporating legumes into forage systems in the southeastern United States. Alfalfa significantly enhanced the nutritional value of conserved forages. At the same time, red clover improved digestibility and reduced the effects of fescue toxicosis. Interseeding legumes into perennial grass pastures offered a low-input, sustainable alternative to feed-based supplementation. These results support the broader adoption of legume-inclusive systems to optimize forage quality and cattle performance across the region.