Forage Composition and Growth and Physiological Characteristics of Cattle Grazing Several Varieties of Tall Fescue During Summer Conditions

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Abstract
This study measured differences in plant chemical characteristics of two varieties and two experimental lines of tall fescue (Festuca arundinacea Shreb.) and the effect of these grasses on growth, physiological changes and health of grazing steers. Twenty-four 49-ha paddocks were seeded to either variety Kentucky 31 (KY 31), variety Kenhy, line G1-306 or line G1-307 of tall fescue. The experimental lines, G1-306 and G1-307, were selected to represent grasses with a high (over 500 mg/g DM) or low (less than 500 mg/g DM) perloline concentration. In addition, G1-307 contained a high level of loline alkaloids (.17%) and was infected with endophyte, Epichloe typhina (100%). Acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), total non-structural carbohydrates (TNC) and amino acid composition were similar among all varieties and lines. During 3 consecutive years, gains of steers grazing G1-307 were lower (1976, P<.01, .32 vs .61 kg/d; 1977, P<.05, .22 vs .41 kg/d; 1978, P<.05, .38 vs .46 kg/d) than the average of steers grazing the other pastures. In addition, steers grazing G1-307 had the lowest body condition scores and lowest hair coat scores. Only steers grazing G1-307 showed signs of elevated respiration rate, increased heart rate and excessive salivation, particularly during high summer temperatures. During the daylight hours, animals in this group were under shades or standing in any available water, which suggested a decreased ability to dissipate body heat. Results indicate that G1-307 contains a factor(s) that causes steers to exhibit visual signs of toxicity when the grass is consumed during periods of environmental heat stress. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science

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