Summer Fescue Toxicosis in Lactating Dairy Cows and Sheep Fed Experimental Strains of Ryegrass-Tall Fescue Hybrids

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Abstract
Two experimental strains of tall fescue derived from ryegrass-tall fescue hybrids and selected for either high or low perloline content were compared with Kentucky 31 tall fescue. For 2 years, the grasses were fed as soilage to lactating Holstein cows during July and August. In the first year, digestion trials were conducted with lactating cows fed the soilage and with sheep fed hay harvested from the same fields. Summer toxicosis symptoms were evident for the cows receiving the Gl-307 (low perloline) fescue. Average feed intake (kg/day) and milk production (kg/day) for 2 years were, respectively, 5.5 and 10.8 for the Gl-307 (low perloline selection, 8.7 and 17.3 for the Gl-306 (high perloline) and 9.0 and 16.7 for Kentucky 31 fescue treatment. Differences between Gl-307 and the other fescues were significant (P<.01). In addition, cows that received the Gl-307 selection had elevated rectal temperatures, increased respiration rates and a decrease in body weight. The poor performance of the cows fed the toxic fescue was not related to the digestibility of the forage. In the selection of a fescue for low perloline content, another anti-quantity factor(s) was evidently increased which resulted in rather severe summer toxicosis. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.

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