ABSTRACT
Summary Tall fescue (Festuca arundinacea Schreb.) contains several alkaloids. Studies in our laboratory showed that perloline is a principal alkaloid in tall fescue during the summer and that concentration peaks at a time when cattle grazing tall fescue pastures frequently have severely reduced performance (summer syndrome or summer fescue toxicosis). The objectives of the following studies were (1) to determine the influence of perloline on in-vitro fermentation and in-vivo ruminant metabolism and (2) to determine the effects of two tall fescue strains selected for perloline concentration on performance of growing cattle and lactating dairy cows and on interrelationships with environmental temperature. In-vitro fermentation studies showed a concentration-dependent inhibition of cellulose digestion, volatile fatty-acid production, and growth of ruminal cellulolytic bacteria by perloline. Isolated perloline fed to lambs resulted in decreased cellulose digestion and nitrogren retention and increased body temperature. As a result of these studies, two strains of tall fescue were developed, one of which is high (G1-306) and the other low (G1-307) in perloline. A summer grazing study showed that gains of cattle on G1-307 were lower than those on Kentucky 31, Kenhy, or G1-306. In a 2-year study with lactating dairy cows fed Kentucky 31, G1-306, or G1-307 soilage, cows consuming
723G1-307 had the lowest intake and milk production and highest respiration rate. These studies indicated that in the selection for low perloline, compound(s) more toxic and detrimental to animal performance were increased in G1-307. Further studies were conducted with dairy calves in environmental rooms to determine the influence of temperature and time of harvest of G1-307 on potential toxicity. Calves were fed July-cut G1-306 and G1-307 at 10°-13°C, 21°-23°C, and 34°-35°C. Intake and weight change in calves decreased, while body temperature and respiration rate increased on G1-307 at 34°-35°C, resulting in temperature x forage interactions. In a subsequent trial in which silage was fed in environmental rooms at 31°-35°C from May, July, and October harvests, gain and intake were decreased, and body temperature and respiration increased. Selection for low perloline in G1-307 resulted in concomitant increases in N-acetyl and N-formyl loline. Also, G1-307 N-acetyl and N-formyl loline concentrations were related to infestation with Epichloë typhina. Fields were established from seed of untreated and benomyl-treated G1-307 plants. Hay produced from benomyl-treated and untreated G1-307 had N-acetyl plus N-formyl loline concentrations of 115 and 875 μg/g and E. typhina infection estimates of 44% and 95%, respectively. Calves fed hay in 31°-32°C rooms from benomyl-treated G1-307 had higher intakes and lower temperatures and respiration rates than those fed hay produced from untreated G1-307. These studies show that the toxic factor(s) in G1-307 are present from May through October. N-acetyl and N-formyl loline concentrations are related to E. typhina infestation, and toxic effects to the animal are potentiated by elevated environmental temperature.
