Endophytes and heat tolerance in lambs grazing perennial ryegrass

Abstract

Endophytes in perennial ryegrass protect their hosts against attack by Argentine stem weevil but cause adverse affects, including heat stress, in grazing animals. Ten lambs were grazed on Grasslands Nui ryegrass without endophyte or with its wildtype or a high ergovaline-producing endophyte (196). Five lambs from the 196 treatment were swapped for 5 on the endophyte-free treatment after 20 days. Rectal temperatures and respiration rates were measured daily; on one day they were measured every 2-4 hours. There was a significant difference in respiration rate and body temperature between lambs grazing endophyte and endophyte free treatments but not between the two endophyte treatments. There was no interaction with ambient temperature within the range 12-30°C. When lambs where transferred from toxic to non-toxic treatments there was no significant decrease in body temperature or respiration rate witbin 14 days. Ergovaline, even at low concentrations, affects thermo-regulation in lambs and is undesirable in perennial ryegrass endophyte associations.