Ryegrass endophyte mixtures for improved animal health : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

In New Zealand, perennial ryegrass (Lolium perenne) with endophyte (Epichloë festucae var. lolii) is a standard ingredient of pastures where insect pests challenge the persistence of the ryegrass. Farmers currently have multiple ryegrass cultivar x endophyte strain combinations from which to choose the best match for their requirements. However, no single cultivar x strain combination provides both the highest insect protection and lowest occurrence of ryegrass staggers and heat stress in animals grazing pasture with endophyte. Furthermore, the current industry protocol for testing the safety of animals grazing a grass x endophyte combination involves exposing the animals to a simulated worst- case scenario and needs reassessment. This research aimed to examine the effects of endophyte diversity in perennial ryegrass on the health and performance of sheep using a modelling approach so that an animal response of any mixture could be predicted as a function of the mixture’s endophyte proportions, thus minimising the need for animal testing in the future. At Barenbrug Plant Breeding Station, Courtenay, Canterbury, eight pasture treatments of Maxsyn perennial ryegrass – seven that varied widely in sown proportions of three endophyte strains – nea3, nea12, and standard endophyte (SE) – and an endophyte-free control (nil), were tested over four experimental runs from February 2020 to December 2021. There were three monocultures (100% of each strain), three binary mixtures (50% of each of two strains) and one ternary mixture (33.3% of each strain) of endophyte based on a simplex centroid design. The eight treatments were randomised in three blocks of 0.156-ha plots. The animal responses of interest were ryegrass staggers, liveweight gain, heat stress, and diet selection of grazing sheep. The first experiment run was a test for ryegrass staggers in February 2020. Endophyte toxicity in late summer is typically near its annual maximum in Canterbury, so the timing of this run created a ‘worst-case scenario’ for ryegrass ...