Growth, persistence, and alkaloid levels of endophyte-infected and endophyte-free ryegrass pastures grazed by dairy cows in northern New Zealand

A farm-scale trial was conducted over three years at the Dairying Research Corporation, Hamilton, New Zealand to compare the growth and persistence of endophyte-infected and endophyte-free perennial ryegrass (Lolium perenne) pastures established with or without white clover (Trifolium repens), when rotationally grazed by dairy cows. Endophyte-free ryegrass areas were also undersown with endophyte-free seed in March and April of the second and thi rd years, respectively. Average total herbage yields were similar for all t reatments in each of the three years, ranging from 12.8 to 13.9 t DM ha(-1) . Pasture growth rates in all treatments were lowest in the first summer/au tumn after drilling, averaging 17 kg DM ha(-1) day(-1) for 90 days, coincid ing with the highest herbage concentrations of lolitrem B (2.37 to 3.04 mu g g(-1) DM) in the high-endophyte ryegrass. Ergovaline herbage concentratio ns rarely exceeded 1 mu g g(-1) DM and were highest (1.6 mu g g(-1) DM) in high-endophyte ryegrass pastures at the start of the third summer (December 1995), probably because of a high seed-head content (30% of DM). Contamina tion of endophyte-free ryegrass areas with volunteer endophyte-infected rye grass was rapid, averaging 26, 41, and 50% of plants after the first, secon d, and third years from sowing, respectively. Further research is required to identify sources of this contamination and management strategies to main tain purity of endophyte-free ryegrass or ryegrass containing novel endophy tes.