Endophyte toxins and performance of spring-calving dairy cows in Northland

An on-farm trial was carried out at Te Hana, in Northland, to measure milk production responses in 2 groups of 16 spring-calving, 3-year-old Holstein-Friesian cows maintained throughout the trial on pastures with or without the ryegrass endophyte toxins, ergovaline and lolitrem B. The trial began in October 1997, with second calving cows balanced for calving date and production worth. Milk volumes of all cows were recorded for 10 consecutive days each month followed by a herd test in which milk volume, protein, fat and lactose contents were determined from milk samples. There were no differences in milk volume or milk solids production in the October and November measurement periods. In December, the group grazing toxin-free (-Ev) pastures produced 24% more milk than the group grazing toxincontaining (+Ev) pastures. These differences increased progressively as the trial proceeded, until terminated in mid-April. Throughout the trial period the -Ev group produced 23% and 19% more milk and milk solids, respectively, than the +Ev group. A rise in levels of the endophyte toxins in ryegrass coincided with the start of differences in milking performance. A toxin-free maize based supplement was fed to both groups during the January to March period to maintain the trial when pasture growth was insufficient. A negative correlation was found between milk production of the +Ev group in January and the prevailing temperature and humidity conditions during the night. Keywords: endophyte toxins, ergovaline, lolitrem B, milk production, Neotyphodium, Northland, ryegrass