Ryegrass endophyte and cattle growth in Northland

Perennial ryegrass pastures infected with or free of the endophyte (Neotyphodium lolii) were compared for growth and health of young grazing cattle. Heat stress, indicated by excessive salivation, was observed on several occasions among cattle grazing endophyte-infected ryegrass, but there were no differences between groups in body temperature. Liveweight gains were generally slow and inconsistent. During one period of rapid liveweight gain in March-April 1997, heifers grazing endophytefree pastures gained 7 kg more than heifers grazing infected pasture. Taking data from three four-week grazing periods in summer and autumn, liveweight change of cattle grazing endophyte-free pastures showed a consistent advantage over cattle grazing endophyte-infected ryegrass. Significant differences in serum prolactin were recorded on two occasions, and on one day in February 1998 weaner bulls grazing infected ryegrass were breathing significantly faster than their counterparts on endophyte-free pasture. These results can be compared with previous reports that endophyte status of ryegrass pastures has little effect on grazing cattle, and contrast with the published literature for tall fescue. Keywords: liveweight gain, Neotyphodium lolii, perennial ryegrass, ryegrass endophyte