Effect of Ambient and Black-Globe Temperature on Plasma Prolactin Levels in Ewes Grazing Endophyte-Free and Endophyte Infected Ryegrass

Reduced plasma prolactin levels are one of the more consistent responses in animals grazing ryegrass and tall fescue with endophyte. The ergopeptine alkaloid, ergovaline is believed to be responsible. A selected endophyte, AR6 (formerly 187 BB), produces higher levels of ergovaline than its wild-type counterpart (Davies et al., 1993). Prolactin levels in healthy sheep tend to increase as photoperiod, ambient temperature and consequent heat load on the animal increase. However ambient temperature takes no account of the heat increment due to solar radiation or relative humidity.