Effects of endophyte infection of perennial ryegrass on somatic cell counts, mammary inflammation, and milk protein composition in grazing dairy cattle

Concentrations of selected milk and blood components were determined for da iry cows grazing perennial ryegrass pasture with either high or low levels of endophyte (Neotyphodium lolii) infection during the summers of 1998 and 1999. Cows (Jerseys in 1998 and Friesians in 1999) grazing high endophyte p asture did not exhibit any increase in somatic cell count in either study, as measured in the bulk milk of cows and in milk from individual udder quar ters. Measurements of Na, K, serum albumin, and IgG(1) in milk, together wi th concentrations of lactose in blood plasma, provided no evidence that hig h endophyte pasture was associated with mammary inflammation. The level of endophyte infection in pasture did not alter milk concentrations of a-lacta lbumin and beta-lactoglobulin. Similarly, no effect of endophyte on plasma prolactin concentrations was observed.