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 dairy 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 pasture 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 quarters. Measurements of Na, K, serum albumin, and IgG(1) in milk, together with concentrations of lactose in blood plasma, provided no evidence that high endophyte pasture was associated with mammary inflammation. The level of endophyte infection in pasture did not alter milk concentrations of a-lactalbumin and beta-lactoglobulin. Similarly, no effect of endophyte on plasma prolactin concentrations was observed.