Milk production in Ireland, New Zealand and Australia is seasonal, with the majority of cows calving in spring. This pattern of production makes the maximum use of grazed grass, and in Ireland >80% of total milk for manufacturing is produced between April and November inclusive. Such a seasonal pattern of production results in a large variation in the gross composition of milk due to stage of lactation effects (Phelan et al. 1982). Some studies have investigated the relationship between milk composition and its processing characteristics (O'Keeffe et al. 1982; Grandison et al. 1984); however, in these studies the effects of diet and lactation stage were not segregated. Kefford et al. (1995) attempted to segregate the effects of diet and stage of lactation and concluded that diet quality (type and quantity) had a larger effect on Cheddar cheese quality than the stage of lactation.

The nutritive value of the diet of cows fed on grazed grass can change owing to changes in grass supply or quality. In the current study, changes in grass supply were achieved by altering the daily herbage allowance (DHA) to the herds. The objective of the current study was to investigate the effect of varying the DHA in the range 16–24 kg grass dry matter (DM), which is typical of the variation in pasture allowance in Ireland in mid lactation, on milk composition and its processing characteristics.