Influence of nutrition, genotype and stage of lactation on milk casein composition

Variation in milk protein content and the casein composition is observed in many production systems. This is associated with changes in the level of nutrition, with stage of lactation and with cows having different milk protein variants, all of which affect cheese yield and properties to variable extents. Casein composition is difficult to change experimentally but, in those cases where it has altered, this has been associated with cows at sub-optimal levels of nutrition, a situation which occurs throughout the annual production cycle of cows at pasture. Changes of up to 25 % (2.8 to 3.5 % (m/v) range) are commonly seen in milk protein content and milk casein fractions can vary within a 10 % (casein fraction/total casein) range. Milk protein variants have a profound influence on casein concentration and processability, however the influence on casein composition is not clearly defined. The interaction of milk protein variants, stage of lactation and level of nutrition has not been adequately studied.