Processability of late-lactation milk from a spring-calved dairy herd

The processability of late-lactation milk from a spring-calved herd in Ireland was investigated. A group of 26 cows with a mean calving date of 16 February was established. Bulk milk from this group was collected at two consecutive milkings weekly and analysed over an experimental period extending from 22 September to 21 December. The 13 weeks of the experiment were divided into two periods for statistical analysis: Period 1, 22 September to 3 November while cows were on pasture; and Period 2, 4 November to 21 December when cows were indoors. The fat and lactose contents in milk were similar in Periods 1 and 2. The N fraction contents comprising total protein, casein, casein number and whey protein did not differ significantly between the two periods. The renneting properties of milk at both natural and adjusted pH (6.6) were not affected by lactation period. Somatic cell count, polymorphonuclear leukocyte level and plasmin activity also remained similar as the trial progressed. However, plasminogen levels, together with the plasminogen: plasmin ratio, were reduced (p < 0.05) in the period 4 November to 21 December and the free fatty acid level in the milk was higher (p < 0.001) in the later period compared to the earlier period examined. In conclusion, good composition and processing characteristics of milk from spring-calved cows can largely be sustained to the end of lactation when good herd management practices are in place.