Effect of decreased milking frequency of cows in late lactation on milk somatic cell count, polymorphonuclear leucocyte numbers, composition and proteolytic activity

Abstract

The effects of reducing the frequency of milking of cows in late lactation on milk somatic cell count (SCC), polymorphonuclear leucocyte (PMN) content, chemical composition and proteolytic activity were investigated. Intermittent milking is frequently practised by Irish farmers in late lactation, and the objective of this study was to determine whether this procedure could be linked to altered quality of milk. Seventeen Holstein Friesian cows in late lactation (>215 d in milk) were assigned to two treatment groups, and were either milked twice a day until drying-off (control group) or milked intermittently as the yield fell (test group). Milk composition and enzymic characteristics were measured on two occasions. At the first sampling, day 7, test cows were on once daily milking and at the second, day 15, the test cows were being milked every second day. Milk yields were significantly lower in test than control animals and decreased between days 7 and 15 in both groups. Milk SCC and PMN levels were increased on reducing milking frequency and, at day 15, the increase was not linked to decreased milk yield. Milk lactose levels were significantly decreased and pH, α-lactalbumin levels, plasmin activity and plasminogen activity significantly increased by reducing milking frequency. In conclusion, reduced frequency of milking in late lactation leads to the production of milk that is abnormal in character and this may be linked to reduced quality of dairy products manufactured from such milk.