PARTITIONING OF MILK ACCUMULATION BETWEEN CISTERNAL AND ALVEOLAR COMPARTMENTS OF THE BOVINE UDDER - RELATIONSHIP TO PRODUCTION LOSS DURING ONCE-DAILY MILKING

Experiments were undertaken to validate a method (using adrenaline inj ection) for determination of the size of cisternal and alveolar compar tments in the udder, to use this method to determine the pattern of mi lk accumulation in the udder over time and to determine the relationsh ip between the size of the alveolar and cisternal compartments and tol erance of once daily milking. Cows received intrajugular injections of adrenaline (3 mg) immediately before milking, to block milk ejection and allow harvesting of the cisternal milk fraction. This was followed by removal of the alveolar fraction 30 min later after intrajugular o xytocin (5 i.u.) injection. Results obtained were similar to those obt ained by catheter drainage. The alveolar compartment was 90% full at 1 6 h post milking while the cisternal compartment filled more slowly an d was only 70% full at 24 h post milking. At full capacity (measured a t 40 h), the volumes of milk contained in the cisternal and alveolar c ompartments were similar. In a further experiment involving identical twin cows, it was shown that the greater the degree of filling of the cisternal compartment at 24 h, the lower was the production loss on on ce daily milking. This suggests that the freedom of the alveoli to dra in was an important factor in the production loss on once daily milkin g. Although there were significant correlations within twin sets for m ilk yield and the size of udder compartments, the relationship within twin sets for yield loss on once daily milking was not statistically s ignificant.