Once-daily milking reduces fixed costs, may be used strategically as a quota-management tool and could become the production system of choice in a programme of extensification. However, milk secretion is reduced during once-daily milking, through the action of an autocrine feedback inhibitor. This natural milk protein is active in milk stored within the secretory tissue, but not in cisternal milk (since it is then remote from its site of action). Consequently, large-cisterned cows should tolerate infrequent milking better than those with small cisterns, by virtue of storing a greater proportion of their milk in a site where the inhibitor is inactive. The aim of this experiment was to test this hypothesis.

A group of 9 multiparous and 2 primiparous Friesian-Holstein cows from the Hannah herd calving in March and April 1991 were selected for study. All had been free of clinical mastitis during the current lactation. Throughout the experiment the group were managed routinely at grass as part of the main herd, and were fed a flat rate of 2.4 kg/d of an 18% protein concentrate feed. Normal milking was twice daily at 15:9 h intervals, and yield was recorded at each milking.