Measuring milk flow of dairy cows.

Milk flow measurements on 124 cows were analyzed to deternfine how they are affected by vacuum level, pulsation rate, pulsation ratio of the milking maehine, and the breed, age, stage of laetation, and milk yield of the cow. Average rate of flow prior to machine stripping, yield during the first minute, and yield during the first 2 rain of milking were highly correlated with maxinmm rate of milk flow. These measurements were significantly inereased by days in milk, vacuum level, pulsation rate, pulsation ratio, and total yield. Age at calving had a slight effeet on yield during the first minute of milking. The use of yield during the first 2 rain of milking is outlined as a method for evaluation of milk flow of daughters of bulls used in artifieial insemination. With increased competition for labor in the dairy industry, more emphasis is being placed on inereasing the effleiency of the milking operation. One measure of nfilking efficiency is number of cows milked per man-hour. This, in turn, is influenced by the milking rate of the cows. Milking rate is dependent, in part, upon the anatomy of the teat (1); therefore, it would appear to be a heritable trait and seleetion for faster milking eows would seem possible. Seleetion for milking rate will probably receive emphasis in the future because of labor requirements, even though the amount of sueh seleetion by artificial breeding establishments at the present is somewhat limited and the subjective measurements, such as the farmer 's opinion of a cow's milking rate, are somewhat crude. Since milking maehine factors, such as vacuum level, pulsation rate, and pulsation ratio affect milking [for smnmary, see Schnfidt et al. (6)] , selection for a part icular milk flow deternfination should be done under standardized conditions or the milk flow records eorreeted for a standard vacuum level, pulsation rate, and ratio. The objectives of this study were to determine the influence of maehine faetors, age, stage of lactation, breed, and milk yield on Received for publication July 25, 1968. milk flow measurements and to develop a procedure to evaluate the milk flow characteristics of daughters of bulls used in artificial breeding organizations. Experimental Procedure Par t of the data h'om which milk flow rate correction factors have been developed have been reported previously (5, 6). These papers reported the effect of changes in milking machine design on the milk flow determinations. Milk flow measurements were made with a milker pail suspended from a dairy seales. Milk yields were recorded at 15-see intervals. Machine str ipping was begun when the yield dropped .14 kg or less during a 15-see interval. The machine was removed when milk flow had stopped. The cows in the experiments were milked for periods ranging from 14 to 56 days, with 59% of the eows milked for 28-day pcriods. ~iorning milk flow measurements were recorded on Days J, 4, and 7 of the first week and twice during each sueeeeding week. Milk flow deternfinations reported in this paper are averages for tbe experimental periods. Measurements obtained include time before machine stripping, maehine s tr ipping time, total milking time, yield before machine ,stripping, machine str ipping yield, total milk yield, average rate of flow prior to machine stripping, average rate of flow including machine stripping, maxinmm rate of milk flow (peak flow rate)~ yield during the first minute of milking, yield during the second minute of nfilking, and yield during the first 2 rain of milking. The maehine factors measured were: vaeuum levels, 12, 12.5, 15, 18, and 24 in. Hg; pulsation rates, 40, 50, 60, 80, and 120; and pulsation ratios, 1:1, 2:1, 3:1. Other variables studied in these trials but not included in the analyses were type of liner, type of milker unit, presenee or absence of an air bleed in the claw, and adding weights to the teat cup claw assembly. Two types of milker units, De Laval and Perfeetion, were used. Most cows produced between 9 and 14 kg of milk during the morning nfilking and were past their peak of lactation when the experiments were begun. Cows of all age groups were ineluded. Age was caleulated in months at the time when the experiment was begun, which is