Effects of Unequal Milking Interval on the Milk Yield and Composition and Mastitis in Dairy Cows

Effects of 7.5 and 16.5 hours Interval Milkings

Abstract

Effects of unequal milking interval on the milk yield, milk composition and udder engorgement which might be caused by it in dairy cows were studied by two trials. Six (Trial I) and eight (Trial II) Holstein cows producing daily 24.5kg milk on average (range 20-38kg) were used, and milked twice daily at intervals of 7.5 and 16.5 hrs for unequal interval milking period or experimental period and 11.0 and 13.0 hrs for the control period in each trial. Each trial was made up of a three-period double switch-back experiment, each period consisting of three weeks. Each cow was individually fed at the level based on the Japanese Feeding Standard for Dairy Cattle; 6kg of alfalfa-hay cube, 3kg of beet-pulp and 3kg of timothy hay, and concentrate at the rate of 1kg per 3kg milk yield were given daily throughout the experiment. Milk yields were measured at each milking and the milk fat, milk protein, lactose and SNF content of the morning and the evening milk were determined once a week. The modified California Mastitis Test (CMT) and the Wisconsin Mastitis Test (WMT) were also applied weekly to detect clinical and subclinical mastitis. The statistical analysis was made according to the modified analysis of two-treatment switch-back design15). The average daily milk yields were 24.2Kkg for the unequal interval milking period and 24.8kg for the control period, respectively. The difference, 0.6kg, was statistically significant (P<.05). Compared to the control period, the percentages of milk fat, milk protein, lactose and SNF content during the experimental period decreased by 0.02, 0.04, 0.10 and 0.13, respectively. Those decreases were significant except fat. The percentage of the morning milk yield to the daily milk yield was 5600 for the control period and 68 for the unequal interval milking period, both of which corresponded very well to that of the expected milk yield based on the length of milking interval. The fat percent of the milk obtained after the long interval (16.5hr) was lower than that obtained after the short interval (7.5hr) (2.80vs. 4.28%). The contents of milk protein, lactose and SNF were little affected by the length of preceding milking intervals. The CMT score and the WMT value for the unequal interval milking period were slightly higher than that for the control period, but only the former was significant. The relationship between the production capacity of individual cow and the decrease in milk yield due to extending milking interval was also discussed.