The effect of prolonged milking interval on milk yield and quality in an automated milking system

Abstract

Automated milking systems allow cows to be milked voluntarily based on setting time. This typically leads to an increased milking interval, which may affect milk yield and milk quality. This study was performed to evaluate the effect of the prolonged milking interval of cows on milk yield and composition and milk quality in automated milking systems. A total of 29 lactating Holstein cows were divided into control group (N = 10) and treatment group (N = 19). The milking interval of the control group was maintained from 11-h to 12-h in automated milking systems (VMSTM with Delpro 3.0; Delaval). The milking permission time in treatment group was gradually increased from 11-h to 20-h to prolong milking interval. As a result, cows in the treatment group gradually increased milking interval from 13-h to 22-h during the 20-d experimental period. Milk yield, milk composition, and total bacterial count were measured at starting day (0-d), 7-d, and 20-d of experimental period. Somatic cell counts were measured daily during 20 experimental days. Milk yield, milk protein content, and milk lactose content were lower (p < 0.05) in the treatment group than in the control group at 20-d but not at 0-d and 7-d, whereas milk fat content was not different between two groups at all time points. Total bacterial count was higher (p < 0.05) in the treatment group than in the control group at 7-d and 20-d. Somatic cell counts was numerically higher in the treatment group than in the control group on 18-d and 19-d, but not at other days. Correlation analysis revealed a moderately positive correlation between milking interval and daily somatic cell count (R2 = 0.31, p = 0.011). Based on days in milk, treatment cows were sub-grouped into early to mid-lactation cow group (less 200 days in milk) and late-lactation cow group (over than 200 days in milk). The late-lactation group showed a moderately positive correlation (R2 = 0.36, p = 0.005), whereas early to mid-lactation group did not show significant correlation (R2 = 0.12, p = 0.138) between milking interval and somatic cell count. In conclusion, prolonged milking interval up to 22-h reduces milk yield, milk protein and milk lactose contents, and milk quality (total bacterial count), and it increases somatic cell counts especially during late lactation period.