Prospective cohort study of the relationship between milking machine liner slip, milking performance, and cow characteristics

Abstract

We conducted a prospective cohort study to investigate the associations of machine milking liner slip with (1) milking performance and (2) cow characteristics. Parlor data including milk flow characteristics and data on the occurrence of milking machine liner slips from a 4,000-cow dairy with a thrice-daily milking schedule were obtained with electronic on-farm milk meters over a 2-mo period. We analyzed data from a total of 686,330 milking observations. A multivariable general linear mixed model revealed no association between liner slip and milking unit on time. Least squares means (95% confidence intervals, 95% CI) were 237 (235-238) s for milking observations with and without a liner slip. We observed statistically significant differences in average milk flow rate; however, these were biologically irrelevant. Least squares means were 3.40 (3.37-3.42) kg/min for a milking observation with and 3.42 (3.40-3.44) kg/min without a liner slip. A multivariable generalized linear mixed model showed an association between liner slip and cow characteristics. Compared with late-lactation cows, the odds ratios (OR, 95% CI) of occurrence of a liner slip were 2.03 (1.59-2.59) in early lactation cows and 1.26 (0.97-1.64) in cows from 101 to 200 days in milk. Presence of a nonlactating quarter increased the odds of liner slip occurrence [OR, 95% CI: 10.35 (8.02-13.35)]. Bimodal milking observations had higher odds of occurrence of a liner slip compared with milking observations with a unimodal milk flow curve [OR, 95% CI: 1.05 (1.005-1.09)]. A 1-kg increase in 2-min milk yield increased the odds of a liner slip [OR, 95% CI: 1.26 (1.25-1.28)]. We conclude that, in the study cohort presented herein, the negative effect of liner slips on milking performance can be diminished. The identified cow characteristics could offer unique opportunities to identify and manage cows at increased risk of liner slips.