Milking dynamics following individual quarter dry-off in Holstein cows in an automatic milking system

Individual quarter dry-off (QDO) is a targeted management strategy used to address persistent IMI that lead to chronic subclinical mastitis, as well as cases of clinical mastitis that are recurrent or unresponsive to treatment. Although the interest in the use of individual QDO as a non-antimicrobial strategy for mastitis control is growing, the impact of this management on subsequent milk production has not been widely explored. Moreover, detailed information on the individual performance of the remaining functional quarters following QDO is scarce. The objective of this observational study was to investigate the effect of lactational QDO following clinical mastitis on short-term milk yield in the remaining individual quarters. This retrospective study was conducted in a commercial dairy farm located in northeast Colorado, equipped with an automatic milking system. The analysis included 114 multiparous cows with one quarter dried off through abrupt cessation of milking following unresponsive clinical mastitis therapy. For comparison, one healthy control cow was matched to each affected cow based on DIM and parity number. Individual quarter milk yield of the remaining functional quarters and from control cows was collected for each milking visit from the on-farm management software and summed as a daily value per quarter for the 30 d following QDO. The herd average DIM at the peak of lactation (68 DIM) was considered to categorize the study cows based on their DIM at QDO into prepeak and postpeak groups. All the analyses were conducted separately for these 2 stage of lactation groups and cows were also categorized based on their dry quarter location (DQL). Least squares means (SE) for daily average milk yield per functional quarter and per cow up to 30 d post QDO were calculated and compared among DQL groups (including matched control cows) using ANOVA for repeated measures analysis, with cow ID as the repeated statement, with compound symmetry selected as the covariance structure. Multivariable models included DQL as explanatory variable of interest and DIM at QDO and calving season as potential covariates. In addition, milk yield curves up to 30 d post-QDO were built for milk yield per DQL using daily LSM calculated by repeated measures analysis. Cow-level milk yield was also compared between DQL groups, including unaffected control cows using t-test for repeated measures analysis. Differences in quarter milk yield were only identified for the prepeak group (≤68 DIM). Milk yield from the left rear and right rear quarters was smaller in control cows than in cows with the right front quarter dried off. When total milk yield per cow was compared within the prepeak group, control cows had greater yield than cows subjected to QDO of the right rear quarter. In the postpeak group, control cows had the highest milk yield compared with the 4 groups of cows with a dry quarter. In conclusion, following QDO, the levels of milk yield compensation in the remaining functional quarters were variable and smaller when QDO occurred post peak (>68 DIM). Nonetheless, in most cases the cow-level milk yield remained lower in 3-quarter cows compared with unaffected controls.