A retrospective cohort study investigating the association of individual quarter dry-off with udder health, milk production, and culling risk.

Individual quarter dry-off (QDO) has been increasingly employed as a strategy for managing cows with chronically elevated SCC and recurrent clinical mastitis. However, little knowledge is available on the effects of QDO on milk production, SCC, the risk of clinical mastitis, and the risk of removal from the herd. Therefore, this retrospective cohort study aimed to investigate these associations. Data from 471 dairy cows subjected to QDO were analyzed. The cows were housed on a 4,000-cow dairy farm with a thrice-daily milking schedule. The cows were grouped based on the reason for QDO: (1) cows detected with a nonlactating quarter at a fresh cow check (QFRESH); (2) cows with recurrent clinical mastitis (QMAST); (3) cows diagnosed with Staphylococcus aureus IMI (QSA); and (4) cows with chronic subclinical mastitis (QSCC). Additionally, we randomly selected herd mates at a ratio of 1:1 to serve as a control group (CON). Cows in the CON group were matched in terms of parity and stage of lactation. Generalized linear mixed models with an identical link were used to estimate milk yield and SCC at 1 test day before QDO (T-1) as well as 1, 2, and 3 (T1, T2, and T3) test days after QDO. All cows subjected to QDO exhibited a decrease in milk yield following QDO compared with their respective control groups. All QDO cows approached the yield of their control group by T3. In particular, the difference in milk yield between QMAST cows and their controls at T3 was less than the difference at T1. Cows in the QMAST and QSCC groups exhibited a decrease in their SCC following QDO. In particular, the SCC was significantly higher among QMAST cows than among their controls at T1, but this difference was no longer significant by T3. Proportional hazards regression models revealed that QDO was associated with clinical mastitis occurrence and removal from the herd. Compared with CON cows, the hazard ratio (95% CI) for clinical mastitis occurrence was 3.70 (1.65-8.28), 1.80 (1.31-2.47), and 2.27 (0.93-5.54) among QFRESH, QMAST, and QSA cows, respectively. The hazard ratio among QSCC cows was modified by the effect of parity. The hazard ratio (95% CI) for removal from the herd was higher among cows subjected to QDO than among CON cows (hazard ratio [95% CI] values of 2.30 [0.99-5.33], 3.27 [2.20-4.86], and 4.87 [1.81-13.12] for QFRESH, QMAST, and QSCC cows, respectively). We conclude that QDO can be a viable strategy for managing cows with recurrent clinical mastitis. However, the results for the cows that underwent QDO for other reasons are less clear, partially due to low statistical power. Therefore, future research should examine how to decrease the risks of clinical mastitis and removal from the herd among cows subjected to QDO.

Effect of enhanced hygiene on transmission of Staphylococcus aureus, Streptococcus agalactiae, and Streptococcus dysgalactiae in dairy herds with automatic milking systems.

The objective of the study was to evaluate the effect of hygiene measures in automatic milking units on the transmission of 3 mastitis pathogens considered to be mainly or partly transmitted from cow to cow during milking events. Two studies were conducted as within-herd experimental trials in 2 Danish commercial dairy herds (A and B) with automatic milking systems. Interventions to enhance hygiene were implemented on the automatic milking units. The 2 studies evaluated separate interventions. In herd A, the hygiene interventions were manual wash with the Lely foam unit and adjustments on the brush-mediated teat cleaning procedure. In herd B, the hygiene intervention included automatic disinfection spray on the upper surface of the brush motor and daily change of brushes. Composite milk samples were collected longitudinally at 3- or 4-wk intervals from all lactating cows. Additional milk samples were taken from cows entering or leaving the study groups. Milk samples were analyzed with quantitative PCR. A hidden Markov model implemented within a Bayesian framework was used to estimate the transmission probability. For analysis, 701 samples from 156 cows were used for herd A, and 1,349 samples from 390 cows were used for herd B. In the intervention group in herd B, transmission of Streptococcus agalactiae was reduced to 19% (95% posterior credibility interval: 0.00-64%) of the transmission in the control group, whereas transmission of Streptococcus dysgalactiae was reduced to 17% (95% posterior credibility interval: 0.00-85%) of transmission in the control group. This suggests that automatic spray on the upper surface of the brush motor with disinfectant along with daily change of brushes collectively reduced transmission of Strep. agalactiae and Strep. dysgalactiae. Results on Staphylococcus aureus in herd B and results on manual foam cleaning and brush-mediated teat cleaning adjustments in herd A were inconclusive.

The effect of individual quarter dry-off in management of subclinical mastitis on udder condition and milk production in organic dairy herds: A randomized field trial.

The objective of the study was to evaluate the effect of individual quarter dry-off in management of subclinical mastitis on clinical development, behavior during milking, and short-term production loss. The study was conducted as a controlled randomized trial in 5 commercial organic dairy herds. Seventy cows meeting the inclusion criteria were randomly allocated to 1 of 2 treatments: individual quarter dry-off (QDO) or continued milking. The inclusion criteria constituted an increase in somatic cell count from below to above 400,000 cells/mL at milk recording and identification of a quarter scoring of at least 3 and higher than the remaining quarters at California mastitis testing (scale 1-5). Quarters were evaluated clinically for atrophy, swelling, firmness, signs of pain, and milk leakage, and rectal temperature of the cows was measured. Behavior during milking was assessed as average frequency of hind limb tripping and kicking during milking obtained by registrations on video recordings. Milk production loss was estimated based on average daily milk yield for 19 d subsequent to treatment start, with reference to average daily milk yield in 19 d before treatment. The QDO treatment was associated with quarter swelling and increased quarter firmness around d 10 from treatment start and with quarter atrophy around d 40 from treatment start. However, around d 40 from treatment start 35% of the dried-off quarters remained nonatrophic and only 6% of the quarters were completely dry. The QDO was associated with signs of pain related to the dried-off quarter. No obvious effects on behavior during milking of QDO treatment was observed. On average the production loss associated with QDO was 4.1 kg/d (95% confidence interval: 3.1-5.0) greater than for continued milking. The production loss depended on parity, days in milk, and prior yield on the quarter subjected to dry-off (Q1). The production loss increased with increasing prior yield on Q1. For the majority of cows the increase in production loss was below 1 kg of milk/d when the prior yield on Q1 increased by 1 kg of milk/d, demonstrating a compensatory production potential of the nontreated quarters. Early lactation multiparous cows showed the greatest compensatory potential. Further studies into the effect on welfare, cure rates, and transmission are needed to determine the feasibility of individual quarter dry-off.