Relationship between postmilking standing duration and risk of intramammary infection in freestall-housed dairy cows milked 3 times per day

Recent evidence exists to suggest that the risk of subclinical mastitis, particularly those infections caused by environmental pathogens, in dairy cows is related to standing and lying patterns. The objective of this study was to determine the association between postmilking standing duration (PMSD) of dairy cows milked 3×/d and risk of intramammary infection (IMI). Four commercial freestall dairy herds in Eastern Ontario, milking 3×/d, were enrolled in a longitudinal study. Forty Holstein-Friesian cows per herd were randomly selected as focal animals from those cows in each herd that met our selection criteria of days in milk (<200 d) and somatic cell count (<100,000 cells/mL). The study consisted of three 28-d periods. The study began following a regularly scheduled Dairy Herd Improvement test with the collection of quarter-level milk samples from all focal animals. Bacteriology was used to confirm infection status at the start of the study and for determination of incidence of IMI throughout the study. A new IMI was defined as having a culture-positive quarter-level sample when the previous sample (28 d prior) had been culture negative for the pathogen of interest. Four sets of quarter-level milk samples were obtained for each focal animal. Lying behavior was recorded for 5 d after each milk sampling using data loggers. For these 5 d, individual milking times, production, and feeding times were also recorded. Postmilking standing duration was analyzed by milking event, with increased PMSD being positively associated with provision of fresh feed or freshly pushed-up feed around the time of milking, greater feed bunk space per cow, and lower freestall stocking density. Over the study period, 456 new IMI were detected, resulting in a mean herd incidence rate of 3.22 IMI per quarter year. Coagulase-negative staphylococci (CNS) and Corynebacterium spp. IMI were statistically analyzed to determine relationship with PMSD; they were the 2 predominant pathogens representing 45 and 31% of IMI, respectively. Only CNS IMI was associated with PMSD. A nonlinear relationship between PMSD and incidence of CNS IMI was found; cows with a PMSD of 90 to 120 min were at a reduced risk for CNS IMI. The risk of experiencing CNS IMI was also reduced with increased frequency of feed push-ups and provision of fresh feed 60 min before to 90 min after milking and >540 min after milking. These results indicate that management practices that promote PMSD of 90 to 120 min, such as the provision of fresh feed or freshly pushed-up feed around the time of milking, providing ample feed bunk space per cow, and keeping freestall stocking density low, should be encouraged to reduce the risk of CNS IMI in freestall-housed cows milked 3×/d.