Cross-sectional study of the relationships among bedding materials, bedding bacteria counts, and intramammary infection in late-lactation dairy cows

Abstract

Objectives of this study were to (1) describe the intramammary infection (IMI) prevalence and pathogen profiles in quarters of cows approaching dry-off in US dairy herds, (2) compare IMI prevalence in quarters of cows exposed to different bedding material types, and (3) identify associations between bedding bacteria count and IMI in cows approaching dry-off. Eighty herds using 1 of 4 common bedding materials (manure solids, organic non-manure, new sand, and recycled sand) were recruited in a multi-site cross-sectional study. Each herd was visited twice for sampling. At each visit, aseptic quarter-milk samples were collected from 20 cows approaching dry-off (>180 d pregnant). Samples of unused and used bedding were also collected. Aerobic culture was used to determine the IMI status of 10,448 quarters and to enumerate counts (log 10 cfu/mL) of all bacteria, Staphylococcus spp., Streptococcus spp. and Streptococcus-like organisms (SSLO), coliforms, Klebsiella spp., noncoliform gram-negatives, Bacillus spp., and Prototheca spp. in unused (n = 148) and used (n = 150) bedding. The association between bedding bacteria count and IMI was determined using multivariable logistic regression with mixed effects. Quarter-level prevalence of IMI was 21.1%, which was primarily caused by non-aureus Staphylococcus spp. (11.4%) and SSLO (5.6%). Only modest differences in IMI prevalence were observed between the 4 common bedding material types. Counts of all bacteria in unused bedding was positively associated with odds of IMI caused by any pathogen [ALL-IMI; odds ratio (OR) = 1.08]. A positive association was also observed for counts of SSLO in unused bedding and SSLO-IMI (OR = 1.09). These patterns of association were generally consistent across the 4 common bedding materials. In contrast, the association between counts of all bacteria in used bedding and ALL-IMI varied by bedding type, with positive associations observed in quarters exposed to manure solids (OR = 2.29) and organic non-manure (OR = 1.51) and a negative association in quarters exposed to new sand (OR = 0.47). Findings from this study suggest that quarter-level IMI prevalence in latelactation cows is low in US dairy herds. Furthermore, bedding material type may not be an important risk factor for IMI in late lactation. Higher levels of bacteria in bedding may increase IMI prevalence at dry-off in general, but this relationship is likely to vary according to bedding material type.

Cross-sectional study of the relationship between cloth udder towel management, towel bacteria counts, and intramammary infection in late-lactation dairy cows

“…Housing systems used for lactating cows included freestall (n = 64, 95%), dry lot (n = 2, 3%), and combinations of freestall and dry lot (n = 1, 2%). These demographic descriptors for the 67 herds enrolled in this study were similar to the original 80 herds enrolled in the larger bedding study (Rowe et al, 2019).…”

“…Sample Size Calculation. Sample size calculations were conducted for the larger study of bedding management and IMI, which this study was conducted within Rowe et al (2019). No additional calculations were performed before proceeding with this study.…”

“…The Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary Extension (STROBE-Vet) statement guidelines were followed in the reporting of this study (Sargeant et al, 2016). A cross-sectional study of dairy herds in the United States was conducted between December 2017 and April 2018, as an extension of a larger study of bedding management and IMI (Rowe et al, 2019). Investigating CUT management was not part of the original design for the bedding study.…”

“…Furthermore, we decided to use 2 towels (and not more) because our towel culture method could not be performed on more than 2 towels at once. Unused and used bedding material samples were also collected into separate resealable plastic bags, using methods described in Rowe et al (2019). Bedding, CUT, and milk samples were immediately chilled and stored at −20°C at the study site before being freighted overnight on ice to the Laboratory for Udder Health (LUH) at the Veterinary Diagnostic Laboratory, University of Minnesota (St. Paul).…”

“…The detection limit for towel culture is 32 cfu/cm 2 of towel. Bedding bacteria counts for unused and used bedding were determined for each farm using methods described in Rowe et al (2019).…”