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 (log10 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 late-lactation 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.
Bibliographical noteFunding Information:
We thank the Zoetis Quality Milk Specialist and Dairy Technical Services teams (Julio Alcantar, Michele Barrett, Karthryn Browning, Ruben Gonzalez, Samuel Herrera, Bernard Kwaku, Shawn Hull, Doris Ledwith, John Lee, Francisco Rivas, and Bill Sullivan), who conducted the fieldwork in herds located outside of Minnesota. We also thank doctor of veterinary medicine students from the University of Minnesota, Samuel Basquin, Edouard Cotten, Wanda Weber, and Aaron Rendahl. M. Boyle is an employee of Zoetis. He was involved in the study design and conceptualization with review of the manuscript. He was not involved with any analyses of data. All others have no competing interests to declare. S. M. Rowe was involved in fieldwork, laboratory work, data management, analysis, and manuscript preparation. S. M. Godden was involved in supervision, study conceptualization, fieldwork, and manuscript editing. E. Royster was involved in study conceptualization and manuscript editing. B. A. Crooker was involved laboratory work and manuscript editing. J. Timmerman was involved in laboratory work and manuscript editing. M. Boyle was involved in study conceptualization, fieldwork coordination, and manuscript editing. This study was funded by Zoetis (Parsippany, NJ).
- dry cow therapy
- intramammary infection
- manure solids