Healthy replacement heifers are one of the foundations of a healthy dairy herd. Farm management and rearing systems in Switzerland provide a wide variety of factors that could potentially be associated with intramammary infections (IMI) in early lactating dairy heifers. In this study, IMI with minor mastitis pathogens such as coagulase-negative staphylococci (CNS), contagious pathogens, and environmental major pathogens were identified. Fifty-four dairy farms were enrolled in the study. A questionnaire was used to collect herd level data on housing, management and welfare of young stock during farm visits and interviews with the farmers. Cow-level data such as breed, age at first calving, udder condition and swelling, and calving ease were also recorded. Data was also collected about young stock that spent a period of at least 3 months on an external rearing farm or on a seasonal alpine farm. At the quarter level, teat conditions such as teat lesions, teat dysfunction, presence of a papilloma and teat length were recorded. Within 24h after parturition, samples of colostral milk from 1564 quarters (391 heifers) were collected aseptically for bacterial culture. Positive bacteriological culture results were found in 49% of quarter samples. Potential risk factors for IMI were identified at the quarter, animal and herd level using multivariable and multilevel logistic regression analysis. At the herd level tie-stalls, and at cow-level the breed category "Brown cattle" were risk factors for IMI caused by contagious major pathogens such as Staphylococcus aureus (S. aureus). At the quarter-level, teat swelling and teat lesions were highly associated with IMI caused by environmental major pathogens. At the herd level heifer rearing at external farms was associated with less IMI caused by major environmental pathogens. Keeping pregnant heifers in a separate group was negatively associated with IMI caused by CNS. The odds of IMI with coagulase-negative staphylococci increased if weaning age was less than 4 months and if concentrates were fed to calves younger than 2 weeks. This study identified herd, cow- and quarter-level risk factors that may be important for IMI prevention in the future.
In heifers, intramammary infections caused by Staphylococcus aureus affect milk production and udder health in the first and subsequent lactations, and can lead to premature culling. Not much is known about Staph. aureus isolated from heifers and it is also unclear whether or not these strains are readily transmitted between heifers and lactating herd mates. In this study, we compared phenotypic characteristics, spa types, and DNA microarray virulence and resistance gene profiles of Staph. aureus isolates obtained from colostrum samples of dairy heifers with isolates obtained from lactating cows. Our objective was to (1) characterize Staph. aureus strains associated with mastitis in heifers and (2) determine relatedness of Staph. aureus strains from heifers and lactating cows to provide data on transmission. We analyzed colostrum samples of 501 heifers and milk samples of 68 lactating cows within the same herd, isolating 48 and 9 Staph. aureus isolates, respectively. Staphylococcus aureus strains from heifers, lactating herd mates, and an unrelated collection of 78 strains from bovine mastitis milk of mature cows were compared. With 1 exception each, characterization of all strains from heifers and lactating cows in the same herd yielded highly similar phenotypic and genotypic results. The strains were Staphaurex latex agglutination test negative (Oxoid AG, Basel, Switzerland) and belonged to agr type II, CC705, and spa types tbl 2645 and t12926. They were susceptible to all antimicrobial agents tested. In contrast, the strains from mature cows in other herds were spread across different clonal complexes, spa types, and SplitsTree clusters (http://www.splitstree.org/), thus displaying a far higher degree of heterogeneity. We conclude that strains isolated from colostrum of heifers and mastitis milk of lactating cows in the same herd feature highly similar phenotypic and genomic characteristics, suggesting persistence of the organism during the first and potentially subsequent lactations or transmission between heifers and mature herd mates.
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