Prevalence of Teat Apex Colonizations by S. Chromogenes in Young and Primigravid Dairy Heifers

Little attention has been paid to intramammary infections (IMI) in dairy heifers as their non-lactating udders have traditionally been considered as uninfected. However, high prevalences of IMI in non-lactating and freshly calved heifers, mainly caused by Non-aureus staphylococci (NAS), were reported [1]. Prevalence of teat apex and teat skin colonizations is also high. They are mainly caused by the same species [3]. The aim of this study was to examine the prevalence of teat apex colonization with Staphylococcus chromogenes, one of the most prevalent NAS, in young and primigravid dairy heifers, and the effect of age on this prevalence.

In a cross-sectional study, teat ends (n = 492) were sampled from in total 123 heifers, on eight dairy herds. The age of the heifers varied from 8 to 34 months. The heifers were immobilized and the teat apexes were cleansed with a sterile cloth, sampled with a swab (Cultiplast^® and put on to a transport medium. All swabs were streaked on a blood agar plate and incubated aerobically at 37°C. Bacterial growth was recorded after 24 and 48 hours of incubation. Identification was performed as described by [2]. A teat apex was classified as infected with S. chromogenes when at least 8 colony forming units were isolated. Prevalences were calculated as the percentage of heifers with at least one infected teat apex and as the percentage of infected teat apexes. The mean number of infected teat apexes per heifer was also calculated. Logistic regression was used to analyze the effect of age of the heifers on prevalence of S. chromogenes. Odds Ratio's (OR) per age group, using the youngest age group as reference, were calculated (95% Confidence Intervals-CI)(SPSS 10.0).

The mean age of the heifers at the moment of sampling was 18.7 months. Overall, 20.3% of the heifers had S. chromogenes infected teat apexes, while 9.7% of all teat apexes were infected with S. chromogenes. There was a significant influence of age class on the prevalence of infected heifers (P < 0.05). Prevalences of infected heifers (with OR), prevalences of infected teat apexes per age class, and mean number of infected teat apexes per heifer are presented in Table 1.

Table 1 Prevalences of S. chromogenes infected heifers and S. chromogene s infected teat apexes per age class and mean number of infected teat apexes per heifer

This study shows that heifers older than 20 months of age run a higher risk of having S. chromogenes infected teat apexes than younger ones Further longitudinal studies will reveal whether IMI post partum can be predicted by S. chromogenes teat apex colonizations and whether there is a quantitative effect If an association exists possible risk factors for teat apex colonization can be identified and can be used to reduce the high prevalence of IMI in freshly calved dairy heifers