Bacterial counts on teat skin and in new sand, recycled sand, and recycled manure solids used as bedding in freestalls.

All bedding materials for cows have advantages and disadvantages and the choice of farmers is therefore mainly based on practicality and economics. However, cleaning and storage of contaminated bedding are often the source of exposure to environmental mastitis organisms, which on modern dairy farms are usually the predominant cause of mastitis. Researchers R.F. Rowbotham and P.L. Ruegg were interested to see how different bedding materials will affect pathogen build-up and therefore designed an experiment to determine bacterial populations of four different bedding types. They published their results in the Journal of Dairy Science, Volume 99 of 2016, pages 6594 to 6608, the title of the paper being: Bacterial counts on teat skin and in new sand, recycled sand, and recycled manure solids used as bedding in freestalls.

They evaluated deep-bedded new sand (NES), deep-bedded recycled sand (RS), deep-bedded manure solids (DBMS) and shallow-bedded manure solids over foam core mattresses (SBMS) as bedding material. For the evaluation they used teat skin swabs of primarily multi-lactation cows which were housed in a single facility over all four seasons. Samples of bedding were collected weekly for 49 weeks from pens that each contained 32 lactating dairy cows. Throughout the length of the same period, composite swabs of teat skin were collected weekly from all cows before and after pre-milking teat sanitation.

The average numbers of streptococci and streptococci-like organisms (SSLO) were about 8.6 × 10⁶ cfu per gram and 6.9 × 10³ cfu per teat swab for all bedding types and teat swabs, respectively. The numbers of SSLO were greatest in the samples of SBMS and least in the samples of NES, RS and DBMS. The numbers of gram-negative bacteria in bedding were fewer than the numbers of SSLO. The numbers of coliform bacteria were greatest in samples of DBMS and least in samples of NES. In general, the relative number of bacteria on teat skin corresponded to exposure in the bedding. The numbers of gram-negative bacteria recovered from pre-preparation teat swabs were greatest for cows bedded with DBMS and RS and least for cows bedded with NES. The average numbers of coliform and Klebsiella species recovered from pre-preparation teat swabs were below the limit of detection for all cows except those bedded with DBMS. The numbers of SSLO recovered from pre-preparation teat swabs were least for cows bedded with DBMS and greatest for cows bedded with RS or SBMS. The numbers of all types of measured bacteria (total gram-negative, coliforms, Klebsiella species, SSLO) on post-preparation teat swabs were reduced by up to 2.6 logs from numbers of bacteria on pre-preparation swabs, suggesting that the preparation procedures were effective. Significant correlations between bacterial counts of bedding samples and teat skin swabs were observed for several types of bacteria. As compared with other bedding types, the least amount of gram-negative bacteria were recovered from NES and may indicate that cows on NES have a reduced risk of exposure to pathogens that are typically a cause of clinical mastitis. In contrast, exposure to large numbers of SSLO was consistent across all bedding types and may indicate that risk of subclinical mastitis typically associated with streptococci is not as influenced by bedding type; however, significantly greater numbers of SSLO were found in SBMS than in other bedding types.

These findings indicate that different bedding types result in exposure to different distributions of mastitis pathogens which may alter the proportions of dominant species causing the clinical mastitis. However, the incidence of clinical mastitis did not differ among bedding types.