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

Abstract

On modern dairy farms, environmental mastitis pathogens are usually the predominant cause of mastitis, and bedding often serves as a point of exposure to these organisms. The objective of this longitudinal study was to determine bacterial populations of 4 different bedding types [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)] and of teat skin swabs of primarily primiparous cows housed in a single facility over all 4 seasons. Samples of bedding were collected weekly (n=49wk) 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 premilking teat sanitation. Median numbers of streptococci and streptococci-like organisms (SSLO) were >8.6×106 cfu/g and >6.9×103 cfu/teat swab for all bedding types and teat swabs, respectively. Numbers of SSLO were greatest in samples of SBMS (2.1×108 cfu/g) and least in samples of NES (8.6×106 cfu/g), RS (1.3×107 cfu/g), and DBMS (1.7×107 cfu/g). Numbers of gram-negative bacteria in bedding (5.5×104 to 1.2×107 cfu/g) were fewer than numbers of SSLO (8.6×106 to 2.1×108 cfu/g). Numbers of coliform bacteria were greatest in samples of DBMS (2.2×106 cfu/g) and least in samples of NES (3.6×103 cfu/g). In general, the relative number of bacteria on teat skin corresponded to exposure in bedding. Numbers of gram-negative bacteria recovered from prepreparation teat swabs were greatest for cows bedded with DBMS (1.0×104 cfu/swab) and RS (2.5×103 cfu/swab) and least for cows bedded with NES (5.8×102 cfu/swab). Median numbers of coliform and Klebsiella spp. recovered from prepreparation teat swabs were below the limit of detection for all cows except those bedded with DBMS. Numbers of SSLO recovered from prepreparation teat swabs were least for cows bedded with DBMS (6.9×103 cfu/swab) and greatest for cows bedded with RS (5.1×104 cfu/swab) or SBMS (1.6×105 cfu/swab). The numbers of all types of measured bacteria (total gram-negative, coliforms, Klebsiella spp., SSLO) on postpreparation teat swabs were reduced by up to 2.6 logs from numbers of bacteria on prepreparation swabs, verifying effective preparation procedures. 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 use of different bedding types results in exposure to different distributions of mastitis pathogens that may alter the proportion of etiologies of clinical mastitis, although the incidence rate of clinical mastitis did not differ among bedding types.