Associations between dairy cow bedding and milk quality

The objective of this thesis is to generate knowledge that can be used to improve milk quality, animal welfare, and profitability on dairy farms. Large Wisconsin dairy farms use sand (58%) or recycled (10%) sand, organic materials (primarily wood products over mattresses; 22%) and manure products (10%) as bedding. These farms produce exceptional quality milk with minimal bacterial counts and low BMSCC which are associated with their almost universal adoption of best management practices for milking management. Use of Inorganic bedding was associated with greater productivity and lesser bulk milk SCC as compared to farms using organic bedding. Use of manure bedding was associated with lesser productivity, greater SCC, more cows with non-functioning mammary quarters, and a greater proportion of cows with milk not sold due to treatment for mastitis. Risk of exposure to potential mastitis pathogens is different for cows bedded with different materials. In a longitudinal study, large numbers of streptococci were found in all bedding types and on teats of primiparous cows bedded with all bedding types with fewest numbers recovered from teats of primiparous cows bedded with new sand and deep bedded manure solids. With the exception of deep bedded manure solids where numbers of streptococci and total Gram-negative bacteria were similar, numbers of Gram-negative bacteria were much fewer than numbers of streptococci in bedding. Numbers of Gram-negative bacteria (including subsets of coliform and Klebsiella spp.) were much fewer in new sand and on teats of primiparous cows bedded with new sand than other bedding types. Different pathogen distributions among bedding types represent different potential risks of subclinical and clinical mastitis. Large numbers of streptococci in all bedding types represent potential risk of subclinical mastitis with elevated SCC due to a long duration subclinical phase. Fewest numbers of all categories of Gram-negative bacteria in new sand represent least potential risk of clinical mastitis. Primiparous Holsteins bedded with new sand had fewer culture positive subclinical mastitis cases and greater survival times to incidence of mastitis than cows bedded with recycled sand or manure. Economic modeling demonstrated clear advantages for the use of sand as dairy cattle bedding.