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Bacterial counts were monitored for 1 yr in bedding materials used on nine commercial dairies. Organic materials used to bed lactating cows had significantly higher moisture content and gram-negative bacterial, coliform, Klebsiella species, and streptococcal counts than did inorganic materials. Klebsiella species counts were higher in sawdust than in chopped straw. Streptococcal counts were higher in chopped straw than sawdust. Bacterial counts did not differ between sand and crushed limestone. Gram-negative bacterial and coliform counts were higher during summer and fall than in winter and spring months. Streptococcal counts did not differ among seasons of the year. Linear relationships were significant between total rates of clinical mastitis during lactation and both gram-negative bacterial and Klebsiella species counts in lactating cow bedding. These data indicate that bacterial populations differed between both types of bedding and among seasons of the year. Rates of clinical mastitis were related to bacterial counts in bedding.

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Incidence of clinical mastitis and duration of clinical symptoms for complete lactations were evaluated for 80 cows randomly assigned to one of four groups: vitamin E supplemented- and selenium injected, selenium injected, vitamin E supplemented, and controls. Vitamin E supplementation and selenium injection were during the dry period. Log-linear analysis of incidence data revealed a significant 37% reduction of clinical mastitis by vitamin E. Incidence was not affected by selenium alone, nor was there any evidence for interaction of vitamin E with selenium on incidence. However, duration of clinical symptoms (calendar months clinical/quarter lactating) was reduced by 46% for the selenium group, 44% for the vitamin E group, and 62% for the vitamin E-selenium group as compared to controls. We conclude that dairy cow diets deficient of vitamin E may elevate incidence of clinical mastitis. Selenium deficiency may result in greater duration of clinical symptoms, and selenium may interact with vitamin E. Coliform bacteria and species of streptococcus other than Streptococcus agalactiae were isolated from 70% of the clinical cases.

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