A cow’s housing environment is the primary source of environmental mastitis organisms. Organic bedding presents the greatest risk for environmental mastitis, and according to a USDA survey, approximately 54 percent of freestall facilities are bedded with some form of organic bedding.

One management practice that may reduce the risk of environmental mastitis is the alteration of bedding pH to make it a less hospitable environment for mastitis pathogens, says Peter Krawczel in the "Alumni Corner" of the William H. Miner Agricultural Research Institute March 2013 Farm Report.

In the article, Krawczel, a dairy research and extension specialist in the Department of Animal Science at the University of Tennessee in Knoxville, discusses research from the University of Connecticut and Washington State University. The research evaluated the effect of an acidic clay-based bedding additive on the bedding quality and pathogen counts within sawdust-bedded freestalls, as well as teat-end condition of mid-lactation Holstein dairy cows.

In the treated stalls, researchers spread about 1 pound of additive (containing 45 to 65% sulfuric acid) across the third of the stall closest to the curb and an additional 0.25 pound added to the same amount of sawdust as the control treatment.

To determine the effect of the additive, the researchers evaluated the following parameters:

1. Teat cleanliness – Scored daily from 1 (no bedding/manure) to 4 (more than half the teat surface covered with material)
2. Stall cleanliness – The rear portion of each stall was scored daily using a 3 × 3 grid with each cell of the grid scored on a 0 (clean sawdust) to 5 (manure covering entire cell) scale.
3. Bedding samples – All sawdust used during the study was sampled for environmental pathogens before being used to bed the freestalls. On delivery as a bedding material, sawdust samples were collected on days 1, 2, 7, 14, and 21. Samples were analyzed for total gram-negative bacteria and bacteria counts. Bedding samples were also analyzed for dry matter content and pH on the same days.
4. Teat swabs – On the same days that bedding samples were collected, a swab was run over each teat end before cows were prepped for milking. These swabs were analyzed for growth of Streptococcus spp., coliform pathogens, and Klebsiella.
5. Milk samples – Milk from the right front quarter and a composite sample from all quarters, was collected on days 0, 3, 7, 14, and 21 and analyzed for SCC. Additional milk samples collected on days -4, 10, 17 (with an additional sample on day 3 of period 2) were analyzed for environmental mastitis pathogens.
6. Teat end callosity – Teat ends were scored as either smooth or rough on days 0, 7, 14, and 21

Krawczel says the bedding additive did not affect teat-end cleanliness, teat-end callosity, or somatic cell counts. No meaningful treatment differences were observed in freestall cleanliness. Total bacteria counts were greater in the control for the first two days of sampling, but by day 7 there was no difference between the two bedding management approaches. On the other hand, environmental strep counts were greater in the control than the treatment. Counts increased over the course of the study for both control and treated sawdust. Coliform counts did not differ, but did increase over time. The additive did lower pH, but there were no differences in the overall dry matter. Fewer pathogens were found on the teats of cows housed with the treated bedding. There was a greater risk for pathogens found on the teat ends as pathogen load increased within the bedding and increased pH of the bedding.

The bedding additive worked as expected and was effective at lowering the risks of mastitis for dairy cows housed in freestalls using sawdust bedding. It still needs to be determined how practical its application may be on commercial farms. Within this study, freestalls were completely cleaned of bedding and pressure washed after 3 weeks. The additive would need to be added directly to the base of the freestall for effective use, so it would require all materials to be removed at regular intervals. Still, this may be worth the effort if current mastitis control practices are insufficient to control environmental pathogens, Krawczel says.