“Common wisdom” says that bedding should be refreshed often to provide a clean environment, while a close reading of the research literature suggests that to be ill-advised from the point of view of pathogen regrowth (as well as being less economical). Pathogens in organic bedding reach high levels within a day or two of being placed in stalls and rebedding provides fresh organic materials that serve as food for the organisms – thus, frequent rebedding may not make a difference. Two farms that used DMS directly from the separator in deep beds assigned two pens of animals to this study. The cows in each pen were of approximately the same parity and stage of lactation and were kept in the same pen for four full weeks in July and January.

Farm 1 housed only first-lactation animals in the two pens, while Farm 2 housed multiparous animals. One of the pens was bedded daily with fresh DMS, while the other was bedded every seventh day. Stalls in each pen were scraped and raked daily as per normal farm practices.

Quarter and bulk milk samples were taken at the beginning and end of the two trial periods and analyzed for bacterial concentration (i.e., milk culture) and SCC, respectively.

During the second and fourth weeks of bedding, samples of unused and used bedding were taken on day 0, 1, 2, 5, 6 and 7 and analyzed for bacterial counts and physical properties. In addition, farm records were accessed for individual cows in each of the pens over the two study periods to assess individual cow SCC and mastitis incidence.

Bedding bacteria
The frequency with which stalls were bedded with DMS had very little to do with the amount of bacteria found in the used bedding. The only bacteria found in significantly greater amounts in weekly versus daily used bedding was E. coli, and it occurred only in the summer at Farm 1 and only in the winter at Farm 2.

Season had much more effect on bacterial levels than did frequency of bedding. Summer showed higher levels of coliform bacteria, while winter showed higher levels of streptococci.

Bedding physical properties
Frequency of bedding had an effect on the moisture content and percent of fine particles of the used bedding. It was drier and less fine in the weekly bedded stalls. Both of these characteristics of bedding have been attributed to affecting SCC and mastitis.

When teat ends are exposed to bedding that is wet and fine, it is more likely to cause higher SCC and mastitis. If this is the case, then weekly bedding of DMS could have a positive impact on SCC and mastitis.

Udder health: Milk cultures
Culturing milk samples for mastitis pathogens can provide a great deal of valuable information for a dairyman. A single milk sample from an individual cow may provide significant information for that particular cow; however, multiple samples from many cows will provide much more information for mastitis prevention and control within the herd.

Bacteria found in the milk of a cow can help identify infections early, facilitate treatment decisions and allow management changes that will have the greatest impact resulting in fewer new infections. Generally, milk culture results can be divided into two or three categories:

• Positive culture results:
• Major pathogens (Staph aureus, Strep spp., A. pyogenes, serratia and proteus)
• Minor pathogens (Staph spp., C. species, G+ bacillus)
• Negative culture results

The animals in each pen on both farms had milk samples taken at the beginning and end of each four-week trial to determine if length of time between bedding would have an impact on the number or odds of an animal having a positive culture at the end after having a negative culture in the beginning.

The odds of having a positive milk culture at the end of the bedding frequency scheme were not affected by frequency of bedding. It was affected by the farm and lactation number.

Since Farm 1 had only heifers, and Farm 2 had only multiparous cows on the study, the two variables are basically the same. Heifers were less likely to have a positive post-culture than second-or- greater-lactation cows.

The number of animals with positive post-cultures at Farm 1 was affected by frequency of bedding and the amount of E. coli in the bedding.

However, heifers in the daily bedded pens were 7.2 times more likely to have a positive post-culture than those in the weekly bedded pen and E. coli was negatively correlated, meaning that the more E. coli found in the bedding, the fewer animals with positive cultures.

Since daily bedded pens had more moisture and fine particles than weekly bedded pens, increased positive cultures makes sense, but higher bacterial levels causing fewer animals to have a positive culture is hard to explain. There were no indicator variables at Farm 2 that had an effect on the number of animals with positive post-cultures.

Somatic cell count
SCC was evaluated on all animals in each of the pens to determine if those with a normal count in the beginning would have an abnormal count at the end of the four-week period based on whether they were in the daily bedded or weekly bedded pens.

The number of animals with abnormal post-SCC was affected by frequency of bedding at Farm 1 and the amount of E. coli in the used bedding at Farm 2.

At Farm 1, weekly bedded cows were more likely to have an abnormal post-SCC than daily bedded cows, which was the same farm where weekly bedded cows were less likely to have a positive post-milk culture. If SCC has a direct relationship with the amount of bacteria in the milk, this does not make a lot of sense.

At Farm 2, the amount of E. coli in the used bedding was positively correlated with the number of animals with abnormal post-SCC. However, at Farm 2, there was no difference in E. coli levels between the two pens.

Because the farms responded differently, it is more likely that other variables, such as milking parlor procedure and/or cleanliness of the animal, are playing a bigger part in the number of animals with abnormal cell count.

Mastitis
Mastitis events over the study period were few; 5 out of 400 animals (1.3 percent) at Farm 1 and 12 out of 350 animals (3.4 percent) at Farm 2.

The odds of a cow getting mastitis were significantly higher for those cows that had an abnormal pre-SCC at Farm 2, while none of the indicator variables had an effect on the odds of getting mastitis at Farm 1. In addition, the number of mastitis events was not affected by any of the indicator variables.

Daily bedding of DMS can be time-consuming and expensive and may not have any positive impact on bacterial levels or milk quality and mastitis. Less frequent bedding in deep beds may even have a positive impact by reducing the moisture and the amount of fine particles. PD

References omitted due to space but are available upon request to editor@progressivedairy.com .

—Excerpts from Cornell Waste Management Institute.

Jean Bonhotal
Cornell Waste Management Institute cwmi@cornell.edu