Dairy cows are large, awkward animals and this is especially evident when they lay down. They basically drop to their knees and then allow the rest of their body to fall down into place. Observing cows as they lay down makes it obvious just how hard they hit the surface with their knees and from this it is clear some type of cushioning material is needed to minimize injuries. Bedding materials should provide a cushioned stall surface and act as a shock absorber.
Coliforms and Klebsiella species are capable of growing extensively on moist wood product bedding materials. Freshly defecated manure provides large number of coliform bacteria. When manure is placed on bedding material it inoculates it and can quickly produce large numbers so long as there is adequate moisture and nutrients. Such bedding material, when sampled, may show extremely high bacteria counts. If sampling is done be prepared to find very high numbers, especially if the conditions have been warm and humid and the bedding is soiled and damp.
Environmental Streptococcal species tend to flourish on straw bedding. That may be their preferred niche for some reason. That doesn’t mean they won’t grow on sawdust but they flourish well on straw. This is a concern for dry cow and maternity areas since these areas frequently are bedded with straw. The environmental Strep population may build up significantly in this material putting recently dry and near fresh cows at risk. Even clean looking bedding can contain very high concentrations of these bacteria. In herds experiencing environmental Strep mastitis problems, especially early in lactation, take a hard look at these areas because they may be a contributing factor.
Limiting Bacteria Growth in Bedding
Organic bedding materials frequently used are capable of trapping materials between bedding particles. Also the particles themselves may provide large surface areas for bacterial adherence. Finely chopped straw, fine sawdust or manure solids offer a large surface area and excellent opportunity for bacteria growth. Even if these materials start with very low bacteria counts, in short order the number can grow to very high numbers once contaminated.
Sand on the other hand offers nothing for bacteria to metabolize since it is an inert silica material. It also allows water, urine and milk to drain reasonably well through it reducing the surface moisture and nutrient supply for bacteria.
Generally speaking, even under the best of conditions organic bedding bacteria counts will exceed those found in sand bedding and this is one reason why sand is frequently used in free-stalls as bedding.
Can materials be added to the free-stalls that slow down or limit bacteria growth? This is a tall order. Compounds that might do so often are detrimental to the cows skin and therefore are unacceptable. Also, it is very difficult to apply disinfecting compounds so that all of the bedding is contacted. Typically the surface layer may be treated but the deeper material may not be. Finally, even under the best of conditions bacteria are constantly being added to the stall bedding as cows enter and deposit additional bacteria from manure, mud etc.
Adding lime to stall bedding appears to slow bacteria growth for about 24 hours by raising the pH beyond the optimal range for the bacterial growth. It also ties up some of the moisture. Within 24 hours the affect deteriorates and growth again speeds up.
Bedding also helps keep the stall surface clean and dry. Different bedding materials do so in different ways. Sawdust, shavings and straw absorb moisture resulting in a drier bed when bedding materials are changed frequently. When bedding becomes heavily soiled and wet, soon cows are also dirty and wet and the problem passes through to the milking center.
Sand performs differently as a bedding material. Due to its porous nature it allows moisture to drain through leaving the surface reasonably dry.
Bacteria Growth in Bedding
Bacterial growth in bedding materials occurs after the bedding has been contaminated and then provided food, moisture and warmth, the three essentials for bacterial growth. These issues are where potential problems commence and they are also where solutions can be implemented.
Organic bedding material naturally has some level of bacteria associated with it. In addition, shortly after placement in freestalls, it becomes soiled with manure, leaked milk and other body fluids such as uterine discharges etc. Plenty of bacteria, food and moisture are placed on the bedding to quickly seed and promote bacterial growth.
Limiting moisture slows bacterial growth by denying bacteria sufficient water to meet their needs. For this reason dry bedding helps slow bacterial growth.
Bedding moisture content varies due to ambient conditions, added water and the starting moisture content of the material. Fresh bedding, added to stalls, needs to be as dry as possible to help limit bacterial growth. Wet sawdust has been documented as capable of supporting large numbers of Klebsiella species of bacteria, which are similar to coliforms. Kiln dried sawdust is preferred because of the low moisture content and reduced initial bacteria counts.
Organic bedding materials absorb and retain water and stay damp, especially under conditions where barns are closed and airflow is limited. Sawdust, shavings, paper products and recycled manure solids all have this characteristic. Once wet they tend to stay damp providing bacteria exactly what they need.
For these reasons stall bedding must be frequently replenished to reduce soiled and damp material. Correct stall dimensions and positioning of neck rails and brisket boards also are important. The objective is to position cows so they urinate and defecate in the alleyways rather than in the stalls.
Bacteria are adaptable and develop abilities to flourish in certain niches. This holds true for dairy cattle housing and bedding materials.
Other compounds such as organic acids, bleach, quaternary ammonia compounds are quickly neutralized by bedding materials plus, in the short term, they may pose too much risk for teat skin irritation to justify their use. They also represent a cost in terms of labor to apply the materials plus the cost of the material.
Bedding has been linked to several mastitis problems. Wet sawdust bedding has been directly associated with large numbers of Klebsiella bacteria. Such concentrations increase the risk of Klebsiella mastitis, which often produces serious clinical cases. For this reason, use of wet sawdust, as bedding material, is strongly discouraged.
Temperature also plays a role. In the late spring and early summer ambient temperatures and humidity often rise quite quickly. The temperature increase accelerates the rate of bacteria reproduction and bedding counts may rise to very high levels rapidly. This may reoccur in the heat and humidity of the late summer. There is likely a correlation between these changes, and increased new infections related to coliforms and environmental Streps often seen at these times.
Organic bedding materials have to be changed frequently to limit bacterial growth. Each time cows exit the housing area to be milked the back of the stalls need to be cleaned out and the fresh bedding in the front of the stall pulled to the back to provide relatively clean, dry material.
Cows spend a good deal of their time lying in the freestalls. They need to be clean, dry and comfortable. Dirty stalls leads to dirty teats and udders which in turn leads to more water used to clean cows in the parlor. Water sprayed on the udder and teats is difficult to control and frequently allows bacteria to float from various locations to the teat end and that increases the risk of new mastitis cases.