Climatic factors affecting exposure in herds where cows are maintained on dry lots differ from those of traditional Midwestern and Eastern herds. Dry lots are used primarily in hot, arid areas where temperatures are seldom below freezing for an extended time. In these areas, the rainy seasons of late Fall through early Spring are when bacterial populations are greatest. Manure in dry lots during the Summer tends to be desiccated, thus limiting the moisture essential for bacterial growth. Ideally, bedding should be inorganic materials that are low in moisture content and contain few nutrients for bacteria to utilize.
Washed sand has little nutritive value to common mastitis pathogens, thus limiting their growth.
Compared to organic materials such as sawdust, recycled manure, straw, and dirt, washed sand consistently contains fewer mastitis pathogens. Many free stall barns are forced to use organic bedding materials that are compatible with liquid manure handling systems. There appears to be little advantage in using one organic material over the use of another. For example, straw tends to have highest streptococcal counts, while sawdust and recycled manure have highest coliform counts in comparisons among these bedding materials. A ny material to be used as bedding should be stored in a dry area to prevent saturation by rain and ground moisture.