When faced with a subclinical mastitis problem, the first inclination one might have is to cull your way to success. Some herd management software and Dairy Herd Improvement (DHI) reports actually list the cows to cull to reach your Somatic Cell Count (SCC) goal. These "Hot List" reports identify the percent of contribution each cow on the list makes to the overall bulk tank or herd SCC. If only life were so simple!
Individual cows with high SCCs fluctuate dramatically. The cow at the top of the "Hot Cow List" that produces 150 pounds of milk a day and has a SCC of 10 million could very well be down to a 600,000 SCC three days later. Also, SCC measuring equipment can fluctuate ±10 percent and still be in DHI-approved range.
Producers who have used only these lists are amazed that on the next test day other cows with high SCC step up to replace the ones culled the previous month. Staying on this carousel means continually culling profitable cows that occasionally have high SCC.
Preventing New Infections
AgSource Cooperative Services has taken a different approach. We focus on preventing new infections. Every herd has chronically infected cows, and over time these cows will be culled because of low production or reproduction. At the same time, by limiting new infections, a producer can make long-term improvements in herd SCC. Even a producer who has to cull a significant number of cows immediately to get below a SCC limit needs to work towards prevention of new infections.
Management Considerations to Reduce SCC
The next step in lowering new infection rates is to determine if the majority of infections are caused by the environment or if they are cow-to-cow infections. Individual cow milk cultures can answer this question.
Be sure the cows chosen for culturing answer the question you are asking, "What are the major pathogens causing problems today?" Culturing longterm, chronically-infected cows will give a historical perspective, but we are not interested in solving last year's mastitis problems. The goal is to find the cause of the most recent infections, so pick cows that are infected for the first time on the most recent test day. Since fresh cows were identified as a problem area for this herd, select some animals from that group.
If the culture information indicates environmental infections are prevalent, the focus needs to be on overall cleanliness including clean bedding and clean aisles. It is also important to correctly post-dip teats.
Cow-to-cow infection prevalence indicates the focus needs to be on preventing milking machine liner slips. This includes making sure milking equipment is functioning correctly and cows are prepped properly for letdown. Post-dipping the entire teat end with an approved product is also important for these infections. If possible, segregate infected cows.
Moving from a mastitis control regime of treating infected cows and culling non-responders to a program focused on preventing new infections will save time, increase profits, lower the risk of antibiotic contamination and result in a higher quality product.