Raising the bar on milk quality

After being in practice for more than 40 years, Dr. Pam Ruegg, DVM, Michigan State University, has seen many changes not only in how mastitis is detected, but how it’s treated. “What I’m seeing around the U.S. is a lapse in people using DHIA individual cow data, fewer people doing foremilking and recording cases and fewer people reporting all clinical cases,” said Ruegg in a presentation on key performance indicators (KPI) for milk quality. “We need to go back to basics and the process of managing milk quality.” Ruegg sees fewer herds on DHIA with individual cows, fewer who are forestripping every milking and fewer herds reporting all cases. While every dairy farm has access to their bulk tank somatic cell count (SCC), that information doesn’t provide sufficient data. Both subclinical and clinical mastitis are costly and reduce farm efficiency. In managing for high quality milk, it’s important to detect subclinical mastitis with individual cow cell count values. Clinical mastitis data are also necessary, which requires observing foremilk to find abnormalities. All mastitis cases, not just treated cases, should be recorded. “Even in low cell count herds, we can be losing a lot of money from subclinical and clinical mastitis,” said Ruegg. “We also need udder hygiene scores and teat dip coverage, which are reporting systems that allow us to identify risk factors. We need to be able to monitor, measure and manage both subclinical and clinical mastitis events. Many farms aren’t alarmed if the cell count is 229,000 because ‘it isn’t that bad.’ It used to be great, but it isn’t good enough anymore.” In 2000, the average bulk tank SCC for the top 10 dairy states was about 300,000, which now looks extremely high. “Fast forward to 2010, the average bulk tank SCC across the top 10 states was about 225,000,” Ruegg said. “Now forward to 2024 – requirements for the milk the market wants are more stringent, which has a lot to do with our export market. The goal today for bulk tank count should be less than 175,000.” Bulk tank SCC is driven almost exclusively by the percentage of cows in the herd that have subclinical mastitis. For high quality milk, this means minimizing the number of cows in the herd above 200,000. The KPI should be fewer than 9% of cows tested for two consecutive months maintaining high cell counts. “This is an important KPI to manage,” said Ruegg. “Cows that become chronic infect other cows and produce the least amount of milk. The second KPI is managing subclinical mastitis. Watch for new infections, and check milk that appears to be normal. Milk can have white blood cells that don’t show up.” According to Ruegg, one quarter can have millions of somatic cells yet have normal-looking milk. To detect mastitis, milk from individual cows must be tested. Suitable testing is via a CMT or biomarkers obtained via an automated milking system (AMS). “It’s also important to understand that the SCC values we’re managing are composite milk samples,” said Ruegg. “That means milk from all four quarters are in one sample. To get to the magic 200,000 threshold, one quarter has to hit at least 800,000 if the other three quarters are healthy. When we see the value hit over 200,000, there’s confidence there is a subclinical mastitis infection.” Ruegg outlined the KPI for managing prevalence of subclinical mastitis: “Prevalence” is the percentage of cows with a SCC of about 200,000, which should be less than 15% of lactating cows. “Incidence” refers to new infection rates, which is available from herd management software. Incidence is the percentage of cows developing new subclinical mastitis infections based on two consecutive months of cell count testing. Only cows eligible to become infected are included. Cows must be on Month 1 with a healthy cell count (under 200,000), but perhaps in Month 2 they are above 200,000. This indicates how the farm’s current prevention program is working. There are interventions to identify chronic cows. “If you don’t have DHIA testing, you should get monthly SCC and find these cows,” said Ruegg. “Chronic cows are costly. They increase the bulk tank cell count, are infective long-term, shedding bacteria that infect other cows, produce a lot less milk, have more clinical cases, require more antibiotics, require more dry cow antibiotics and have lower conception rates.” With high beef prices, the best solution may be to cull these animals and replace them with younger, healthy animals. Any cow diagnosed with Mycoplasma bovis , Staph aureus or Prototheca bovis should be culled. “It’s almost impossible to cure these cows and they are infectious to others,” said Ruegg. “You’ll end up with more new infections.” Consider culling cows with multiple quarters affected by mastitis. “Identify and segregate or consider culling cows that have more than two clinical cases in one lactation” said Ruegg. “It’s hard to make up lost money by tossing milk.” Ruegg also suggested culling older cows that have more than three SCCs over 200,000. An older cow with a high cell count that isn’t dropping is unlikely to respond to interventions. “If a cow dries off with high cell count, receives antibiotic dry cow therapy then calves in the next lactation infected again, don’t breed or keep them,” she said. “The odds of an intervention curing that cow diminish the longer they’re infected.” Milking technicians should be trained to detect clinical mastitis by looking at foremilk at each milking. Ideally, three streams of foremilk should be removed and examined. Failure to forestrip results in missing at least 50% of mastitis cases. Managing antibiotic use on farm is another KPI. This is an area that’s undergoing scrutiny from legislators and milk purchasers. The standard daily dose is the dose of an antibiotic given to a cow in one day – a major reason to reduce antibiotic use is to save money. If routine treatment protocols for non-severe clinical mastitis are longer than the minimal label discard, Ruegg said farmers can save money by reducing the duration of treatment by one day. Alternatively, find a shorter duration treatment for lower risk cows. “It’s important to manage milk quality by using data,” said Ruegg. “To use data, we have to have it, and we have to record it. We want to benchmark, have goals, actions, evaluate and keep moving forward. If we want to stay in this business, we have to be doing better.” by Sally Colby