It is easy to overlook a case of mastitis, particularly if there are no visible signs. And checks at the bulk tank or composite samples mean producers still run the risk of missing individual cases due to the dilution by milk from other healthy quarters and cows. Mastitis results in waste and lost income due to milk losses, potentially high veterinary bills, including the more wide-spread use of antibiotics and negatively impacts cow welfare. Catching it early is a win-win for everyone.

What are the disadvantages with traditional methods for measuring somatic cell count?

SK: SCC indicates an immune response of the udder tissue. It can be monitored in various ways: via the bulk tank, by taking composite milk readings (a combined sample from all four teats) or by taking samples from individual teats. The first two methods have been used for decades, with the information made available either from the dairy processor or via on-farm milk recordings using sensor technology, either on farm or in the laboratory. Quarter level samples, meaning from each udder, have not been used widely, given their tendency to be time-intensive and costly.

Although bulk milk somatic cell count (BMSCC) provides an overview of udder health, the quality of this information is limited. A high incidence of new clinical infections may not be revealed by an increase in BMSCC as milk from clinically infected cows should not be delivered to the dairy processor but rather discarded. On the other hand, a high number of subclinical infections, which may often be chronic, will lead to an increase in BMSCC. Subclinical infections are more difficult to identify than clinical cases, necessitating individual cow observation and examination. As increased SCC leads to a reduction in milk production, the effect of high SCC cows is masked and may go undetected until a critical level is reached in the bulk tank or the infection becomes clinical. And as already mentioned, there is a risk of undetected cows shedding bacteria and infecting other cows. The SCC in the bulk tank gives an indication of udder health for an entire herd, however the clinical and treated cases of mastitis are left out.  

Analyses of SCC measurements from individual cows are normally available via monthly milk recordings or by taking herd samplings. However, both strategies are disruptive to farm and herd routines. After laboratory analysis, farmers must wait at least a couple of days for the results. Based on this information, cows with an elevated cell count in the composite milk can be identified; this is extremely important for heifers and freshly lactating cows. In late lactation, this information may be used for decisions concerning the drying-off period.

Although this method does provide some information at the individual cow level, it still leaves much to be desired, largely because it only provides a snapshot of 1-2 milkings per month – revealing nothing about what’s happening in between samplings. A subclinical mastitis, for example, could go undetected if it occurs between two control days. This, in turn, could lead to a decision for drying-off treatment which could subsequently increase the risk of renewed infection in the next lactation cycle. Likewise, if a cow has only one or two quarters with a high cell count and consequently reduced milk production in the sum of the composite SCC, she can still appear ‘normal.’

As milk production and mastitis risk vary throughout lactation, the way to use the information changes as well. At the beginning of lactation, cow and udder are at risk of acute infection, often clinical, due to the transition phase and stress on the immune system. During this time, early detection is important and does have an impact, given quick intervention can reduce drops in milk yield and lead to quicker recovery.

Likewise, treatment progress can be monitored. This means that even if the cow is treated and its milk discarded, cell count per quarter continues to be analyzed at every milking. Decreases in cell count class can therefore be detected immediately. If treatment is unsuccessful and the cow remains at the top of the alarm list, then the treatment can be adapted quickly. After peak lactation, the risk of acute mastitis decreases, however the chance of subclinical infections may increase, either due to an acute mastitis becoming chronic and subclinical, or due to an infection with cow-associated bacteria. These animals can be identified, and either treated, separated or other management decisions taken swiftly.  

Ultimately, the opportunity to track individual quarter cell count class throughout the entire lactation period enables all parties involved, including farmers, herd managers and veterinarians, the opportunity to base their decisions on sound data.