The hidden costs of mastitis

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“Doc, the plant just doesn’t pay me much of a somatic cell count premium anymore. What’s the point of having a low SCC?”
Most dairy veterinarians have heard many versions of this statement.
The beauty of those SCC premiums was they were visible. You saw them right on the milk check every two to four weeks. However, premiums still exist; it is just that they are more hidden.     
The costs of mastitis has been discussed for many years, but most discussions focus on the cost of clinical mastitis because this is the most obvious cost. For clinical mastitis, the biggest cost is normally the cost of discarded milk. For subclinical mastitis, there is normally no discarded milk because the term subclinical just means something we do not notice, so the milk gets sold and you get paid.
One might assume the costs are, therefore, minimal. But, they are still real and significant.
Because the incidence of subclinical mastitis is typically many times greater than clinical mastitis, even minor costs per case can add up to be significant. A 2018 paper by Potter et. al., in the Journal of Dairy Science, looked at two of the biggest costs of increased SCC: reduced milk production and reduced feed efficiency. The authors looked at seven experiments between 2009 and 2015 using over 1,000 observations at Penn State University. As one would expect, the linear score of the SCC was negatively correlated with milk production and energy-corrected milk production. However, it was also negatively correlated with feed efficiency for milk and for feed efficiency for energy-corrected milk.
For example, if we compare a cow with a 250,000 SCC to a cow with a 50,000 SCC, the results suggest the cow with the higher SCC produces about 3.52 pounds less milk per day, produces 0.04 pounds less milk per pound of dry matter intake and produces 0.03 pounds less energy-corrected milk per pound of DMI.
Let’s assume our clean cow produces 90 pounds of milk per day and eats 56.25 pounds of dry matter. Then, let’s assume a milk price of $22 per hundredweight, feed cost of $0.16 per pound, and that feed cost is 50% of the cost of producing milk.
According to a little spreadsheet I constructed to calculate the losses, our lower SCC cow produces $0.77 per day after subtracting feed costs, from more milk, for a net gain of $141.33 per year.
When we include the loss of feed efficiency for the higher SCC cow, we find an additional cost of $0.17 per day, or $60.43 per year.
The total difference between our two cows is $0.55 per day, $201.79 per year or $0.50 per hundredweight using 90 pounds of milk per day. In this example, loss in feed efficiency is about 30% of the total loss. This estimate is just for milk and feed efficiency. It does not include more culling, actual SCC premium losses from the processor or anything else. It also does not include the cost of clinical mastitis.
To calculate the cost of clinical mastitis, let’s assume a herd of 1,000 lactating and dry cows has a rate of 3% and 4.5% for new clinical (this lactation) and total clinical cases per month.
Then, let’s assume another 1,000-cow dairy next door has a 50,000 herd SCC and rates of new clinical and total clinical mastitis for 0.35% and 0.5%.
While clinical case rates are strongly dependent on how determined one’s team is to diagnose clinical cases, it is a fair assumption that low SCC herds typically have very low clinical case rates, and high SCC herds have high rates. It is also a reasonable assumption that substantially reducing herd SCC will substantially reduce clinical mastitis rates.
Using a cost of clinical mastitis of $444, from another peer-reviewed paper (Rollin), we find the cost of clinical mastitis to be $173,160, or $173 per cow, for our high SCC herd. The total cost is $374,948, or $375 per cow, of which 54% is from subclinical mastitis.
Data from the University of Minnesota’s FINBIN system show an average profit after labor and management for 2022 for all dairy farms in the dataset of $328 per cow. Thus, the gains in reducing SCC from 250,000 to 50,000 in our fictional herd exceed the total average net profit of a dairy farm in 2022.
Notice that in this example, using fairly high rates of clinical mastitis in the high SCC herd, the cost of subclinical mastitis is still greater than that of clinical mastitis. We can adjust the assumptions and recalculate, but in all cases, the costs of subclinical mastitis are substantial. Thus, to answer my client’s question, I would say, “Healthy cows. Healthy cows will make you more money.”
Either way, the hidden costs of subclinical mastitis are real and substantial. Having a low herd SCC does indeed generate substantial premiums. They just show up in a different column on your milk check.
Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.

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