Can somatic cell counts get too low?
That seems to be a question I receive often from producers who are trying to achieve optimum milk quality.
Low SCC herds usually have low levels of contagious bacteria and limit the spread with good milking procedures and management practices. When these herds do get an infection it is usually environmental. These organisms are opportunistic, not invasive, meaning most animals that get these infections are immune suppressed or stressed, such as dry cows or early lactation animals. Low SCC cows are not more susceptible to environmental organisms, but clinical signs tend to be more visible and grab the attention of producers.
High cell counts cost money. The cost of a high cell count doesn't just come from the penalties imposed or bonuses foregone when targets are not met; high cell count cows produce less milk than low cell count cows. A high cell count herd will also have more clinical mastitis. So reducing cell count can provide substantial savings - on average, reducing the bulk cell count from 250,000 to 150,000 will result in savings of around £50 per cow per year, most of which comes from a reduction in production of around 0.5L more of milk per day. So cell counts are a valuable tool which can be used to identify a problem, assess the cost of the problem, give a guide as to the solution, and to monitor the response to control programmes.
What is a somatic cell count (SCC)?
When the udder is infected somatic cells from the blood (white blood cells) move to the udder and into the milk to defend the organ against the invading bacteria. Without this response, elimination of mastitis, even mild cases, would be very slow and tissue damage greatly increased.
For an individual cow the ideal cell count is 100 - 150,000. Below 50,000, there is some evidence that cows respond more slowly to infection, particularly with E. coli, so they have an increased risk of mastitis. So as reducing bulk milk below 100/150,000 may increase the proportion of very low cell count cows, it may also increase the risk of clinical mastitis. Nevertheless because of the other benefits of low bulk cell count the answer is not to increase cell count but to maximise immunity (such as by minimising negative energy balance) and to keep the cows in as good an environment as possible