Afarmer I attended to recently had issues with heifers calving down with mastitis. This is frustrating given the impact it can have on the cow’s lifetime milk production. A sample of milk from the heifer was tested and the infection which caused the mastitis was determined to be coagulase negative staphylococci (CNS) or non-aureus staphylococci(NAS) as they have more recently been described.

These bacteria live naturally in the lining of the teat canal, and therefore account for a large proportion of positive results on cultured milk samples. In most cases they do not cause clinical mastitis, ie changes in milk/inflammation of the udder. But in this case the heifer had some clinical mastitis, therefore we treated her with intramammary and injectable antibiotics and anti-inflammatories, based on the results of the antibiotic testing carried out on the milk sample.

Recent research indicates CNS bacteria can be cultured from the milk of many heifers and cows post-calving. There is evidence that the presence of CNS can be protective against infection with some of the more significant causes of clinical mastitis, such as staphyloccus aureus or streptococci. Therefore, the presence of CNS in a milk sample does not necessarily mean the heifer should always be treated with antibiotics. In fact, the opposite is the case, as many of these CNS bacteria have resistance to antibiotics, and the use of antibiotics in these non-symptomatic cases may contribute to further antimicrobial resistance. It is only by culturing the milk samples from individual high-cell-count cows that we can get a true picture of what is going on at farm level.

In addition to treating the mastitic heifer, we reviewed the pre-calving nutrition, which can have a major effect on clinical mastitis rates in all cows, including first-lactation heifers. High protein levels can lead to excessive flagging, while low levels of minerals and vitamins, particularly selenium, can increase mastitis risk. There is also evidence fly activity can introduce bacteria to the udder of the heifer before she calves, so a fly control programme will be useful on some farms.

John Gilmore is a practising vet and managing director of FarmLab Diagnostics, an animal health testing laboratory www.farmlab.ie