Mastitis and new infection risk – staying aware of fundamental principals

Mastitis and new infection risk – staying aware of fundamental principals
By John Penry, Veterinarian and Researcher, Anexa Vets

Mid-lactation presents an opportunity for all herds to assess their new mastitis infection status. For farms enrolled in herd testing, the second herd test has generally been done and with this comes the ability to compare groups between test #1 and #2 for the season. The percentage of animals with an elevated individual cow cell count (ICCC), above the subclinical mastitis threshold, in HT#2 that were below the threshold in HT#1 is an indicator of new infection rate, or new infections per month. Here the heifer group are of particular interest as it is assumed that, where clinical mastitis has not been observed, this is a true new subclinical infection. In a similar vein, measuring the number of new clinical mastitis infections, in mid-lactation cows over the past two months also allows us to assess new infection rate, and hence risk. Here, we do not wish to see any rate over 1-2 new clinical mastitis cases per 100 cows per month.

So, assessing new infection rate, and hence new infection risk is straight forward, useful and of benefit. It is also worth recalling that the main drivers of new infection risk are simple ones – in fact, there are only two principles to remember.

Principle #1: Maintain and optimise teat tissue health: teat tissue health sounds vague but it can be described in specific terms. The teat – any teat – does not like milking conditions that either increase hyperkeratosis (callous formation at the teat end) or congestion in the teat-end/teat-barrel. While adverse Winter weather conditions can increase the risk of teat tissue health being compromised, in reality it is actions associated with milking that pose the main risk factors for reduced tissue health. There is ample evidence from the past 30 years that associates an increased risk of new infection with either an increase in teat-end hyperkeratosis, or increased teat congestion post milking, or both.

Principle #2: Reduce the number of bacteria around the teat: This principle is really simple in concept – the teat-canal has a magnificent defence mechanism, but it can only cope with so many bacterial numbers between milking. If this threshold is crossed the defences progressively become less able to cope with bacterial numbers and new infection risk increases accordingly. It is not just a matter of the bacterial numbers on the teat-end but also on teat skin as the presence of increased organic material makes it more difficult for teat skin to remain healthy. The most obvious example of this is teats that spend a high proportion of time covered, or partially in mud. Here there is excellent evidence showing the association between increased bacterial load around teat skin and a incremental increase in new infection risk.

Virtually all mastitis control measures can be traced back to these two principles. They are simple to remember, clear to understand and the foundation of any control advice.

Date Added: Wednesday, 5th December 2018