Keep acting to reduce clinical mastitis levels

Farmers may have worked hard to reduce national average somatic cell counts, but it is essential they do not become complacent when it comes to the number of clinical cases of mastitis.

Independent dairy consultant John Sumner, speaking at the British Mastitis Conference in Worcester last week, told producers there was still a long way to go to reduce the number of clinical cases of mastitis.

Since 1980, average somatic cell counts have dropped from 469,000 cells/ml to 197,000 cells/ml in 2008. However, mastitis incidence has remained similar in a range of 50 to 55 cases for every 100 in 2008 compared to about 54.6 cases in 1980.

“The fact that a single mastitis case costs £200-£250 has been talked about for many years. But why is this significant loss not driving a reduction in cases?

“Sometimes we need to stand back and ask whether we are applying well-established control strategies correctly,” he said.

Implementing a full milking routine is crucial to minimise problems, but lack of time may be a limiting factor on most farms. However, in these cases, employing additional labour could be worthwhile in terms of reduced mastitis cases.

And many farmers have the potential to reduce mastitis incidence by tackling ventilation in existing cattle buildings, according to Jamie Robertson, Livestock Management Systems. “Ventilation can directly influence the survival rates of E coli and Strep uberis. For example, when bacteria is aerosolised – as with airflow across a straw bed or cubicle – loss of water molecules by evaporation may cause loss of microbial activity.”

Fresh air also influences survival rates, with E coli demonstrating a 97% mortality rate after being exposed to fresh air for 90 minutes.

However, according to Mr Robertson, half of all buildings are inadequately ventilated for the animals housed in them. “People often emphasise nutrition and stocking rate in dry cow sheds, but too often I see these animals housed in grotty buildings.

“Problems are rarely a result of inappropriate stocking density, but more because of insufficient removal of vast quantities of heat and moisture,” he said.

When ventilation is not up to scratch, moisture is unable to escape, landing on beds and creating an ideal environment for mastitis causing bacteria.

“We need to get the environment working against pathogens and for animals. A common misconception is that, because a building has some vents in the roof, it will ventilate adequately. But a building with only 50% of the required outlet area will only provide ventilation for 50% of stock housed.

“When air speed drops to calm, the only way fresh air can enter the building is when air leaves the building. With inadequate outlets, there will be an increase in heat and moisture.”

And Mr Robertson said that any opposition to putting holes in the roof is misplaced as concerns over water entering the building can be managed by using a covered open ridge. Most rain ingress will also be prevented by the warm air leaving the building.

“Ventilation and stack effect requires a basic matching of inlet and outlet areas to be able to work to maximum efficiency. The relationship between inlet and outlet areas is building specific. But at minimum, an inlet to outlet ratio of 2:1 and typically 4:1 is recommended.”