Two or more mastitis bacteria a year are diagnosed on most dairy units as causing a significant proportion of the disease, highlighting the importance of continuing to use long-acting dry cow therapy with efficacy against both Gram-positive and Gram-negative mastitis organisms.

That's the message from Schering-Plough Animal Health veterinary adviser Andrew Montgomery, who points out that although diagnostic data from the regional VI Centres continues to show that Streptococcus uberis and Escherichia coli are still the two most prevalent mastitis organisms - accounting for over 50% of diagnoses between them - a closer look at the figures shows that a range of different mastitis-causing bacteria occur on many farms.

"The latest VLA Farmfile data give a full herd analysis rather than individual cows and shows that 63% of farms had two or more mastitis bacteria during the course of a year. It also shows nearly 40% had 3-4 organisms implicated, whereas 5% of units had to wrestle with five or more. What's more, two thirds of the farms with multiple infections struggled with both a Gram-positive (eg. S. uberis) and a Gram-negative bacterium (eg. E.coli)," he says.

According to veterinary researcher Eric Hillerton from the Institute of Animal Health, milk producers striving for better mastitis control should both improve overall unit hygiene and use a broad-spectrum dry cow tube that covers the whole dry period1. This is because cows are highly vulnerable to new mastitis infections during the last two weeks of the dry period.

"It's crucial to follow a disease management strategy based on these two principles if the persistent environmental organisms in particular are to be controlled more effectively," he says.

"S. uberis is now the most common disease pathogen implicated in dry cow mastitis and remains prevalent largely because of its ubiquitous nature, its ability to infect the cow during the dry period and the fact that it seems more able than E. coli to persist as a sub-clinical infection. It is also a year-round threat," he stresses.

"As an environmental organism, S. uberis is synonymous with dry cow yards in the winter. But our UK research - as well as farmer experience from New Zealand and soil culture studies from dry cow paddocks in the USA - suggests summer calving herds need to pay as much attention to S. uberis as winter calvers."

The Institute's UK study discovered S. uberis infections in both winter and summer calvers. And of the cows not receiving dry cow therapy, half those infected with the pathogen went on to develop mastitis.

"In dry hot summers cows may lie under trees for shade and these areas may become fouled with dung. This faecal contamination can be a potent source of S. uberis, so you cannot confine the environmental risk to the housing period," Eric Hillerton points out. He also says some S. uberis strains are more persistent than others and appear able to survive for longer in the environment.

"On this basis and because of the quite often multifarious nature of mastitis, an accurate diagnosis of the problem is essential if vets are to recommend the most effective prevention and control strategies. In herds where S. uberis is identified as the primary pathogen causing mastitis, producers should pursue aggressive treatment of clinical cases and review consistently high somatic cell count cows to see if they are harbouring subclinical infection. Similarly, during the dry period, it is important to use a tube with prolonged Gram positive cover, ideally for the whole dry period - as well as opt for broad-spectrum efficacy for added insurance2," he advises.