MMN July 2024 – Contagious Mastitis: Tackling High SCC’s

Being above the standard litre target for somatic cell count (SCC) can have a significant impact on your milk cheque. High levels of contagious mastitis within a herd often result in high SCC’s. The common contagious mastitis bugs are Staphylococcus aureus and Streptococcus dysgalactiae, and to a lesser extent, Streptococcus agalactiae and mycoplasma. Streptococcus uberis, while usually considered an environmental bug, is also a cause of contagious mastitis, although is a lesser cause of a raised SCC.

Contagious pathogens are those that spread from cow to cow and are found on the cow’s skin on the teats and udder. They tend to be transferred to other cows during milking from the milking equipment or the milker’s hands. Given how well these bugs adhere to the skin’s surface and can easily enter the teat canal, post-milking teat dipping/spraying is very important in controlling its spread.

If bulk tank SCC’s are consistently high, first test a sample from the tank to determine whether the main culprit is environmental, contagious or other. This will help narrow down what the best strategy is to help combat the source of infection. In addition, it can be useful to test milk samples from individual cows (before treatment), especially those that regularly have a high SCC or those with a new infection to establish the main cause. It only takes a few cows in a herd to raise the bulk tank SCC and individual SCC results are useful to identify problem cows, helping make good culling decisions.

The spread of infection can be reduced by having robust milking procedures in place for staff to follow. These include:

• Ensure liners are changed regularly (every 2000 milkings), including liners that are cracked.
• Have effective pre-dipping and post-dipping procedures. Use a product known to be effective against the main mastitis causing bugs and ensure good teat coverage with product.
• Care with cleaning cloths – using a clean one per cow for wiping and drying teats. Wash reusable cloths at 90°C and ensure they are dry before reusing.
• Wear gloves when milking and clean in disinfectant or renew when dirty/necessary.
• Form a high cell count group of cows to be milked last through the parlour to avoid spreading mastitis bugs to other healthy cows.
• On-going staff training is crucial so that they understand the importance of good milking procedures in the fight against mastitis.

 

Antibiotic dry cow therapy is generally much more successful in curing contagious mastitis compared to during lactation. In a high cell count herd where mastitis is mainly of contagious origin, it may be worth using a lower SCC threshold from the last three monthly milk recordings for targeting infected cows with antibiotic dry cow therapy.

Antibiotics are not always effective at treating mastitis caused by S. aureus as the bacteria can “hide” in fibrous mammary tissue that is difficult for the antibiotics to reach. In chronic cases where the infection has not been effectively treated, animals can develop fibrous swellings or bumps on the udder. These animals are susceptible to recurring mastitis infections.

Maintaining good teat condition is important. Rough rings on teat ends indicates overmilking and makes it more difficult to thoroughly disinfect. Affected cows will be more susceptible to infections. Check ACR and vacuum settings and use a post-dip with emollients for skin condition.

Bear in mind that your herd’s average SCC may be higher than the bulk tank SCC. This is because milk from high SCC cows might not be going into the bulk tank. Also, cows with high SCC’s tend to have lower yields and would contribute more to the bulk tank SCC than a higher yielding, lower SCC cow. Therefore, individual cow data on SCC is much more valuable, as it tells you the percentage of infected cows in the herd, which cows those are, how long they are infected for and how often new infections are occurring.

Key performance indicators for mastitis to monitor include:

KPI	Target
Clinical mastitis cases/100 cows/year	<30
Dry period cure rate	>85%
Mastitis in 1st 30 days post-calving	<1 in 12 or <8.3%
% animals with SCC ≥ 200,000	<20%
Recurrence rate	<10%

 

lorna.macpherson@sac.co.uk; 07760 990901