Questions and answers on somatic cell counts

What are somatic cells?

Somatic cells are a type of white blood cell found in milk. They are measured in cells per millilitre, so if your SCC is 250,000 cells/ml it means there is this amount of white blood cells in every millilitre of milk. The white cells are fighting infection due to a bacterial attack in the udder.

What is the main cause of a high SCC?

There is only one cause of a high SCC — mastitis. Whether it is clinical (swollen quarter and clots in milk) or sub-clinical (no visible signs), there are bacteria getting into the cow’s udder through the teat canal and causing infection.

There can be a number of different causes of infection, e.g. poor hygiene, milking machine faults or not post dipping cows, but they all affect SCC by causing some form of mastitis.

If my SCC is very low (less than 75,000 cells/ml), does my herd have reduced immunity towards mastitis?

No. Cows can still respond equally well to an infection when challenged. Also, the same good practices which have allowed you to achieve an SCC of less than 100,000 cells/ml will minimise future infection risks. If mastitis occurs, it is likely to be environmental as little or no infection is being passed between cows.

The Teagasc CostCheck Mastitis calculator says I am losing €5,000 on my 80 cows as my SCC averaged 250,000 last year. How can this be?

Reducing your SCC will lead to increased milk yield, reduced culling because of SCC problems, reduced treatment costs and, depending on your co-op, it will increase your milk price. Each farm is specific but there are massive benefits to consistently getting SCC under 100,000. With milk price at 40c/l on many farms at the moment, a cow with mastitis out of the tank for four to six days producing 20 litres a day is a loss of €48 alone, along with treatment costs and reduced milk yield post infection. Culling two or three of these cows and paying for the replacement heifer will see €5,000 reached easily.

What is the big benefit for the co-op in processing milk with lower SCC?

The lower the SCC, the more protein can be recovered from the milk during processing. This means more saleable product which is why some co-ops pay a bonus for low SCC milk. A low SCC is important to access some markets with high milk quality standards.

Many co-ops are increasing the standard of SCC in milk for the future — Glanbia and Lakeland will penalise for milk over 300,000 in 2015 while Carbery is bringing in this standard from next year.

Is the reduction in milk yield post mastitis permanent or will it return to normal?

This depends on the causal bacteria. Infections caused by Staph aureus attacks the secretory tissue deep in the cow’s udder. They cause scar tissue which will reduce the cow’s ability to produce milk, even though her SCC will reduce in time.

They can also become dormant and cause another mastitis outbreak later in life. Infections caused by Strep agalactiae occur in milk ducts and are easier to treat.

If I have an SCC of 300,000, what are the first steps I should take to reduce this?

Milk recording is the best tool to control SCC as you get a specific SCC figure for each cow. Even more powerful is a series of milk recordings where you can monitor trends in each cow’s SCC over time. The California Milk Test (CMT) is a good way of identifying problem quarters of cows with an SCC of over 300,000. These cows could then be treated or kept an eye on for new infections.

What is the best cure for a high SCC cow?

There are only two methods of curing a cow. One is with antibiotics either during lactation or at dry off — this may not always be successful.

The other is that the cow will eliminate the infection herself.

In contrast, there are so many ways you can help prevent the spread of mastitis — glove wearing, proper teat spraying, machine servicing, etc. If you get these areas right, you won’t have to worry about curing cows.

How can I improve cow teat condition?

The teat doesn’t secrete any chemicals that will kill bacteria so ensuring it is fully functional as a barrier is essential. This means avoiding over milking and ensuring the machine is working properly to prevent any teat damage. A teat spray with a conditioner is also helpful.

What SCC must you have to consider once daily milking?

SCC will rise when milking OAD so your average should be under 200,000 cells/ml when you start. Individual records are more important — even if your herd average is under 200,000 cells/ml, some cows may not be suitable. You must be very tuned it at milking as if you miss a developing mastitis infection, it will have 24 hours to develop before you get a chance to see it again.

What do you need to look for during daily inspections in your milking machine?

Daily, you should make sure there are no air leaks, liners are lined properly, the vacuum gauge is 47KPA to 50KPA (and doesn’t fall much when switching clusters; otherwise, vacuum reserve is too low), regular pulsation, clean air bleeds, vacuum shut off within two seconds when removing clusters.

Read more

Controlling somatic cell counts in 2016

CellCheck working to bring down SCC

This article was first published in 2013.