This month there is an important new tool available to us to assist in mastitis control.

From February 2002, the Australian Breeding Values (ABVs) include useful extra information –on cell count. Bulls with daughters that are relatively more resistant to mastitis can now be identified. This means that farmers can bring a genetic component into the management program for mastitis control in their herds.

It is now possible to select bulls that increase production and concurrently reduce susceptibility to mastitis. It’s great news. But before getting too excited, remember that management factors remain the major drivers for mastitis control. Genetic selection can make your herd less susceptible but it will not magically eliminate mastitis from your herd.

With the introduction of this new ABV, it is timely to look at how genetics can be integrated into your mastitis management plan.

Nearly all udder infections are caused by bacteria that enter the quarter through the end of the teat. The likelihood of an infection occurring is a balance between the number and type of bacteria around the teat end, and the ability of the cow’s teat and immune defences to inactivate them.

Most of the factors that affect the balance of infection and defence are influenced by the cow’s environment. For example, the number of bacteria “challenging” a cow is greatly increased if she has sores and cracks on her teat skin. These teat sores may have occurred for diverse reasons, many of which are environmental. Perhaps the laneways are wet and muddy, or the teatcup liners are not matched correctly to the teatcup shells, or the teat spray has been made up to the wrong concentration.

But while critically important, environmental factors are not the only consideration. Genes also play a part. For example our cow with the teat sores may also have a genetic tendency for poorer teat skin health, or she may have inherited genes that specify longer than average teats which are more prone to damage.

There is no doubt that the greatest impact on milk quality is achievable by day-to-day management of the udder health of cows before, during and after the milking process. Management practices account for about 85% of the likelihood of high cell counts occurring. That leaves only a 15% contribution of genetic factors to cell count, which tells us that at best, genetics can only play a supporting role in preventing infections.

Breeding decisions will never be a panacea for mastitis. And genetic changes can take years to impact on a herd’s existing problems. (Don’t ask the dairy company to wait until you’ve bred out this season’s penalty cell count!) But gains from better breeding decisions have two important benefits. They are low-cost and cumulative, making them very worthwhile in the long-term.

Estimating in dollar terms the benefit of lowered herd cell counts has allowed incorporation of the new ABVs into the Australian Profit Ranking. Every 1% reduction in milk cell count in an average herd provides a net profit of about 34 cents per cow per year.

For a farm choosing a semen portfolio with an average cell count ABV of -20% this means genetic gain could be worth $3.40 per cow every year. (The bull provides half of the genes to the progeny, so the gain is 10 times 34 cents). So it’s clearly worth considering cell counts when buying semen.

Congratulations to the team at the Australian Dairy Herd Improvement Scheme  for bringing the research to a practical outcome for us all (and a vote of appreciation to the Dairy Research & Development Corporation for its substantial investment of research dollars in this area). Countdown recommendations now include this new genetic resource. Application of this new tool is set to benefit individual farmers and the wider Australian dairy industry.

Pull quote

“Now we can select bulls that increase production without a mastitis penalty”

• ABVs now include values for cell count

• Breeding plans can target higher milk production AND reduced susceptibility for mastitis

• Good management is the key to mastitis control

• Genetic selection can help improve cell counts over time

• Genetic selection for low cell counts is low cost and cumulative

How the cell count ABVs work

Australian Breeding Values (ABVs) are the best estimate of a bull’s genetic merit–his ability to pass certain characteristics to his daughters. They have already been calculated for many production and working traits such as milk yield and milking speed by analysing the performance of the bull’s daughters and other family members across many herds. The Australian Dairy Herd Improvement Scheme has now added an estimate of breeding value for resistance to mastitis through the new cell count ABV.

Bulls with lower cell count ABVs will breed daughters with lower milk cell counts.

Half of each bull’s ABV value will be passed on to his daughters (for the daughters the other half will come from their dams).

Because a bull’s cell count ABV is a measure of percentage change, the impact in each herd will depend on the cell count status of the herd. Herds with low cell counts will see smaller changes in absolute terms than herds with high cell counts.

From the Farm Guidelines

Milk cell counts–what’s in a name?

When bacteria enter the udder, the cow responds by sending large numbers of white blood cells to the mammary gland and into the milk. Their role is to surround and destroy bacteria.

In Australia, the concentration of body cells in milk from all four quarters of a cow taken at a Milk Recording (Herd Testing) visit is usually called an Individual Cow Cell Count or ICCC. Sometimes it may be referred to as a cow’s Somatic Cell Count, or SCC (“soma” means “body” in ancient Greek).

Cell counts provide a method of measuring udder infection rates because mastitis is the major cause of any rise in cell counts in milk.

For more information consult the Countdown Downunder Farm Guidelines and your vet.

Introducing the Countdown team: Robert Poole

Robert Poole is the Executive Officer of the Australian Dairy Herd Improvement Scheme (ADHIS), the industry’s independent genetic evaluation service.

In this role he has been a strong supporter of Countdown since its instigation. Robert is also a member of the Australian Mastitis Advisory Council which guides Countdown’s development.

ADHIS has been an important partner for Countdown, helping with many projects. The highlights have included:

• Processing data for The Weekly Times Countdown Downunder Milk Quality Awards

• Determining the national herd milk cell count statistics

• Creating new herd improvement reports that include mastitis-related data

• Incorporating cell counts in the Australian Breeding Values.

Robert was brought up on his family’s mixed sheep and grain property at Wedderburn in northern Victoria and maintains an interest in his family’s dairy, sheep and grain operations in the region.

On completing his Bachelor of Agricultural Science degree at the University of Melbourne, Robert joined the Jersey Society as Executive Officer, then the Rural Finance Corporation before taking up his current role at ADHIS in 1997.

”Farmers are getting better value from both ADHIS and Countdown as a result of the strong collaborative links between the two organisations”, says Robert.