19 December 1997

NEWSCC profile helps cut mastitis incidence

Dairy producers will soon be

able to breed for lower

somatic cell counts and less

mastitis

KEEN to reduce somatic cell counts and mastitis incidence? From next February help will be at hand.

Official bull proofs published by the Animal Data Centre will include a predicted transmitting ability (PTA) for somatic cell counts.

That will allow producers to add somatic cell counts to the list of traits on which they base sire selection. ADC geneticist Gordon Swanson believes that using SCCs as a selection tool will help cut mastitis.

While SCC is lower in heritability than milk yield (11% compared with 35%, respectively), there is enough genetic variation to enable differences between animals to be identified, explains Mr Swanson.

For this reason, he advises farmers with high cell counts herds to select bulls with a negative SCC PTA, and research suggests a fall in cell count of 1% would be worth a £15 a cow when herd average SCC is 325,000/ml.

SAC and the University of Edinburgh have estimated the financial effects of reducing herd cell counts. Using data from Scottish herds, the group looked at the effects of lowering SCCs over a range of herd average cell counts, from 325,000 to 150,000/ml.

Within each herd there was the usual spread of counts. The group reduced each of these by 1% and recalculated the milk price, based on Milk Marques cell count payment bands.

They found that a herd with an average cell count of 325,000/ml would benefit by £15 a cow a year for every 1% cut in cell count, those with an average count of 250,00/ml would benefit by £4 a cow a year, and herds averaging 200,000/ml by 50p a cow a year. For herds with cell counts as low as 150,000/ml, reducing SCCs by a further 1% would earn an extra 1p a cow a year.

Sire evaluations for SCCs will be expressed as percentages. The overall range of % PTAs for SCCs is from +30% to -30% and in practice, apart from a few extremes, 95% or proven dairy bulls will be between +10% and -10%, says Mr Swanson.

A bull with a PTA for SCC of -10% will be expected to reduce his daughters cell counts by 10% whereas one with a PTA of +10% will be expected to increase SCCs by 10%, he adds.

SCC PTAs for the top 15 Holstein Friesian bulls ranked on ITEM are shown in the table. SCC PTAs for the first five do not cause concern, says Mr Swanson. The high production sire Mascot, for example, transmits only a 1% rise in SCC to his progeny.

Three bulls also in the top five, Kolhorner Floris, MOET Elsas Crewman and Genus Pathfinder, are predicted to reduce SCCs, so there should be no difficulty in using these in any herd, says Mr Swanson.

But he suggests that bulls such as MOET Flirt Dilemma with a PTA for cell count of +24% would be hard to justify in any herd breeding programme. That also applies, although to a slightly lesser extent, with French sire Ugela Bell who has a SCC PTA of 16%.

ADC will be publishing SCC PTAs for both black-and-white and coloured breeds. Because of the lower heritability of SCCs, to achieve 70% reliability the ADC needs information on 80 daughters in the proof, compared with just 24 daughters for milk yield, warns Mr Swanson.

Consequently, high reliabilities will not normally be found for a bull until second crop daughters are added. This highlights the need for caution when using SCC evaluations.

He advises against over-emphasising the value of SCC evaluations and to base their initial sire selections on indices such as PIN or ITEM. But where average cell counts are high, he would recommend use of bulls which will reduce herd SCCs.

In future, ADC may incorporate SCC PTAs into a national profit index where the emphasis given to it can be balanced with other traits, explains Mr Swanson.n

Selecting sires with negative PTA scores for somatic cell counts will help reduce bulk tank cell counts and could save £15/cow/year.

Somatic cell count PTAs for top 15 Holstein Friesian bulls (Aug 97)

BullRelSCC PTA

(%)(%)

Singing Brook N-B Mascot861

Southwind Bell of Bar-Lee983

Kolhorner Floris31-4

Moet-Elsas Crewman58-7

Genus Pathfinder42-5

Sir Marke Acclaim465

Nordkap93-3

Kashome Bell Jurist7213

Art-Acres Ned Boy Oscar56-14

Main-Acres Chief Force76-8

Moet Flirt Dilemma6524

Moet Jenny Ensign33-5

Genus Longview53-2

A Mark C J Cilbrook Grand89-6

Honette Jason Energetic711


BullRelSCC PTA

(%)(%)

Singing Brook N-B Mascot861

Southwind Bell of Bar-Lee983

Kolhorner Floris31-4

Moet-Elsas Crewman58-7

Genus Pathfinder42-5

Sir Marke Acclaim465

Nordkap93-3

Kashome Bell Jurist7213

Art-Acres Ned Boy Oscar56-14

Main-Acres Chief Force76-8

Moet Flirt Dilemma6524

Moet Jenny Ensign33-5

Genus Longview53-2

A Mark C J Cilbrook Grand89-6

Honette Jason Energetic711

REDUCING CELL COUNTS

&#8226 Select bulls with a negative SCC PTA.

&#8226 PTA of -10% will reduce SCCs by 10%.

&#8226 Low heritability, use with caution.