31 March 2000

Index could save £813m

By Emma Penny

AN all-encompassing index for dairy cows which includes PLI, mastitis and fertility traits would save the UK dairy industry £813m over the next 20 years.

SAC Edinburgh geneticist Jennie Pryce said that opting for broader breeding goals would pay.

"Our research considered the effect of four indexes over the next 20 years – PIN, PLI, PLI plus a predicted transmitting ability for mastitis, and PLI plus mastitis plus fertility based on calving interval."

The increase in average PIN value is worth £5.41 a cow a year, while using PLI pushes that gain up to £7.66. Using a PLI plus mastitis index would give a gain of £7.74 a year, and PLI plus mastitis and fertility would result in a gain of £9.63 a year (see table).

"There is less genetic progress using the index combining PLI, mastitis and fertility, but there is less mastitis, a reduction in calving interval and longer lifespan," said Dr Pryce.

"Selection on PIN has led to major economic benefits, but there will be a substantial cost in mastitis resistance and fertility if selection is continued on production criteria alone."

She calculated that while PIN alone would benefit the industry by £457m over 20 years, PLI would benefit it by £647m and using PLI and mastitis would result in a boost of £653m. But the greatest benefit – £813m – comes from using PLI plus mastitis and fertility.

Responding to questions, she admitted that 20 years was a long time to forecast across, and said there may be changes.

"Breeding goals are periodically updated; we used to use PIN and now people are increasingly using PLI. The future milk price may change, and the rate of genetic progress may change, particularly if use of sexed semen becomes widespread. Both PIN and PLI are also sensitive to heritability, which might also change the figures."

But she added that there were benefits to be had from using a broader selection index, and that the cost benefits were great.

"In the UK, we spend £6m a year on progeny testing, evaluation and research. The benefit to cost ratio after 20 years of using PIN alone would be 4:1, but would rise to 7:1 using an index covering PLI plus mastitis plus fertility."

But would producers facing crippling prices and focused on production use a broader index?

"Production is not necessarily the be all and end all; cutting the cost of production is equally important," added Dr Pryce. &#42

Expected annual response to selection a cow

PIN PLI PLI+m PLI+m+f

Total response (£) 5.41 7.66 7.74 9.63

Milk (kg) 103.0 93.5 90.7 53.2

Fat (kg) 4.56 4.12 4.00 1.88

Protein (kg) 3.36 3.05 3.00 1.94

Calving interval (days) 0.60 0.28 0.24 -0.57

Lifespan (lactations) 0.0 0.059 0.06 0.099