By Jessica Buss
TOP bulls PIN and PLI values will fall by 60 to 70 in Februarys proof run as the genetic base is recalculated and new economic values come into effect.
Linear type proofs will also be realigned.
Base changes take place every five years in accordance with international recommendations, explained Gordon Swanson of the Animal Data Centre, at last weeks British Cattle Breeders Club conference.
The move means that an average cow born in 1995 and milking now should be of average genetic merit, so national genetic values for predicted transmitting abilities (PTAs) should be reset.
For PIN value, an average merit 1995-born cow will become 0 PIN.
In the past base changes have been small.
However, genetic progress over the last five years has been rapid and PTA values for production and type will reflect this in February, he said.
Type changes are difficult to predict and will not be consistent, added Matthew Winter of Holstein UK and Ireland.
But they will bring linear proofs into line on a scale of -3 to +3 which some trait figures are outside.
For all Holstein bulls, Mr Swanson estimated PTA2000 production values will reduce by 317kg milk, 9.4kg fat and 9.7kg protein compared with their PTA95.
This amounts to a fall of 24 PIN and 27 PLI. Producers will also see cow values fall by these amounts on herd reports.
Other breeds values will also fall, but by less because genetic gain is slower.
“There will be no change in ranking achieved, but there will be fewer positive animals listed.
“By changing the base we eliminate the problem of using bulls with genetic merit below the average cow population,” he said.
This base change timing has coincided with research recommending changes in economic weightings for PIN and PLI indexes.
MDC breeding projects manager Brian McGuirk explained that indexes must be brought into line with future commercial reality.
This meant lowering milk price in PIN calculations to 19p a litre. Defending the use of this milk price, Mr McGuirk said future price was open to debate.
“But experts viewed it as realistic with EU fat intervention price and a weaker pound.”
However, PINs will continue to be calculated using constituent values. “We are falling back on constituent values because it reflects the national need in terms of end product,” he said.
Fat is worth 50p/kg, after changes to feed costs and lower quota costs, and protein 300p/kg.
This has altered the fat to protein ratio, putting slightly more emphasis on fat.
Deductions are made for liquid produced based on transport, cooling and lactose feed energy costs at about 3p/litre.
These new values will change the bull ranking. In practice no top bull moves more than a few places, but they will lose 40 to 45 in PIN, because of the new weightings, said Mr McGuirk.
PLI values will reduce by a similar amount, but these are also affected by lower replacement values in lifespan calculations.
While admitting changes to figures would shock producers, Mr Swanson said they reflect genetic improvement and give more realistic financial values.
But one milk producer delegate, Philip Kirkham, thought such large changes would devalue genetic merit perception on farms.
“If we see an improvement in genetic performance, then see it diminished, it will lower the value I put on indexes – even though I understand the changes.”
Mr McGuirk believes one solution is to review economic weightings used for indexes more frequently and he hopes to review them again in about two years.
Midlands ADAS dairy consultant Nick Holt-Martyn added that the reasons for changes are logical, but there will be a negative perception about a system in which animals seem to go backwards in merit.
“But it wont affect the real genetic value of stock,” he says.