PLI eases path to longer lives…
PLI eases path to longer lives…
How will the new PLI genetic index for dairy cows work on one Notts farm?
Jessica Buss finds out
BREEDING cows that last longer should be easier now producers can use the new Productive Life Index launched this month to replace ITEM.
Thats what Midlands-based ADAS consultant manager Nick Holt-Martyn tells farm manager William Donger and herdsman Dave Elliot at the University of Nottinghams Manor Farm dairy unit at Sutton Bonnington.
Mr Elliot explains that the 180-cow herd has been bred for production, using PIN to help select sires and then shortlisting on fat and protein production. The herd now averages 8500 litres and has an average PIN of £51.
"But for the last couple of years weve felt cows needed better udders, so have selected udder improvers. We need to breed cows that last longer, but which can sustain high production."
Mr Donger is also keen for cows to last longer. "It must be good for cow welfare. And if a cow lasts an extra lactation it must be worthwhile because its expensive to keep replacing them."
Mr Holt-Martyn says the herd has made good genetic progress. But because peak yields have increased to up to 70 litres, udders have become more important.
Mr Elliot and Mr Donger admit to taking little notice of ITEM bull rankings. Mr Holt-Martyn says thats typical of many producers.
While ITEM included traits to extend productive life, there was little difference in £PIN and £ITEM values. He believes this slowed uptake of ITEM.
"PLI, which replaces ITEM, is about making cows last longer and it should be used in preference to PIN for initial selection. The financial value for longevity is increased in PLI, so the difference between PIN and PLI will be greater. Some bulls will also have a lower PLI than PIN because their daughters have a shorter lifespan," he says.
Lifespan is measured in lactations and typically varies by between plus or minus half a lactation. The value of an extra lactation is estimated at £38. Most bulls, therefore, will have a PLI within £17 of their PIN, he explains.
"PLI will alter the ranking of bulls compared with PIN. Those higher up the PLI list should breed daughters which have an increased productive life. This will be a combination of yield in each lactation and the number of lactations she is predicted to survive," says Mr Holt-Martyn.
"For bulls with a UK proof measuring productive life is a major advance in index and it has been well researched."
It is a direct measurement based on the fact that when an animal completes one lactation it is more likely to survive another. Many milkers fail to last a single lactation in the herd, he adds. But, the more lactations a cow completes, the more lactations she is likely to survive.
Bulls with proofs from other countries will be given PLI values based on type traits. Research has lead to these traits being given a heavier weighting, so differences will again be greater than between PIN and ITEM. But reliability percentages will be lower than bulls with UK proofs, he says.
"However, PLI is just an index – a tool that is part of the selection proceedure. It brings together a vast amount of data, which can be confusing, to rank the 450 bulls available. But selecting bulls for use in a herd on index alone would be misleading," says Mr Holt-Martyn.
Mr Elliot agrees that the data in bull brochures is confusing. He says its difficult to know where to start unless he uses an index to make his initial selections.
That means obtaining a list of bulls ranked on PLI and then deciding the minimum value to meet his criteria, explains Mr Holt-Martyn. For example, £100 PLI and 1.5 points of type merit, or £100 PLI and a price of less than £20 a straw.
When Mr Elliot has a PLI list of a manageable size, he should set his specific breeding goals for production and type against it, advises Mr Holt-Martyn.
"Some bulls on your PLI list will have higher yield values and some wont fit your other criteria for udder improvement, so can be crossed off."
But its also important that progress in improving cows legs and feet doesnt go backwards, adds Mr Elliot.
That means bulls that are extreme for feet and legs should be crossed off the list too, advises Mr Holt-Martyn. This will produce a manageable shortlist, from which Mr Elliot can select bulls on price.
Price limits are set be Mr Donger, who doesnt want spending on semen to increase above about £20 a straw.
Mr Holt-Martyn says that this is feasible, and that there are enough bulls to select from without spending more. But he says Mr Donger should check that bulls costing a few pounds more dont offer more of the required traits, and then consider whether they are worth more.
"PLI will save Manor Farm from making inappropriate choices – such as a bull offering high milk production, with a poor life expectancy – which is possible when selection is based on PIN alone." *
WHYUSEPLI?
• Greater productive life.
• Suvivability increasingly important.
• Balance yield and type goals.
HOWTOUSEPLI
• Set breeding goals.
• Use as first selection tool.
• Shortlist other traits.