Livestock Event 2014: Guide to the changes to this August’s bull proofs

The August dairy bull proofs will see some big changes to the profitable lifetime index as well as a new economic index for spring block calvers. Aly Balsom looks at how farmers will benefit.

Changes to how a bull’s profitable lifetime index (PLI) is calculated will place greater emphasis on health and fitness traits, better reflecting present-day economics.

The PLI gives an economic indication of the extra profit a lifetime that a bull’s daughter will give versus the breed average.

Having last been updated in 2007, DairyCo and The Genetic Advisory Forum made the decision to reassess the index to take into account the changes in input costs and milk price that have occurred in the past seven years.

See also Two stars reach £300 PLI in genomic bull proofs

The new PLI, which comes into effect in DairyCo’s August bull proof run, will put less emphasis on production and also take into account two completely new traits. The average breed base to which bulls are compared will also be updated from animals born in 2005, to those born in 2010.

For the first time, spring-calving, low-input herds will also be able to use a new spring calving index (SCI) instead of PLI to better select bulls suited to their system.

How has PLI changed?

Production will get a lower weighting of 32.3% in the new PLI. Instead there will be a greater emphasis on traits such as longevity, functional type and maintenance, says Marco Winters, DairyCo’s head of genetics.

“We are still interested in efficient production, but alongside that we know costs on farm are going up. We want to ensure efficient production of milk and we don’t want to increase the cost of the animal,” he says.

Two new traits have been introduced into the PLI: calving performance and maintenance.

See also How the new PLI and SCI may affect bull rankings

Weighted at 1.8%, calving performance takes into account direct and maternal calving ease, explains Mr Winters.

“We wanted to put emphasis on this as we know a difficult calving is costly. We’ve also included the cost of maintenance for a cow through her lifetime, weighted at 9.6% as we know most farmers are saying cows are getting too big.

“A heavier cow will have a higher maintenance as she will eat more. We need to put a break on it so cows are not getting too big and more inefficient,” Mr Winters explains.

Fertility will also have a slightly greater weighting of 20.3%. However, Mr Winters says because traits are genetically linked, all the changes to PLI will benefit fertility. For example, reduced emphasis on production automatically favours better fitness, which will benefit fertility.

What will the PLI look like?

The new PLI figures will be bigger than the old PLI figures, which reflects the economic changes that have occurred since 2007. The PLI of top-ranking bulls could more than double, but it is likely there will still be familiar names at the top.

“Some bulls may have dropped out. These will be the poor fertility ones or those throwing heavier daughters,” says Mr Winters.

What is the SCI?

The SCI is a completely new economic index modelled in the same way to PLI, but targeted at lower-yielding, easy-care cows.

“We know the industry is polarising and a proportion is moving towards low-input, block-calving, grass-based systems. The SCI is targeted at this group,” says Mr Winters.

The SCI puts more emphasis on fertility (21.8%), reflecting the trait’s importance in block-calving herds. The need for smaller cows with low feed requirements will also be reflected in a higher weighting for maintenance (16.2%).

Of particular significance to cross-breeding herds is the fact SCI uses a common reference base for all bulls across all breeds. This means it can be used to directly compare bulls between breeds – something that is not possible with PLI unless using a conversion formula.

How should PLI and SCI be used?

The new PLI should be used as the main starting point for selection in the same way as the old PLI. The SCI should become the primary focus instead of PLI for low-input, spring-calving herds only. All other systems should use PLI.

Mr Winters recommends initially selecting the top third of bulls based on PLI or SCI (depending on system) and then fine tuning based on individual farm aims.