Spring-calving herds set for genetic boost (April 26)

The spring calving index has had an upgrade that will push sires that breed larger, higher production daughters further down the rankings. We find out how this will benefit producers with low-input systems

TEXT ANN HARDY

Producers running spring-calving grass-based systems will have a refined breeding tool at their fingertips from April, when AHDB launches an update to its spring calving index.

Although the formula of the spring calving index (£SCI) will remain substantially the same – continuing to reward high quality milk, fertility, health, functional type and efficiency – a ‘penalty’ for tall, high production animals, with a high energy demand will be introduced. And some sires that have previously listed high in the £SCI rankings will fall.

This re-formulation is expected to displace some high production Holsteins from the leading places in favour of more Friesian and Jersey genetics.

“Like all indexes that recognise profitability, the £SCI is calculated using an economic model,” says AHDB geneticist Marco Winters. “This type of linear model rewards every extra kilogramme of output where it has been calculated to be worth more than the feed required to produce it.

“When feed inputs are not limiting this model works well and, if animals score well for the other traits in the index such as health and fertility, it can push high-production and high-energy-demand cattle to the top of the rankings,” he explains.

Grass-based systems

“These animals may certainly be more profitable if they are fed extra concentrates, but this only suits systems where feed intakes can be increased. And that’s not the philosophy of spring-calving herds, which aim to make milk from grazed grass and limited concentrate intake.”

He says feedback from producers was that they’d like to see the £SCI ranking feature more sires that breed smaller daughters with lower maintenance costs and energy demands. “So we have revised the index to better reflect their requirements.”

The new penalty will continue to push production up to a point, but will introduce boundaries that are typical for spring block-calving herds. The result is that animals which have a total dry matter intake requirement of more than five tonnes per lactation will be penalised.

“Typical spring calving animals are unable to sustain that high energy demand in the long term,” says Mr Winters. “So the new £SCI will continue to reward production, but not where this is excessive and likely to lead to negative energy balance.”

Gloucestershire-based dairy manager Keith Davis admits he has struggled with some of the taller Holsteins in his spring-block-calving herd, which he runs at Lydney Park Farm.

Figure 1: Trait weightings in revised £SCI

Working group

He welcomes the developments in £SCI and has been part of the working group that steered the changes. He aims to breed cows with a mature liveweight of 500kg that produce 500kg of milk solids per lactation for the unit’s grass-based setup, and he has used £SCI for many years to drive the herd’s genetic progress.

Today the 850-cow herd has exceeded its initial target, producing around 509kg of solids from cows averaging 510kgLW.

“But when our cows get too big that’s detrimental in this system because they struggle to eat enough feed for both maintenance and milk production,” he says. “They just don’t have enough time to eat the amount of grass they need.. “If a Jersey requires about eight hours a day of grazing to maintain her bodyweight, a Holstein needs closer to 12 hours.”

He aims to feed just 500kg of concentrate per cow per year, but he admits this is sometimes ‘blown out of the water’ in years of poor grass growth. Herd average yield is around 5,200kg of milk, at 5.3% butterfat and 4.1% protein, and 3,460kg comes from forage. Milk is sold to Yeo Valley via First Milk through the Naturally Better Dairy Group.

Milking a combination of Jerseys, New Zealand Friesians, British Friesians and some Holsteins, he likes to measure their efficiency in terms of kilogrammes of solids per kilogramme of liveweight. Using this parameter, he has found his Jerseys to be his most efficient cows (108% for the Danish Jerseys) while the crossbred Holsteins or New Zealand Friesians also fare well at 100%.

“We’ll definitely be using £SCI for genetic selection going forward because I feel it more closely reflects the type of cow we need for our system,” he says.

The change to £SCI has been led by AHDB, with support from an industry-wide working group that includes producers managing spring-calving herds and AI companies.

Best genetics

The group is confident that, with the changes, producers will become more focussed on using £SCI for genetic improvement. “The revised £SCI ranking will help producers identify the best genetics to improve herd and business,” says Mr Winters. “It is far better that they use a UK index, rather than one that has been developed for milk payment structures or climatic conditions in other countries. We know this has been a temptation for some producers running spring-block-calving herds.

“Since the changes will place less emphasis on high output and more on the right cow for the system, £SCI will be better suited for UK producers than ever before,” he adds.

As well as this development, he says spring-calving herds are increasingly seeing the benefits of using sexed semen. With genomic testing also now available for cross-bred cattle, Mr Winters says a better tool kit is available to producers managing their herds on these systems.

“In the past, there was more blanket semen use than individual matings in these herds but as confidence in £SCI grows and genomic testing heifer calves becomes more common, producers now have a suite of tools which supports both parentage testing as well as genetic improvement,” he says.

Spring-calving index changes

·       AHDB is refining £SCI to more closely suit grazing-based systems

·       £SCI rewards moderate cow size, efficient grazers, and improved fertility, longevity and milk solids

·       It penalises large, high-energy-demand cows needing more supplementary feed

·       Friesian and Jersey breeds are expected to move up the rankings

·       The changes come into effect from April 2026’s genetic evaluations