The role of genetics when selecting for profitability and growth from forage

Article recently written by Katie Fallon, Farmers Guardian 

As more farmers are looking to maximise lamb growth from forage, EBV's are becoming an increasingly helpful tool in selecting the right ram to help realise improved performance.  

Assessing an animal's genetic potential simply by looking at it is not easy, says Sam Boon, breeding services manager at Signet Breeding Services, part of AHDB. And with growth and carcase traits greatly influenced by feeding, he says making comparisons between sheep from different flocks at multi-vendor sales is virtually impossible.  

As well as trying to predict terminal traits based on appearance, Mr Boon says the maternal traits a ram may hold are even harder to gauge solely on handling and inspection, with no amount of handling able to identify how prolific a ram's daughter may be or its milking capabilities.  

And with many unrecorded, show winning rams been proven to have below average potential for growth and muscling, once their progeny has arrived, Mr Boon says assessing genetic merit based on estimated breeding values (EBV's) is essential. EBVs are particularly important for farmers wanting to purchase later born rams, which have often been raised solely on forage-based diets, says Mr Boon.

"Rams fed solely on forage tend not to be as big as those fed on high levels of concentrates, however rams from performance recorded flocks will tend to have high generic merit for traits of economic importance," he adds. As more farmers are looking to maximise lamb growth from forage in the face of rising input costs, EBV's are becoming an increasingly helpful tool in selecting the right ram to help realise improved performance. 

While there are clear financial benefits to finishing lambs faster on a traditional falling market, getting lambs off farm earlier can also reduce the risk of encountering performance limiting conditions such as worms or drought."The earlier lambs are finished also benefits the rest of the flock, whether it means leaving extra forage for the remaining lamb crop or reducing the winter grazing pressure for flock ewes and store lambs."  Selecting rams based on their EBVs means producers can have confidence in purchasing the right genetics for their system, allowing them to buy from flocks with similar, forage-based management systems.  

Mr Boon says while growth is important, ram selection should still be about balance. "Rams should have good breeding values for growth, but rams with superior breeding values for muscling across the loin, hind quarter and overall muscle yield in the carcase are important when selling lambs on a deadweight basis. "He adds breeding values for fat depth also provide an extra indication of the amount of finish that lambs are expected to lay down.  

When selecting rams with a view to maximising profitability, Mr Boon explains how the recently released breeding values derived from abattoir data can assist farmers in selecting the most economic sires.Developed as part of the commercial progeny test and released as part of AHDB's national terminal sire evaluation, Signet have identified days to slaughter, carcase weight, carcase conformation and carcase fat class as ram traits which can be selected for, to help increase flock profitability.  

With a ram's genes having a marked impact on progeny performance, Mr Boon says days to slaughter and carcase weight traits are proven to have a heritability value of around 20 per cent, with carcase conformation and carcase fat class just over 30 per cent heritable.  

To highlight how these traits can be used to help farmers choose the most profitable sires, a sub-index has been developed to rank animals according to their genetic merit for abattoir traits. Mr Boon explains the sub-index will take into account the improvements in carcase value and savings attributable to a reduction in days to slaughter. "This will generate an overall ranking of recorded rams according to their financial merit, providing a direct indicator of the most profitable sires," he says.

When looking at how these traits can help farmers to select rams which will maximise growth from forage, Mr Boon says that under any farming system, the advice is to select rams with the genetic merit which will make the most money. "When selecting a terminal sire this is relatively easy, they need to produce a live lamb that is born easily, with the potential to grow quickly and hit market requirements."

However, where farmers are unable to access the new abattoir derived breeding values for carcase weight and days to slaughter due to a lack of data, he advises focusing on the scan weight EBV, an indicator of growth potential. And where breeding values for conformation and fat class are not available, breeding values for proxy traits of muscle depth and fat depth are good indicators of carcase quality.  

When it comes to maternal traits, Mr Boon says growth and carcase traits should take more of a ‘back seat' with the number of lambs reared, lamb survival, milking ability, parasite resistance and ewe mature size taking on more obvious importance.