Advice for buying rams based on EBVs

Ram selection is key to a successful sheep enterprise, with trials showing that the right tup can be worth an extra £600 over his working lifetime.

With 50 years’ worth of performance-recording and new data from the RamCompare national progeny test, it has never been easier to select the right sire for an individual flock, says AHDB genetics specialist Samuel Boon.

With wider use of computerised tomography (CT) scanning for predicting carcass composition, and reliable performance recording data, there is no reason to take a gamble based on appearance alone.

See also: More than one-fifth of rams are sub-fertile, research shows

In fact, spotting the “good” sires by eye alone is impossible, given the large genetic differences between sires. Furthermore, high levels of feeding can easily mask poor-performing genetics, warns Mr Boon.

Below, he gives advice on selecting rams with the right estimated breeding values (EBVs) for your farm.

Advice for selecting traits: Where to start?

Farmers should first consider which EBV matters the most to their business and select rams accordingly.

Selecting rams with the right combination of traits should be a good match for business profitability, but remember that a ram’s EBVs should be halved when estimating how much of his genetic potential will be passed to his progeny, as the other half will come from the ewe.

Breeding information is often displayed on charts with the central line representing the average level of performance within the breed. The charts will list EBVs, indexes, and accuracy values.

Terminal traits to consider

RamCompare has clearly shown that a high scan weight EBV results in increased growth rates and reduced days to slaughter. High scan weight and muscle depth EBVs equal increased carcass weights.

The data has also shown that EBVs for superior muscle depth and gigot muscularity enhance carcass conformation. Fat depth EBV is a good indicator of the fat classification achieved by sire progeny.

Progeny performance data from RamCompare is already being used by Signet to enhance existing EBVs and support research to develop new ones for traits such as days to slaughter and carcass conformation.

CT data, which is funded by levy organisations such as AHDB, has also played a pivotal role in the improvement of terminal sire breeds.

CT measurements show the weight of fat, muscle and bone in the carcass; the distribution of muscle, including the percentage of muscle in the leg, loin, or chest; and spine length and vertebrae number. Intramuscular fat percentage and gigot shape are also measured.

This raw data is used by Signet Breeding Services to create nine EBVs that can enhance carcass yield and shape.

When buying rams, producers selling on a deadweight basis should take into account breeding values for scan weight, muscle depth, and CT lean weight.

© Tim Scrivener

Maternal traits to consider

Most flocks seek positive breeding values for eight-week weight, litter size, and maternal ability to influence early lamb growth rates; the number of lambs reared; and milking ability of female replacements.

Breeding values for traits influencing carcass conformation should be considered, too.

Some traits are breed-specific. For instance, the Lleyn and Scottish Blackface have EBVs for lamb survival, a trait that has high economic importance.

Another economically important trait is ewe longevity – it is a trait that considers the length of time when the ewe is productive in the flock, so it is actually an indicator of reproductive lifespan within a flock.

In recent years, breeders have become increasingly interested in enhancing the overall efficiency of the ewe, increasing her output without increasing her mature size.

New breeding values for ewe mature size, which have been developed as part of research funded by AHDB and the Centre for Innovation Excellence in Livestock, are being introduced to enable breeders to limit future increases in ewe mature size.