Look at more than EBV score when picking sire
By Jeremy Hunt
RAMS with exceptionally high index scores should not fool commercial prime lamb producers buying in sires from performance recorded flocks.
It is essential to assess each trait score independently, says Yorks sheep breeder Charles Marwood. "Achieve a balance of trait scores which will do the best job on your own type of commercial ewes.
"In conformation terms there may not be much difference between a ram with a sire reference EBV index of 200 compared with one with an index of 300. Geneticists say a higher index ram will achieve faster genetic progress, but we are dealing with animals with finite capabilities. If we concentrate on size and sheep become too big we will lose carcass quality."
He believes high index scores are often a reflection of the pre-occupation with selection criteria for growth rate and leanness. But these traits may not contribute to the conformation and meat eating quality of prime lambs.
Mr Marwood, chairman of the British Charollais Sheep Society, runs the Foulrice flock of 400 Charollais ewes, with his wife Valerie, at Whenby. Although he has been involved in performance recording for almost 20 years, he now feels it is time for a review.
The four trait scores which combine to create the overall EBV index – eight-week weight, 21-week weight, muscle score and fat depth – must be assessed individually by commercial ram buyers, says Mr Marwood.
The best ram will depend on the type of ewe. "Mules are tall, long and milky with reasonable carcass quality, so its necessary to use medium-sized, meaty rams with full loins, well developed hindquarters good shoulders and a tight skin. However, it could be that a 200 index ram is better to use on Mules than a 300 index one, as high growth rate does not mean superior muscling."
But for early lamb producers high eight-week weight scores are beneficial. "They produce the early growth spurt, essential for this type of system. But it is less important if the fat EBV of rams used for early lamb production is low, because muscle grows before fat is laid down."
Mr Marwood believes the EBV system is too harsh in its identification of animals considered over-fat. "A lamb at 21-weeks with 1mm or even 2mm of fat barely has enough fat on its carcass for it to be cooked properly and ultimately enhance its flavour.
"EBVs quickly highlight animals considered over-fat, but only excessively fat animals need eliminating." A fat EBV score of -0.2 is acceptable. There is no need for a fat EBV as high as -1.0, he adds.
Fat may have become a dirty word, but the consumer wants flavour. Mr Marwood fears that selection for ultra-lean sires could damage flavour. "We sell a few lambs for the home freezer trade and our customers ask why they cant buy lamb that tastes as good from the supermarket."
Mr Marwoods flock is recorded through Signets Sheepbreeder scheme. Although a firm supporter of performance recording, he feels sire referencing has not had the anticipated beneficial impact on UK sheep breeding.
"There are still too many producers who feel performance figures are an affront to their visual stock selection skills and will not accept the benefits in terms of improved profitability.
"But equally there are pedigree breeders concentrating too much on high index sires. There are undoubtedly rams in the top 50% of terminal sire referencing schemes just as good as elite sires in the top 10%. It is probably more important within any recording flock to narrow the band of genetic variation and present a more consistent product, be it for pedigree or commercial use.
"Some sire referencing schemes are hung-up on traits like leanness and growth rate. The result is over-lean lambs with big frames that wont finish until they reach 50kg. Thats not what the market wants.
"There is also still confusion caused by presentation of indexing from sire reference recorded flocks and Sheepbreeder in-flock recording, as each operates from a different base." *
Charles Marwood believes the type of ram selected should be based on the flocks and markets needs rather than going for the highest EBV.
• Look beyond EBV score.
• Fat too heavily penalised.
• Lamb needs flavour.