The value of a top ram is still generally measured in hundreds. But things are changing in the genetics of sheep breeding.

Robin Johnson is part of a new wave of breeders, using ultrasound scanners and computers to work out which bloodlines give the best returns.

He can tell you exactly what the traditionalists would say: "If you can't tell a good 'un by looking, you shouldn't be breeding them."

But he has been in the business long enough to know about the old ways and still believe there is room for new ones.

Look at the standard North of England Mule, he says – the successful cross-breed on which most Yorkshire hill farmers depend.

A Swaledale ewe is mated with a Bluefaced Leicester to produce mule gimmers with "hybrid vigour" which can be mated with a fleshier lowlander, like a Texel, Suffolk or Beltex, to produce a reliable output of butchers' lambs and mule wethers which will be sold for slaughter or for a bit more fattening, followed by slaughter, at sub-prime prices.

Mr Johnson is concerned at how rough the science of it all still is. A Bluefaced sire is commonly chosen on the basis of "a good head", which will produce "bonny-faced" ewes.

The head would be a show criterion. But it does not say much about the likely fecundity of the ewes that inherit its noble looks. Central though the Northern Mule is to the economy of the hills, there is no organised breed improvement scheme for it.

Mr Johnson thinks that makes it more vulnerable to competition than it should be. He also thinks it is a mistake for the hill men to regard the gimmers as their end product and the wethers as incidentals.

"Hill farmers will do everything to put £5 on the value of the ewe lamb when they might be better off looking for another fiver for the wether," he said.

He is talking about making sure the meat buyers get what they are looking for in the end products which the whole supply chain hangs from.

Half of all the English lamb crop is not ideal for mass production of trimmed and jointed meat. That was the gap in the market which meant New Zealand could still sell lamb in the UK after all direct subsidies for its farmers ended.

The Kiwi secret is the appliance of science, to make sure the product consistently hits the requirements of the market – meaning, above all, the western supermarket.

The New Zealanders have been getting out of lamb because they drove the prices down so far even they were squeaking – Mr Johnson said that about a year ago "they were getting 20 dollars and they needed 40 to make a profit and 60 to compete with what they could get for milk".

But the only opportunity the Kiwi move into dairy creates is for somebody else to be as ruthlessly efficient at turning grass into lamb. That is the point of the Better Returns Programme, run by the English Beef & Lamb Executive (Eblex), a government body financed by a levy on farmers.

A subsidiary, Signet Breeding Services, organises the monitoring of flock performance using a standard set of measures known as estimated breeding values.

Questions include: How many lambs per lambing? What do they weigh after eight weeks? What is the depth, at maturity, of the "eye muscle" that produces the chump chop? How is the fat distributed?

Mr Johnson said it was surprising how much might be wrong by rule of thumb.

He has his best Bleu du Maines weighed at eight weeks and weighed again and measured with a mobile ultrasound scanner at 21 weeks. Some Texel and Charollais breeders ship top rams to hospital-style scanning rooms for a full 3D analysis. It all helps to identify the fittest parents and measure the progress achieved by spreading their genes.

And the Bleu du Maines at Low Whinholme, Danby Wiske, near Catterick, showed the best progress measured by Eblex over 2007-08.

At eight weeks, the rams average 3.47 kilos more than the average for the breed 10 years ago. At 21 weeks, it is 5.5 kilos.

Those genetics translate into butchers' lambs worth around an extra fiver a head, compared with taking luck of the draw. Mr Johnson culls 90 per cent of his tup lambs and 25 per cent of the ewes.

The Most Progressive Flock Award was official recognition that at 48, he is roughly back to where he was in 2001, when the pedigree flock he had spent 20 years building was thrown on a £1m bonfire as part of a culling operation which emptied 40 farms. It included a commercial flock he ran from crossing the Bleus with Hexham Mules.

He says they always fetched a better price than the standard Suffolk/Mule cross. But when it came to starting again, he abandoned the enterprise in favour of working up the dairy business he runs with his brother, Colin.

He had some frozen semen from his top rams, though, and has rebuilt the pedigree Bleu herd to the biggest of its kind in the country – 120 breeding ewes and four rams at the moment.

When restocking, he bought in some of both genders on "type", meaning appearance, and he wins show prizes from the top type lines. But experience has reinforced his faith in science over lore.

He said: "Production traits are the bricks and type is the mortar that holds it all together."

He can sell every shearling ewe he can spare, at £120-£150, to other Bleu du Maine fanciers.

Rams go for up to £800 – some to specialist breeders but most to commercial lamb producers looking for an alternative to Suffolks and the like for a terminal sire.

Lambs fetch £60-£65 a head from the butcher and even the old ewes have been worth that lately.

But there are extra costs, too. £10 a head to register 30 new animals with the breed society every year, for example, and £500 a year for using the Signet computer programme and organising the scanning and weighing.

It ends up being more or less a hobby, Mr Johnson says – but he can hope it is a hobby which will one day pay off, as respect for sheep genetics spreads.

He says that the high cost of disease in sheep will drive a trend towards "closed flocks" – meaning those which breed their own replacements as well as output.

And that is going to mean much more genetic selection. He is getting close to self-sufficiency. Scab was one motivation for moving that way and worm-resistance is the latest problem to make him glad he is not buying much in any more. He has experimented with putting a Hampshire Down on to Bleu ewes and was impressed with the progeny.

He has sold a Bleu tup to a man who wanted to cross it with Llyns to produce breeding ewes and another to be crossed with a Friesian sheep to breed milkers for the small sheep-milk business.

He is also supplying performance-tested ewes to be crossed with Beltexes in an effort by his breed society to popularise a new kind of terminal sire – the Millennium Blue, seen above.

For the time being, the paying business is the dairy herd of 150 – mainly Holstein Friesians, but with a few Meuse-Rhine-Issels and Swedish red-and-whites reflecting the brothers' interest in experiment, inherited from their late father, David. The cows are fed mainly from the 100-acre farm's own wheat, barley and maize.