With the autumn sales now underway sheep farmers and shepherds have been spending a lot of time examining, selecting and preparing their sheep.

After weaning, the wethers, or castrated male lambs, are separated from the ewe lambs. While all sheep are ultimately slaughtered, wethers are destined for the abattoir as soon as they are in prime condition. That can be anything from between 12 weeks of age to over a year-old, depending on how well they are fed and how fast they grow and fatten, or finish as we call it nowadays.

To determine the amount of fat cover on prime lambs, farmers place their hand firmly on their backs at several points and feel their tails. An experienced handler can easily feel the spine and tail joints on those that are too thin for slaughter, while that is much harder on those with a generous covering of fat. The trick is to select them when they are just right, and that involves examining them every fortnight.

Some don't finish their wethers, but prefer to sell them as "stores" to be finished by someone else, and that involves drawing them into even-sized batches. You might think it would be easy to hide a few smaller ones among a large bunch, but nothing could be further from the truth. Small lambs tend to be pushed to the edge of a group by the bigger, stronger ones, and end up walking round on the outside of the ring in full view of the buyers, who then bid accordingly.

Scotland's sheep industry is stratified, with surplus pure-bred breeding sheep from our high hills being sold to upland farmers who then breed prolific, crossbred ewe lambs that are sold to lowland farmers who mate them with meaty, "terminal" sires.

The system starts in the autumn when hill farmers select the best pure-bred ewe lambs as breeding replacements for their flocks.

Among many other things, good breeders carefully check the mouths of their sheep. Sheep only have one set of incisors on the lower jaw that should meet the middle of the dental pad on the upper jaw. Those that have short lower jaws, like a pig, are called "sow-mouthed" and can struggle to graze properly. Those with a longer lower jaw that allows the incisors to protrude beyond the upper-lip are just as undesirable and called "showing-gub". Their teeth can become very long, slack and fall out. Both types invariably end up being slaughtered.

The next draw of ewe lambs, or mid-ewe lambs as we call them, that aren't quite good enough to be bred pure, are sold to upland farmers to breed crossbreds. Poorer, smaller ewe lambs that didn't make the grade often join the wethers to be finished as prime hoggs in the run-up to Easter.

Some upland farmers prefer to buy "draft" ewes which are better quality breeding sheep than the mid-ewe lambs rejected by hill farmers. They are drafted out of the pure hill flocks when they are five-year-olds after they have had four "crops" of lambs. Such ewes are deemed to be too old to survive another year on a high hill, but are perfectly capable of breeding for another couple of seasons on a kinder farm.

The remaining breeding ewes on a hill farm also go through a meticulous selection process. They have their mouths checked to see if any teeth are slack or missing, and their udders checked for defects. Ewes that haven't got sound mouths find it difficult to graze our harsh hills during the winter months when grass is short, while a healthy, disease-free udder with two functional teats are essential if lambs are to have an adequate supply of nourishing milk. Those that fail on those two counts, as well as ill-thriven ones are drafted out of the flock to be fattened for slaughter.

Prior to the sales, dedicated stockmen scrub and groom their sheep, or snip and clip unwanted hair or wool off them, so as to make them look their best for those precious few minutes in the sale ring. It's all about catching the eye of the buyers in the hope of a few extra bids.

I curse the men who developed the concept of dressing sheep as it trapped everyone else into that time-consuming ritual. Make no mistake, while all that titivation may seem frivolous and unnecessary to the uninitiated, it can result in hundreds of pounds extra for the vendor,

Mind you, most do it because they take pride in their sheep and want them to look their best on the day.