This is the time of year when sheep farmers wean, or spean their lambs, as we call it. That's probably the most cruel thing we do to our sheep, but it's done for their own good.

Most low-ground sheep are already speaned, while hill farmers are currently gathering in their hill flocks for that task. It's simply a matter of separating them by running them up a "shedder".

"Shedding" involves running the sheep into a funnel that leads to a narrow walk-way or "race", the width of a sheep, that leads to a shedder gate that divides sheep one way or another. Once the ewes have been shed off from their lambs they can be kept from them in separate, stock-proof fields.

That leaves the air full of the sound of lambs constantly bleating for their mothers, but after a few days they soon settle down and can be then be put on to the best pasture for fattening.

It's a sad fact of life that all farm animals - young and old - are ultimately slaughtered for meat. Most of our livestock production are prime animals - that is to say, as the name implies, in their prime - but there are also the older breeding animals that are culled for slaughter at the end of their productive lives.

This is also the time of year hill farmers select breeding stock for next year so that the right number are kept for each heft on the hills.

Managing sheep on an unfenced hill relies on a phenomenon called hefting. If sheep were allowed to randomly graze over large tracts of land there would be no way of controlling grazing, or managing a breeding programme. Rams could end up mating with their daughters. To overcome that problem, many hill ewes are hefted.

A heft is a family group of females that can range from as little as fifty ewes to hundreds. They graze a clearly defined area of land that may be bounded by a road, burn, skyline, loch or trees, and may extend to hundreds of acres.

Over the years shepherds have worked out the optimum number of ewes for each heft and vigorously maintain the system by having distinct marks for each heft so that they can easily identify and chase any strays back. It's amazing how sheep learn not to stray from their heft, and return to it like homing pigeons after being released from a day in the sheep pens.

Once the best ewe lambs are drawn off for flock replacements, older ewes are drafted to be sold for further breeding on kinder, low-ground farms or to be fattened for slaughter.

Sheep farmers tell the age of their ewes by saw marks on their horns, or small nicks and notches on the ears of those breeds like Cheviots that don't have horns.

If there is no saw mark it means it was born in 2010, one mark means it was born in 2011, two for 2012, three for 2013, four for 2014, and none if it was born this year. The cycle is repeated every five years.

Once the five-year-olds are shed off, the rest 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 two functional teats and a disease-free udder 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 also drafted out of the breeding flock to be fattened for slaughter.

Farmers aren't hard-hearted, callous people. We care for our animals as best we can, and often become attached to them, but we also have to remember that we keep animals for food.

As we load them onto the lorry that will transport them to their final destination, we often remember individual animals that we have got to know well.

Whatever the history, most animals will have drawn attention to themselves one way or another in their lifetime. After all, we tend our animals every day of their lives.

Farmers have to content themselves with the knowledge that they looked after their livestock as best they could, that they will be transported in comfort to the market or abattoir, and finally humanely slaughtered.