As cocks get older, their spurs get longer. Some spurs can become very sharp and pointed and can cause damage to the sides of a hen during mating.
Sometimes, this damage on hens can be missed as the wings cover this area, you should always inspect hens regularly and as soon as favourite mates can be identified (or if you have a small number of hens running with a cock) they should have saddles fitted to protect their backs. If the skin becomes torn, the hen risks getting an infection. Spurs can be trimmed back a little on cocks to round the ends off, as well as keeping them to a suitable length.
To trim spurs, you will need a sharp pair of cutters. Large dog nail clippers are ideal, or tool shops sell almost identical round cutters that are suitable and a file for rounding the edges off afterwards.
Care should be taken that you don't trim too much off the spur. There is a blood vessel that runs down the centre of a spur, usually about ¾ of the way along it that should not be cut.
Trim the point, then keep nipping small pieces off millimetre by millimetre until you see a tiny dot of blood appear in the centre of the spur. This is the blood vessel and is as far as you can go.
Using the file, you can round the edges of the spurs off to make them neat.
If you trim too far, the spur will bleed and be difficult to stop bleeding. If you have a number of male birds, you may want to consider buying a Veterinary Silver Nitrate Pencil from your local vets. This can be dabbed on the end of the spur to stop the bleeding and is also useful when trimming dogs nails.