THE LEGALITIES OF CASTRATION
* The legal requirements applying to castration are outlined in the
terms of testicular growth rate, but still best done by the time they're four weeks old. If left too long the ring may cut off the blood flow in the scrotal vein, but not the artery, leading to engorgement of the scrotum which invariably leads to major complications.
When I was a novice farmer, we got into some trouble doing a couple of bull calves too late. On both calves the scrotum swelled, causing discomfort for the animals for a longer period than should have been the case and the enlarged scrotum then caused ongoing problems because it did not die and drop off as it should. Neither became infected, but both had to have the dead and stinking big lump surgically removed, leaving a large wound. Both recovered well, but it was an expensive and a stupid mistake to make.
High tension banding by a veterinarian using local anaesthetic is a humane way of castrating older animals if necessary. Pain relief is mandatory with this method. Farmers are currently still permitted to castrate animals without the use of pain relief within the first six months of life, but it must be done properly to avoid the need for later expensive and stressful intervention.
If you have never done it yourself, get someone experienced to demonstrate and assist you, or get a vet in the first instance, especially if there are other things you require, like dehorning/disbudding. If you only have a small number of animals or don't have the equipment or experience, that may be the best option, especially if you'd prefer to follow best practice and have pain relief administered to minimise any distress in your animals.
The biggest risk for calves and lambs (and kids) with castration is tetanus, a deadly disease caused by one of the Clostridium bugs which get into the bloodstream via injury sites.
Lambs and calves whose mothers received a 5-in-1 vaccine before lambing/ calving (either a sensitiser and booster around six and two weeks before, or an annual booster two to four weeks before birth) should receive adequate cover against tetanus via the colostrum, for the first six or so weeks. They can be safely castrated at birth or very soon after. Lambs whose mothers have not been vaccinated must receive a lamb vaccine containing an anti-toxin for tetanus at the time of castration. The same product can be used for calves, but it's an off-label use that you'd need to discuss with your vet who would advise correct dose rates.
Consult your vet about the best timing for docking/castration if a lamb vaccination is required and subsequent vaccine administration.
LEFT: this pus-like matter is common above a ring on a castration wound.