Join Date: May 2012
Location: CT USA an English transplant
There's no doubt that incorrect weaning will cause problems which is why it's so important to do it correctly. By the time a foal is weaned it should already be eating well and not totally reliant on its mother's milk
If the foal is going to be handled for shots and castration etc then its best if this is done well prior to weaning - all my foals were handled as soon as possible, usually on the day they were born so they could be checked over and the umbilical cord area treated. A foal that sees its mother calm and trusting around humans is less traumatised and more accepting of being touched and restrained
I prefer to take the mares away for a month and leave the foals in familiar surroundings amongst other horses that they feel secure with. I've never had one whinny for long or get distressed as they're already quite secure and socialized with a group and each other.
***As for the question on getting the weight on the mare - she is going to keep producing milk on a supply and demand basis and as the foal gets older it will drink a lot more than it did at 2 months old even though its eating other stuff. Sometimes just seeing the foal will cause her to produce milk and will give her as much or more stress as taking the foal away altogether because in a few days she'll forget about it
OP - you are in a Catch 22 situation where you are now. The foal smells the milk and will want to feed off her. If you remove her grain she'll pull on every other resource she has to feed her baby - which is why many mares in the wild die of starvation in hard times. To get weight back on her and keep weight on her you are going to have to feed her a lot more and she will keep producing milk as long as the colt keeps asking for it
This is why the only real answer to your question is that the solution to your problem is to wean now.
I wouldn't castrate while there are still flies about but once they've gone over if he's dropped it needs to be done before the frosts get too severe
The older he gets the higher the risk of him breeding with any mares you have and if they don't want his attentions he's going to get attacked by them. Even in an adjacent field there's a good chance that he'll try to jump out or break through the fence to get to them especially if you have a flirty mare that plays up to him.