Increased levels of cortisol (a hormone secreted by the adrenal cortex) which can weaken the immune system.
Poor sleep
Become panicky increasing the chance of injury
Before you wean put together a plan. It will take her a few days to "'dry up" , so she will be sore and grouchy. Don't milk her out since this encourages continued milk production. If she is in good condition physically you may try reducing her grain ration for a few days to help her out.
Weaning the Foal in Hot Weather
For those of us with foals born this spring, it is weaning time. This is a stressful situation for both mare and foal, not to mention the owner who has to listen to all the whinnying and look at those pitiful foal faces! Usually we wean at 5-6 months. But, the weather is so hot (100+ for days and days) here in Oklahoma that when we often have to wait. There is no reason to cause additional stress because of the weather when a couple months won't make that much difference. If you are preparing to wean, please take into consideration the weather and other factors. It is easy to lose a foal due to stress in these circumstances.