we keep it for years... I like thawing it just before using it, but apparently even if it's curdled it's actually still ok... but I don't like feeding the calves something I wouldn't want to drink myself
the last 2 calves I lost were from breech births.. one was the second twin which I only found the next day (the first was 110 lbs, so I didn't figure on another 110 lb'er in there), and the hind legs were forward to make matters worse, the other one I lost was a single with the hind legs forward too, and the mother adotped a twin the real mother didn't want, so that worked out too... I've been close a couple times on them when they were backward but the hind legs facing the right way.. my old cow was one this spring, and it just took a little bit of helping.
It seems to help grafting a calf to a new mother if the cow has never had a chance to sniff and lick it's calf... the one that adopted the twin (2 days after she lost hers) was love at first sight... I brought the calf up the chute, the cow MMm'd, and she accepted it right away... it was so nice after I was fighting the calf's real mother for a couple hours at 2 AM in the cold with no luck... I had taken the calf into the shop, gave it a quart of colostrum, and went to bed so I could deal with it again in the morning, and it all worked out. Turned out to be a fantastic heifer, but since she was a freemartin I didn't keep her