We leave ours together till the next lot start to arrive - the 'last year' calves get very excited at the new arrivals and can be a bit over exuberant and this passes on to the rest of the herd. Too much pushing and shoving and the new mums who are first timers can get a bit intimidated.
At the moment our 2013 calves are still with their mums - who are due to calve in Apr-May. We'll put the 2013s in with the bull once the 2014s arrive. We do check the condition of the mums to ensure they're coping with this, and keep a good eye on udders. Not had any significant udder problems so far.
We've found Shetlands a good breed - we started with 4 heifers and now have a small herd of 24 beasties. The Shetlands are easy to handle (if you spend time with them from when they are born) and the cows make excellent mothers, producing lots of milk.
But as always with livestock, there can be problems. Last year we had a first timer lose interest in her calf - she wandered off without it. So we had to keep it warm and do a couple of tube feeds. After it was properly on its feet, we shut the calf and her mum in a pen overnight and kept holding the calf up to the udder. By the next day, everything was OK - calf & Mum bonded nicely and calf was suckling well. The calf, Dilic, (that's pronounced Dilys) is fine, if a little smaller than the other calves.
Even Shetlands can give the odd problem, so don't get the idea that nothing can go wrong. Saying that, there is a good amount of support available from other Shetland owners - there are a few of us on here as a starter if you have any questions.
Sue