My 15 month old dalmatian has 99% recall, I've been using the whistle for approx 4 weeks now and she's improved dramatically rather than just yelling for her. The 1% is sheep and cows, she once chased sheep, months ago, I'm obviously very vigilent now and she's straight back on the lead if I spot any. Anyway the other day I was walking her in an unfamiliar place along a track next to a field where there were cows, it was well fenced off, she found a gap in the fence and got into the field, it was obvious she wanted a chase as she was running up to the cows and turning and runing away. Thankfully the cows weren't interested in her. I was whistling for her to come back and she completely ignored me. I've heard cows don't like dogs much anyway so she was lucky this time. I realise I'm going to have to keep her on a lead at all times now where there's a chance of sheep or cows, Will she always do this or is it because she's still young and wants to play with everything? She never attempted to go too close to the sheep or cows, just wanted to play.
Would walking her next to sheep and cows (on lead) get her used to them?
Someone mentioned introducing their dog to a ewe worked.
Has anyone had a similar experience and their dog has grown out of it or found a way to stop it?

Angela Stockdale runs very successful livestock classes http://www.dog-partnership.co.uk/sheepintro.htm

Every time your dog DOES escape and chase will reinforce this behaviour and make it more likely to happen again as it is so obviously rewarding to her so prevention and/or proper training is essential.

I am afraid whether she is motivated to chase to play or to kill is immaterial; your dog could be shot just for being loose in field of sheep for example as the mere sight of dogs may cause sheep to abort; cows with calves are extremely dangerous to dogs and their owners and steers will chase and of course cattle and sheep may be injured by being caught in barbed wire, drowning etc etc.

Dogs do not "grow out of" this type of behaviour; they can be "trained out" however; you MUST keep your dog on a lead at all times if your dog is not 100% reliable around livestock.

I've e-mailed Angela to see if there are any plans to have any classes nearer me (Newcastle upon Tyne) or if she knows of anyone up this way that runs similar courses.
Thanks.

If your spotty monster is anything like mine (or any other dalmatian I've met) it's unlikely that she'll grow out of anything until the age of about 9 years :-D
My dog's recall is also pretty good but he does chase sometimes so I've found it's best to put him on a lead as soon as there's any sign of livestock and not run the risk of him geting into trouble. Since mine is nearly 6 I don't think that I'll ever be able to change this.