topspec don't make the broodmare and youngstock supplement anymore. They now recommend a product named 'all in one', I believe they have combined most of their supplements and recommend it for most types.
Here's a link to the product
http://www.topspec.com/products/topspec-all-in-one/
Where were the loanees based and is it worth posting on facebook or advertising in a magazine? Also it might be helpful if you post a picture. Hope you have some luck tracking him down :)
The great nature v nurture debate again: yes I think that genetics can play a part but if you're finding that your youngster is a little quirky then I think that regular handling will definitely play a positive part. Keep on top of it and don't let it be an excuse for bad behavior. The end...
If you buy dectomax from an agri store be prepared for questions as they should not sell it for use on a horse without a prescription from your vet. Obviously you could lie an tell them that it is for your pet cow though! :D
ETA you can also use it at the sheep/goat rate which is 1ml/33kg which...