You debit your 'sheep' account (maybe called sth like inventory) and you credit your cash account, or a liabilities towards suppliers account. Your equity stays constant in either case (no profit or loss impact), if you paid cash you've swapped X worth of cash for X worth of sheep, otherwise your liabilities went up by X.
When they die, you debit some kind of expense account (extraordinary losses or sth like that), and you credit the sheep account. In that case, you've made a loss of X and your equity (when you next draw up your balance sheet) will be lower by X (assuming that's the only business case). It might even go negative, eg if the sheep were your only asset and you still have the liability towards the guy who sold them to you.