Colorado State Fair officials say they'll be aggressive about watching for livestock tampering in the competitions when the fair begins in late August.
The State Fair released new guidelines over the matter.
One of the new rules involves removing protective coverings from lambs at weigh-in to allow for close inspection.
State Fair General Manager Chris Wiseman says the move is to protect the participants who "endeavor to do the right thing."
Earlier this year, officials at the National Western Stock Show in Denver said 18 lambs, had been injected with a substance to make the animals appear more muscular.
The substance used on the lambs -- two of them were top winners -- caused swelling and inflammation.
The Denver district attorney is investigating the case.