Sentence:  The introduction of purchased animals from herds which have not been tested, the “over-the-fence intimacy of tested animals with cattle which had not been tested, and the feeding of milk to young stock on accredited farms which had been purchased from neighboring farmers whose herds had never been tested resulted in the <WSD>deranking</WSD> of these, erstwhile accredited herds. 
Meaning of the word marked with <WSD> tags:  To lower or remove an official ranking or accreditation.