SANTA FE, New Mexico – Drugs used to treat horses renders the meat adulterated and therefore unfit for human consumption or sale in New Mexico, according to a legal analysis by Gary King, the state attorney general.

"Our legal analysis concludes that state law does not allow for production of meat that is chemically tainted under federal regulations," King said in a statement. "New Mexico law is very clear that it would be prohibited and illegal."

The opinion presents a potential block to Valley Meat Co., Roswell, NM. The owner, Ricardo De Los Santos has been trying to re-open his former beef slaughter to process horse meat. If he is successful, Valley Meat would be the first plant to process horse meat since the federal government banned the practice in 2007. In May, De Los Santos received a letter from the US Department of Agriculture recommending his application be processed and a grant of federal inspection be issued. De Los Santos plans to sell horse meat to foreign markets.

But in King's opinion, horse meat could be considered adulterated because of drugs used to treat them, and state laws mandate that adulterated food products cannot be manufactured, sold or delivered anywhere in New Mexico regardless of where the food is ultimately sold or consumed. King investigated the matter at the request of New Mexico state Senator Richard Martinez, who had expressed concern that Valley Meat would be operating in the state illegally.

In a letter to Martinez, King cites numerous studies that warn against consumption of US horse meat. A 2010 article in the journal Food and Chemical Toxicology raised questions about the use of phenylbutazone, also known as 'bute'. That article stated that the drug was marketed in the US in 1952 as a treatment for rheumatoid arthritis and gout. But "serious and often fatal adverse effects such as aplastic anemia and agranulocytosis appeared in the literature within three years of its use."

The Food and Drug Administration has set no safe levels for the drug in food animals, and "bans the administration of this drug in any horse sent to slaughter for human consumption."

In aNew York Timesreport, a lawyer representing the company said a drug residue testing program is in place at the facility, and plans to open the plant are moving forward.