DES MOINES, Iowa (AP) — The U.S. Department of Agriculture says it considers many factors when determining ways to euthanize large numbers of animals during a disease outbreak. The agency released the statement Thursday in response to a letter from an animal rights group criticizing a USDA proposal to respond to a future outbreak of bird flu.

The Humane Society of The United States’ letter focused on statements made by USDA Chief Veterinary Officer John Clifford during a Senate committee hearing last week. Clifford said shutting off ventilation systems to barns when the highly contagious disease is found may be more humane and efficient than gassing or using foam to suffocate the birds. Those methods were used amid this year’s outbreak.

The animal rights group says the latest idea is gruesome and should be scrapped.