Given the arduous nature of their duties, horses generally serve for about 17 years while mules for 15 years and dogs for six to eight years. Once they retire, these animals are shifted to Army centres. Those animals which fall sick or are injured and not respond to treatment are put to sleep. Following strong objections by the Animal Welfare Board and more than 20,000 online petitions against euthanasia, the Army is mulling over handing over retired animals to interested NGOs, officials said. Once the policy is firmed up and given clearance by the Defence Ministry, the Army plans to advertise inviting NGOs to adopt animals.