Ovine pulmonary adenocarcinoma be predisposed to OPA. Most affected sheep show signs at 2 to 4 years of age. OPA is not a notifiable disease, and therefore it is difficult to assess its prevalence. OPA was first described in the UK in 1888, and described in detail in South Africa in 1891. The disease was initially known as "jaagsiekte" , a word derived from Afrikaans, meaning "chasing sickness," so called because animals are in respiratory distress as if they are out of breath from being chased. It has also been known as sheep pulmonary adenomatosis and ovine pulmonary carcinoma. OPA has been used
Animal welfare Animal welfare Animal welfare is the well-being of nonhuman animals. The standards of "good" animal welfare vary considerably between different contexts. These standards are under constant review and are debated, created and revised by animal welfare groups, legislators and academics worldwide. Animal welfare science uses various measures, such as longevity, disease, immunosuppression, behavior, physiology, and reproduction, although there is debate about which of these indicators provide the best information. Respect for animal welfare is often based on the belief that nonhuman animals are sentient and that consideration should be given to their well-being or suffering, especially when they are under