Insulin-like growth factor 1 (IGF-1) is one of the more studied areas of known overlap between metabolism and longevity, but given the innate complexity of biology in mammals there is always some debate over the degree to which IGF-1-related mechanisms are actually determinants of life span, or even correlated with life span. Here is a study in sheep, not the usual species in investigations of the biochemistry of aging: "Longevity in livestock is a valuable trait. When productive animals live longer fewer replacement animals need to be raised. However, selection for longevity is not commonly the focus of breeding programs as direct selection for long-lived breeding stock is virtually impossible until late in the animal's reproductive life. Additionally the underlying genetic factors or genes associated with longevity are either not known, or not well understood. In humans, there is evidence that insulin-like growth factor 1 receptor (IGF1R) is involved in longevity. Polymorphism in the IGF1R gene (IGF1R) has been associated with longevity in a number of species. Recently, 3 alleles of ovine IGF1R were identified, but no analysis of the effect of IGF1R variation on sheep longevity has been reported. In this study, associations between ovine IGF1R variation, longevity and fertility were investigated [in] 1716 New Zealand sheep belonging to 6 breeds and 36 flocks. ... Ovine IGF1R C was associated with age when adjusting for flock [and] a weak negative [correlation] between fertility and longevity traits was observed."