Flexural limb deformity occurs in two forms. The first form, also known as contracted tendons, clubfoot, or knuckling, is the inability to extend a limb fully. The condition may be present at birth (congenital) due to improper positioning in the uterus (which can lead to dystocia in the mare), abnormal fetal development, disease or malnutrition in the dam; or acquired as the result of nutrition (abrupt changes in amount or quality of feed leading to rapid growth), polyarthritis, trauma, or disease. It is a common condition in foals, usually occurring anytime from birth to 14 months of age.

Fragile Foal Syndrome (FFS) is a lethal genetic disease of connective tissue which has been reported most frequently. in Warmbloods. However, a recent study has found that the genetic defect responsible is present across a range of other breeds.

Warmblood Fragile Foal Syndrome Type 1 (WFFS) is an inherited defect of connective tissue characterized by hyperextensible, abnormally thin, fragile skin and mucous membranes that are subject to open lesions. Affected horses may also have hyperextensible limb joints, floppy ears, accumulation of fluid (hydrops), subcutaneous emphysema, hematomas, and premature birth. The disease is present at birth and affected newborn foals are euthanized shortly after birth due to the poor prognosis of this untreatable condition.

A poll on HORSEJournals.com asked the question: Should equines be cloned? Some 83 percent of respondents said no, not until more research has been done; 15 percent said maybe, in special situations with strict parameters; just two percent said yes, and that registration of clones should be allowed.