VN September 2023

September 2023 31 Common Avian Clinical Problems Part IV Dr Coetzee de Beer BVSc (Hons) MANZCVS (Avian Health) This article is sponsored by V-Tech Orthopaedic problems • It can be difficult to distinguish between congenital and acquired malformations, especially in neonates and juveniles. • Factors that can have an effect on normal skeletal conformation include: o Pre-laying factors (parental genetics, health and diet - see above) o Incubation procedures and parameters • Artificial incubation is more likely to produce chicks with limb malformations than natural incubation • Incorrect incubator temperature, humidity, ventilation, and rate and degree of egg turning can have deleterious results on the development of the embryo and result in malformations • The nesting environment • Nest box design can have an effect on neonates in several ways: o Slippery floors are believed to contribute to coxofemoral subluxation (‘splay leg’) in budgerigars o Inexperienced parents who can enter the nest box quickly and land heavily on the chicks can cause injuries resulting in malformations o Birds that are hand reared in a brightly lit, roomy container are often encouraged to move around more than they would in a dark and relatively cramped nest box. This can lead to excessive weight bearing on the legs with subsequent bowing and malformations. o Nutritional secondary hyperparathyroidism and rickets (collectively referred to as Metabolic Bone Disease) are underlying factors behind many of these problems • Rickets is a metabolic bone disease in growing animals caused by a Vitamin D3 deficiency. (This can be due to inadequate nutrition, lack of exposure to sunlight, defective vitamin D activation, defective vitamin D receptors, hypoparathyroidism, renal failure, renal phosphate loss, or gastrointestinal malabsorption.) The result is impaired mineralisation of osteoid tissue or epiphyseal cartilage, leading to thinning and weakening of the bones and excessive growth of cartilaginous structures. This, in turn, causes deformity at the ends of the bones, particularly in the proximal tibiotarsus, the beak (rubber beak) the head of the ribs and sometimes the costochondral junction (rachitic rosary). Radiographically there may be widening and distortion of the growth plates. • Nutritional secondary hyperparathyroidism is commonly seen in adult birds fed a diet that is either calcium-deficient or has an excess of phosphorous (or both). For example, seed-only diets may have a calcium: phosphorous ratio as low as 1:10. Fruits, nuts and most vegetables are also calcium deficient. When these diets are fed to birds, especially parents rearing chicks or to recently fledged juveniles, the parathyroid gland releases parathyroid hormone which, amongst other effects, withdraws calcium from the bone to maintain normal serum calcium levels. The result is thin bones which bend or break easily, leading to malformations. • The types of limb malformation that are commonly seen include: o Coxofemoral subluxation (splay leg) may be the result of a lack of non-slip substrate in the nest box. This allows the legs to splay out laterally away from the body, subluxating the coxofemoral joint and leading to laxity or damage of the medial collateral ligaments of the stifle, angular limb deformities of the femur, tibiotarsus, and tarsometatarsus, or slipped tendons. Sometimes, if the chicks have metabolic bone disease as well, folding fractures of the tibiotarsus will result in secondary “splay” deformities. Technical I Article >>> 32