Today, one of the priority tasks in animal husbandry and veterinary medicine is the creation of a highly productive, stable herd with a stable level of metabolism. A large load on the animal's body reveals high milk productivity; in connection with this, metabolic processes slow down, directly reducing milk productivity and requiring a balanced diet and high-quality feed. An increase in milk productivity is often directly related to metabolic disorders and the appearance of diseases, including the intensity of physiological and biochemical metabolic processes associated with converting a significant amount of energy and nutrients from feed into milk. Metabolic pathologies in animals can be caused by hereditary defects in the metabolism of nucleic acids, congenital insufficiency of enzymes responsible for the synthesis and breakdown of amino acids, disorders of organic acid metabolism, fatty acid deficiency, etc. Timely diagnosis of rickets and rapid therapy in the initial period is essential in treatment because the earlier the diagnosis is made, the easier it is to treat the disease. This will lead to the termination of the further destructive process, the occurrence of bone deformations, and changes in internal organs. The article deals with the issue of vitamin D deficiency in young cattle from a modern perspective. Materials on the classification, etiology, and pathogenesis of vitamin D-deficient rickets in calves are covered. The role of vitamin D in the prevention of rickets and its importance for general animal health and welfare are summarized. It is noted that this disease's characteristic feature is mainly the course's hidden stages. Clinical symptoms of D-hypovitaminosis appear in the late stages of the disease when restoring the animal's health is impossible. The essence of the pathology is a violation of mineralization of the organic matrix of bone tissues (D-hypovitaminosis) or osteolysis of already formed structures. The work aimed to find out the distribution, etiology, biochemical and clinical manifestation of D-hypovitaminosis in calves in one of the farms of the northern districts of Zhytomyr region, which belongs to the natural-geographical zone of Zhytomyr Polissia. The material for the study was clinically healthy calves and calves with rickets aged 1–3 months. The conditions of keeping and feeding animals on the farm were studied. Diagnosis and spread of D-hypovitaminosis among calves 1–3 months old were carried out with the help of clinical and unique methods; first, preference was given to laboratory studies. Clinical manifestations are described, and laboratory features of the course of vitamin D deficiency in animals are presented. It has been established that vitamin D deficiency in calves is quite widespread on the farm. Thus, the subclinical (hidden) course was registered in 45.8 % of animals and the clinical – in 24.1 %. The disease was more often registered in the winter-spring period. The leading cause of the disease in calves is insufficient motor activity (hypodynamia) in the absence of insolation, as well as a low level of feeding: reduced provision of cholecalciferol (25.8 %), violation of the calcium-phosphorus ratio (2.7–4.2:1 versus 1.5–2.0:1), deficiency of microelements – cobalt, zinc, copper, the provision of which was, respectively, 57.6, 85.6 and 96.2 % of the need. Pathognomotic manifestations of the disease in calves are licking, allotriophagia, thickening of carpal joints, partial resorption of the last ribs and tail vertebrae, and loose teeth. Vitamin D deficiency prevents the efficient absorption of calcium and phosphorus in feed. With vitamin D deficiency, only 10–15 % of feed calcium and 50–60 % of phosphorus are absorbed. The most informative laboratory markers for diagnosing pathology are determining cholecalciferol content, total calcium, inorganic phosphorus, alkaline phosphatase activity, and its bone isoenzyme in blood serum.
