Lactation tetany of mares is a metabolic disease characterized by hypocalcemia that typically affects lactating mares around 10 days after foaling or 1-2 days after weaning. Clinical signs include muscle tremors, stiffness, and potentially tetanic spasms as calcium levels drop below 8 mg%. Diagnosis is based on history, clinical signs, and low serum calcium levels below normal ranges. Treatment involves intravenous calcium injections to rapidly resolve symptoms, while prevention focuses on vitamin D supplementation after foaling and weaning.