David C. Van Metre, DVM, PhD, DACVIM
Multiple physiologic mechanisms act in concert to maintain the concentration of ionized calcium in the extracellular fluid (ECF) within a very tightly-regulated range. Hypocalcemia most commonly occurs when the physiologic demand for calcium for fetal bone growth or milk production exceeds the dietary supply of calcium and overwhelms the homeostatic systems aimed at maintaining adequate ionized calcium in the ECF.
In a 1996 survey of over 5,100 U.S. sheep producers, 9.4% of lambs born alive were reported to have died prior to weaning. Worldwide, hypothermia and starvation are considered to account for the majority of preweaning lamb losses, with predation and respiratory disease also being important causes.
Urinary calculi, or uroliths, are concretions of solid mineral and organic compounds that cause disease through direct trauma to the urinary tract and obstruction of urinary outflow. The urethral process is the most common site of obstruction in sheep and goats.
Enterotoxemia is characterized by proliferation of and exotoxin production by Clostridium perfringens in the lumen of the gastrointestinal tract. Although limited tissue invasion by the causative organism does occur, most local and systemic lesions result from the local and systemic effects of potent exotoxins produced by certain genotypes of this bacteria.
Small ruminants constitute a rewarding component of a mixed or rural veterinary practice. In such practice scenarios, certain common medical disorders of small ruminants may be encountered on a fairly regular basis. The following cases are valuable teaching cases because they involve differential diagnoses that are commonly encountered in small ruminant practice.