Before coming to vet school, I didn’t know that alpacas existed—I thought everything with a long neck, thick wool, and long ears was a llama. Lecturing clinicians always include camelids (llamas, alpacas, camels) in their discussion of large animal medicine, and although the large animal hospital sees mostly equine patients, there’s usually a token goat or alpaca admitted every time I’m on selective. I’ve really enjoyed getting to know these slightly odd animals, with their soft fleece and unique, insistent humming sounds. One of the first alpaca cases I observed was a 7-month-old alpaca (correctly termed a cria) that arrived markedly underweight and undersized for his age.
He had a history of not wanting to get up and walk around, and his posture indicated that standing was painful. Also, it seemed like his forelegs might not be completely straight. After a full physical exam, the clinicians took some different radiographic views of his legs—and boy, were those films dramatic! In our different classes the clinicians make it a point to familiarize us to “normal” radiographs, as well as training us to notice subtle changes in opacity, margins, and lucencies of joint spaces. (I put “normal” in quotes, because the normal radiographic appearance of a bone can vary with species and age of the individual, as well as patient positioning and exposure of the film, among other factors.) So it was exciting to be given a clearly abnormal radiograph and to really understand why it was abnormal: the cria’s distal radius and ulna were enlarged, flaring out like an elongated triangle and cupping the carpal bones, a classic appearance of rickets.
As it turns out, alpacas are prone to vitamin D deficiency, both because of their incredibly high dietary requirement, and because of the relative lack of sunlight exposure here in the U.S. Alpacas in South America are much closer to the equator, so they receive more direct sunlight for longer periods of the year. Mammals make a vitamin D precursor from cholesterol, but it must be activated in the skin to have its biological effects of promoting dietary calcium absorption and kidney reabsorption, and of keeping blood levels of calcium at a normal level (by promoting bone degradation, if needed). In our case, this cria had been born in late fall, and with limited winter sun to soak up and no vitamin D supplementation, he developed rickets.
With some aggressive vitamin D supplementation, the clinicians were able to stop the progression of bone loss, but it’s likely that this cria will have permanent limb deformity. The clinicians also recommended herd-wide vitamin D supplementation, because it’s very likely that other members of the herd also have vitamin D deficiency, even if they weren’t symptomatic.