Does the lack of sunlight during winters in the Pacific Northwest result in weaker bones in llamas and alpacas? That was the basic question asked in a research project performed at OSU by a group of faculty in both the College of Veterinary Medicine and the College of College of Health and Human Performance. The results of this project, which was funded by the Willamette Valley Llama Foundation and Morris Animal will be published in the American Journal of Veterinary Research, one of two veterinary scientific journals published by the American Veterinary Medical Association.a
As I wrote in the May-June 2001 Llama Letter article about fractures and their management ("The Nuts and Bolts of Broken Bones"), llamas and alpacas seem to fracture bones fairly often, and some breaks seem to occur with little trauma. That led Dr. Karen Timm to wonder whether the development of some of these fractures was due to decreased bone strength associated with seasonal changes in vitamin D levels.
From previous research in llamas and alpacas, done at OSU, led by Drs. Brad Smith and Bob Van Saun, we know that vitamin D levels in the blood varies by season, with the lowest levels in the winter and highest in the summer. This change goes along with the changes in sunlight in parts of the Pacific Northwest. Inadequate vitamin D causes a condition called hypophosphatemic rickets, which shows up as limping, poor growth, joints that appear swollen, and crooked legs. We know that supplementing vitamin D prevents this condition, and corrects it if it is not too advanced. Since this discovery, most crias, particularly those born in fall or winter, receive vitamin D supplementation, and as a result, the number of animals with crooked legs or other signs of rickets seems to be far less than only a few years ago. Although some vitamin D is contained in the diet, most vitamin D is created in the body by the action of sunlight. That is how inadequate sunlight can result in low vitamin D.
Vitamin D stimulates absorption of dietary calcium within the intestinal tract. Calcium absorption also causes an increase in phosphorus absorption. So if there is not enough vitamin D, there will be less calcium and phosphorus absorbed. Because calcium is so important to many body systems, not just strong bones, the blood levels of calcium generally stay in the normal range, even when intake is low. This occurs by increased bone breakdown when calcium levels drop, resulting in release of both calcium and phosphorus, the major minerals in bone. The extra phosphorus is eliminated in the urine, while the calcium is retained. This causes the low phosphorus levels seen with hypophosphatemic rickets. Hypophosphatemic therefore refers to low phosphorus.
If enough calcium and phosphorus are removed from the bone, the bone density will decrease, and consequently bone strength will decrease. This could lead to fractures, and may explain why some llamas and alpacas develop fractures with minimal trauma.
With that in mind, we performed the study I mentioned earlier to find out if bone density changes in llamas and alpacas in association with the seasonal changes in vitamin D, as well as changes in calcium and phosphorus levels.
To perform the study, we measured bone density in the left cannon bone (metacarpus) in five alpacas at four different times during the course of a year. We used alpacas for the study, rather than llamas, because alpacas were small enough to fit on the "Dual-Energy Absorptiometer," which was the machine used to measure bone density. We expect the same changes in bone density to occur in llamas as well as alpacas, and hypophosphatemic rickets has been seen in both. This machine uses X-ray technology to measure bone density, and it is the same unit used to measure bone density in people. This technique of measuring bone density is considered the "gold standard" in people, and has been useful in determining the risk of hip fractures in women, for example. It has the advantage of being non-invasive and therefore nonpainful, as well.
The alpacas in the study were all adult geldings. We avoided growing animals because of the effects of growth on bone density. However, younger animals would likely have greater changes in bone density with season, particularly if these young animals did not receive supplemental vitamin D. We included only castrated males because pregnancy in females can influence bone density. All of the animals were relatively light colored and all were sheared twice during the study to allow similar skin exposure to sunlight.
In addition to measuring bone density, we measured serum levels of vitamin D, calcium, and phosphorus. We also kept track of daily solar radiation and analyzed the feed the animals were eating. We wanted to meet all nutrition requirements without providing dietary supplementary vitamin D, because some vitamin D is absorbed in the intestines.
There was seasonal variation in bone density in the alpacas, with the density being lower in May (after the winter season) compared with the previous October (after the summer season). Bone density measurements also varied between individual animals. Some had higher bone density than others at each measuring time, so measuring the bone density of an individual animal may not be helpful in predicting fracture risk, but this has not yet been studied specifically. As with bone density, we found that vitamin D levels varied between individual animals, and that vitamin D concentration decreased between October and January, as sunlight decreased, and it increased from May to the following September, as sunlight increased. As expected, calcium levels did not vary. Also as expected, sunlight varied over the course of the year, being highest in July and lowest in December. The changes in bone density lagged behind the changes in vitamin D, which lagged behind the changes in solar radiation. This makes sense because it takes time for bone to release calcium and phosphorus in sufficient amounts to change bone density, so this effect would be seen later than the decrease in vitamin D.
None of the five animals sustained fractures during the study, and we were certainly not expecting any. However, the findings of this study show that seasonal changes in vitamin D are associated with a decrease in bone density. This in turn supports the theory that the decrease in bone density could make some animals more susceptible to limb. We are hoping to be able to evaluate bone density, as well as serum calcium, phosphorus, and vitamin D levels, in llamas or alpacas with fractures. By comparing bone density in these animals with normal animals of the same age, we can find out if seasonal changes in bone density are associated with the development of fractures. A project to do this, funded by the Willamette Valley Llama Foundation, is in progress, and we are looking for llamas or alpacas to include in the study.
a. Jill E. Parker, Karen I. Timm, Bradford B. Smith, Robert J. Van Saun, Kerri M. Winters, Peerapol Sukon, Christine M. Snow. Seasonal Interaction of Vitamin D and Bone Density in Alpacas (Lama pacos). Am J Vet Res, accepted with minor revision, 2002.