Rickets has been seen as being a problem, mainly in cria, but also in older animals. It has been put down to the fact that, during winter, vitamin D generation is reduced in temperate parts of the world because of lower intensity light and shorter days than would be experienced in native countries. The solution has been to give susceptible animals vitamin D, or multivitamins, injections periodically throughout the winter months. Some people have seen signs of abscesses from repeated injections and prefer fortnightly pastes, but the concept of intermittent treatment has been well accepted.

Is this necessary? Wouldn’t daily intake, as part of the normal diet, be as effective and more easily controlled?

To answer this we need to look more closely at what role vitamins, and vitamin D in particular, have in the body. A vitamin is defined as an essential nutrient, that the animal cannot synthesise in sufficient quantities, but requires in small amounts to avoid deficiency symptoms. They vary in their function having effects on vision and fertility (Carotenoids, including vitamin A), combatting oxidation (Tocopherols including
vitamin E; vitamin C), having a supportive role in a vast range of enzyme mediated biochemical pathways (B vitamins,) and hormonal-type roles like Vitamin D.

Vitamin D is known to be involved in the process of bone development and therefore presumed to play a part in calcium and phosphorus metabolism, because bone is basically a calcium phosphate. This is wrong on two counts.

Firstly, the role of D is to increase the absorption of calcium from the diet by improving the permeability of the gut wall to calcium. It does this by controlling the production of a calcium binding protein that transports calcium across the gut and induces its absorption into bone. Secondly it is not vitamin D but its metabolite 1,25-Dihydroxycholecaciferol that induces the calcium binding protein and bone resorption. 1,25-DHC also moderates the resorption of phosphorus from the kidney tubules and so its role in calcium/phosphorus balance and bone function is essential (Tryfonidou et al, 2003. Dittmer K, 2012). It also has a role in the immune function (O’Brian & Jackson, 2012, Barreda et al, 2014).

There are around 10 forms of vitamin D, D2 & D3 being the most important. Of these D3 is the prime precursor of 1,25-DHC and is likely to be given to livestock as an additive.

In addition to dietary sources there are two pro-vitamins and one, 7-dehydrocholesterol is found in the fatty tissues of the skin. Under sufficient UV light 7-DHC is converted to D3 and it is this pathway that “converts” sunlight into vitamin D. Where UV light is restricted (temperate regions in winter, housed animals etc.) the 7-DHC activation is insufficient to complement dietary sources and deficiency symptoms occur (Japelt & Jakobsen, 2013).

 
Natural dietary sources of D are limited to animal tissue and some sun dried forages and so the feeding of a supplement is necessary for alpaca of all ages.

The question is: During winter is it better to inject or increase the daily intake of D? D3 can be stored in the lipid layers of the body and can be slowly released; this makes injectable sources attractive as it can be converted into the active form over months. Research has shown that over wintering injections of 1,000 - 1,500 IU/kg body weight in adult alpacas was adequate to combat vitamin D inadequacy. The results for both cria and adults gave 12 to 16 week’s cover – so 2 injections per year are probably required (Judson & Feakes, 2018).

Where some owners prefer to use a vitamin paste, and so avoid the possibility of the negative aspects of injections, there has been a concern that vitamin D will be degraded in the fermentation chambers and so prove to be ineffective. It was assumed that microbial activity in the fore-stomach does degrade fat soluble vitamins and so large quantities need to be introduced in the paste for it to be effective. This was based on the apparently low levels, especially of vitamin E, circulating in plasma. However recent work has shown this not to be the case. Using radioactive tracers in two forms of vitamin D (D2 & D3) and one of vitamin E, in single high doses -as would be used in dosing alpacas – researchers found no degradation in the rumen of dairy cows (Hymøller & Jensen, 2010) . Although not alpacas, the similarity of rumen and fore gut microbes strongly indicate fat soluble vitamin stability is not affected in camelids.

If pastes are an acceptable alternative to injections as there appears to be no loss of vitamin in the fore gut, why not simply increase dietary level son a daily basis during the shorter day lengths of winter?

Recommended daily requirement for alpacas is 30 IU/ kg body weight (NRC, 2007). This is based on the observation that bioavailability of vitamin D is lower than in other animals. However, assuming a 60 kg adult that is 1800 IU per day, which is about twice the amount given by injections, when they are administered. Interestingly oral doses give about the same daily amount so it would seem that
bioavailability of vitamin D is not an issue.

It was understood that vitamin D was absorbed by passive diffusion. This means that bile salts produced small droplets of fat in which the vitamin dissolved and was carried across the gut cell walls by one of three methods, that did not require an energy transfer system. More recently researchers have determined that there are also active transport mechanisms involved and so bioavailability is higher than first thought. The implication is that daily dietary supplementation is probably more efficient than previously thought (Reboul et al, 2011).

Practically, it is likely that, during most of the year in the UK Vitamin D3 generation in the skin complements dietary input and the injections cover day light shortfall, then increasing dietary intake over winter by a similar amount would be sensible.

This value would be 900 IU per day, based on injected or paste levels and frequencies, although this amount would include an overage to compensate for the half-life of the stored product.

When feeding Camelibra at the recommended maintenance levels a 60kg alpaca would receive 900IU per day of vitamin D3, leaving 900 IU to be supplied by sunlight. Over winter the “missing” amount” from sunlight that an injection supplies can alternatively be supplied by increasing the amount of Camelibra from 1g to 2g per kg live weight per day. This would have added benefits in nutritional terms; most herbivores link feeding to day length and may have lower levels during winter. Shortfalls in forageintake could be compensated with higher levels of balancer. This would include enhanced levels of other fat-soluble vitamins, omega-3 fatty acids and other nutrients that may help offset negative effects of poor environmental conditions.

There is no definitive data on the bio-availability of Vitamin D3 but the evidence of active transport, and so less competition with vitamins A & E -as was once thought – implies that its value is high. Increasing feeding level over the winter months, with its added benefits of extra nutrients, could well be a cost effective, simple alternative to injections or pastes.

References

• Barreda DR, Konowalchuk JD, Rieger AM,Wong ME, Havixbeck JJ. Novel roles for vitamin D in animal immunity and health. J. Anim. Sci. 2014.92:930–938
• Dittmer K, It’s not just bones anymore: The new and exciting world of vitamin D. The Veterinary Journal 194 (2012) 5–6.
• Hymøller L, Jensen SK. Stability in the rumen and effect on plasma status of single oral doses of vitamin D and vitamin E in high-yielding dairy cows. J. Dairy Sci. 93 :5748–5757. 2010
• Jäpelt RB, Jakobsen J. VitaminDinplants:areviewofoccurrence,analysis,andbiosynthesis. Frontiers in plant science. May2013|Volume4|Article136 |
• Judson GA, & Feakes A. Vitamin D doses for alpacas (Lama pacos). Australian Veterinary Journal · June 1999.
• National Research Council. Nutrient requirements of small ruminants. Washington, DC: National Academy Press; 2007.
• O’Brien MA, Jackson MW. Vitamin D and the immune system: Beyond rickets. The Veterinary Journal 194 (2012) 27–33
• Reboul E, Goncalves A, Comera C, Bott R, Nowicki M, Landrier J, Jourdheuil-Rahmani D, Dufour C, Collet X, Borel P. Vitamin D intestinal absorption is not a simple passive diffusion: Evidences for involvement of cholesterol transporters. Mol. Nutr. Food Res. 2011, 55, 691–702
• M.A Tryfonidou, M.S Holl, M.A Oosterlaken-Dijksterhuis, M Vastenburg, W.E van den Brom, H.A.W Hazewinkel, Growth hormone modulates cholecalciferol metabolism with moderate effects on intestinal mineral absorption and specific effects on bone formation in growing dogs raised on balanced food, Domestic Animal Endocrinology, Volume 25, Issue 2, August 2003, Pages 155-174