Much has been made in the national press about vitamin D and the effect on human health when a deficiency occurs. Many of the points made can also be true for ruminants and the effect on the health and production of livestock when inadequate levels of vitamin D are in the diet, says James Brinicombe, R&D Director for the Denis Brinicombe Group.

Much has been made in the national press about vitamin D and the effect on human health when a deficiency occurs. Many of the points made can also be true for ruminants and the effect on the health and production of livestock when inadequate levels of vitamin D are in the diet, says James Brinicombe, R&D DIrector for the Denis Brinicombe Group.

Vitamin D is important for a number of reasons, the main  being that it increases absorption of calcium and phosphorus from the digestive tract. This is important to aid the regulation of blood calcium levels and the development of strong teeth and bones, advises Mr Brinicombe.

Vitamin D is a fat soluble vitamin that is stored in the animal's liver and subcutaneous fat, enabling them to draw from these reserves when required. Fat soluble vitamins can be stored for several months; therefore daily supplementation is not necessarily essential to meet maintenance requirements.

Known as the 'Sunshine Vitamin', an animal having direct contact with sufficient  sunlight should not require supplementation of vitamin D in the diet, if this is compromised in any way particularly in young, growing animals or in pregnant & lactating animals then supplementation is essential, suggests Mr Brinicombe.

Housed stock are at greatest risk of deficiency, as animals are not exposed to the crucial Ultra Violet rays from the sun for vitamin D production in the skin. Breed, type and management of animals will also play a role in how much vitamin D is produced, heavy coats/wool & dark pigmented skins are less effective at producing vitamin D than lighter coloured skin with finer covering.

Pregnant ewes brought indoors for lambing are potentially at high risk from suffering from the symptoms of a shortage of dietary vitamin D. By the time ewes are housed they are likely to have grown a thicker fleece, which would have hampered exposure of the skin to Ultra Violet rays in the last few weeks at grass. During the last 8 weeks of pregnancy the unborn lambs complete up to 70% of their growth, so they will be pulling on the ewes reserves of vitamin D for their own skeletal development. The lambs' greater requirement comes at a time when the ewe is preparing for milk production; with colostrum containing approximately 6-10 times more vitamin D than milk. This puts the ewe in danger of going down with Lambing Sickness, a particular problem in older ewes, and often the symptoms are confused with those of Twin Lamb Disease.

A deficiency of vitamin D in pregnant cattle may predispose them to Milk Fever. Also, if low levels of vitamin D are available to the developing young, it may mean that a greater number of animals are born weak, deformed or even born dead in severe cases.

Sun dried forages are a good source of vitamin D for stock kept indoors, but they need to be of good quality as it has been suggested that some mycotoxins can reduce the levels and functioning of vitamin D in feeds.

Pregnant or lactating animals all have greater requirements for the vitamin, so supplementation should be considered to prevent health and welfare issues particularly when housed, concludes Mr Brinicombe.