NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare.

Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

Cobalt deficiency in lambs

Last year there were several NADIS reports during August and September of ill thrift in weaned, growing lambs due to cobalt deficiency. Affected lambs were frequently empty, pot bellied and depressed in appearance. A watery discharge associated with a low-grade conjunctivitis was often present at the eyes. Severely affected animals are sometimes pale and anaemic, although in these cases the differential diagnosis of haemonchosis should be investigated.

Cobalt requirements

Cobalt is required for the manufacture of vitamin B₁₂, which is used in the liver for energy production. Growing animals have a higher requirement for vitamin B₁₂ than adults, but the requirements of pre-ruminant animals are low. Consequently, clinical signs are most commonly reported in weaned lambs during the summer.

Cobalt deficiency appears to be a bigger problem in some years than in others. Areas of low soil cobalt are well recognised, but the relationship between soil, plant and animal cobalt status is complex, and it is difficult to predict a ‘bad’ season in advance. Soil pH above the optimum range of 5.8 - 6.3 can affect cobalt availability and soil compaction associated with rotational grazing may reduce pasture uptake of cobalt. Pasture cobalt uptake is lowest when pasture growth is rapid and in mature pasture. Pasture grown on waterlogged soil has a higher cobalt concentration than pasture grown on well-drained soils. Plants differ in their ability to accumulate cobalt, although when soil cobalt is low the concentrations in all plant species are low.

If cobalt deficiency was diagnosed in your flock last year, it would be prudent either to check the cobalt status of weaned lambs, or to assume that the problem will recur this year and supplement the lambs at weaning.

Diagnosis of cobalt deficiency

The diagnosis of cobalt deficiency is usually based on blood (serum) vitamin B₁₂ concentrations, which reflect the immediate dietary cobalt intake. However, yarding for a period of more than 6 hours before sampling, concurrent liver disease and poor handling of samples can result in markedly elevated serum vitamin B₁₂ concentrations. Furthermore, unless animals are severely deficient, the individual variation in serum vitamin B₁₂ concentrations is high, and it is recommended that a minimum of 7 samples be collected. Liver vitamin B₁₂ concentrations provide a guide to the limited continuous body storage. There is little between animal variation in liver vitamin B₁₂ concentrations, and 3 samples are adequate. Liver samples collected from casualty or slaughterhouse animals can be used to monitor the flock cobalt status.

Short term cobalt/vitamin B₁₂ supplementation

Short term cobalt supplementation of fattening lambs is usually achieved through oral drenching of weaned lambs with cobalt sulphate or vitamin B₁₂ injections. Oral drenching with cobalt sulphate provides an effective supplement for about 7 days. However, weekly drenching is required to provide adequate supplementation, which is not practical in most sheep flocks. Mineralised anthelmintic drenches probably don’t provide enough cobalt to be worthwhile in most flocks. On many farms, vitamin B₁₂ injections are considered to be a practical and cost effective method of short-term cobalt supplementation for fattening lambs, although where repeated injections are required, supplementation becomes expensive in terms of labour and the cost of the drug.

Long term cobalt supplementation

Long term supplementation of replacement ewe lambs or long-keep store lambs can be achieved using intraruminal cobalt bullets. On most farms intraruminal cobalt bullets raise the vitamin B₁₂ levels of sheep for over one year, although there are some reports of poorer efficacy. Care of administration is required, in order to avoid injury to the back of the throat.

Neil Sargison 10^th August 2001