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Vet View: Trace Element Deficiencies in Lambs By Penny Stewart, ARMAC Vets Ltd.

With lambing finished for another year, it is time now to focus on maximising returns from this year's lamb crop. Ill thrift in growing lambs caused by trace element deficiencies (TED) is costly due to increased feeding, medicine and veterinary costs and higher mortality rates. Therefore monitoring growing lambs over the next few weeks and months is key to reducing the potential impact of such deficiencies. It is important to note that TEDs also can cause production losses in adult animals and if issues are highlighted in the lamb crop investigation of other groups may be warranted.

The signs of trace element deficiencies in sheep are often gradual in onset, and therefore problems can be overlooked until groups of poorly grown lambs are identified in late summer. The nutritional stress of weaning can initiate these deficiencies, and levels can diminish to low, and therefore performance limiting, levels within weeks. The symptoms of TED are non-specific and parasitic disease can be a compounding factor in ill thrift so further investigation is always warranted where lambs are not growing as well as expected.

TED can be very localised, mainly due to variations in pasture caused by soil type and pH, drainage and fertiliser applications. In addition, pasture mineral levels can vary greatly year on year. Last year at Armac we diagnosed cobalt and selenium deficiencies in several flocks which had never had an issue in previous years.

Diagnosis

Regular weighing of lambs and recording of growth rates if possible is an excellent tool in identifying poor doing lambs, allowing problems to be identified quickly. If a concern is raised your vet should be notified and investigation initiated. This could involve:

  • Examination of the animals to assess clinical signs and to rule out conditions such as under-nutrition, lameness and pneumonia
  • Worm egg counts to assess if parasitic disease is contributing to the problem
  • Blood samples on a small proportion of the group
  • Post mortem examinations

 

Symptoms

Symptoms can include water eyes, anaemia, poor wool growth and diarrhoea. For a detailed table explaining the symptoms and the possible corresponding mineral deficiency, head to the QMS website.

The clinical signs of each TED are summarised in the table below. These can be explained by the role that each mineral plays in the body.

Symptom

Copper

Cobalt

Selenium

Iodine

Ill thrift

Watery eyes

 

 

 

Anaemia

 

 

 

Poor wool growth/changes

 

 

Bone disease

 

 

 

Diarrhoea

 

 

 

Reduced immunity

 

Poor milk production

 

 

 

Poor reproductive performance

 

Muscle disease

 

 

 

Enlarged thyroid

 

 

 

Perinatal mortality

 

 

Swayback

 

 

 

 

Cobalt

Cobalt is required in a lambs diet to produce vitamin B12. B12 is necessary for the optimal metabolism of energy and protein as well as for wool growth and the production of red blood cells. Lambs are most susceptible to deficiency due to their high energy demand.

Very acidic or alkaline soils or soils high in iron or manganese are more likely to be cobalt deficient. Spreading lime on pastures, high rainfall and rapid pasture growth have also been attributed to deficiency. Swards containing clover tend to be higher in the mineral.

 

Selenium

The main role of selenium is to protect cells from damage. In addition it is important in the function of the immune system and production of hormones.

Rapid pasture growth can reduce selenium concentrations. In general, rye grasses contain more selenium than clover.

 

Copper

Copper is required for energy metabolism in the brain and for the normal function of the nervous system.

Pasture deficiency can occur in its own right, however high sulphur, molybdenum and iron levels in pasture will bind copper therefore reducing its availability. Pig manure is high in copper. Some feeds such as distillers dark grains are also high in copper.

Excess copper is stored in the liver, however the capacity for this is limited. Once this limit is reached, copper is released into the bloodstream causing damage to the liver and red blood cells, leading to death. Copper poisoning is one of the most common toxicities of sheep and supplementation should only be given under veterinary advice.

 

Iodine

Iodine is essential for the manufacture of thyroid hormones which are used in energy metabolism. Furthermore it is required for foetal development.

Certain crops such as brassicas are known to increase the requirement for iodine as they contain substances which interfere with the production of thyroid hormones. Pastures on farms in coastal areas tend to be higher in iodine.

 

Treatment

Once TED is diagnosed, the next hurdle is identifying the most cost effective method of supplementation. This will depend on various factors, such as how often it is practical to handle lambs, whether they are destined for slaughter or breeding and which trace elements are to be supplemented. The timing of treatment should coincide with the period of perceived risk, which may begin at weaning for lambs and pre-tupping for adult animals. If supplementation is initiated it is worth sampling animals every 1-2 years to ensure it is still appropriate. Various methods of supplementation are available and your vet can give advice on these, which include: drenches, mineral blocks, injections, bolus and pasture treatment.

Drenches

  • Can be an effective short term method of supplementation
  • Most drenches only increase blood levels effectively for 1 week, although drenching every 3-4 weeks is often sufficient
  • Suited for lambs destined for slaughter due to short term effect, often used from 3 months of age

Mineral blocks

  • Efficacy is variable due to variations in intake by individual animals
  • Therefore may not be cost effective
  • If blocks contain copper then there is a risk of toxicity
  • Some vitamins eg. Vitamin B1 are not well absorbed from oral supplements by ruminants

 

Injections

  • Longer acting cobalt, iodine, copper and selenium injections are available
  • Some preparations eg. Iodine injections can be difficult to inject
  • Generally provide cover for 6-12 months (2-4 for copper)
  • Therefore suitable for breeding replacements or for ewes if deficiencies also present in older animals

 

Bolus

  • Available for all trace elements
  • Provide cover for 6-12 months
  • Provide peace of mind that all animals have been sufficiently supplemented
  • More labour intensive to administer

 

Pasture treatment

  • Less commonly practised in the UK due to cost

 

In conclusion, the key aspects to TED management are early detection, exact identification of the problem and cost effective supplementation. Seeking veterinary advice each step of the way is essential in reducing losses due to these preventable deficiencies.