Vet column: Dr Charles Marwood shares reasoning for supplementing

Minerals and trace elements are an essential part of our livestock's balanced diet. From a healthy immune system, reproduction, growth rates and healthy skin, muscle and bone, minerals are involved in all our body systems.

Generally, we class minerals into two broad groups, our macro minerals – calcium, magnesium, potassium, sodium and phosphorus – which we require in relatively large quantities and readily available from a balanced diet. Deficiencies in blood calcium near calving and lambing can be common but managing the diet beforehand will significantly reduce the risk. Low blood magnesium, ‘Grass Staggers’ is also very common at risk grazing periods, when pasture magnesium levels and forage intakes are low. Most people are aware of the risks and supplement grazing with forage and a high magnesium mineral at risk times of year.

The second class of minerals are our trace elements – Copper, Cobalt, Selenium, Iodine and Zinc – these are required in smaller qualities but still essential.

Copper is essential for fertility, immunity and white blood cell function. Deficiencies can lead to early foetal death, swayback in lambs, anaemia and poor growth rates. High levels of sulphur, iron and molybdenum bind copper in the rumen so it can’t be absorbed leading to deficiencies. Copper poisoning is common in sheep, causing jaundice and death. High risk breeds are Texels and Bluefaced Leicesters. Young, growing and housed sheep are particularly at risk. Never supplement high risk breeds without vet advice. Chronic copper toxicity in cattle leads to weakness, depression and jaundice.

Selenium is essential for fertility, growth, hoof and skin health, iodine utilisation, prevents white muscle disease and helps prevent retained placenta.

Iodine stimulates metabolic rate and used to manufacture thyroid hormones, it is important for the absorption of Vit B12 and foetal development. Deficiencies can present as still births, weak calves that are slow to suckle and have poor growth rates. Over supplementation has also been linked with poor colostrum absorption in the new-born leading to neonatal disease.

Cobalt is essential for the production of Vitamin B12 in the rumen, fertility, thrift and glucose metabolism. Deficiencies result in poor growth rates, ill-thrift and poor fertility. Ruminants cannot store Cobalt so require a daily supply.

Zinc is required for immune function, hoof, bone, cartilage and skin health. Deficiencies result in poor growth rates, abnormal skeletal development, dermatitis and hair loss.

Trace element testing: It’s easy to under and over supply trace elements. Under supply will result in serious production losses whereas over supply is a waste of money but can also result in toxicity. In order to supply the correct level of trace elements, we need to understand our livestock's current levels, and what their diet is supplying them. The corner stone for this is blood testing and forage analysis. Soil testing is useful when we are growing arable crops but doesn’t tell us what our forage is taking out of the ground and delivering to our livestock.

Forage analysis: This tells us which trace elements are available to the animal. But forage is sometimes only part of the diet, so consider the whole diet. We know what recommended levels to feed in the diet allowing accurate supplementation. Analysis will also detect copper antagonists, allowing us to predict relative deficiencies.

Blood Testing: This tells us actually what is happening in the animal. Consider testing 8 –10 animals, six weeks before management events, sheep pre-tupping, beef cattle mid-gestation and dairy cows at dry-off and pre-service.

Plasma copper will show us deficiencies and toxicities. Copper is also stored in the liver, so low blood copper may suggest storage is running low too. Liver copper analysis may be very useful when looking at longer term copper levels, these can be taken at post-mortem, from abattoir collection or liver biopsies.

Blood selenium levels give us an idea of supply over the previous two to three months and liver sampling may be also useful.

Testing blood samples for iodine is expensive, so we often pool individual samples together. This gives us an idea of short-term iodine levels and highly susceptible to changes. Results must be interpreted alongside diet and clinical signs.

Blood Cobalt levels are useful in sheep as an indicator of their Vit B12 levels.

How to supplement:

• Drenches: Cheap and simple but short acting, labour intensive and expensive to repeat. They are less useful for Cobalt deficiencies, where daily intake is required as ruminants can’t store Cobalt.
• Lick buckets: Easy and low labour but we have no control on their intakes. Some animals won’t take any and some will over consume. Also consider field buckets as a risk factor for the spread of respiratory borne disease in sheep.
• Trace elements in feed: Whether you’re feeding a Total Mixed Ration (TMR), concentrates, or top dressing, these can be a general mineral or ideally bespoke to the livestock, based on forage and livestock testing.
• Injectable Trace elements: This is a good for targeted treatments at risk periods, especially Copper and Selenium for preventing swayback in lambs and white muscle disease. Some of these products have had licensing and supply chain issues, which has resulted in variable availability.
• Boluses: These can be targeted, long lasting, delivering continuous supply for daily requirements. We do see bolus gun injuries and regurgitation in cattle and sheep, so be careful when administering.

There is a massive variation of products on the market, differing in quality and concentration. Be careful of over supplementation, this is expensive and can lead to toxicity, especially, Copper and Selenium. Remember over supply of Iodine can also affect the new-borns ability to absorb colostrum. Cobalt cannot be stored in the body and the rumen needs a daily supply to make Vit B12, oral drenches are not good for long term management.

We should only be supplementing based on evidence from forage analysis and livestock testing, this is the cornerstone of responsible Trace Element Health Planning.

Scotland has large variations in mineral deficiencies, but they are very common. Levels vary depending on geography, rainfall, soil and forage type. With a modest amount of investment, testing and targeted supplementation we can maximise our livestock’s health and productivity.

VET facts

Dr Charles Marwood is clinical director of the expanding Clyde Vet Group, based at Lanark. Born and brought up on a well-known pedigree Swaledale unit at Long Green Farm, North Yorkshire, Charles knows all too well how sheep are born to die!

He also has more than 20 years of veterinary experience and head of 15 farm vets in the Clyde Vet Group, which boasts in excess of 500 beef, sheep and dairy farmers on its books across the country