Deficiency of iodine can often come as a surprise to producers following a bad calving season. Adult animals can appear to cope relatively well for extended periods of time in spite of being deficient in iodine. While they may appear clinically healthy to the naked eye, regular monitoring of performance indicators would give an early warning that action and investigation may be appropriate.
Ideally farmers should be scheduling regular monitoring of trace element blood status into their herd health plan in late pregnancy (approximately 3 months pre-calving). This would allow them to take action while disease is sub-clinical and before more serious production losses are accrued.
Iodine is a component of the thyroid hormones which regulate the rate of metabolism and increase the rate of absorption of carbohydrate from the gastrointestinal tract. Thyroxine (T4) is produced in the thyroid gland and circulated to the body tissues. A selenium dependent enzyme is required to convert it to the active Tri-iodothyronine (T3). This is why selenium and iodine deficiencies can be interlinked.
As adult animals can cope so well in spite of being deficient generally the first clinical signs of deficiency are noted in the new-borns. This is because the foetus requires a supply of iodine to support brain, heart and lung development.
Ruminants cannot store iodine indefinitely so are susceptible to deficiency during periods of reduced dietary intake or increased demand (such as during pregnancy). Any excess iodine which the animal cannot utilise will be excreted primarily in the urine with a small amount excreted via the milk in lactating animals.
Indicators of Iodine Deficiency Include:
- Still born calves
- Hairless calves
- Weak calves slow to stand and suckle
- Cows may retain afterbirth
- Reduced fertility
- Goitre (enlarged thyroid)
Trace Elements Also Important During Gestation
Iodine isn’t the only important trace element for the gestation period and it’s important to be aware of other critical trace elements.
For example, Selenium plays a role in the immune system, fertility, muscle tissue health and iodine utilisation. Animals deficient in selenium can give birth to calves affected by white muscle disease which occurs when the muscle tissue becomes damaged and unable to function. Deficiency of selenium is also a risk factor for retained foetal membranes which can increase the time taken to get back into calf.
Copper is the trace element which gets the most attention in terms of reproduction. Copper is an essential component of a number of different enzymes which allows the animal to thrive including enzymes responsible for energy utilisation and fertility.
How Can Farmers Tell If Stock Are Deficient?
Farmers should work with their vet to determine which, if any, trace element imbalances are present within their herd. This is very important because there is no benefit to giving additional trace element supplementation where no deficiencies exist and it may even harm your cattle. Selenium and copper in particular can be dangerous if over supplied.
Forage is incredibly variable from both field to field and year-on-year. Variations in diet can cause animal status to change. Analysing forage, in conjunction with blood sampling, is the best way to determine trace element status. If liver samples can also be obtained for analysis then this gives the greatest information.
From a commercial aspect there are two main considerations which justify the importance of investigation:
- Farmers could be spending money on trace elements which are not required
- Farmers could be losing animal productivity to sub-clinical disease.
Sub-clinical trace element deficiencies are not severe enough to be visualised by eye but will have an impact on the productivity of the animals. If farmers wait until the deficiency is so severe that clinical signs have appeared, they will already be out of pocket.
Which Form Of Trace Element Supplementation Is Best?
There is an array of different forms of trace element supplementation available and it can be difficult to know which is best for herds. Let’s take a look at the advantages and disadvantages of some of the most popular methods:
Drenches can be a cheap and convenient option however they are relatively short acting and repeated doses mean greater labour. For trace elements which cannot be stored in the body, such as iodine or cobalt, they are not appropriate to treat deficiencies. A form of continuous supplementation must be supplied, which is especially important for in-calf cows and their developing foetuses.
Free Access Systems, Such as Licks and Blocks
Where a need to supplement trace elements has been established, we need to ensure that all animals receive an amount of trace elements which is compatible with their daily requirements. Too much of a trace element can prove toxic; too little and the deficiency will not be addressed.
Unfortunately, the free access lick and block systems do not provide this guarantee and an independent study highlighted that intakes between animals are extremely variable, with some consuming nothing and others consuming excessive quantities.1 A more scientific approach to supplementation is required.
Injections can be suitable for targeted administration in conjunction with the advice of your vet. They can be appropriate where only a single trace element, such as copper or selenium is required.
In Feed Supplementation
Trace elements can be provided by the provision of TMR, concentrates or bag minerals.
Often these are specified based on ‘averages’ or ‘common requirements’ as opposed to being based on what has been determined is deficient and required on farm. Ideally these mixes should be prepared based on an investigation in to the animals’ trace element status and requirements. This method can add significantly to the cost of production and can be difficult for extensively managed cattle.
Trace Element Boluses
Boluses provide an convenient, cost-effective and controlled method of trace element supplementation. Bimeda soluble glass bolus CoseIcure cattles provides exactly the same amount of copper, cobalt, selenium and iodine every single day for up to 6 months in cattle.. This means there are no variable intakes and no variation between animals. The continuous, controlled release of the bolus is particularly important for animals requiring cobalt and iodine which cannot be stored in the body and therefore a daily supply is required. Their long-lasting nature is also highly convenient and reduces labour costs as regular bolusing is not required.
- Blood testing in conjunction with forage analysis in the simplest way to obtain information on the animals trace element status
- Deficiency of trace elements can cause poor productivity but there are many other causes which your vet may advise you also investigate
- Over supplementation does not improve productivity and can be dangerous, particularly where selenium and copper are concerned.
- Establish the need before supplementing with trace elements
- Pay particular attention to stock in late pregnancy as deficiencies in trace elements can have serious implications for both cow and calf.
CoseIcure cattle bolus contains copper, cobalt, selenium and iodine and lasts up to 6 months in cattle.
Before supplementing trace elements, particularly copper and selenium which can be toxic, it is recommended that you seek advice from a vet or nutritionist.
About the Author
Rachel Mallet is a Veterinary Surgeon, who now works as a Professional Services Vet providing technical support to vets, SQPs and farmers in the UK. Rachel is passionate about animal health and about promoting best practice and preventative medicine amongst farmers.
1. McDowell, 1992