Hello and welcome to part two of our webinar series on trace element deficiencies in sheep. Your speakers for these webinars are both from the School of Biodiversity, One Health, and Veterinary Medicine at the University of Glasgow. You'll be hearing from Kim Hammer, an academic clinician and lecturer in the farm animal department and a diplomat of the European College of Small Ruminant Health and Management, and me, Rena Jones, a resident of the same college working towards diplomat status under the sponsorship of Habre, but also undertaking a PhD in ruminant nutrition.

In part one we gave a brief introduction to trace elements. We went through some really common clinical scenarios and looked at some trace element specific history taking that may be pertinent when investigating a potential deficiency. In part two, we're going to go through the options for testing.

What we should consider when planning a treatment or a prevention strategy and how we should monitor once we've, instigated a treatment strategy. The materials throughout these webinars relies heavily on the work of Neville Suttle, who has reviewed the published literature extensively in his books. We have mostly used the 4th edition of his Mineral Nutrition of Livestock book.

However, there is now a 5th edition of his book out which came out in the middle of 2022, but our, copy hadn't arrived in time for us to, use it for this webinar. If you are interested in trace element nutrition. This is, is definitely the book to buy.

So testing. Before we get into the meat of how we confirm a trace element deficiency associated problem, we should address one of the most common misconceptions about diagnosis and treatment, that is, the fact that sheep consume free access mineral is not evident in and of itself of deficiency, and therefore sheep will not self-regulate their consumption of free access mineral like licks or buckets to alleviate any potential issue. In fact, sheep will continue to consume as much of a free access mineral, even when the underlying deficiency has been rectified by other means.

Testing in the face of a clinical problem can be very different to testing animals for monitoring purposes, where in this instance, monitoring means the assessment of current supplementation levels or response to intervention. Kim will discuss monitoring in a little bit more detail later on. It is important that we understand why we're testing and what our aims are for testing, as this will contribute to the number of animals that we will recruit.

The calculations that I reference over the next few slides have been performed using the online calculator EITools, and the link can be seen on the slide here. I highly recommend that you have a look at this online calculator because it provides a very user friendly way of calculating the number of animals to test. I'll also be referencing a 95% confidence interval, which in this instance means that in 19 out of 20 times when we test a subset of animals that these animals will be truly representative of the flock or group and standard deviation, which is the measure of the variability within the range of values, so a high standard deviation would mean a high inter-animal variability, whereas a low standard deviation would mean the opposite.

So in practise we often calculate the mean tissue level within a population, usually by calculating the mean blood level of a parameter using a subset of animals from a group. The number of animals we need to get an accurate mean tissue level is calculated by setting our confidence interval at 95%. Knowing how many animals there are in the group, so let's say 200 in this instance, and deciding how much variability we are willing to tolerate by setting our standard deviation, let's say 0.5, this would mean sampling 15 animals to get an accurate mean tissue value in this instance.

But why can't we just sample 15 animals from any group of 200 all the time? Well, some parameters have a large inter-animal variability even within the same group or flock. We can see this in the case of copper in the table below, where within herd group variance is up at 51% for plasma copper levels.

In this instance, it may be worth reducing a standard deviation so that we increase the number of animals sampled. To ensure that we're truly representing the mean tissue level of the population. In other instances, a farmer may want to know if it's cost effective to supplement, and so would like to know the proportion of animals in a group that are deficient and therefore likely to respond to supplementation.

This often relates to the supplementation of cobalt and selenium to growing lambs. In most cases, the number of animals that need to be tested to accurately estimate this figure is quite high. Instead, I would use production data that we already have access to to produce these estimates.

This estimates can then be used to calculate the number of animals that we need to test to confirm our suspicion. So given that we've estimated our prevalence using production data and animal records, we can calculate the number of animals we need to test to find evidence of deficiency at that prevalence. Using Epitools again, we can calculate the number of animals we need to test to be 95% confident of finding evidence of deficiency at a set prevalence.

For example, if we found that 25%. Of 200 lambs were growing poorly and suspected that it was due to cobalt deficiency, we could assume that at least 25% of our flock are cobalt deficient, . I a 25% prevalence and therefore we'd need to test 12 animals to be sure of detecting at least one deficient animal at this prevalence.

In cases where deficiencies result in high mortalities or greater economic losses, then we may want to find evidence of deficiency at a lower prevalence which would necessitate testing more animals. Now that we know why we're testing, we've been able to infer how many animals we should test. But what we haven't discussed is which animals are most suitable for testing.

Ideally, animals should be chosen at random. These animals should be representative of the group and shouldn't be the sickest or the thinnest animals in that group. This is especially important when taking blood samples, as many comorbidities will affect trace element absorption and metabolism.

This leads to false positive or or false negative results. And finally, make sure the animals that you're presented with weren't treated before you take blood samples. So now that we know why, who, and how many we're testing, we need to know which animal specific tests are available and most appropriate for which trace elements.

Blood samples are likely the most commonly performed trace element tests in the UK. The results are obtained fairly quickly and they're relatively cheap to perform per animal. This enables us to sample a larger number of animals, which gives us, gives us a better understanding of the trace element status of the group.

However, the results aren't always conclusive and need to be interpreted in light of the history that we've taken for the problem. Tissue sampling can be much more reliable in some instances, but this either involves obtaining biopsies or sacrificing individuals. Abattoir samples can be used, but these need to be representative of the group with the problem.

Alternatively, samples can be collected from deadstock at postmortem. But these animals have died for a reason, so the results need to be interpreted with care. Histopathology has similar advantages and disadvantages to tissue sampling.

With the added benefit that the results can be quite conclusive. Compared to other sampling techniques, this is also potentially expensive. And finally, supplementation trials might be the only way in some cases to confirm a problem.

Here you assess the effect that treatment has on production and therefore you get an idea of how cost effective it is to supplement. This can be quite time consuming, initially to set up and then to perform and needs to be managed in a similar way to a clinical trial to be truly informative. You're also leaving a proportion of the animals untreated.

And this might not be feasible in many cases. Now that Reg has given us a really good overview of the animals we're going to be testing, and who to choose, how many to choose, and the types of tests we can run, we're going to look in a bit more detail at some of these tests, and we're going to start with blood sampling here. Before you take samples for blood testing from animals, ensure that you have a good idea of the dietary history of those animals being tested, and so that you don't take samples unnecessarily or and waste money on tests that may not tell you very much.

You need to know what feeds they've been on, where they've been fed, so whether they're at pasture, whether they're indoors in a shed, whether concentrate feed is being fed in a trough or on the ground. And, and also, It's important to know how long animals have been on the diet that they're on and what the previous diet was if it was within a reasonable time frame. Now, a reasonable time frame varies depending which trace element we're talking about.

So, for selenium, it would be several months, whereas for cobalt, it would only be a few weeks. Also, be careful that you're aware of any supplements that have been given to animals. So whether they've been given bonuses, they have access to concentrate feed, or they have access to buckets in fields and know when these were introduced.

When taking blood samples to assess cobalt status in a group of animals, it is vitamin B12 that we test for. Vitamin B12 is sensitive to recent dietary cobalt intake. And so if there has been a change of diets recently, this can alter the results.

For example, the introduction of concentrate feeding to lambs at grass, which happens very commonly when they're not growing very well. And also vitamin B12 changes with starvation and like a starvation of only just a few hours. So if animals are gathered for more than 4 hours before sample collection, the vitamin B12 levels can actually increase relative to what they would have otherwise been.

So, you can underdiagnose cobalt deficiency in these cases. As always, interpretation levels vary between authors, but weaned lambs with a vitamin B12 level of less than 250, have been shown to have an increased chance of responding to cobalt supplementation. However, That it's been found to be variable between vitamin B12 levels of 100 and 300.

And also methyl meloic acid or MMA can be used as an indicator of dysfunction, and this increases with decreasing vitamin B12 in a sort of curvilinear fashion. And but MMA needs to be interpreted with care as levels do differ depending on the stage of production. So this test, and although it's thought to be fairly usable, is not commercially available.

When testing for copper deficiency or toxicity, it is worth bearing in mind that copper levels in the blood are tightly regulated by the liver, so they are maintained within the normal reference range until either the liver runs out so low in copper that it can no longer maintain blood levels, or copper storage in the liver is so high that it is about to be released and can and cause a hemolytic crisis. Therefore, plasma copper levels are only diagnostic when there is severe and prolonged deficiency, or animals are about to succumb to toxicity. Another complicating factor is that plasma copper levels are increased by inflammatory processes due to recent vaccination or disease.

Acute phase proteins can be measured at the same time as plasma copper if you're suspicious of concurrent disease. Tissue liver samples are a more reliable indicator of copper status, but are much more invasive to take from live animals. And at the time of recording, labs in the UK are unable to analyse the small samples acquired.

Larger liver samples can be taken from postmortem cases provided that the reason for death was relatively rapid and that the animal has not suffered any chronic disease prior to death that they may alter their copper status. Abattoir samples can also be used, but are rarely able to be taken from the population of interest or the stage of production of interest. When testing for selenium levels in animals, both plasma selenium and the red blood cell enzyme glutathione peroxidase can be used.

Selenium gives an indicator of recent selenium intake, but can be increased by homolysis, so careful sample handling and storage are important. And, and plasma selenium levels can decrease in severe infection, for example, sepsis, and it's also unreliable in neonates. And as well as being slightly more expensive as a test than glutathione peroxidase.

And glutathion peroxidase, commonly known as GSHPX, is an enzyme that is incorporated into the red blood cells at erythropoiesis and therefore gives an indication of long-term selenium status. Sheep red blood cells have a lifespan of approximately 120 days, so GSHPX is thought to give an indication of selenium intake over a 2 to 3 month period prior to sampling. Iodine deficiency can be quite challenging to diagnose, especially if it's secondary to the consumption of goitergens.

Serum iodine mostly consists of protein-bound iodine and reflects current iodine intake, but importantly, it doesn't reflect thyroid function. If the current iodine supplementation is good, sodium iodine levels will be within the normal reference range. However, in cases where iodine deficiency is secondary.

Serium iodine remains high or normal, but uptake by the thyroid or iodine metabolism is affected downstream. Serum T3 and T4 may be low or normal in primary iodine deficiency depending on the level of iodine depletion and criicity of the problem. T3 and T4 are especially important when attempting to diagnose iodine deficiency due to goutrogenic interference with iodine metabolism, or secondary to selenium deficiency.

Serum T3 will be low in all cases except for primary iodine deficiency where it may be normal. Whereas T4 remains high or normal in all cases except for when caused by thyro peroxidase inhibition. It's important to distinguish which goitergens that's causing the issue as supplementation will not cure deiodinase inhibition.

Both T3 and T4 can be influenced by many other factors and shouldn't be interpreted without concurrent iodine levels. Blood zinc levels can be affected by the animal's cytokine and glu glucocorticoid levels, confounding your results. To combat this, you could test for both blood zinc and alkaline phosphatase as each mirrors the other's blood profile.

Therefore, a low alkaline phosphatase and a high zinc may indicate interference by other bodily processes. There are quite a lot of other things that also increase or affect alkaline phosphatase, so please be aware of that when you interpret these results. You should also be aware that zinc levels can decrease with fasting, so timing between gathering and testing should be as short as possible.

As discussed previously, tissue sampling can be quite challenging, as it involves euthanasia or sacrifice of animals that could potentially be cured. Alternatively, it can involve analysing samples from dead stock at postmortem, which require very careful interpretation. In this table we've provided some indication of what's considered normal or deficient.

However, these references may vary between laboratories. Before we go on to testing soil, forage and feed, I want to return to a means of confirming the presence of a clinically relevant deficiency that we briefly mentioned earlier, and that is diagnosis by supplementation trial. This form of diagnosis looks for an improvement in clinical signs or production after supplementation.

It's therefore not suitable for conditions which result in a high economic losses, so those with high mortality rates, for instance, or those syndromes that have an extended period between insults and diagnosis, so fertility associated conditions. It is very suitable and sometimes the only way to diagnose deficiencies which once corrected should have a near immediate effect on production, so ill thrift in lambs caused by cobalt or selenium deficiency. It is especially useful if these deficiencies.

Cause marginal production losses. When performing a supplementation trial, it's important that a sufficient number of animals are included. This calculation can be done using EITools, as discussed previously, or your friendly veterinary school would may be happy to assist you.

You could treat the entire group using pre and post daily live weight gains to assess er success, but there is no way of telling if these animals would have gotten better regardless of treatment. The best practise would be as summarised in the schematic on the slide, to only treat half the group and compare one group's growth rate to the other over the next 2 to 4 weeks. Animals shouldn't be assigned to these groups at random, as each will have different potential.

So each animals will have a different potential for growth. So animals should be paired by age if if possible, but I realise that this could be quite challenging and therefore paired within a time frame for age would be, would be OK. And they should also be paired by weight.

With one animal in a pair receiving the treatment and the other left untreated, the daily live weight gain of these lambs can then be calculated from treatment to 2 to 4 weeks post-treatment. Make sure to wait at least 2 weeks before reweighing. As variations in room and fill can make interpretation of the results quite difficult.

Once you've got all the data, a simple chi square test can be done to use to see if there is any significant difference, and this can be done in Excel. When confirming a clinical deficiency, it's more appropriate to test the animal, as we know that what's in the soil doesn't necessarily reflect what's in the plant, and what's in the plant doesn't necessarily reflect what's in the animal, exceptions being selenium and zinc. But there may be instances where animal testing might no longer be an option.

Animals might have been moved or have already been treated. If grass or soil samples are the only option, then it's important to make sure that the samples taken are representative of that field. This can be done by walking the field in a W pattern and taking small samples as you go.

Any herd which samples taken should be as close to what the animal consumes as possible, so it's better to cut the grass with scissors, not rip the plants from the ground. Samples shouldn't be washed as any soil contamination would have been ingested by the sheep and therefore could have contributed to the overall trace element intake. Samples are either analysed by a near infrared spectroscopy.

And you can see an example of a report on the right hand side of the slide here, or they could have been analysed by laboratory chemistry. Results should be interpreted with respect to the expected dry matter intake to assess predicted consumption by animals. We should bear in mind that this is an indicator of potential for deficiency, not a confirmation of disease.

As with soil and grass testing, any samples taken should be representative of the diet fed. Compound feeds tends to be homogeneous, but there may be slight variations between the batches of the same feed. So it might be useful to retain a sample from each new batch.

This is something that's already been done in the pig and poultry industry. The mineral contents within preserved forages will vary between bales, fields, and cuts. So a really broad sample encompassing all of these variables should be taken.

Home mixes and TMR rations often incorporate loose mineral mixes in addition to the minerals provided in the major constituents of the diet. Inappropriate mixing or formulation can lead to loss or inconsistent incorporation of these minerals. Remember how the diet is fed is as important as what is in the diet.

We've come to the end of our testing section here, and Kim's going to take over now and continue with the treatment and prevention section. Once it has been established that trace elements deficiencies are causing disease or significantly reducing production in a flock, then supplementation needs to be considered. So we're now going to look at the options for treatment and prevention and the trace element supplements that are available and their pros and cons.

The former supplementation used will often depend on the farm management setup, the farmer preference, and the vet preference. And, but the biological characteristics of the element needing to be supplemented should always be considered. Some elements need to be provided very often because they have low body storage, for example, cobalt and zinc.

So for these elements, the discontinuous short acting supplements such as drenches and injections can be very labour intensive, especially in situations where gathering and handling of animals is costly, such as on hills that could take days to gather. For these short-lived elements and in these situations, long acting bolus and injections or continuous forms of supplementation in blocks, etc. Can be useful.

And where animals are being fed concentrate feed, adding minerals is convenient and inexpensive. But if, but to give concentrate feed just for the sake of minerals is pretty expensive. Selenium and cobalt, on the other hand, can be supplemented intermittently with supplements several weeks apart due to the high animal storage potential.

So animals can be supplemented when they are gathered for other management purposes, which is convenient. And then we've got indirect supplementation through treatment of pasture, and this can be useful for elements that are needed daily, but only where the grazed area is not too extensive and can be or can be treated in strips, and the element is likely to be taken up by the herbage on the pasture. So we'll go into a bit more detail about each of these forms of supplementation in the next few slides.

So if we look at the pros and cons of each form of supplementation in a bit more detail, and, and then we'll start with the discontinuous forms. So oral drenches can be cheap form of supplementation, and they're very popular, partly, probably partly because they're cheap and they're good because they give uniform coverage of all the animals treated. And for most of the elements given, they give quite rapid uptake, so they're useful in clinical situations where rapid rectification is needed.

The drawbacks of oral drenches, however, are the risk of dosing injuries which are normally fatal and disturbingly common. And Oral drenches also have a high labour cost where handling is expensive and time consuming. So for elements such as cobalt, where drenches only give short-lived supplementation and need repeating frequently, for example, every 3 to 4 weeks, this form of supplementation is labour intensive.

But This might be a positive where lambs are nearly fat for slaughter and supplementation is only needed for a short time. Injections can be similar to oral trenches in some ways because the level of supplementation is uniform across the group and they're often more expensive than oral drenches. There is the potential for slow release products for some elements, including cobalt, and this can drastically reduce the labour costs where cobalt deficiency is an issue.

Unfortunately, at the time of recording, injectable selenium products are not available for sheep in the UK. Both oral trenches and injections share the advantage that many farmers are used to giving this type of product, and so they're quite good at handling and applying them. Blues and pellets can be used to reduce the required dosing frequency and so reduce labour costs.

And, and this needs to be weighed against the increased purchase costs of some of these products compared to oral drenches. These products also give uniform supplementation, but they can be regurgitated, or they can become coated in the room and and fail to release the minerals. And glass boluses and some of the other new technologies are helping to overcome the issue of coating.

But glass bolus can crack if they're cold when they're given. So they should be warmed up first if it's a cold day, such as in people's pockets or in the bonnet of the car. And one thing that is a potential pro or con to bonuses is that they contain many multiple elements and which, if needed, is beneficial, as only one form of supplementation needs to be given.

And but if it's not needed, it can be a waste of money and could potentially be toxic to both animals and the environment. Copper oxide needle capsules are a useful form of slow release supplementation of copper, with reduced risk of acute toxicity compared with some other supplementation methods. But chronic toxicity is still a risk of supplementation if if it's not needed.

Providing minerals in feed is a good way of getting relatively uniform supplementation across a group and is cheap provided that animals are being fed additional concentrates anyway. But in commercial flocks, feeding sheep purely to supplement minerals is expensive and potentially reduces usage of the available nutrition from forage. Also, if feeds are not fed as a pellative compound, then animals might sort the diet and not eat all of the elements in the intended quantities, so they may not actually be adequately supplemented.

And mineral supplementation in water has been tried, but intakes vary with the weather as grass, water content can be high, removing the need for sheep to drink much additional water. And also if continual supplementation is needed, then it can be expensive to install the systems that support this in water. Buckets, blocks, licks, and powders are widely used, and with farmers spending huge sums of sums of money on a variety of products marketed for different stages of production and different purposes, some of which may match the farm's needs and some which do not.

And the labour cost associated with putting blocks out for sheep is low. However, intakes vary hugely between individual animals, with some consuming none and some consuming consuming more than would be helpful. And Uptake of granulated minerals may be higher, and possibly more uniform but then compressed blocks, but it still varies between animals and over time.

Pasture dressing with deficient minerals can be an effective form of supplementation provided that it is economically viable. Where pastures are accessible, not excessively large, and frequency of application is minimal or can be combined with other treatments such as fertiliser application, it might be economically justifiable. A consideration needs to be given to other factors that might inhibit plant uptake of the mineral or even animal absorption and use of the mineral.

For example, adding cobalt to alkaline or heavily limed pastures is unlikely to improve pasture uptake. And there are also some health concerns over application of cobalt salts as they may be carcinogenic. It is important to differentiate between the treatment of current clinical signs related to trace element deficiency and the supplementation of trace element deficiencies diagnosed using laboratory testing that have not yet become production limiting, as one needs rapid onset of supplementation and the other requires long term mineral provision.

Some of the clinical syndromes we face can be treated at the time of presentation. Others are based on historical dietary deficiencies, and the damage is already done, but consideration needs to be given to the effect of ongoing deficiency on the same of the same elements on subsequent stages of production and in subsequent years. Especially if the diet is likely to remain unchanged.

Many of the reproductive disorders are historical, and treatment of affected animals has little or no impact. For example, high barren rates at scanning due to selenium deficiency during breeding or lambs born to iodine deficient dams. However, ill thrift in lambs due to cobalt or selenium deficiency can be treated with rapidly absorbed forms of supplementation at the time of presentation.

For cobalt, this can be cobalt in the form of drenches, or injections with vitamin B12. Then these lambs need ongoing supplementation to maintain good growth rates. So feed or buckets are not going to be used, and then a mineral bolus can be given for long term supplementation.

The graph here shows lamb plasma vitamin B12 levels after oral drenching with cobalt, and this gives some illustration of the rapid increase in vitamin B12 12 levels after drenching. Also, it shows the relative, relatively rapid decline in vitamin B12 levels. However, these lambs were not deficient at the time of supplementation, so duration of active supplementation cannot be determined.

For selenium, the main form of rapid supplementation is oral drenches. Lambs with white muscle disease, if they survive, can become. Can recover well with selenium supplementation and supportive treatment.

But in severe cases they may remain ill thrifty despite treatment. Lambs with sway back are unlikely to respond to supplementation, and therefore supplementation of other lambs in the group may prevent further cases, and supportive care of those that survive can be attempted. Otherwise, prevention of the deficiency in subsequent pregnancy should be targeted.

When thinking about preventing clinical disease or production loss, multiple factors need to be taken into consideration, such as the cost of supplementation compared to the financial implications of losses, and the cost of supplementation needs to take into account the cost of the product being used, as well as the cost and frequency of administering that supplement. And then the level of risk of disease or production loss is important. And so what evidence is there that the deficiency exists and that it is significant enough to cause problems.

That evidence comes from farm data and the clinical signs, the history that was discussed in webinar one, and the testing section of at the start of this webinar. The number of elements that need to be supplemented and may also influence what form of supplementation is used, and obviously the availability of suitable products. And we've discussed already the need to consider how much of the element can be stored in the body and how long that will last for.

And then lastly, safety considerations can be significant when we're talking about trace element supplementation, so we need to think about avoiding giving access to animals that may lead to toxicity but also may involve extra expense and environmental contamination. Kim has already discussed the pros and cons of different forms of supplementation. However, when it comes to treating a syndrome, you may need to integrate different treatment types so as to provide continuous or targeted supplementation.

This will depend on how the diet is likely to change over the next few months and if the farmer has already made any changes before you decide on a treatment plan. A common example would be that farmers may choose to feed a minerized concentrate to lambs that have suffered from a cobalt deficiency. To try and regain some lost growth.

As cobalt has fairly limited storage in the body, we should aim to provide a continuous source. Initially, the aim would be to supply cobalt as soon as possible. Often this is in the form of a discontinuous trench or a vitamin B12 injection, as they are readily available and farmers are comfortable with their administration.

However, this may only provide 2 to 6 weeks' worth of supplementation. Infeed cobalt could be used as a continuous source but will be expensive in the long run. Therefore, any initial pulse dose should be followed up with a long term source like a bolus or a long-acting injection.

As with cobalt, there are multiple forms of selenium supplementation, but supplying a continuous source isn't essential, as there is some facility for long-term storage in the body. Selenium supplementation could be provided as pulse drenches every 1 to 3 months. However, this decision should be led by the level of production deficiency experience.

So it could be that bolus are a better option for long term control. If providing pulse doses, animals should be treated at pertinent times, that is mating, late pregnancy, and pre weaning. Pasture dressing could be an option in some instances for kind of longer term controls.

However, this is affected by soil pH with lower plant absorption rates in acidic soils and the form of selenium used as well. Plant absorption and length of efficacy is highly variable. Remember that slime can be toxic and care should be taken not to supplement with multiple sources.

Administering copper to animals presenting with swayback is unlikely to mitigate any clinical signs, but it can be worth treating all other animals in the group, as this can prevent the development of further cases. All ewes should be treated in late pregnancy to prevent swayback in their lambs, but often this is provided as mineralized concentrate. Administering copper doses intermittently can be quite effective as a short and long-term supplementation or option, provided that molybdenum levels are low, below 5 milligramme per kilogramme dry matter.

Copper sulphate trenches are mostly used, and there are no real advantages of using other chemicals except possibly copper glycinate, which might resist antagonism to some degree by molybdenum and sulphur. Other long term options include bulluses and copper needles which last for several months. Great care should be taken when choosing how to supplement, given the potential for copper toxicity in some breeds of sheep.

However, there is a potential to introduce these sheep onto farms with low copper as a means of reducing the need to treat it all. If copper deficiency is mainly secondary to antagonism, then steps can be taken to reduce molybdenum uptake by plants through lining and draining the pasture. It might also be a good idea to reduce soil ingestion by an appropriate grass management, which then reduces iron ingestion.

These mitigating steps may have unintended consequences on the availability of other trace elements. It's often too late to supplement with iodine to mitigate any reproductive effects, and a plan should be put in place for the following year. Supplementation with an iodine dose is effective for simple primary iodine deficiency or antagonism due to thyro peroxidates inhibition.

But will not compensate for digenase inhibition. Thankfully, the former is much more common in the UK. If the deficiency is secondary to a lack of selenium, then selenium should also be administered at the same time.

Well timed drenches with potassium iodide or calcium iodate, which are very available to the animal, given premating and mid to late pregnancy may be sufficient supplementation. However, bolus are very efficacious. Iodine may also be fed in licks, blocks, and concentrates, although in humid climates, iodine may leach from these supplements.

Kelp can be used as a high iodine feed material, however, sourcing kelp in sufficient quantities can be quite problematic. Iodine fertilisers shouldn't really be considered as a cost effective form of iodine supplementation. Zinc should be provided continuously if deficient, especially in the diet provided to the replacement breeding males.

Boluses are likely the best form of targeted supplementation, as pasture correction is expensive. In all cases, blocks could be used. These are especially useful on extensive units where gathering sheep is labour intensive, although intakes will vary from sheep to sheep.

You may have come across the ongoing conversation about organic versus inorganic trace element supplementation. This is mainly a conversation that occurs when choosing a mineral to include in a concentrate who mix or in a TMR. Inorganic compounds are oxides, sulphates, hydroxychlorides and so on, are what is mostly used, whereas organic compounds are believed to mimic metalloproteins found in nature.

However, there is no evidence at the time of recording that organic compounds are more bioavailable than inorganic compounds, and given the cost of production of organic compounds, it is unlikely that they are cost effective. There is, however, some evidence that the hydroxychloride compounds are more available given their different pattern of absorption compared to sulphate compounds. But this area of research is fairly new.

So for the last few slides, we're just going to talk a little bit about monitoring, and both monitoring of supplementation that's been implicated in the face of clinical disease or production limitation and from trace elements, and trace element audits, which are quite often, promoted by some laboratories. For monitoring supplementation that has already been administered, we need to consider what we're going to monitor. So we have the option to monitor production levels, for example, pregnancy rates, neonatal lamb survival, and lamb growth rates, or we can monitor lack of clinical disease as proof of the data supplementation programme has been a success.

And these forms of monitoring can be useful and cost effective, especially for growth rates, but for some of the other syndromes, there can be too much of a lag time between the risk period for deficiency and the manifestation of losses. So it takes too long to get the results, and the damage may already be done by the time if the supplementation is insufficient by the time we get those results. So therefore, in some situations, you might decide to use additional laboratory testing.

And these tests are the same as those discussed at the start of this webinar with the same limitations. But we need to make sure that testing is done just before or at the time in the production cycle when the deficiencies would have the most impact, for example, just before breeding or in mid-pregnancy. And we need to make sure that we're not handling time at a handling animals at a high risk time for.

Stress, so for example, at the beginning of pregnancy is not a good time to be taking tests, samples. So frequency of testing is also important and obviously monitoring through production levels and clinical disease should be done continually and be ongoing, but the frequency with which we use laboratory tests needs to be considered carefully because it can be expensive to collect samples and run the tests. In the first couple of years of supplementation, testing may be more frequent if different forms of supplementation are trialled in order to find the most cost effective supplementation that gives the intended outcome.

And thereafter, frequent testing frequency can be reduced or stopped until management changes are made, or changes in clinical presentation are seen. Remember that testing can also help to pick up when excess supplementation is being given for some elements. And testing can also be beneficial if management practises or pastures change to ensure that supplementation is still needed.

And in these circumstances you might want to test unsupplemented animals, so maybe testing them before supplements are given and or by leaving a few untreated to test at the risk period for deficiency. But because of the costs associated with testing and to help with accurate interpretation, we need to be sure of the reasons for the testing that we're doing. So then when you're faced with the option of doing trace element testing where there hasn't been any clinical signs or production limitation identified, and we still need to consider.

The similar things and discuss similar issues with our clients, such as what is the cost of testing compared with the potential benefit of having the results. And, and that decision needs to be based on whether we think production is meeting the expectation of the farmer and or meeting reasonable expectations for the the type of farm. And again, if management practises or pastures change, then possibly doing some trace element status assessment may be of benefit to prevent future losses in production or future clinical disease, though testing must be performed at the time of year or the time in the production cycle when deficiencies would be problematic as trace element levels change with the weather and the time of year.

And and the demands of the animals change with the timing of the production cycle. So as with any testing that we do as vets, we need to know the reasons for the testing that we're doing in order to be able to adequately interpret the results. So in conclusion, getting a successful diagnosis of trace element deficiency relies on three things the presence of clinical or subclinical signs, and evidence of inadequate trace element provision at a stage of production where this is likely to be detrimental, and that improvements in clinical disease and or production are seen when supplementation is given.

And in some cases this is the only definitive way of confirming the diagnosis. We're very grateful for the sponsorship of Harbro from Reg for his residency, and we'd like to thank many people for the pictures that they contributed to this webinar, including Mike Evans, Isabel Willison, Piers Davis, and Jill Hunter. Thank you very much for watching these webinars.

We hope that you have, they have helped you to understand or refresh your knowledge of trace elements, their associated clinical presentations, confirmation of deficiency, and supplementation options. If you have any questions, then please do bring them to the question and answer session or email Reg or myself. Take care and happy sheep vetting.