Hello and welcome to this set of 2 webinars on trace element deficiencies in sheep. We're going to focus on the common clinical presentations seen in the UK and how to approach these. Your speakers for these webinars are both from the University of Glasgow, the School of Biodiversity, One Health, and Veterinary Medicine.
I'm Kim Hammer, an academic clinician and lecturer in the farm animal department and diplomat of the European College of Small Ruminant Health Management. Reg Jones is a resident of the same college working towards diplomat status under the sponsorship of harbour, but also undertaking a PhD in ruminant nutrition. During the two webinars, we're going to take you through the outline shown here, starting with a bit of background introduction, and then we'll go straight into the clinical scenarios that you are most likely to encounter in clinical practise in the UK.
And, and then we'll move on to looking at the history that is important to determine whether trace elements are likely to be implicated in those clinical scenarios. And during the 2nd webinar we'll focus on how testing. Can help confirm that trace element deficiencies, are forming part of the clinical picture, and the shortcomings of the available tests, which you need to be aware of when interpreting these tests in field conditions.
Once testing has confirmed deficiencies, we can then move on to how they can be tackled both in the short term, at the time of presentation, and then in the longer term. And we will talk very briefly about further monitoring of supplemented and unsupplemented animals on farms with known deficiencies. The Material 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 the mineral nutrition of Livestock stock book. And there is now a 5th edition available. It's just come out in 2022, but we've not actually managed to get our hands on a copy of the book in time for this webinar.
And but we would really recommend doing so if you have an interest in mineral nutrition, and which as ruminant vets, we certainly do. During this webinar we were focused almost entirely on these five elements selenium, cobalt, iodine, copper, and zinc. Although zinc is only mentioned briefly in a couple of places.
These are the most common trace element or micro mineral deficiencies faced by sheep in the UK. We will not be dealing with the macro minerals, and we will only touch on the toxicities of a couple of the elements mentioned here. There will be some discussion of the antagonists that are important to the clinical manifestation of these trace element deficiencies as their presence and management are key to controlling the clinical syndromes and associated production losses that are seen.
And there's immense geographic variation in the presence or absence of these deficiencies, which is dictated both by the geology of the area but also the prevailing weather conditions. And so we'll be talking about those as well. And there is a variation in the manifestation of these deficiencies which depends on the stage of production of the animals involved.
As requirements vary with age, maturity, breeding, and lactation. For example, growing lambs have higher requirements for both cobalt and selenium and compared with adults, and pregnant ewes have increased requirements for iodine, copper, selenium, and cobalt compared with when they're not pregnant. And all of these variations are complicated by the potential for concurrent disease such as endoparasites in lambs, which also inhibit growth rates alongside cobalt and selenium deficiencies.
Clinical presentation is often the starting point for most vets in practise, and that's where we're going to start this webinar. Although we're very aware that many people are doing preventative health work, and this is not necessarily where you're going to start. But these clinical scenarios do set the scene for understanding why trace element management is so important to animal health, welfare, and productivity.
And so most of the scenarios will be clustered into one of these three stages of production. That's how we're going to progress through them. Some will affect breeding success, some perinatal survival, and others growing lambs.
We're going to start with breeding and the effects that tra trace elements have on reproductive success in sheep from breeding time signs of ongoing ram activity beyond the expected two cycles where in many farms we're aiming for approximately 98% conception rate, and this can be demonstrated by raddle markings if they're used. So trace elements can affect fertilisation and conception rates, but going forward, they can also affect early embryo survival and then obviously late embryo survival as well, which can present so that early embryo deaths can present as low scanning percentages and both early embryo survival rates and low late embryo survival rates can then present with low lambing percentages. And if the rams remain with the ewes for an extended period, the length of lambing can be affected with poor fertilisation and poor conception rates and increased early embryonic death resulting in an extended lambing period, which we know is poor for lamb survival but is also bound to be poor for farm staff mental health.
When thinking about high return rates during breeding, there is a long list of potential causes of poor productive performance at breeding. Which must be considered when faced with a high return, a case of high return rates that is demonstrated by ongoing RAM activity beyond that that's expected. Although if raddle marking is not used on a farm, then the fallout from this may only be picked up at scanning or at lambing time, by which time there are many other differential diagnoses for low lamb numbers or high baron rates to add to the list.
Therefore, getting as much information about the flock from different stages of the production cycle is so key to these clinical investigations. But if we assume that we know that the problem is happening at fertilisation, then this is the list of differentials we should consider. Please do note that the list of differentials given on the right hand side of the pages on in the clinical section of this presentation are a good starting point, but they're by no means to be considered complete.
So then if we turn our attention to the trace element deficiencies that can result in high return rates, and zinc, selenium and iodine are the main culprits. And at fertilisation, these are considered to mainly affect rams. And although the diet that resulted in reduced ram fertility is often historical, with especially with zinc deficiency affecting testicular development of growing rams, and then later affecting spermatogenesis, which we know needs to happen in the two months prior to breeding.
So with selenium and iodine dietary levels, and they do also impact the quality of spermatozoa and semen. So, dietary levels prior to breeding are important. And then clinical irgen deficiency at the time of mating can lead to reduced libido.
And it's worth just noting at this point that the need for dietary zinc is higher for growing male animals that are intended for breeding than those that are intended for slaughter, and because the effect on testicular development is greater than that on growth. Moving on to early embryonic survival, selenium and iodine are known to be important to the maintenance and pregnancy. Selenium deficiencies in early pregnancy are commonly associated with increased numbers of ewes that are not carrying any lambs at all, and due to high embryonic death around the 3rd or 4th week of pregnancy.
Whereas reports of the clinical presentation of iodine deficiency in early pregnancy appear to vary slightly, which may just reflect the level of deficiency encountered in different situations. Some reports from New Zealand, for example, give a reduced numbers of lambs conceived per year as the main manifestation of iron deficiency in early pregnancy, whereas other sites reduce numbers of of actual use in lamb. There are also reports of cobalt deficiency in early pregnancy having an impact on lamb numbers.
However, this is not, it doesn't appear to be a common presentation in the UK, which may just reflect the time of year that flocks breed use in the UK as herbage on wet pastures are unlikely to be cobalt deficient for grazing animals. And in the UK, most sheep flocks would breed in the autumn when pastures are wet. In late pregnancy, iodine deficiency has been linked to abortions, although other perinatal manifestations appear to be more commonly associated with dietary deficiency in iodine in late pregnancy, such as stillbirths, wheat lambs, and both of these with or without goitres and with reduced fleece production.
When percentage of farms with increased return rates of breeding, reduced scanning or lambing percentages, or extended lambing periods, it is important to collect enough information to help you decide whether it is worth spending the money on trace element testing. We will come back to this in more detail in the history section, but as a quick overview, things that to include in your decision making armoury would be obviously the local knowledge of the trace element status of the area and of the farm itself. And this information is often known by farmers and vets in the area.
And also knowing what the animals have been fed, Before, during, and after breeding and, and where that feed has come from. And then moving on to the animals themselves, getting a good clinical history of those animals. So any reports of stressful events, for example, dog worrying, and any reports of disease that's affected them during, before or after breeding such as liver fluke or sheep scab.
And, and actually a clinical examination of the animal, some of the animals as well. So all of the rams involved in the flock or the group groups within the flocks that are affected and need to be examined and a proportion of the ewes. Now the proportion of ewes.
And examined will be, will vary depending on the size of the flock as to what's logistically possible. And, but should be represented, the uses that are examined should be representative of the flock and maybe a few outliers, a few of the thinner ones and a few of the fatter ones, for example, but most of them should be representative. And your clinical examination may, reveal something that that is an obvious cause of fertility, particularly amongst the RAMs.
And then getting a feel for the body condition score of a large proportion of the ewes can be really helpful. Again, the proportion involved will vary with the size of the group or flock affected. However, if the farm keeps records of new body condition score at weaning, breeding, and scanning, then this data can be analysed as absolute low body condition score, and relative changes in body condition can impact fertility significantly, and so that can be a useful resource.
Once the history and clinical examinations are done, if no appropriate explanation has been found for the production loss, that's been encountered. And the findings suggest that further investigation is warranted, then blood samples can be taken to test for the presence of common infectious agents associated with poor reproductive performance, such as toxoplasmosis and maybe border disease virus. And if the history is suggestive that trace elements could be involved, then samples can be taken for testing.
Details of testing will be discussed in the second webinar. There are many different resources available that give suggested feeding requirements for trace elements, including the very useful AHDB's booklet on feeding the ewe, which is worth finding online and downloading. And also Neville Suttle's book, Mineral Nutrition of Livestock, which we've mentioned before, and the diseases of sheep textbook can be very helpful, and the National Research Council's and nutritional requirements of small ruminants.
These sources do give slightly, or in some cases very significantly different figures for these requirements, because some are aimed at human health, so that the health of the humans consuming animal products, and others are more focused on the animal health. Also, these sorts of figures can be reached through such different methods, and that it, it often gives it gives different results. So it's worth taking these values as approximations of the range of safety and that's required.
So now we're moving on to the next cluster of clinical syndromes, which sort of approximately fit into the perinatal period, most of them do. And here we're talking about trace element effects on ewes as well as the effects of pregnant ewe diets on their lambs. Firstly, colostrum and milk production by the ewes themselves.
And ewe milk has some of the highest ash content levels of the domestic farm species, and deficiencies in some of the trace elements can have an impact on milk production rates as well as on the concentration of these elements within the milk produced. And these are quite complex interactions and we're not going to delve very deep into them. So in summary, colostrum has higher milk mineral concentration than milk, and zinc is quite high in milk and colostrum, whereas copper is relatively low in milk and lostrum.
And whereas deficiencies in cobalt actually can reduce milk production. And this can be reflected in reduced lamb growth rates. On the other hand, copper and iodine deficiencies decrease the concentration of these elements in the milk, but do not affect the yield.
And, and the extent to which supplementation of trace elements affects their milk concentration. Varies quite considerably. So for iodine supplementation, this will increase iodine concentration in milk, but for copper, manganese, and zinc supplementation, they generally won't significantly impact the milk concentrations of of the elements.
With selenium, it actually the effect on milk concentration of selenium depends entirely on the form of selenium being supplemented. This is just a quick deviation as a reminder of one of the risks of concentrate feeding and potentially other forms of supplementation around lambing time, which is the provision of excess dietary copper. Breeds that are particularly sensitive to copper toxicity include the taxol, the Suffolk, and the North Ronald Sea.
And excess dietary copper at low to moderate levels is stored in the liver until it reaches a crisis point, and then it's released resulting in a hemolytic crisis. Acute copper toxicosis can also be seen with sudden intake of high levels of copper, but this is much less common as a presentation and she. Risk factors for copper toxicosis include the feeding of cattle or pig feed, as these are high in copper compared with sheep feed.
And drinking of copper sulphate foot bath solutions and provision of copper through multiple different forms of supplementation. Carcasses of affected animals are very distinctive, and showing significant jaundice throughout the carcass. You'll find haemoglobin your rea, yellow or orange discoloration of the liver.
Blackened kidneys. It's called the gun metal black. And in acute cases, you can find necrosis of the Amazin and small intestine.
As well as potentially a blue-green diarrhoea. Live animals, if you see any that are alive, show depression, weakness, abdominal pain, and increased heart and respiratory rates. Confirmation of the diagnosis is achieved through copper levels in the liver and kidneys, and, and it has implications for the sale of animals for human consumption.
So if you see suspect cases, take, do try and take feed samples if you can at the time, even before you've got a diagnosis because Otherwise later on farmers can forget to bring them into the practise, or that batch of feet can be used up by the time you get a diagnosis. And these feed samples can be really helpful for trying to determine the source of increased copper in many situations. Now for the lambs, low lamb survival rates are a common and frustrating problem on UK sheep farms, and, but finding an underlying cause can be very rewarding and hugely beneficial for your clients.
There are many causes of stillbirth, and the birth of wheat lambs in sheep flocks. And these are really important for the productivity and profitability of flocks, as high losses can be incurred at this stage of production, and anything that weakens neonatal lambs and can reduce the chance of good colostrum intake and timely colostrum intake and so reduce their chance of survival. The main trace elements implicated in neonatal losses are iodine and selenium, but there are also reports of copper and cobalt deficiencies being implicated as well.
Iodine deficiency can result from insufficient iodine in a used diet in late pregnancy or from the presence of goitergens that interfere with the uptake of and or function of iodine in the animal. Affected lambs have poor vigour and so are unlikely to get up and suck in a timely manner, and they very often have little or no wool production and poor thermoregulation, and all of these things lead to a reduction in survival. And some of these lambs will also have a goitre, and lambs with a thyroid gland that weighs more than 0.8 grammes per kilogramme of their body weight have a 90% likelihood of coming from a flock that has iodine responsive issues.
By contrast, go are rarely seen in adult sheep, even on iodine deficient diets. Do you remember that the function of thyroid and iodine containing hormones also rely on selenium. So if there's concurrent selenium deficiency in a flock, then supplementation with iodine alone will not rectify rectify the problem.
There is, however, a need to take care with iodine supplementation and try to avoid overdoing it. So it's important to avoid multiple sources of iodine and being given to pregnant uses. The problem that has been associated with high dietary iodine in pregnant uses is a reduction in immunoglobulin absorption by lambs, so they can consume plenty of Clostrim but can't make use of it.
So they still succumb to increased levels of neonatal infection. Slee deficiency in pregnant dam diets can present similarly to iodine deficiency, and but without, obviously without the goitre and without the lack of wool production. The main signs are stillbirths and weak lambs that fail to suckle.
But care must also be taken with selenium supplementation, as it too is toxic. Stillbirths, weak lambs, and increased neonatal infections are not as commonly associated by vets and farmers with cobalt and copper deficiencies in new diets as they are with selenium and iodine. Though these are reported.
Therefore, on farms where cobalt or copper deficiencies are known to exist and the high perinatal lamb mortalities are a concern, then supplementation of late pregnant ewes and maybe even lambs with these elements should be considered. Cobalt deficiencies have been associated with high perinatal lamb mortality, stillbirths, and a failure of lambs to suck colostrum in a timely manner. There have also been reports of increased perinatal infections and mortality in lambs from ewes deficient in copper, for which supplementation of the ewe may prevent swayback but not these other losses, and therefore supplementation of the lambs may also be needed.
Sway back in lambs may be the only sign of copper deficiency seen in a sheep flock, as it is the most sensitive expression of deficiency. This syndrome is much more common in breeds of sheep that have low copper absorption, such as the Scottish blackface. And also it's sometimes more likely to be seen after a mild winter when supplementary feeding of pregnant ewes is low.
And there are 3 main forms of sway back presentation. The typical neonatal presentation with which lambs are bright but uncoordinated, and myelin aplasia during mid gestation results in CMS dysfunction, leading to ataxia that progresses then to paralysis and then death. And some lambs suffer from aplasia of additional myelin afterbirth to present with the delayed form at 4 to 12 weeks of age.
And normally this presents after a stressful incident. And signs are normally progressive, and this form is the most common to be seen in goats. There are reports of atypical an atypical form of swayback in older lambs in which lambs stand stationary with a head tremor and exhibit apparent blindness.
And on postmortem, they show cerebral edoema. This syndrome presents as a group problem, so multiple lambs are likely to be affected, and, and wool changes such as steely wool, where the wool loses its crimp, are also quite sensitive indicators of copper deficiency. Other signs that can be seen if copper deficiencies are more pronounced and include pigmentation of coloured wool, bone disorders such as osteochondrosis, osteoporosis leading to spontaneous fractures, and beading of ribs where the costochondral junctions proliferate.
Mobility may also be affected by connective tissue disorders. Also, anaemia is seen where deficiencies are prolonged. Copper deficiencies can be absolute, but often they result, the syndromes result from association with high antagonist to copper ratios in the diet.
On the next slide, you will see a video of a lamb with sway back. So again, when presented with a clinical scenario for which trace elements may be implicated, it is important to gather as much evidence as possible to guide further investigations. As for fertility issues, knowledge of the local trace element status is essential, as well as ensuring that animals have been fed enough macronutrients such as energy, protein, and macro minerals.
Again, clinical examination of animals is needed, and this time the ewes and the lambs, and plus postmortem examinations of recently dead or failing individuals are very useful. And animals that you postmortem should ideally have clinical signs representative of the group problem. Individuals with other presentations can be postmortemed and give useful information, but extrapolating these findings to the group must be done with caution.
Farmers are often reluctant to sacrifice animals that may recover, but sometimes this is necessary to get a full picture of what's going on. And the more postmortems you can do, often the better chance you have of getting a full diagnosis, unless of course you find something definitive in the first one or two postmortems and such as sway back. And if labs aren't very close to where you work or the farms are and you're not very confident with postmortems, you can try and do them yourself and then take photographs and samples and send these to experienced VIOs at the labs.
And even speaking to these vets beforehand about which samples to take and what to watch out for can be really useful. The tests that you run should be dependent on the history and clinical presentation. Otherwise it can be quite difficult to interpret your results and To get it, get a, get a diagnosis.
Again, we have provided the NRC recommended dietary levels of the important trace elements and a few other minerals put into this stage of production. You can pause this recording to make a note of these if you choose. The last stage of production that we're going to look at in detail is growing lambs, including the trace elements syndromes that reduce mobility, induce sudden death, potentially, or interfere with growth, or even cause weight loss.
Firstly, the locomotor issues. Remember that delayed and atypical sweaty back can be an issue in older lambs, so they may become apparent at this time. And we will not go over this syndrome again here, so please refer back to the neonatal section of this presentation.
And similarly, fractures, secondary to osteoporosis in more more severe copper deficiency may be occasionally encountered. The main syndrome we will focus on though is white muscle disease. Please note that differential diagnoses for mobility issues in lambs are numerous, and some are very common, for example, joint, which you'll come across all the time.
White vessel disease will be familiar to many of you. It is most dependent on selenium deficiency and ruminants. The vitamin E involvement is dependent on the degree of selenium deficiency.
And so at moderate selenium deficiency, vitamin E can provide some compensation for the antioxidant function of selenium. And lack of vitamin E will increase the likelihood of disease. Whereas when when selenium deficiency is significant, then vitamin E levels make little difference to the expression of disease.
And the clinical presentation of white muscle disease may be precipitated by exercise or stress. So for example, docking, bad weather, transport, etc. And lambs are often well and fast growing prior to sudden onset of disease, and signs can vary but may be may be combined if multiple muscle groups are affected in one lamb.
Affected lambs are often reluctant to move and may show respiratory distress. When the cardiac muscles are affected, cardiac signs increase as death approaches or sudden death may be seen. At postmortem, bilaterally symmetrical white striated lesions can be seen in affected muscles, and lesions in the thigh and shoulder muscles are often, quite apparent.
And sometimes chronic lesions may be calcified as well. For confirmation of diagnosis, collect hardworking muscles such as the diaphragm, intercostal muscles, or cardiac muscles, and send samples both as fresh frozen and fixed samples. So the fresh frozen are for senium malalysis and the fixed are for histopathology, although often the histopathology is all that's needed.
Another well recognised syndrome associated with trace element deficiencies for which farmers and vet students tend to have trace elements at the forefront of their minds is poor growth rates and weight loss in growing lambs. Insufficient available feed and endoparasites must be ruled out before trace elements should be considered in most cases. And then after gastrointestinal parait is ruled out, trace element deficiencies would be a common cause of ill thrift in lambs.
And cobalt and selenium deficiencies are well recognised causes. Therefore, we will focus on these. And the effects of copper deficiency on lamb growth rates have been reported but are disputed by other experts in the field.
And even though Copper deficiency is a well established cause of ill thrift in growing calves. Cobalt deficiency can cause significant ill health as well as ill thrift in growing lambs, and where deficiencies are severe, these signs are seen in adult sheep as well. Sheep have a higher cobalt requirement than other grazed species, so we will exhibit signs of deficiency on pastures that cattle can thrive on.
And in growing lambs, cobalt requirements increase as their main source of energy switches from milk to forage, because energy production from forage requires more vitamin B12, the active compound containing cobalt in the body. And the most well recognised syndrome associated with cobalt deficiency is known as Pine, and although mild cobalt deficiency will result in reduced growth rates before other clinical signs of pine develop. Lambs with clinical pine can look quite characteristic because they appear thin with a hollow paralumbar fossa due to anorexia, and they have tear stained faces and an unkempt fleece.
And some people refer to this as an open fleece. Some lambs will also be anaemic with chronic exposure to cobalt deficiency. And then ovine white liver disease is another potential presentation which results from fatty infiltration of the liver and can present as photos sensitization and or hepatic encephalopathy with depression, central blindness, fine muscle tremors of the head, neck, and ears, and head pressing, and these are alongside anorexia, anaemia, and ill thrift.
Mortal mortality rates can be quite significant with cobalt deficiency if it's allowed to continue unchecked, and is up to 30% in some reports. Another effect of cobalt deficiency in some reports is the increase in lamb susceptibility to some gastrointestinal nematodes. And although both, both of these conditions do induce anorexia and any significant reduction in feed intake will reduce cobalt intake, so it can be difficult to determine which came first and therefore making sure that end of parasite infections are dealt with.
In the first instance and then checking if growth rates improve or not. Well, if they don't improve to a satisfactory degree, then investigate whether deficiencies may also be present and It might be beneficial to correct them. Potential increases in growth rate with supplementation of cobalt on deficient pastures can be economically significant, as we found on a farm in the east of Scotland a few years ago.
And this case report is available in the vet record case reports if the details would be of interest. In the UK, selenium responsive ill thrift is often seen in the autumn as pasture selenium is reduced by increased rainfall, so the reduction in lamb growth rate is not responsive to vitamin E supplementation in this case, and lambs can be affected on pastures where calves thrive and And also the effect of selenium deficiency on milk production has been noted in cattle, but has not specifically been studied in sheep. And so we don't really know whether whether it affects milk production in sheep.
And again, when considering poor growth rates in lambs in autumn, gastrointestinal nematodes must be considered before trace element supply can be elucidated. Both cobalt and selenium deficiencies can affect adult sheep in a similar way to their impact on lambs. But that's only if the deficiency is significant enough, as growth increases the requirement for these elements in lambs compared to adults.
And where pine is a significant risk to adult sheep on a farm, ewes in late pregnancy should be actively supplemented in order to avoid the inhabitants involved in pine from increasing the risk of pregnancy toxaemia in those ewes. And then For selenium and iodine deficiencies at relatively low levels, wool production can be reduced. So when we think about conditions in growing lambs that may be associated with trace elements, we need as much of the same history as we did for the fertility and perinatal conditions.
But pasture management, grazing, and antalmantic history, are also really important for understanding the end of parasite risk of the growing lambs. Also, diet, effective dietary management of the ewes and absence of mastitis in ewes are important to enable good milk production to support growth. As any lack of nutrition or any disease seen early in the lamb's life can significantly impact on that lamb's growth later on.
And so it is important to get as much background information as you can on the affected lambs. And nevertheless, generally neonatal disease and mastitis in use will impact a minority of lambs in a group or in a flock, whereas endoparasites and trace element deficiencies have the potential to impact a large proportion of the lambs. So knowing how many lambs are affected and the duration of the impact on growth rates are useful for helping to narrow down your differential diagnosis.
And then faecal sample analysis and postmortems are essential to help determine the level of endoparasite infection in affected lambs, and though these must be interpreted in conjunction with clinical and grazing history. And then once gastrointestinal parasites are ruled out, then samples can be taken to determine the trace element status, of which there will be more in the second webinar. You can see here that growing lambs have significantly higher requirements for both selenium and cobalt than an adult year of 4 times the weight needs for maintenance.
And also note that the growth rate allowance of these figures is relatively modest and should be the minimum target for commercial lambs of this weight. So I just got a bit of a change of topic to give your brain a break because this is a condition that is not really talked about in other species much and yet is relatively common in goats. So we thought it was worth a quick mention.
And so when faced with a goat with thick and scaly skin that may be fissured and that may or may not be pruritic, do remember to consider dietary zinc deficiency as a major differential diagnosis. And it's worth noting that some individual goats appear to have high zinc requirements to control this condition, so higher than just standard and non-efficient diets would be. And laboratory testing, diagnostic testing.
It is suggestive, so your blood zinc levels and histopathology is distinctive, but it's not definitive in making a diagnosis, whereas response to zinc supplementation is, however, it takes several weeks to months for the response to the supplementation to become evident, which makes diagnosis quite long-winded and challenging. Also, supplementation needs to be given daily because the body has low stores of zinc. So now we'll have a quick overview of the approach to clinical presentations for which trace elements are potential differential diagnoses, and then we'll move on to history taking with Reg Jones.
And when clients request a veterinary attention for a clinical issue, your approach is going to be generally fairly standard. And you'll start with establishing what the client perceives to be the problem, and then delve into taking a thorough history and performing clinical assessments of the animals and their surroundings. In farm practise, the conclusions that you might draw from your history and clinical examinations could include that there is a clinical disease present that needs investigating and treating, or that there is are production losses.
Although There are occasions that you may decide that the client's expectations are unrealistic and that their perceived issue cannot be resolved in the way that they would like it to be, although this is a relatively rare outcome. When trace element deficiencies are on your mind for a case, remember the other important differential diagnoses that need to be ruled out and that they may complicate the diagnosis of trace element deficiencies. For example, if you've got a condition that induces anorexia and therefore reduces the intake of minerals.
So the approach to a clinical investigation for trace element deficiencies is not really any different to any other disease. Now we're going to move on to history and I'm gonna hand you over to Reg Jones for that. He's spoken to you about the huge variation in clinical syndromes that can stem from trace element deficiencies.
Next we're going to talk about taking a history which is beyond the scope of the individual animal. Concentrating on factors that increase or even decrease the probability that the clinical scenario you're presented with is related to a trace element deficiency. The likelihood or not have a trace element problem occurring on one of your client's farms can be predicted to a degree by the history of the local area.
As new graduates or when moving to a new area, it can be incredibly useful to call upon the experience and local knowledge of the senior vets in the practise, or the farmers in the area, and the local APHA and SRUC. These people and institutions can tell you if every farm in a particular valley struggles to finish lambs on pasture or that goitres would want a common postmortem finding in a specific area. If this specific local knowledge isn't available, then there are resources such as the UK Soil Observatory, which provide maps giving a broad view of soil trace element content.
On the slide we've got the molybdenum map on the left here and the copper map on the right, and these maps are from the Soil Observatory, and they look at the concentration of these trace elements at a granularity of around 1 kilometre squared. The hot colours represent soils of high values, whereas the cooler colours represent soils with lower values. The long view of history within the boundaries of a specific farm can also be very useful.
There may be a history of poor lamb growth, even though you're currently presented with a fertility problem. Such comorbidities push the trace element deficiency diagnosis up the differential diagnosis list. Even routine management practises which may appear as habit could be pertinent.
For example, lambs are never grazed in a specific area after weaning or ewes are not fleshed or bred in another area. This can indicate knowledge of a historical deficiency. It is, however important to remember that these factors are only indicators of likelihood, not indicators of disease.
In addition to this collective social knowledge of historical deficiency or syndromes that may be associated with deficiency. There are quantitative aspects of an area, farm, or individual field that can indicate an increase in risk of disease. The type of soil farmed can indicate trace element concentration within that soil or influence the availability of specific trace elements to uptake by plants.
The soil type can vary within a farm, and many farmers will be able to inform you about the soils within the pastures that are currently under investigation. If not, then maps are available from the British Geological Survey, which can provide a rough indication of soil type. The table on the slide provides a simplified view of the risk of deficiency posed by different soil types for each of our major trace elements.
However, other factors within soil can also influence trace elements availability. For instance, a high organic matter content can limit copper availability. Another soil associated factor which influences trace element availability is soil pH.
As with soil types, some farmers may be able to tell you what the pH of their soil is, or, as with mineral contents, the UKSO provide interactive maps for you to find out. Soil pH specifically affects the plant's ability to absorb trace elements, and different pHs benefit or hinder different elements. From this figure taken from subtle 2010, we see that relatively acidic soil pHs benefit cobalt, zinc, and manganese absorption by plants.
This then decreases as soil pH becomes more alkaline. Soil pH doesn't seem to affect copper absorption by plants, however, molybdenum absorption increases as soils become more alkaline. As molybdenum is a copper antagonist, alkaline pHs can result in low copper availability to animals and subsequent deficiency.
But but more on antagonists a bit later. The effect of pH on iodine availability is particularly interesting as different forms of iodine, iodide in acidic soils and iodate in alkaline soils are taken up by the plants. At different pHs.
Therefore, availability to the plant is dependent on both the form and the pH. If you're interested in the dynamics of pH on absorption. More information is available in Cal 20 Twenty's paper in Advances in agronomy.
In addition to considering the effect that soil has on trace element availability, we need to consider the effect that the herbage grazed has to play. There are huge variations in the trace element content of different species of plants, with generally more herbaceous plants having a higher trace element content than graseous plants. Leuminous plants like clover also tend to have a higher trace element level, especially copper, cobalt, and molybdenum.
Although iodine concentrations may be lower than that seen in grass. Even within a monoculture pasture, trace element levels can be considerably different in one part of the field to the other. To complicate matters, different sections and different light stages of the plant will have disparate trace element levels.
Mostly, this results in more copper, cobalt, and zinc in leafy areas, flower heads versus the stem. Logically, therefore, we see a reduction in plant trace element content as they mature. That is to say, as the season progresses, we see less leaf and more stem, and therefore a reduction in trace element content of plants in later summer.
Given the variability within the pasture, drastic changes to the diet, like feeding brassicas, will have a different effect on trace element availability, especially as many of these type of plants contain goitergenic compounds that antagonise iodine. Now, we know that both soil type and plant variety affects how likely we are to be dealing with the trace element deficiency. And weather will affect both of these trace element uptake by plants will be reduced in high plant stress situations due to a reduction in root activity.
These situations could be an extended dry period, extreme heat waves, or unexpected cold snaps. Milder changes can be somewhat beneficial. Selenium uptake by plants may increase in drier weather.
Cobalt, manganese, and molybdenum uptake and to a degree iodine uptake tends to be better in wetter water-logged pastures. However, extreme water logging can lead to trace element leaching, especially iodine. As mentioned in previous slides, there is a potential for some minerals and chemicals to have an antagonistic effect on our five main trace elements.
High soil manganese levels have been associated with a reduction in cobalt availability to plants and therefore, the cobalt presented to our sheep. It's well documented that iron, molybdenum, and sulphur antagonise copper. This happens in the rumen where molybdenum combines with sulphide to form thio molybdates which in turn form insoluble complexes with copper preventing absorption.
In some instances, thiamoliates can be absorbed into the blood and may induce liver copper release into the bile. They may increase copper binding to albumin, which reduces copper transport, and scavenge copper from metallo enzymes. Sulphur can reduce copper by availability independent of molybdenum by forming insoluble copper sulphide in the gastrointestinal tract.
Iron's antagonistic effect is slightly poorer characterised but depends on the presence of sulphur and only occurs in ruminating animals. Although there are some reports of high calcium levels affecting the iodine status of ruminants, the main antagonists of iodine are goitergenic compounds. These compounds are found in brassicas at varying levels, with modern varieties often containing lower concentrations.
Goitergens can act in two ways. They can be thyro peroxidase inhibitors, preventing the incorporation of iodine into T4, or diiodinase inhibitors, preventing the conversion of T4 to T3. The type of goitergen is an important consideration when it comes to the supplementation of animals which are iodine deficient, and this will be expanded upon in part two.
And finally, selenium selenium competes with both sulphate and phosphorus for transportation into the plant and therefore under high sulphate or phosphorus levels, plant selenium levels decrease. High d dietary sulphur also reduces selenium within the animal, potentially because they are chemically similar and therefore interact competitively. Shorter term pasture management practises can also affect trace element availability.
Therefore, ratcheting trace element deficiency up the differential diagnosis list. Poor pasture management and adverse weather conditions can lead to overgrazing or poaching and subsequent soil ingestion. This could benefit the animal by increasing cobalt iodine, selenium, and zinc uptake.
However, it may also result in an increase in iron and molybdenum uptake which will affect copper absorption. Applying nitrogen fertiliser has been associated with a reduction in plant copper and iodine concentration and inconsistent increases in zinc plant concentration. But no consistent changes in other trace elements.
High sulphur fertilisers reduce the pH of soil and may result in a reduction in selenium uptake. Its application also carries the risk of increasing copper antagonism. The lining of pastures increases the pH of soil and therefore reduces the uptake of those trace elements which are preferentially absorbed by the plants under acidic conditions.
Therefore, liming leads to a potential reduction in cobalt, manganese, and zinc uptake, and a potential increase in molybdenum uptake. And finally harvesting grass for silage or hay will reduce zinc concentration in the herbage with each successive cut. Interestingly, this isn't remedied with the application of zinc-rich fertilisers.
The likelihood of deficiency is largely dependent on the diet, and therefore obtaining a thorough dietary history for animals over the past 3 or even 6 months is critical. Ideally, every field movement, concentrate feed, dose, and mineral block should be accounted for during this time. It isn't only the trace element concentration within the feed that's important.
The composition of the feed and how it's fed will affect the environment within the rumen, potentially changing the pH. Trace element bi availability changes in relation to ruminal pH with increases in potent thiolybinate binding copper seen with lower ruminal pHs. Now we've come to the end of the environmental history part of the webinar.
And as you can see, the factors that affect trace element availability can be quite complex. Therefore, on this slide, we've provided a short summary of these factors for you. So thank you for your attention during this webinar.
I hope it's been useful. So now that we know there is a clinical presentation consistent with trace element deficiency, and other common differentials have been ruled out. And we've got an idea of the farm and animal nutrition history, and know whether it is consistent with trace element efficiency or not.
We can then justify moving on to thinking about spending money and time on confirming those deficiencies with testing. And you can contact either Reg or I by email. Our email addresses are here.
And the second webinar will be available on the from the 7th of September 2022. 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, and including Mike Evans, Isabel Willison, Piers Davis, and Jill Hunter.