3 Jan 2023
Tony Andrews BVetMed, PhD, DipECBHM, DipECSRHM, MRCVS offers a solution to a perplexing farm case study in a follow-up to part one.
Anthony Andrews
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Image: © daviles / Adobe Stock
In the first part of this series (VT52.46), Dr Andrews recalled an incident on a farm primarily concentrated on the finishing of beef animals.
Multiple animals died or were euthanised, others grew poorly and were slaughtered unfin-ished, and infertility problems developed. A recently delivered batch of feed was suspected to be involved; however, no conclusive proof was found or a diagnosis made.
Outlining the facts, Dr Andrews asked readers to treat this case as a conundrum to be solved and to suggest their potential diagnoses by emailing him at [email protected]
Selected responses will be printed in a future edition of Vet Times.
In this second part, Dr Andrews discusses the potential causes for the incident and shares his own suggested answer.
Was the problem due to the feed?
The proprietary pelleted feed was delivered and offered to some cattle, pigs and sheep on the Saturday afternoon. Other cattle groups were fed the ration on the Sunday, with different persons and vehicles being used to those on Saturday. The feed was said to be completely finished on the Tuesday.
It was suggested that a problem might have occurred with the home-mixed feed just before the pelleted feed was delivered. This seemed unlikely as the one group of 27 cattle that did not receive the new ration did not develop signs.
As different people fed various groups of cattle and other species with different vehicles and containers, it seemed unlikely that it was a vehicle or stockperson issue, or indirect contamination. Variable amounts of the suspect feed were provided, but all groups receiving it were said to have animals showing signs to varying degrees. This again suggested that it was not a feed management problem.
The same sources of bedding, roughage, and water were present in affected and unaffected pens.
No animals that entered the farm after the Tuesday developed signs and so again, it is suggestive of a feed cause.
The suspect feed was offered to the cattle on the farm and the severity of the signs that developed depended on the amount fed. The 27 cattle that did not have the feed did not develop signs, nor did a new entry of five to six-month-old bulls. All animals offered the feed tended to have a reduced feed intake, and the pigs and sheep mainly rejected the feed.
Again, this suggested that it was not a problem initiated on the farm before the suspect feed.
The farmer was wise enough to quickly call in his veterinary surgeon. The latter saw the problem within 25 hours of the feed delivery and 22 hours of the feed being offered. This greatly assisted in reducing the possibilities of it not being the feed and offered an independent account of the problem.
In the author’s opinion, all practices should advise their clients to call them in immediately when a problem linked to proprietary feeds is suspected. This one action made it very difficult for the insurance company to suggest that the feed was not involved.
Therefore, it was very probable that the proprietary pelleted feed was the source of the problem.
This appeared to be the case if no other complaints were made. It is probable that on many farms, the new feed load was mixed with previous ones. If the feed was contaminated, this would have possibly delayed or reduced any signs developing; it also meant any association with the new feed would be less likely to be made.
Again, if the feed was contaminated, unless large amounts were fed (12kg on the affected farm), signs would probably have been less, minimal or missed. If only a few cattle developed diarrhoea or rejected the feed, or later developed lameness, then any relationship to the feed might well have been overlooked.
If a toxic agent was in the feed, in all probability, it would not have been evenly distributed throughout the feed batch produced at the mill.
Usually, collections of cereals and so forth from the field would be made in 10-tonne or 20-tonne loads. Average yields would vary, but spring barley in the previous year to the problem, and so used in the pelleted feed, would produce about 7.2 tonnes/hectare, and so a 20-tonne container might contain the product from less than 3 hectares (about 7 acres).
Equally, the average yield of wheat would be about 7.4 tonnes/hectare and so 20 tonnes would probably be the yield from about 2.7 hectares (about six and three-quarters acres). Both these acreages would usually form only a small part of a field. Therefore, any toxic problem may not necessarily be present throughout a field, but concentrated in a few harvested loads.
Unless any mixing occurs, the container load of cereal from the field, whether it is dried, will probably remain in the same part of any larger storage heap. This heap will be subjected to the same climatic conditions of warmth and moisture, and then, once transported to the mill, it will probably enter a silo and undergo little mixing with cereal already present, or subsequently added to the load.
In a continuous flow system, mixing will probably not occur much until it is added to the other ingredients of the feed in the mixing chamber.
Therefore, parts of the 170-tonne feed batch could in theory, and probably in practice, only undergo limited dilution from other container-loads of the same or other ingredients, except during the mixing process.
The extent of any such mixing will depend on the capacity of the mixing chamber and, obviously, would vary between feed producers. Therefore, it is possible that a 10-tonne or 20-tonne load of mixed feed may still contain a large proportion of any contaminated material from the original field of origin.
As many potential contaminants may only affect a part of a field, the previously mentioned suggests it might be possible for much of the affected cereal or ingredient to remain concentrated in one or a few loads of the prepared feed delivered to livestock farms.
The main signs recorded included rapid onset abdominal pain and dark-coloured diarrhoea, possible feed rejection or reduced feed intake, subsequent lameness and reduced growth. Later reproductive problems were also suggested in the history.
The following is a summary of some of the causes, and some of the reasons why they were likely or not to have been involved. The list is far from complete and only some of the rationale is provided.
Some disagreement was had about the colour of the diarrhoea. However, it was dark, and both farmer and vet did not consider blood or melaena to be present.
Most infectious diseases could be tentatively ruled out because no signs of the problems were evident in the 27 animals and five to six-month-old bulls that did not receive the suspect feed.
Acidosis was a very probable diagnosis on the first day. However, signs occurred in some cattle receiving small quantities (1kg to 2kg daily) of the feed, even though they were used to receiving the home-mixed feed that consisted mainly of cereals.
Usually, the diarrhoea would not be dark brown/black, and abdominal pain is not a consistent feature in acidosis. Decreased ruminal movements or stasis might have been expected to be seen.
Lameness was not present at the early stages which, if it had been, might have suggested acute laminitis. However, its presence later on, in many cases resulting in severe signs, often in all feet, is not usually associated with uncomplicated acute acidosis.
Aluminium phosphide can be used as a grain fumigant. It can produce abdominal pain, reduced appetite and toxaemia. It requires acid conditions to release toxic phosgene gas. While this could occur in the finishing cattle, it would probably have resulted in deaths.
The low levels fed to the suckler herd would probably have been insufficient to produce diarrhoea.
Accidental inclusion of antibiotics can result in diarrhoea, often foul smelling, in cattle.
Feed companies are very aware of the risks and so will typically use different equipment or even mills for ruminants, and for pigs and poultry.
Any of the antibiotics likely to be used would be for pigs or poultry, and as such, the pigs would probably have been likely to eat the feed. Their presence can produce abdominal pain, diarrhoea and ruminal stasis in cattle.
Some can also lead to cardiac muscle degeneration and cause congestive heart failure, although no signs of this type were mentioned.
The location of the farm was not in a high arsenic area and it would be in an insoluble form (arsenopyrites). No mine workings were present in the area. It was also unlikely to be present in the feed, although the signs do include diarrhoea and haemorrhage.
Some doubt existed between various people about the faecal colour, but no haemorrhage was seen by the farmer or veterinarian. Also, pigs would not be expected to reject the feed – particularly as organic arsenicals used to be included in their feeds. Pooled samples of horn from the feet of affected cattle and the feed did not show abnormal arsenic levels.
The signs appeared to be too sudden, widespread and with several key ones absent to be bluetongue.
This was confirmed by the apparent, subsequent associated problems that occurred.
While bovine coronavirus can cause severe widespread outbreaks of dark-coloured diarrhoea, often with melaena or haemorrhage, it is usually in older cattle.
It was also unlikely to be so quickly widespread and should have resolved in a short period.
Pooled samples of horn from the feet of affected animals and from the feed showed acceptable cadmium levels.
It was not divulged by the feed company if any of the biscuit and confectionery products contained chocolate, but the dark brown colouration of the faeces might have suggested their presence.
If it was part of the cause, it would not have been expected that the pigs would reject the feed. Several alkaloids can be found in chocolate or cocoa powder, and some of these can cause changes in blood vessel diameter. If the problem persisted, it might have had long-term effects on the feet and sclera. Although the full content of the feed was not disclosed, it was unlikely to be more than partly involved in the problem.
If present, fat rancidity was most likely in the biscuit and confectionery products. It can lead to feed rejection or signs of pain, with lowered heads and arched backs, restlessness, and black, bubbly, foul-smelling diarrhoea.
It would be highly unlikely to result in long-term signs – especially in animals fed outside and having low feed intakes.
The feed was introduced immediately without any changeover mixing programme. This is far from good practice, but in reality does occur on many farms. Usually, the farmer “gets away with it” as ruminants are quite forgiving of feed changes.
The feed was designed for beef cattle and so should not have been given to other species. This is particularly the case with sheep where problems can arise, such as copper poisoning. Again, it is not uncommon for this practice to occur and if the feed is only offered for a short period, then no apparent ill-effects may be seen.
While feed management faults could not be initially dismissed in this case, the continuing and subsequent signs suggested they were not primarily involved.
Such a problem can occur, but it could have been determined by feed analysis of samples on farm and at the mill.
No information was provided by either party that these analyses were undertaken.
It was suggested that several of the signs could have occurred because of magnesium, but they would not be expected to have the long-term consequences present.
Inclusions can occur from medication carry-over from a previous feed batch, poor mixing or wrong ingredients.
Again, this might have been detected in any retained samples present on farm or at the mill.
Usually, it might not have been expected that the problem would have been so widespread or to have continuing effects.
Pooled samples of horn from the feet of affected animals and the feed all showed acceptable mercury levels.
Metaldehyde slug bait can result in signs including diarrhoea, although nervous signs are also usually present in acute cases.
Horn changes and lameness would not be expected.
When present, mycotoxins can be concentrated in parts of the feed. It is not known if a mycotoxin screening was undertaken by the manufacturers, but it was suspected that it did not occur.
Sheep will often reject feed containing some types of mycotoxin.
Pigs are also able to detect some mycotoxins and reject feed containing them. Both species tended to reject the suspect feed.
Many different types of mycotoxins exist and some, such as those in ergot, can produce acute and delayed signs, including permanent damage such as to the lower limbs of some cattle.
This was considered a strong possibility and the toxins could have quite easily been localised to a small quantity of the overall feed batch.
Again, it is not known if the company did any analysis. By the time the suggestion of ergotism was made, neither the feed company nor the farm had any feed remaining.
Palm kernel expellant was considered a possible part cause as the expellant contains sharp-edged hips of nut that can act as a mechanical means of damaging the gut wall and causing bleeding.
However, it would not have been expected that so many animals would have been affected so quickly or that the long-term effects, such as chronic lameness, would have been seen.
Polychlorinated biphenyls (PCBs) are often considered to be of the same chemical type and effect as dioxins. Unless very high levels were recorded in the feed, then the signs would have been slower to develop than occurred in this case.
The signs would have been diarrhoea, possible abdominal pain, loss of appetite and poor growth. Long-term effects can be poor growth, but also increased susceptibility to disease, due to immunosuppression, and so forth. On the basis of signs present, and the very widespread level of problems, even with low levels of feeding, it was unlikely they were involved in the problem.
Rapeseed meal extract is a common source of protein and appears to have been used in small amounts in this feed.
Several toxins can be present in it, and sheep will often reject the feed.
However, they would not be expected to cause such acute and widespread signs in cattle.
Both sodium fluoroacetate and warfarin can occur, but result in nervous signs and death.
However, they do not cause many of the signs described, including diarrhoea and hoof changes.
Depending on the subspecies, salmonellosis can cause severe enteritis, sometimes with obvious blood or melaena, and in some cases, abdominal pain.
Chronic lameness and gangrene of the extremities can occur. The signs did appear very rapidly and were widespread. This would have meant it was not brought in with cattle or animal vectors, although the feed would have had to be heavily contaminated, which would have seemed very unlikely.
At the time, it was considered not to be a probable cause. In consequence, no bacteriological samples were taken.
Pooled samples of horn from the feet of affected animals and the feed all showed acceptable selenium levels.
This feed is a variable quality product and it is not as useful as high protein sunflower, which is from kernel extraction and is without the presence of hulls.
The extracted seed can contain seed hulls, which could result in damage to the gut lining.
The extracted seed was at a high level in the feed. It is not liked and often rejected by sheep.
While it might have caused some initial problems, it would not have caused all the signs seen or the chronic problems that occurred.
Sunflower oil was included in the pellets, and can lead to sticky and clinging dung. However, long-term faecal alteration would not be expected to occur after feeding ceased.
Tannins can be found in cocoa residues. They could, in large quantities, cause abdominal pain, reduced or complete loss of appetite, and constipation, followed a few days later by dark-coloured, foul-smelling diarrhoea.
These signs were not seen in this instance and probably would not have affected the animals, which only had small quantities of the feed at grass.
Problems can arise where an absence of some components exists, adding excess of some components, or where some interaction occurs between some supplement ingredients that are too high and others that are too low.
Usually in most mills, the vitamin/mineral is provided as a supplement, or pre-mix packs or sacks, which are mainly prepared by specialist companies. When problems arise, it is usually because of forgetting to include the whole pre-mix or adding more than one pre-mix pack.
Any such problems could have been determined by analysing the feed for vitamin and mineral levels, and seeing if any component was abnormally high or low. Unfortunately no record exists of this being done. Some of the mix components could, in excess or limitation, have caused one or more of the signs observed.
However, it would not normally be expected that the cattle receiving low feed levels for probably three or possibly four days would have developed problems, and for them to start within about 12 to 24 hours of introducing the suspect feed.
Wheatfeed, a by-product, is quite variable in composition, depending on how the wheat had been used.
Often, it can be low in energy and was probably not involved in the problem.
Provided the history and the signs were more or less correct, it seemed the most likely diagnosis was primarily a mycotoxicosis.
The genus Claviceps contains more than 50 species, mostly occurring in the tropics, but several can be found in the UK. The variety and persistence of some of the signs suggested it was most probably ergotism. The most prominent member of the group is Claviceps purpurea (often called ergot of rye) and it has many strains.
These are much more widely spread than farmers realise. More than 80 indole compounds have been isolated from ergot, some with no or minimal toxicity.
However, others are potent alkaloids, including ergocristine, ergocryptine, ergosine, ergovaline and, the most well-known one, ergotamine. This last alkaloid includes a linkage to lysergic acid (ergoline). Any toxicity will depend on which alkaloids are present, their concentrations and the interactions between them.
The initial signs in this case of abdominal pain and diarrhoea have at times been observed. Diarrhoea is not a common sign, but occasionally reported in some outbreaks (Coppock et al, 1989; Constable et al, 2017). Its occurrence did appear to relate to the offering of the new feed.
Both pigs and sheep have more sensitive senses of smell than cattle, and will more frequently reject feed.
Feed rejection has been recorded on occasions with Claviceps species. (Blaney et al, 2000; Bourke, 2003).
Hyperthermia is not often recognised in the UK, but is recorded as a typical sign in many parts of the world (Constable et al, 2017).
It is possible the increased thirst observed at the slaughterhouse was the result of the cattle’s elevated temperatures.
The later signs of lameness with varying degrees of necrosis, horn erosion, accompanying abscessation and other problems have often been recorded (Figures 1 and 2).
Signs usually start to appear about two to six weeks after the ergot introduction. However, in this case, the signs were confounded by a lack of cutaneous gangrene, which is usually seen over the lower affected limb areas and occasionally ear tips. This was probably because the outbreak began in April at a time of rising ambient temperatures and these were high enough to allow sufficient blood supply to the area to prevent sloughing (Leuschen et al, 2014).
As in this case, mortality directly due to ergotism is uncommon, but can occur (Leuschen et al, 2014).
If the history was correct, both the cattle and sheep showed some signs during current pregnancies, or with their subsequent fertility (Constable et al, 2017).
Signs of scleral congestion/exophthalmos appear not to be mentioned in the modern literature, but have been recorded in experimental work with ergotism in animals (White, 1940; Dale, 1965), and occurred in this outbreak.
While not pathognomonic, bilateral exophthalmos is a rare condition in farm animals other than on an individual animal basis.
Signs of ergotism not recorded in this problem included the following.
The argument exists whether abortions commonly occur (Constable et al, 2017; Leuschen et al, 2014). Most recorded cases follow exposure to a high level of toxin.
No fetuses were found in this outbreak, but the cows were grazed daily and surrounding wildlife was plentiful.
From the history, it was possible to suggest that some known pregnant cows might have aborted because of the ergotism, but this was unproven.
Cutaneous gangrene is commonly present in chronic cases, usually affecting the lower part of the limbs and possibly ear tips. This is often used to confirm the diagnosis of ergotism.
Apparently, it did not occur in this case, possibly because of the rising spring temperatures.
Nervous signs are reported in other countries with ergotism, but are rarely identified in the UK. Here, nervous signs occur more commonly with other Claviceps species.
Overall, on balance, the history and signs suggested ergotism was the most feasible main diagnosis.
When alleged or suspected feed problems occur, it is not unusual for compensation to be refused without a reasonably high level of proof.
It is, therefore, always important to take adequate samples from the feed and ensure they are representative of the suspect batch.
Good records also need to be kept and often compensatory payment will only be made by a diagnosis for each individual animal. In this case, while some signs present were not typical and others were absent, it appeared that ergotism presented the most probable diagnosis.
It is possibly worth noting that three signs not usually recorded in the UK appeared to be present, namely feed rejection, exophthalmos and hyperthermia, and they may be worth considering when trying to unravel cases similar to this uncommonly diagnosed problem.
It is suspected the most important take-home message from this article is that you should impress on your farmer clients that if they suspect a toxicity problem – especially if associated with bought-in feeds – they request the earliest possible visit.
While many will not turn out to be poisonings, when they do, taking the right investigatory steps can be the difference between receiving compensation and a loss – sometimes, in large problems, verging on bankruptcy.
