Toxins in feed – is your horse at risk?

Dr Lucy Waldron PHD reports on the hidden toxins that may be lurking in your horse’s feed

Toxins in ryegrass are well known, but the problem may be more widespread than many horse owners realise

Horse owners have heard much about the dangers of mycotoxins from fungi in our grasslands in New Zealand, but recent evidence shows that the problems caused by these are not confined to staggers and are evident in many other commonly used equine feeds and forages as well.

Research since the 1970s has shown that the toxins produced from certain fungi that live in pastures and grain crops pose a problem in animal nutrition. Symptoms can be bewildering, as they are diverse and difficult to diagnose. Many mycotoxin problems are often misdiagnosed as other issues – meaning that the core problem is not always addressed in a proper manner.

Of course, there are ways of protecting our horses and ponies against such risks, either with feeding toxin binders or by resowing pastures with grass and legume species which do not harbour such fungal species.

But we need to be aware that this will not completely negate toxins, which are likely to be produced by fungi growing in warm and humid summer conditions.

The problem is much more wide-ranging in New Zealand than previously thought, as shown in recent research.

Modern laboratory techniques now allow cheaper, faster and more exacting analysis of the toxins lurking in feedstuffs. In the last couple of years, a survey of a range of toxins has been conducted from samples supplied from various parts of the country and in all kinds of feedstuffs. This has revealed that the actual types of toxins present include those not commonly thought of as major risks, but which can cause severe problems in all animals, including horses. These may range from reproductive failure to neurological disorders.

The equine industry is aware of the problems of lolitrem toxins that cause staggers, and the dairy industry has focussed on aflatoxins, a major carcinogenic group of compounds that can be transferred into milk.

In addition, pythomyces fungi cause facial eczema, which is common in New Zealand.

The survey from the last couple of years, however, showed that many feedstuffs are infected with more than one toxin. Of the New Zealand feedstuff samples, the majority (68%) were infected with five to eight different toxins from fungal sources. Nine per cent contained more than 13 different toxins, with an overall average of six toxins per sample. No samples were free of toxins.

So what damage and symptoms do these toxins cause to the animal? All mycotoxins typically act as pro-oxidants – leading to damage to cell membranes and tissues (eg. the liver) and requiring higher levels of antioxidants to be fed in order to counteract their destructive behaviour.

Aflatoxins – which were found in 22% of the feed and forage samples tested – typically cause liver damage, which can lead to a variety of symptoms and may cause organ failure if exposure is long-term. At post mortem, the liver will have a mottled or pale appearance, rather than the normal dark red, even colour.  In addition, their ability to pass into milk can then lead to poor liver function and reduced growth in foals that are still suckling.

Type B thricothecenes – found in a whopping 63% of the feed and forage samples – are associated with disrupted modulation of the immune system, which can cause the horse problems in reacting appropriately to actual threats which require an immune response. They can also cause mouth and gut lesions, as they cause burns to sensitive membranes.

The penicillin toxins, found in 61% of the samples, are most common in hay, silage and root vegetables, such as sugar beet. These can have a major impact on fertility in mammals, causing uterine problems that may cause infertility with enough exposure.

Other toxins are common in grain, again a common component in horse feeding regimes. Whilst ruminants (sheep, cows) can degrade some toxins in the rumen, horses are unable to do this, and so are more at risk from the damage due to mycotoxin ingestion than other species.

Most symptoms observed, due to the presence of several mycotoxins in feedstuffs, are manifested as poor condition or lack of appetite, such as horses who just can’t seem to put weight on.

Toxin damage can accumulate over time, leading to a perceived sudden onset of disease. The wide-ranging impact on immunity, which has been well documented in many species now, can show up in many ways – most notably in animals who fail to thrive or always seem to have sub-clinical disease issues.

Of course, in-foal mares should be protected from ingesting toxins, and younger horses and ponies are more at risk as their growth and development can be severely restricted or damaged by ingestion of infected feed.

As we continue to learn more about mycotoxins, their threat becomes increasingly apparent, and the avoidance of the problems associated with ingestion is more important.

Remember, never feed mouldy feed or forages to your horse. If in doubt, do not use it, and don’t be tempted to feed it to other stock. Be especially careful with breeding horses and young foals.

I would like to thank Professor Trevor Smith (University of Guelph, Canada) and Nigel Meads (Alltech NZ) for providing data for this article.

  • This article was first published in the March 2014 issue of NZ Horse & Pony