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The GREEN HORSE - sustainable horsekeeping

JUNE JULY 2009
Vol 31-1

In the Current Issue of The Green Horse you will find the following articles:

Information Exchange - Reader’s Tips, Views and Questions
Heavenly Hectares by Chris Ferreira
Equine Pastures Research by Andrea Carmody
Safe Chemical Storage by David Mason-Jones
Deeds, Steeds and Weeds
Weed Watch - Red Clover vs Crimson Clover by Nicola Field
Managing Manure Pt2 by Jane Myers

RED CLOVER VS CRIMSON CLOVER by Nicola Field

One of the ironies of good pasture management is that it may be associated with an increased incidence of livestock health disorders as well-intentioned landholders bring new plant species onto their property. This can certainly be the case when clover is introduced to pasture.

There are a number of clover varieties, almost all originating from Eurasia. White clover (Trifolium repense) is the best-known variety, however, increasingly land owners are able to buy seed mix containing red clover (Trifolium pretense) and crimson clover (Trifolium incarnatum).

Red Clover

Crimson Clover

All clovers are perennials that reproduce by seed, though white clover can also reproduce by stolons (above-ground reproductive stems). Clover has a trifoliate leaf (having three leaflets), with red clover leaves having a characteristic inverted ‘V’ watermark. The flowers of red clover are typically reddish to purple, while crimson clover (also known as ‘strawberry clover’) has a flower ranging from pink through to yellow.
As a legume, most varieties of clover are regarded as a good foraging crop for horses as the plant provides protein, fibre and energy, though these qualities also mean clover should often be fed in moderation. Selecting a low oestrogen variety of red clover will help avoid infertility problems that have been associated with broodmares grazing on high oestrogen varieties.
Along with the positives, clover can also bring problems - particularly red clover. During periods of heavy rain or high humidity, red clover may become infested with the mould Rhizoctonia leguminicola, which appears as rust coloured patches on the upper side of the leaf. This mould produces a mycotoxin called slaframine, which can cause horses to salivate excessively in a condition called ‘slobbers’. This may not be life-threatening if the horse has adequate water but it can cause severe dehydration in warmer weather or over prolonged periods. Removing horses from the source of red clover generally results in fairly quick recovery.
A more serious threat, again often associated with red clover, occurs when the plant is infected with black blotch leaf mould (Cymodethea trifolii), which can be identified growing on the underside of the leaf. This mould has been associated with photosensitivity. Symptoms of photosensitisation include swelling of the lining of eyelids (conjunctiva), inflammation of the muzzle, mouth and tongue, brownish urine and clay coloured manure.
A further complication of black blotch mould ingestion is liver damage, which may not be so easy to observe. This can be caused by the mould’s alkaloids, which cause liver dysfunction. If cirrhosis of the liver is allowed to develop, death may result. Generally, a horse has to consume mould-infected clover for a few months before the liver effects are severe enough to diagnose.
Many horses can forage on red clover with no ill effects, but it isn’t worth taking a risk. The best control strategy is to fence horses out of all clover-rich pasture in periods of high rainfall and high humidity. The chance of mould infecting any type of clover can be reduced by increasing air movement through mowing or improved paddock drainage.
Even when clover doesn’t grow in pasture, horses can still be at risk from the threat of red clover-based mould. Clover is often used as a hay crop, and as both red and crimson clover are becoming more commercially available in Australia, there is a growing likelihood that these varieties will increasingly appear in grass or meadow hay.
The problem is that clover, and in particular red clover, takes longer to dry than other hay forage. This increases the chance of mould appearing in commercially sold bales, so be particular about where hay is sourced from, particularly if any symptoms of slobbers or photosensitivity become present. The clover your horse finds so delectable could be doing him more harm than good.