Clover for horses

Q: Clover in pasture for horses – good or bad? From my high school horticulture lessons, I learned that clover is a nitrogen fixer and thus helps other plants to grow, and that lack of clover means your soil is sick. It also provides food for the bees! But I’ve read a lot lately about horse people spraying out cover, and blaming clover in their pasture for various issues in their horses. I’d like to know what your experts say.

Caroline, via email

Vet Dave replies:

As with most things in life, it’s not that simple. Excessive amounts of clover or ingestion of certain types of clover have been associated with different disease processes, and these situations are best avoided. However, most horses can easily tolerate a certain low percentage of clover amongst the grass that they are eating, and it provides them with a valuable source of good nutrition. 

As you mention, clover is a valuable supply of nitrogen for the pasture, and leads to a healthy pasture rather than having to top-dress with fertiliser to get the same nitrogen fix, a much less desirable situation. 

The exact percentage of clover that is suggested as fine for horses to ingest varies between authors, and the range anecdotally is 10-20%.

 Most of the reports of toxicity from clover come from America: symptoms include photosensitisation, excessive salivation and liver disease. The most common types of clover in New Zealand pasture are red and white clover; aslike clover that is responsible for “clover poisoning” as described in many reports from the US does not appear to be prevalent here. I have yet to see excessive salivation or liver disease as a result of clover ingestion in horses in New Zealand. 

I suspect that most of the clover problems seen here are either as a result ingestion of clover being too rich a feed source for the horse causing either behaviour problems or laminitis, or as a result of endophyte toxicity from endophyte growth on the clover plant.

Nutritionist Lucy replies:

Clover is a legume, not a grass, and is high in protein and sugar and low in fibre. Horses are adapted to live on coarse grasslands, and so have a high requirements for fibre, as they derive a large amount of their energy from its fermentation in the hind gut. Clover is very good at taking over pastures, which can increase the protein and sugar and decrease the fibre intakes. 

Whilst the jury is out on protein at the moment, as studies have been mostly conducted in thoroughbreds rather than more heavily muscled species, which by inference need more protein, we do know that sugar is a problem for both equine behaviour and laminitis. 

Fresh (uncut) red clover contains 21% protein, on a par with fresh lucerne, and around 11 MJ/kg energy, which is higher than seen in other grass species, being around 9-10 MJ/kg.  

In most parts of New Zealand, nitrogen in the ground can be very high, due to the uncontrolled use of fertiliser and from the excreted excess nitrogen from ruminants fed high protein grasses. The latter is a particular problem in lifestyle properties split off from dairy farms. In saying that, the soil in long-term horse paddocks can become poor in nutrients if the have not been regularly tested and managed. 

Hence clovers may have a role in improving certain soils, but the fact remains they are low in fibre, being just over 20% fibre (akin to low-fibre rye grass) compared to other grass species which are 30% fibre or more (timothy, orchard grass). 

Of course, nutrient levels in pasture varies with time of year and climate, so these are guidelines. 

Cut clover for hay, if it gets wet, can contain a fungal toxin that causes a condition called ‘slobbers’ in horses. 

Overall, as for all feed materials, clover can have its place, but these factors should be taken into consideration and clover should not be allowed to dominate in paddocks for horses.

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