Of all the extremes of weather, summer heat is the most uncomfortable for your horse. Driving wind is a close second – shade and shelter is the only way your horse can get relief from either.
Access to paddock shelter is recognised as being so important for a horse’s physical and psychological wellbeing that it is a legal requirement covered under animal cruelty legislation in some states of America. In my opinion, it should be mandatory in New Zealand too.
Last summer we had temperatures exceeding 30 degrees C in many areas of the country, with 38.7 degrees recorded in Alexandra.
These sorts of temperatures cause overheating in all animals, but especially horses – the large body of a horse takes longer to cool down than that of smaller-bodied animals, and their high-fibre diet gives off heat during digestion (an advantage in winter, but a negative in hot weather).
Horses use a number of physiological mechanisms to lower their body temperature. These include thinning of the hair coat in summer, sweating, an increased respiration rate, vasodilation (widening of the blood vessels near the body surface), and increased water consumption to dissipate heat.
But most effectively, they use behavioural thermoregulation. That’s a fancy phrase for finding the best spot in the paddock. Horses will naturally seek out the best micro-climates to protect themselves from any weather extremes.
A lack of shade is more than just hot and unpleasant for your horse, it can lead to sunburn in horses with white skin or facial markings, and eye cancer for horses who have white around the eye (particularly breeds like Clydesdales and Appaloosas). Also, horse’s eyes have evolved to let in lots of light (to improve dawn and dusk vision), so bright sunlight can be uncomfortable, especially if the horse does not have a long forelock.
Flies, both the annoying paddock fly and the equine bot fly, prefer the direct hot sun, making cool shade even more preferable from a horse’s perspective.
A mesh cover and man-made stable or shelter is certainly better than nothing, but by far the best shade is as nature intended, under a tree.
Not only do trees provide protection from the sun, they are natural air conditioners – using a process called evapotranspiration which is the combination of soil evaporation and plant transpiration of moisture to the atmosphere. Add to this any breeze going past, and they are best form of cooling a horse can get.
Another advantage of trees is that their shade moves throughout the day, so the horses are not continuously standing on and potentially damaging one spot of the paddock.
Rick Williams, general manager of The Oaks Stud in Cambridge, notes that trees also appear to affect horses’ temperaments. “Having trees in the paddocks seems to calm horses. They always seem a lot calmer when some trees are around, compared to open spaces, and any shade is good shade – especially through the heat of summer,” he says.
David Benjamin has developed three properties into stud farms, and is well aware of the benefits of providing shade and shelter to his horses.
“We bought 400 acres (160ha) in Okoroire and planted 10,000 trees and shrubs there. Horses just love shade, and we are lucky trees grow quickly here. We’ve planted three or four trees per paddock, and not too close to the boundary fences so they could still run around the outside of the paddock. You’d see the horses move around the trees as the shade moved.”
David favours quick-growing large trees for shade. An admirer of the colourful Kentucky autumns, he also choses trees for their aesthetic value.
Some trees also have medicinal or food value or are a natural anthelmintic (which expels internal parasites). Most trees are beneficial in some way, as horses, just like humans, need variety in their diet.
“Take a horse for a pick alongside the roadside verge. They don’t go for ryegrass and clover pasture. It is really amazing what they’ll seek out. Horses will even eat dirt,” says Rick.
The most important factor when choosing which tree to plant is to choose ones that grow well in your area, and this can be as simple as looking over the fence next door or visiting your local park.
Deciduous trees are preferable, as they allow winter sunlight through to dry the ground and encourage grass growth underneath. And the bare branches still offer a measure of warmth and wind protection in winter.
Here are a few recommendations of suitable trees that are fast growing and provide good shade.
1. Oak (Quercus spp) – There are a wide variety of oaks. Scarlet oaks like dry and sandy situations and provide stunning autumn colour. Pin oaks like damp ground and withstand wind and the common English oak provides the ultimate shade with its wide spreading crown. Their autumn acorns are full of carbohydrates and are excellent fodder for horses, though Benjamin says they are no good for racehorses as the make them too fat. (NB: Sudden and excessive amounts of green acorns can be toxic, so take care if high winds in early autumn cause a big drop of new acorns to a hungry or bored horse.)
A branch or two of oak leaves can also help bind up a horse with loose stools caused by the spring grass, but once again, excessive amounts can be toxic so don’t fell a whole tree to a herd of hungry horses.
2. London Plane (Platanus × acerifolia) – This is one of David’s favourite trees and a common street tree in many towns. Different cultivars can provide shades of autumn colour ranging from golden to brown. The Oriental Plane (Platanus orientalis) is very similar. Both are very quick-growing with wide spreading branches that offer good shade.
3. Golden Elm (Ulmus procera) – A handsome yellow-green spreading tree that turns intensely yellow in autumn. Kereru (wood pigeon) will feast on the spring leaves. Elms are tolerant of adverse and persistent winds but dislike heavy clay and shallow soils.
4. Willow (Salix spp) – a favourite that thrives in most conditions, including wet ground, where it has a drying effect. The leaves and bark are highly beneficial (willow is what aspirin was originally derived from) and branches can be cut and fed to horses in summer when grass is scarce. Be aware, however, that willow can produce a positive swab in competition horses, so do not allow your horses access to willow for a week or so before any shows. The male willow provides pollen to bees during spring when bee feed is usually scarce and some varieties have lovely autumn colour, especially in colder climates. The weeping willow provides a stunning canopy that horses will perfectly trim into an attractive umbrella. Unfortunately, the recent arrival of the giant willow aphid is affecting most trees throughout the country. These can weaken (and even kill) trees and produces an unsightly black residue on the trunk. Research is currently being undertaken on possible biocontrols.
5. Paulownia – Very fast growing, wide spreading tree with large leaves and a stunning display of purple flowers in spring. They tolerate most conditions though prefer rich moist soils. As with willow, the leaves are a good food supplement in summer.
6. Maidenhair tree (Ginkgo biloba) – Slightly slower-growing and smaller in comparison, the gingko is hardy, pest free and turns a stunning yellow colour in autumn, even in mild climates. Chose a male ginkgo tree as the female’s fruit can be smelly and the seed toxic in large quantities. Gingko leaves have long been used in Chinese medicine and have beneficial effects if browsed.
7. Honey Locust (Gleditsia) – An attractive shade tree with purple or golden autumn colour the Gleditsia grows most anywhere and thrives in hot and dry climates. It has sweet edible seed pods that are valued as stock fodder (you can eat them too) and has the added attribute of fertilising the nearby grass by capturing nitrogen from the air and making it available.
8. Pear (Pyrus spp) – A grafted pear tree purchased from a nursery may not grow very tall or live very long, but a real seedling pear tree can become a wonderful shade tree that has been recorded as living for over 400 years overseas. (To grow, store the seeds of a tasty pear in the fridge for six weeks over winter in a bag with sphagnum moss and pot them up in spring.) Horses (and riders) will enjoy munching on the autumn fruit as much as the summer shade.
9. Poplar (Populus spp) – The advantage of poplar is it can be grown cheaply and easily from long poles planted in winter. They grow incredibly fast on sandy loam or silty river flats but will tolerate a wide range of conditions. Their large root system is used to stabilise erosion-prone soil but can be troublesome amongst man-made drains and septic systems. Stock will feed on the mineral-rich leaves as they drop in autumn (farmers call these pennies from heaven) and branches can be cut and offered as a supplementary green feed in summer when grass is scarce.
The yunnanensis variety is the most tolerant to dry sites, resistant to the poplar rust disease and unpalatable to possums.
10. Walnut (Juglans regia) – A superior shade tree, not the least because every household should have access to a good walnut. The common English walnut (the one we eat) is rather slow to grow in comparison to previous recommendations but is a long-lived tree with a lovely shaped shade crown worth waiting for.
Farmers have attributed the walnut with a natural fly repellent but I can find no scientific reason for this, it may just be the coolness under the tree but animals seem to find respite from the persistent pests when resting underneath.
Planting advice
Individual trees provide the best shade, but wind needs to be deflected upwards to go over their tops. This is best done with a low hedge. David considers barberry a great divider between horse paddocks, as horses will not push against the thorny bushes. Feijoas, flax and toetoe are easy-to-establish wind deflectors, and have the advantage of not requiring ongoing pruning. Flax is said to have anthelmintic properties and stock will often self-medicate on any fronds getting too close to the fence.
Note a solid hedge by itself is not a particularly effective wind break. Wind can go over and dump on the other side. But when combined with scattered shade trees, hedges deflect the wind up and over the trees and provide a healthy and comfortable habitat for horses.
Be aware that the cheapest part of planting a tree is the actual tree itself. Since horses like to eat trees, they need good protection to get established.
David built squares of three ½ round or 150x100mm rails, but warns you have to prevent bored horses chewing them.
“We put a 4×2 (11x50mm) v-shaped aluminium extrusion nailed over the leading edge, or a long line of thin netting stapled on. Otherwise a chewer could go through a rail in a night.”
A rabbit and hare protector is a worthwhile investment if these pests are around, and the additives of the slow release fertiliser pellet or compost, and a water-holding gel in the planting hole ensures trees gets established and grows well.
Trees to avoid
There are some trees that can have a negative effect on horses. Andrea Ritmeester, a registered specialist of equine surgery and President of the NZ Equine Veterinary Association says they have had several horses referred from Katikati over the years with suspected avocado toxicity; showing symptoms like depression, swelling of the head and masseter muscles, and inability to open the mouth and eat.
“Horses are quite picky eaters (unlike cows or goats who will eat just about anything) so they tend not to eat toxic plants unless they are short of feed and really pushed. Horses are typically quite finicky about what they put in their mouths. In saying that, there are a few things like avocado leaves and the sycamore tree seeds which they can ingest when grazing which can cause significant toxicity syndromes.”
Other toxic trees to avoid are yew, rhododendron, privet, red maple and many of the conifer/pine type trees whose needles can cause abortion.
- This article was first published in the November 2018 issue of NZ Horse & Pony
