Cooler weather makes winter a favourite time for horses – no flies and midges or itchy sweating just running free and soaking up the winter sun!

Cool temperatures mean less stress — and more time in the ‘thermoneutral zone’ (TNZ), the temperature range in which horses do not need to sweat or shiver. The TNZ varies with age, gender, breed, weather, exercise and feed.

Notwithstanding that with a skin temperature of around 30°C, horses lose heat to the air around them whenever the air temperature is below 30°C, they don’t usually shiver until the temperature is below 0°C for a weanling and –15°C for an adult horse.  The colder the air, the greater the heat loss will be. But, because of the heat generated by digestion and movement, horses do not need to shiver until the temperature is less than zero for a weanling and less than –15°C for an adult horse.

We can help horses stay warm in winter by providing plenty of roughage – hay or pasture is best, and oats too have a role in certain situations. High fibre feeds produce body heat when they are fermented by hindgut bacteria breaking down the fibre – the by-products of which are heat and nutrients for the horse. High starch feeds, such as corn molasses and sweet feeds do not generate this fermentative heat and do not make your horse ‘hot’ —  they can increase their energy and excitability, but they dont generate significant core body heat. If you watch your horses’ hay intake, you will notice they eat more hay as the weather cools down because this helps them keep warm from the body heat generated during digestion.

As a rule of thumb, the most efficient way to keep horses warm during winter, is to feed more highly-digestible hay, at 2–2.5% of body weight and in a ratio of 50-60% lucerne and 40-50% grassy/oaten hay. Beet pulp can also be a beneficial source of fibre. When the weather is wet and windy as well, energy needs increase a further 40-50% and some oats may be useful – but not more than 1-2kg per meal – and as always start with a small amount and increase slowly to allow the gut bacteria time to adapt to the increased starch. Yearling horses fed a high quality diet free-choice are able to tolerate temperatures as low as -11°C with no ill effect. In cold weather, feeding good quality hay free-choice is the simplest way to ensure that the horse will meet its energy requirements.

A warm bran mash is traditionally used for its laxative effect and is a great way to give horses a treat on cold nights. However, loose manure the day after a bran mash is due to the sudden change in diet which irritates the gut wall and compromises the bacteria in the large intestine. Bran should be restricted to less than 10% of the diet as it contains 9 times as much phosphorus than calcium. An occasional bran mash is not harmful, but a separate calcium supplement may be necessary. High phosphorus and low calcium and minerals in grain can unbalance the diet, especially for young, pregnant or working horses — a well-balanced concentrate, based on vegetable protein meals, vitamins and minerals will correct the imbalances.

Increasing the oil in the diet is another safe and effective way of increasing energy – especially for working and performance horses.

Impaction colics are more common in winter, partly because mature hay and pasture have a lower water content than young pastures, but also because horses drink less if the water is <2°C.

Keep an eye on ‘easy keepers’ who can quickly accumulate body fat as they become adapted to the cold. Energy requirements decrease as they get used to winter weather and in no time they can get too forward in condition, especially as the weather warms into spring, energy demands decrease and pasture growth resumes.

Also keep a special watch on timid horses. Groups of horses typically have a pecking order for feed and space and timid horses can become thin, even if plenty of feed is available, because the dominant horses in the group won't allow them to eat. As long as enough individual feeding space (3 – 15 metres between horses) is available for the horses in the group, timid horses should be able to thrive. Using feedbins, rather than placing feed on the ground can reduce feed wastage by 25% - and always make sure a good quality, well-formulated salt and mineral block is available.

If your winter brings ice and snow, make sure clean fresh water is available - horses have to consume ten times their water requirement in snow conditions to meet their needs, and they need to use energy to raise the temperature of the snow to body temperature. This is a huge energy drain and, when hay is poorly digestible, can lead to gut impaction colic.

Enjoy the cooler weather – and remember every horse is different so keep a watchful eye on body condition and growth – and enjoy watching horses loving the cooler weather.

EQUINE CLINICAL NUTRITION
Dr Jennifer Stewart