Winter Diets - what's on the menu?
Winter changes in vitamin and mineral requirements.
by Shannon E Pratt
Changes of season generally call for changes to your horse’s activity level and diet. It is important to consider how nutrient requirements, in this case specifically vitamins and minerals, are affected by the coming season. For the average horse, vitamin or mineral requirements do not change very much during the winter months. Requirements, however, may change if you horse’s activities do change at this time of year.
The biggest change, with respect to vitamins and minerals,
will be due to changes in feed quality in the winter. Factors such as going
from a pasture diet to a mostly hay diet need some thought to rebalancing the
diet, due to the differences in nutrient composition in these feeds.
Furthermore, storage of hay (and some concentrates) over several months can result in vitamin losses
in the feeds due to their lower long-term stability.
Mineral changes
The mineral requirements of the horse includes macro minerals
(these include; calcium, phosphorus, sodium, chloride, potassium, magnesium and
sulphur) and micro minerals (selenium, iodine,
copper, zinc, manganese, iron and cobalt). For the most part, a horse’s
requirements for these minerals will not change. There is also very little loss
of these components in feeds with storage.
However, mineral composition in pasture and hay can vary significantly. If a horse has been kept on mostly pasture forage and is going to be dependent on baled hay over the winter, the overall diet will need to be re-evaluated.
Pasture tends to be a little higher with respect to some minerals. For example, on a dry-matter basis, alfalfa pasture averages 1.71 per cent calcium while alfalfa hay averages 1.19 per cent (NRC, 1989). It would be prudent to have your hay and pasture analyzed every season to account for these variations.
Many horse owners give their horses
bran mash in the winter months to “warm them up”. Bran is extremely high in
phosphorus and is low in calcium (it has an inverted Ca:P ratio) resulting in an imbalanced diet if fed too
often. Horses that have been undergoing heavy work during the competitive
season will have lower requirements for electrolytes (sodium, chloride and
potassium, lost in sweat) and calcium and phosphorus (less bone remodelling caused by exercise) due to reduced training.
Also, pregnant mares that will be entering their third trimester at this time
will have increased mineral requirements (especially calcium, phosphorus, zinc
and copper).
Vitamin changes
Vitamins are classified as water soluble (vitamin B complex and vitamin C) and fat-soluble (vitamins A, D, E and K). Horses can synthesize their own vitamin C (unlike humans) so they don’t have a specific requirement for this vitamin. In addition, the B complex vitamins, for example, niacin, riboflavin etc. and vitamin K are produced by the microbes in the large intestine in the horse in sufficient quantities, such that deficiencies in these vitamins are extremely rare. Vitamin D can be produced in sufficient quantities through the actions of ultraviolet rays on the skin.
The most notable change in vitamin requirements during the winter is Vitamin D. Because its synthesis within the body requires exposure to sunlight, horses must be exposed to sufficient amounts of daylight. In the winter, with fewer hours of sun, shorter hours of turn-out, blankets being worn and increased clouds, there might be reduced ultraviolet rays exposed to the skin. This would lead to an increase in the dietary requirement of vitamin D. Hays that have been sun-cured are a good source of vitamin D, however, as will be mentioned shortly, may have reduced amounts following storage due to instability of this vitamin. Fortunately, most commercially available concentrate products have been fortified with vitamin D.
The stability of vitamins in feeds can be reduced over time. It can be affected by storage conditions and exposure to air and sunlight. The fat-soluble vitamins A, D and K as well as the water soluble vitamin thiamin tend to have the greatest losses. Therefore, feeds stored for long periods of time may have reduced concentrations of these vitamins. Of these mentioned, vitamin A is of the biggest concern, however, because the others have the ability to be produced within the body. Once again, commercially available concentrate products are fortified with vitamin A.
Pasture tends to have higher levels of A and E compared to hay products. Therefore, depending solely on hay during the winter will require increased supplementation of some of these vitamins.
The activity of the horse will also affect vitamin requirements. Pregnant mares may benefit from additional vitamin A, D and E in their diets during their last trimester.
Horses that have the winter off heavy work will also have
lower vitamin requirements, however, because their feed intake is usually
reduced, this will generally compensate for this.
Summary
Overall, vitamin and mineral requirements do not change drastically, however, the quality of these nutrients in
available feeds may be reduced. It is, therefore, important to assess feed
quality and rebalance your horse’s diet as required. Work with your
nutritionist or feed dealer to ensure your horse is meeting its nutrient
requirements in the winter months.
References:
National Research Council. Nutrient Requirements of Horses. 1989.
Lewis. L. D. Equine Clinical Nutrition. 1995. Williams and Wilkins.