Hoof growth isn’t the only thing that slows down in cold weather. The growth of young horses can too [Onoda et al 2013, 2014].
Several studies have now documented a slowing down of growth rate in the winter with a compensatory surging catch up phase the following spring. Winter weather is a physiological stress, and apparently one severe enough to make the body stop allocating nutrients to growth and conserve them for survival.
Winter growth restriction doesn’t permanently stunt the horse’s development but there is concern about the effects of the rebound growth the following spring. This is because a variety of types of developmental orthopedic disease in young horses have been linked to rapid growth.
The young stock studied have been horses being raised on pasture at locations all around the world. They are not feral horses so not being subjected to extremes of near starvation. Researchers feel the root cause of the arrest of growth in winter is loss of pasture. What nutrients are they missing in this scenario?
When a horse goes from fresh grass to hay, digestibility goes down. This can be counterbalanced simply by feeding more so what else is changing? Interestingly enough, a major alteration is in the fat level.
The natural equine diet is low in fat, but winter conditions cut that low level drastically, by at least half. For every 5 kg (11 lbs) of hay the young horse eats they are consuming 100 grams less fat than from an equivalent amount of fresh pasture. This is analogous to 3.5 ounces of pure oil, or 10 to 12 ounces of a full fat seed meal like flax.
Fat is the most dense source of calories, and also the easiest to digest. When replacing this lost fat, at least 50% of the fatty acid make up should be the essential omega-3. You can additionally use highly palatable oils like coconut and high oleic acid forms of sunflower oil which will not disrupt the essential fatty acid balance.
Protein also drops precipitously, and amino acid deficiencies make it impossible for the body to efficiently utilize the dietary protein. If unsure of the protein level in the diet it is wise to provide approximately 100 grams/day of supplemental protein. All growing horses should get at least 10 g of supplemental L-lysine and 3 to 4 g of methionine for essential amino acid coverage.
Vitamins and minerals are the last base to cover. All vitamin levels are lower in preserved forages compared to fresh pasture. There are particularly high losses of vitamins E, C, and A. B vitamin activity can also decline with time which may be an issue for young horses with an immature microbiome which is a major source of B vitamins for adults. Mineral levels are very low in old pasture. Good quality hay will have a better mineral supply but both pasture and hay often need balancing and supplementation, especially for young horses.
A good solution for protein, vitamins and minerals is a 25% protein supplement geared toward growth with a widely compatible mineral balance and full spectrum vitamins. Feed at one pound per day to safely insure against deficiencies. Pair this with fat replacement to help compensate for the seasonal nutritional challenges which may impact the growth of young horses.
Eleanor Kellon, VMD