August 14, 2017 
Whether you are prepping for sales and halter classes or trying your best to raise a healthy and sound youngster, careful attention to nutritional needs is a key component. Yearlings should not be fed like little adults.
An easy way to see this is to compare their calorie needs on a Mcal/kg of body weight basis and their protein and mineral needs as grams or milligrams/Mcal of diet. Those second numbers show you how nutrient dense the diet needs to be.
Compared to the adult maintenance, the yearling needs 113% more calories, 186% calcium, 134% crude protein, and 134% L-lysine. Although the NRC has not gotten around to recognizing it officially yet, formal research (such as Van Weeren et al. 2003) shows an effect of copper on healing of osteochondrotic lesions, as did Dr. Knight’s original work in 1990. Feeding three times the current NRC minimum requirement is safe and cheap insurance. Other trace minerals are increased proportionately to keep them in balance.
If you have a properly formulated weanling diet in place this will also meet all the needs of the yearling simply by adjusting calories. If the horse starts to get too fat, cut back the diet but add 1/2 to 1 lb. of a 25% protein and balanced mineral supplement to keep up the nutrient density.
The usual advice for feeding weanlings is a 50:50 diet of pasture or high quality hay and a commercial concentrate, by weight of each. The first thing I check is the fat content. In a 1999 study by Hoffman et al., young horses fed as little as 1 to 1.4 kg (2.2 to 3 lbs) of an average 10.4% fat concentrate twice a day, with pasture, had reduced bone mineral density despite mineral intakes that were at least 200% of requirements.
Fats form insoluble complexes with calcium and magnesium. Fiber binding some minerals was also mentioned but is far less likely as a cause since horses raised on pasture get more fiber than this. Added fat in the supplement from the study above amounts to about 10 oz of oil.
Unfortunately, many feeds labeled for use in yearlings have too much fat. This also increases calories and results in just the concentrate providing all calories required, if not more, and a fat youngster. This leaves no room for hay and sets the stage for wide hormonal swings, digestive upset and impaired development of the GI tract and its microbes.
Commercial growth feeds do a good job with minerals but don’t correct imbalance issues in the hay or pasture. Protein provided is 60 to 65 % of minimum requirement with most or all lysine being met, depending on the product. If hay is at least 8.5% protein, it will fill in the additional protein. All of this assumes you feed the full recommended amount, typically as much as 7.5 lbs./day for a 650 lb. yearling. If he backs off the recommended minimum 1% of body weight in hay or gets too heavy (and they will with those high fat feeds) you will have to reduce it—and with that the protein and minerals also go down and will have to be added back in.
An alternative approach is a simple concentrate you mix yourself instead of the commercial feeds, adding a separate concentrated mineral mix and protein as needed. For example, by weight, 1 lb. beet pulp and 2 lbs. high grade oats with 1 oz. of flaxseed per pound of mixture is balanced for calcium and phosphorus, about 12% protein and contains about 65 to 70% of the calories of high fat yearling feeds. Ingredients also meet or exceed the % lysine required in protein for yearlings. Other combinations of high calcium (alfalfa, clover, beet pulp) and high phosphorus (grains, brans, seeds) can be used to get a balanced Ca:P ratio.
For a 650 lb. yearling, combine 7.5 lbs. of good quality grass hay with 7.5 lbs. of oats/beet pulp mixture, 2 cups of ground flaxseed (all daily totals) and 1 lb/day of a high quality 25% protein and balanced concentrated mineral supplement. Look for a blend of milk and vegetable protein, 4.5 to 5% calcium, at least 350 ppm copper and 875 ppm zinc with lower manganese.
If needed, an additional 2 to 4 oz of oil can be added for coat conditioning. Boost protein for low protein hays or pastures using a protein supplement without the added high levels of minerals. When more calories are needed, increase all elements of the diet proportionately (e.g. pound each of concentrate and hay, 1 oz flax, 2 oz protein/mineral supplement).
Attention to detail will get you the well developed, muscular-rather-than-fat, shining and structurally sound young horse you are wanting.
All content is for informational purposes only. Contact your local veterinarian if you have any questions regarding the health of your animals.
About the Author
Dr. Eleanor Kellon is a renowned expert on equine nutrition and related health issues. She offers private nutritional consultations and online courses through Equine Nutritional Solutions. Find out more at www.drkellon.com, and read more of her articles at DrKhorsesense.com.
