Feeding on different types of forages offers more variety, which should be plentiful in the natural diet of a horse but may be deficient in many of the diets we create.
It is crucial to understand the advantages and disadvantages of the hays you are using in relation to the particular horse you are feeding. Yearlings are still growing, and this enhances the demand for certain nutrients, especially protein, phosphorous and calcium.
In spite of the fact that they have attained around only 60% of their final adult weight, the daily calorie requirements of yearlings are higher than if they had attained their adult weights and they were not doing any work.
According to the Nutrient Requirements of Horses (2007 edition) manual by the National Research Council (NRC), a normal adult horse weighing 1,100 pounds (500 kilograms) needs 16.7 megacalories (Mcal) of digestible energy (DE) every day when it isn’t working.
This goes up to 20 megacalories of DE per day when doing light work. The same horse, when 12 months old, approximately weighs 706 pounds (321 kilograms) and requires 18.8 megacalories of digestible energy daily. It is not difficult to meet these energy needs if you feed the horse good-quality hay or you can access high-quality pasture.
The calorie content of forage diminishes with maturity. This means that hay that has been cut late will normally provide fewer calories per pound than hay that has been cut earlier, and this can affect the ability to fulfill requirements. Whereas this may be beneficial to easy-keeper mature horses, less stemmy and less mature hay is preferred for growing yearlings. If you are in a position to do hay analysis, get high-quality hay which has an acid detergent fiber (ADF) content of below 32% when measured on the basis of dry matter. ADF is the quantity of the least digestible fibrous part of plants.
With an increase in the ADF content and maturity, the protein content reduces, and it may also become less available if it is trapped inside portions of indigestible carbohydrates. This can be more of an issue for a yearling than decreased calorie intake. Once again taking the above example, the yearling would require 36.4 grams of lysine (which is an essential amino acid) and 846 grams of raw protein. This is comparable to the requirements of a 500-kilogram adult horse that is involved in heavy work.
Grain hays like three-way wheat, oat, and rye are likely to have a lower content of crude protein (between 8% and 10%) than grass hays (from about 10 to 14%) and alfalfa (about 24 %).
This might make it difficult for a yearling to fulfill its amino acid and protein needs if it is only feeding on grain hay. Even when consuming 2.5% of its body weight in 8% raw protein grain hay, a yearling that weighs 321 kilograms will be eating 642 grams of protein, in spite of the fact that it needs 846 grams.
To fulfill raw protein needs from consuming 2.5% weight per day, the raw protein content of the hay would need to be over 12%. Some yearlings will comfortably consume more hay than this, meaning a lower percentage raw protein hay might be used. However, the safer option is to select forage that has a greater protein content particularly because some yearlings will not consume that much hay.
Alfalfa, which has a high content of crude protein, becomes an appealing option in this case. But in some parts of the country like California, alfalfa hay has a very high content of calcium, sometimes even six times higher than phosphorous content. Preferably, calcium content should be 1.5 to 2 times higher than phosphorous content in the total ration. Adult horses are better equipped to cope with high ratios than growing horses. As such, feeding straight alfalfa is not the best option, even if it would obviously solve the protein problem.
Ratios of Calcium and Phosphorus
Grain hays are not only normally lower in protein, but they may have inverted calcium/phosphorous ratios. This means the amount of phosphorous contained in them is at times greater than the calcium content. If they comprised the entire ration, this would be more harmful to bone health than excessive levels of calcium. A diet composed of straight grass hay may not resolve this problem either.
In the event that grass is not an option, it’s suggested that the forage part of the diet be made up mainly of top-quality grass hay combined with a bit of alfalfa. You can keep the alfalfa component at between 25 and 30 percent of the total forage intake so as not to overdo on the calcium but have some that rectifies any inverted calcium/phosphorus ratio in the grass hay and also ensure sufficient crude protein. If you wish, you could substitute some grass hay with grain hay.
The bottom line
Provided that your yearling retains good body weight and maintains growth on a forage-only diet, the only thing that may be added is supplemental vitamins and minerals to make sure the diet is balanced. I especially like the ratio-balancing high-protein feeds marketed by most of the main feed companies since these ensure high-quality protein together with the important micronutrients.
But if body condition and growth are not being sustained using this approach, you will need to provide a commercial, higher-calorie feed that is created for growing horses.
Discuss with your equine nutritionist and veterinarian in case you have concerns regarding the growth of your yearling since it is important that consistent growth is maintained to reduce the likelihood of developmental orthopedic diseases.
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