This month we will return to discussions of nutrient requirement for horses. Remember we discussed energy needs for horses in the earlier articles: Equine Energy Requirements, Energy for Work, and Broodmares and Babies. Now we will look more closely at other nutrient requirements, beginning with mineral requirements. Minerals are involved in a variety of functions in the body, including enzymes, structural components, energy transfer and acid base balance. Minerals are also incorporated into vitamins, amino acids, and hormones. Thus proper mineral nutrition is vital to have a healthy horse. The minerals that are needed in the largest quantities by horses are referred to as the macro-minerals. These include calcium (Ca), phosphorous (P), magnesium (Mg), potassium (K), sodium (Na) and chloride (Cl). These minerals are needed in the diet in concentrations of g/kg or percentages, versus ppm or mg/kg of micro-minerals. Today we start with those most commonly talked about in equine nutrition, Ca and P.

Previously in Broodmares and Babies we had mentioned that the ratio of Ca and P is always important when looking at horse rations. If you recall, we would like to see a ratio of 2:1 Ca:P, with a range of 1:1 to 6:1 being acceptable. What you should avoid is a total diet which is less than 1:1 or in other words, offers more P than Ca. This is due to the fact that phosphorous competes with Ca for absorption in the gut. Remember to calculate the entire diet however! And while the proper ratio is important, it is possible to have the correct ratio, but still be deficient in these minerals if they are in insufficient quantities in the feed. Now let’s talk in more detail about these very important minerals.

Table 1. Calcium requirements (in grams/day) for adult horses at maintenance or work. To determine which class your horse fits into, read Energy for Work.

Table 3. Approximate Ca requirements (g/d) for growing foals based on their estimated mature weight.

Gastrin – a peptide hormone secreted by the parietal cells of the stomach which stimulates secretion of gastric acids (HCL) and increases gastric motility. Gastrin release is stimulated by the presence of protein in the stomach, as well as conditions of hypercalcemia.

Last month we took a more in depth look at the calcium requirements for horses. This month we will look at phosphorous needs in the horse, and then put it all together in formulating some diets for horses.

Table 4. Phosphorous requirements (in grams/day) for adult horses at maintenance or work. To determine which class your horse fits into, read ENERGY REQUIREMENTS FOR THE WORKING CLASS HORSE.

Table 6. Approximate P requirements (g/d) for growing foals based on their estimated mature weight.

Table 7. Common concentrates fed to horses. All % are on a dry matter basis.

Table 8. Common forages fed to horses. All hays are assumed to be harvested at the midbloom stage. Remember that soil type as well as stage of maturity can alter your hays nutritional content.

Now, let’s put some of these numbers together. For simplicities sake, we will work with a generic 1100 lb horse, and then compare the numbers we get with the table values for different classes of horses. For our first example, we will feed this horse two different diets, one solely Bermuda Coastal grass hay, and one of alfalfa. We will feed him at 2% of his body weight per day. All values above are in dry matter, so we won’t have to convert those values.

First, we determine how much the horse will eat.
1. 1100 lbs x .02 = 22 lbs
Now remember all of our Ca and P requirements are in grams, so lets’ convert lbs to kg.
2. 22 lb x 1 kg/2.24 lbs= 9.82 kg of hay
So we know our horse will eat 9.82 kg of our hay per day.

For the grass hay, we will multiply the amount fed by the percentages of Ca and P in that hay.
1. 9.82 kg x 0.0019 =0.0187 kg of Ca
For that to make sense, convert kg into grams.
2. 0.0187 * 1000 = 18.7 g Ca
Now for P.
3. 9.82 kg x 0.0027 x 1000 g/kg = 26.5 g P
Finally, calculate your Ca to P ratio.
4. 18.7/26.5 = 0.71 to 1

So, what does this tell us? First of all, we probably need to have a mineral supplement for our horses to avoid the inverted Ca to P ratio. Alternatively, we could add some legume hay to its diet. When we look at simply meeting the requirements of our 1100 lb horse, we can see we are deficient in Ca if it is a working horse and certainly very low if that was all we fed to a gestating or lactating mare.

Now, what if we fed alfalfa hay instead? Use the same calculations, but insert the new % of Ca and P for alfalfa.
1. 9.82 kg x 0.0127 x 1000 g/kg =124 g Ca
Now for P.
2. 9.82 kg x 0.0024 x 1000 g/kg = 23 g P
Finally, calculate your Ca to P ratio.
124/23 = 5.4:1

Now we can see that our Ca to P ratio is more desirable. Looking at the horses’ requirements, we can see we have more than met the Ca requirement for all classes of mature horses, and are adequate for P for all working horses except those in heavy work. For mares, we are good until the last part of gestation and through lactation. That shouldn’t surprise you, as broodmares should be fed a better quality diet than our other horses.

Lastly, let’s see what happens if we decide to add 6 lbs of oats to this 1100 lb horse’s diet. Note: I am doing this solely for the purpose of calculations. There should always be some rationalization for why we add concentrate to our horse’s diet. For my mythical generic horse in this example, we don’t even know what class it is in or what its body condition score is.

For this example, we will change hays and feed red clover and orchard grass hays.
Let’s begin with the red clover.
1. 9.82 kg x 0.0138 x 1000 g/kg =135 g Ca
Now for P.
2. 9.82 kg x 0.0024 x 1000 g/kg = 23 g P
We will now calculate the contribution from our oats.
3. 6 lbs x 1 kg/2.24 lbs = 2.7 kg oats
4. 2.7 kg x 0.0011 Ca x 1000 g/kg = 3 g Ca
5. 2.7 kg x 0.0040 P x 1000 g/kg = 11 g P
Add the two values together for hay and oats
6. 135 g Ca from hay + 3 g Ca from oats = 138 g Ca
7. 23 g P from hay + 11 g P = 34 g P
Calculate your ratio
8. 138/34 =4.1:1

Looks good!!!

Now again, compare across our class of horses. Calcium is adequate for all classes, and our P requirements are met for all horses except the lactating mares.

Lastly, we will try adding oats to our orchard grass hay. 1. 9.82 kg x 0.0027 x 1000 g/kg =26.5 g Ca
Now for P.
2. 9.82 kg x 0.0034 x 1000 g/kg = 33.4 g P
Our oat values will remain the same as above.
Add the two values together for hay and oats
3. 27 g Ca from hay + 3 g Ca from oats = 30 g Ca
4. 33 g P from hay + 11 g P = 44 g P
Calculate your ratio
30/44 =0.68:1

Doesn’t look like something we should do!!!

To wrap up, remember that these diets were a simple exercise in calculating the contribution of calcium and phosphorous from different feed sources. These are not recommendations for actual diets, as we made no attempt to adjust amount fed, supplements added, or appropriate concentrates selected. Next month we will add in a more sophisticated approach to balancing diets inconsideration of type of horse, energy requirements, and growing horses. Until then, have fun practicing with your calculators!

Selenium is an often talked about micro mineral which has much confusion over its requirements. Certainly those in the nutrition field don’t make it any easier by listing the requirements in concentrations in the diet, where all other minerals are simply listed as the amount the animal should consume per day.

Selenium is an essential mineral that is integral to the enzyme glutathione peroxidase (GSH-PX). GSH Px is a powerful anti-oxidant which helps protect cell membranes, proteins and even DNA from reactive oxygen species such as peroxides, free radicals etc. The enzyme GSH-PX acts by donating an electron and thus reducing these reactive compounds. Less commonly known, Se also serves a role in thyroid metabolism. Selenium is a part of the enzyme thyroid hormone deiodenase, which serves to convert thyroxine (T4) to its more biologically active form, triiodothyronine (T3). Thus Se deficiency can play a secondary role in hypothyroidism.

Selenium is also a confusing mineral because it is more or less of a problem depending on the area of the country you live in. Areas of the country which typically have higher Se concentration in the soil include South Dakota, Montana, Wyoming, Nebraska, Kansas, Utah, Colorado, and New Mexico, while the Great Lakes region, the Northwest and the Southeast are considered Se deficient. The more alkaline or basic the soil, the higher the concentration of Se in the plants that grow there. Dry conditions will also encourage the plant to uptake more selenium, which further increases the Se concentration. High selenium concentrations in the soil can be detected by the abundance of indicator plants, which include locoweed, milk vetch, woody aster and false goldenweed. During drought conditions horses will also be more likely to consume plants they may not eat normally. Therefore it is important to closely monitor pastures for horses during dry conditions.

When we look at complete feeds for horses they typically contain between 0.3 – 0.5 mg/kg or ppm. A quick scan across commercially available equine feeds reveals a typical concentration of 0.3 mg/kg with some feeds slightly higher. In comparison, the Feed Additive Directive in the European Community allows Se to appear maximally in a concentration of 0.5 mg/kg. So how much Se would a normal horse on a complete feed consume? Let’s use a 500 kg horse for simplicities sake (that would be 1100 lbs). Typically we would assume the horse can eat 2% of its body weight per day. At an intake of 10 kg per day of a feed which contains 0.3 mg/kg, the horse would consume 3 mg of Se per day. So clearly horses can tolerate this rate of consumption quite well.

Signs of deficiency of Se in the horse general include disorders of the muscle or myopathies. This can include muscle weakness, gait abnormalities, respiratory distress and cardiac impairment. Foals born with a Se deficiency may have difficulty in nursing. Traditionally Se and/or Vit E deficiency disease is termed as white muscle disease. Numerically, serum Se less than 60 ng/ml or a GSH-Px concentration of less than 25 EU/dl can indicate a Se deficiency. However, these numbers are not indicative of a deficiency unless other clinical symptoms are present. Clearly much still remains to learn of Se metabolism.

Now let’s look at some feeds and determine their contribution of Se to the diet.

A loose mineral supplement that contains 35 ppm of Se and is fed at 2 oz. per day compared.
Or one which contains 15 ppm at 2 -3 oz per day.

First, we need to know that 1 oz is equivalent to 28. 3 grams. If we feed our horse 2 oz. per day, that would be equal to 56.6 grams of supplement. If Se is listed in ppm or mg/kg, we simply convert units. There are 1000 grams in a kilogram, so our horse is eating 56.6 g/1000 g/kg or 0.0566 kg of supplement. Now multiply that by our Se concentration. In our first supplement, 35 mg/kg * 0.0566 = 1.9 mg of Se. That is right in the middle between the Se requirements for the horse and the higher level of intake that has been shown to have beneficial effects. The supplement which contains 15 ppm would provide between .8 and 1.3 mg of Se depending on if you fed 2 or 3 oz of the feed.

So until next time, don’t panic about Se, now you know how to feed it correctly!

Last month we discussed the function of electrolytes and some special disorders of horses related to these minerals. This month we will look at how much of these minerals your feed usually supplies, and determine how much electrolytes you may need to try and supplement to your horse.

Table 1. Average values on a percent basis for sodium, potassium and chloride for four general types of hays.

Table 2. Sodium, chloride and potassium requirements for different exercise classes of a 500 kg horse in grams/d.

Comparing this to the maintenance horses requirements listed in table 2, tells us that the horse really needs to only get extra sodium. In fact, only the heavily exercising horses will probably need additional chloride supplied to them. Again, this is heavily dependent on the temperature in which the horse is working.

Since we know that typically feeds alone won’t meet our horse’s needs, (or we may not really know what they are supplying), the easiest way to meet the horse’s needs is to supply a salt block. Researchers have shown that on average horses willingly consume about 50 g from a salt block per day. However, the variability in intake is high. Individual horses may range between 9- 143 g of salt per day! Therefore, some horses will eat too much, while others not enough. Even the same horse may alter his intake of salt quite a bit from day to day. If you really like projects, and have a sensitive scale at home, you could determine your horse’s average salt intake per day (if he is kept alone with his block) by weighing it every day. Also, some horses just won’t eat their block. If your salt block shows no evidence of licking and is covered with dust, you have a non-licker. Alternatively, you could try to provide loose salt, which some horses prefer or specifically feed salt to your horse. So how much salt should you provide your horse per day, especially if he is a non-salt block licker? For your maintenance horse, that would be about 1 oz. which is 28 grams. If you prefer to use your teaspoons to measure instead, one teaspoon contains 6 g of salt. So your horse would need 4 teaspoons of salt per day.

A horse in heavy work requires about twice the maintenance amount, or about 50 grams of salt per day. However, for those intensely working in hot climates, some researchers have indicated their need for electrolytes may increase 9 fold. Now remember, these are probably the race horses, three day eventers etc. Obviously for the exercising horse in hot climates, they may not be able or willing to consume that much via their salt block, which is why it is important to look consider supplementing your horse. Now remember, these horses would probably be consuming more grain than our example horse above, due to the increased energy demands placed on them. Therefore, you may presume that they are taking in much more salt in the diet. If you are supplementing your horse with table salt, you would increase that amount from maintenance to 2 oz or 8 teaspoons (2 2/3 tablespoons), with an increase to 3 oz or 12 teaspoons (4 T.) in hot climates. There are also many commercially available electrolytes as well which can be added to water or provided in a paste form.

This month we will discuss two important trace minerals, copper (Cu) and zinc (Zn). We will discuss them together, as they are most commonly discussed in relation to developmental orthopedic diseases in young horses. First of all, copper and zinc are classified as trace minerals because they are required in far less quantities compared to Ca, P, Na, Cl etc. While the minerals we previously discussed were described in terms of percentages of the diet, or in grams, trace minerals are only required in mg per day. Typically their requirements are listed in ppm (or mg/kg) of the total diet. It is then assumed that a horse would be consuming a standard 2% of their body weight per day. Thus if a requirement is listed as 15 ppm, then a 500kg horse should consume 150 mg per day. Now let’s discuss what these particular trace minerals do for your horse.

Figure 1. Collagen is made up of several types of proteins. These proteins are wrapped around each other in a helical structure. The crosslinks between separate collagen molecules help to provide the stability in equine tissues such as cartilage, tendons etc.

Figure 2. Alterations in the normal process of ossification can result in cartilage defects.

Figure 3. The cartilage defect in the hock joint is circled in red.

Next month we will discuss Mg and Fe.

This month we continue on our path of discussing minerals required by horses. We will actually be mixing a macro-mineral (magnesium) and trace mineral (iron) together. However, our goal has been to visit minerals in the order of their level of concern by the horse owner and their frequency of need for supplementation.

Remember, the temptation of most horse owner’s is to over supplement their horses. However, this is often unwarranted, contributes to the expense of managing the horse, and may provide no benefits to the animal. Certainly overzealous supplementation may actually be harmful to the horse.