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Interpreting hay analysis results

Trace Minerals - Iron, Zinc, Copper, etc.

Trace minerals are so-named because, while they are essential dietary components, they are required in only small ('trace') amounts.

The following figures are assuming that hay is the primary source of nutrition for the theoretical 1,000-lb adult horse, and that the hay is being fed at a rate of approximately 2% of the horse's ideal body weight per day (approximately 20 lbs of hay per day).

Iron

The recommended daily intake of iron for maintenance in a 1,000-lb horse is 360 milligrams (mg). To at least meet this requirement, the hay would need to have an iron content of at least 40 ppm (parts per million) as sampled, or at least 18 mg/lb of hay if you prefer those units.

I seldom see good quality grass hay that is deficient in iron. Much more common is an excess of iron, which can interfere with the absorption of other minerals. I start to worry about interference when the iron content is at least 5 times higher than needed (i.e., above 200 ppm). If the hay is otherwise suitable, I simply make sure that the horse is receiving a bit more copper and zinc than needed.

Zinc

The recommended daily intake of zinc for maintenance in a 1,000-lb horse is 360 milligrams. To at least meet this requirement, the hay would need to have a zinc content of at least 40 ppm (as sampled), or at least 18 mg/lb of hay if you prefer.

The hay we're examining has a zinc content of 26 ppm, or 12 mg/lb of hay (as sampled), so if this hay is the horse's primary source of nutrition, then a trace mineral supplement that makes up the shortfall in zinc intake (a deficit of 120 mg) would be needed.

How did I get 120 mg? The recommended daily intake of zinc for maintenance in a 1,000-lb horse is 360 mg. This hay contains 12 mg/lb of zinc (as sampled), so 20 lbs of this hay would supply only 240 mg of zinc (12 x 20 = 240), leaving a shortfall of 120 mg per day (360 - 240 = 120).

Copper

The recommended daily intake of copper for maintenance in a 1,000-lb horse is 90 milligrams. To at least meet this requirement, the hay would need to have a copper content of at least 10 ppm (as sampled), or at least 4.5 mg/lb of hay if you prefer.

The hay we're examining has a copper content of 7 ppm, or 3.2 mg/lb of hay (as sampled), so if this hay is the horse's primary source of nutrition, then a trace mineral supplement that makes up the shortfall in copper intake (a deficit of 26.4 mg) would be needed.

Zinc-Copper Ratio (Zn:Cu)

As with calcium and phosphorus, the ratio of zinc to copper is also important. The chemical symbol for zinc is Zn and the symbol for copper is Cu, so the ratio is abbreviated Zn:Cu.

The ideal Zn:Cu is 4:1, or simply 4. There should be about 4 times as much zinc as copper in the total diet. We're assuming in this exercise that the timothy hay we're examining is the horse's primary source of nutrition. Its Zn:Cu (zinc ÷ copper) is 3.7:1 (26 ÷ 7 = 3.7). That's close enough to 4 for maintenance in an adult horse, but as zinc and copper are each a bit low in this hay, I would want this horse to be on a good trace mineral supplement.

Incidentally, it is not uncommon for grass hays to be marginal or frankly deficient in zinc and copper. According to the Equi-Analytical database, the zinc content of grass hays across the US ranges from 0 ppm to 1,070 ppm (as sampled), and the average is only 29 ppm. Similarly, the copper content of grass hays ranges from 0 ppm to 16 ppm (as sampled), and the average is only 8 ppm.

HayResults08

Manganese

The recommended daily intake of manganese for maintenance in a 1,000-lb horse is 360 milligrams. To at least meet this requirement, the hay would need to have a manganese content of at least 40 ppm (as sampled), or at least 18 mg/lb of hay if you prefer.

The hay we're examining has a manganese content of 52 ppm, or 24 mg/lb of hay (as sampled), so if this hay is the horse's primary source of nutrition, then the horse will be receiving adequate manganese.

Molybdenum

There is no recommended daily intake for molybdenum in horses. However, it is included in this analysis because very high concentrations (above 20 ppm) could interfere with the absorption of other minerals.

What about selenium?

Selenium is not included in this report because it's a test that must be ordered separately. In certain parts of the US, notably the Pacific northwest, the selenium content of forages is very often low, necessitating supplementation. However, in other parts of the US, the selenium content of forages can actually be too high. When in doubt, test your forages for selenium.

As a point of reference, the recommended daily intake of selenium for maintenance in a 1,000-lb horse is 0.9 mg. Let's round that up to 1 mg/day, from all dietary sources. Don't be too heavy-handed with selenium supplementation in horses; enough really is enough.

What about iodine?

As a point of reference, the recommended daily intake of iodine for maintenance in a 1,000-lb horse is 3.2 mg, from all dietary sources. As with selenium, don't be too heavy-handed with iodine supplementation.

% Moisture and % Dry Matter

Digestible Energy (DE)

Crude Protein and Estimated Lysine

Fiber - Lignin, ADF, and NDF

Carbohydrates - WSC, ESC, Starch, and NFC

Major minerals - Calcium, Phosphorus, Magnesium, etc.

Trace minerals - Iron, Zinc, Copper, etc.

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