McKinnon: The math behind animal nutrition lingo

When I visit with producers about their feeding program, I often get questions on “nutrition lingo.” Examples include questions on the meaning of a mineral or protein supplement tag or how much supplement do you need to feed to achieve an ionophore concentration of 22 or 33 ppm? Such confusion is understandable, particularly when you consider that many of us still think in imperial as opposed to metric, which unfortunately is the basis for the feed industry. With this column I will try to translate some of the more difficult concepts.

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First, remember that one pound (lb.) equals .454 kilogram (kg) and that one kg equals 2.205 lbs. As well, one ounce (oz.) = 28 grams and one gram is the same as 1,000 milligrams (mg). These conversions are important when we start to think about nutrient concentrations in different products. For example, on mineral and protein supplement tags you will often see protein or mineral concentrations listed as either a percentage or as milligrams per kilogram (mg/kg).

Take a mineral tag that lists the calcium level at 20 per cent. This means that for every ounce or 28 grams of mineral consumed, the animal will consume 5.6 grams of calcium. If the tag indicates that the expected mineral intake is two ounces or 56 grams per head per day, the animal will get 11.2 grams of calcium from the mineral, which depending on the animal could be 20 per cent or more of its requirement.

Trace mineral concentrations will be listed as mg/kg, a term that is used interchangeably with parts per million (ppm). Copper, for example, could be listed as 3,000 mg/kg on the tag. Using the same example as above, if the animal consumes two ounces of mineral, converting this to metric gives 56 grams, or going one step further and converting to kilograms (gm x 1,000) gives 0.056 kilograms of mineral consumed, daily. Since the mineral contains 3,000 mg/kg of copper, the animal consumes 168 milligrams of copper (i.e. 3,000 x .056), a level that meets most of our animal’s requirements.

The confusion deepens when it comes to vitamins (i.e. vitamins A, D and E). On the vast majority of beef cattle supplements, the concentrations of these products are given in international units (IU). An IU is more a reflection of biological activity than of the weight or mass of the vitamin in question.

If we take vitamin A for example, there are a number of natural and synthetic compounds that have differing degrees of vitamin A activity. For example, retinol and beta carotene are two compounds that have different vitamin A activities. As a result, the weight of retinol that equals one IU of vitamin A activity is different from that of beta carotene. Fortunately, cattle requirements are listed in IU and we only need to ensure we are supplying the appropriate number to meet requirements. For example, growing/finishing cattle require 2,200 IU/kg of dry matter (DM). Assuming an inclusion rate of four per cent, a supplement would need to contain 55,000 IU/kg of vitamin A (55,000 x .04) to meet this requirement.

Ionophores such as monensin sodium or lasalocid sodium are widely used in the feeding, cow-calf and grazing sectors. Their benefits include improvement in feed efficiency and control of coccidiosis, bloat and digestive upsets. As with trace minerals, their concentration in a product is given in terms of mg/kg or ppm. Just about every mineral or supplement tag I have seen from a wide variety of companies will have a different ionophore concentration on it. This is because each tag has been formulated for a specific ionophore intake. This is necessary because an ionophore such as monensin sodium is fed at different concentrations depending on the benefit expected. For example, for coccidiosis control it is fed at 22 mg/kg of the total diet (DM basis) and for feed efficiency it can be fed at 33 mg/kg, while lasalocid would be fed at 36 mg/kg. Further, many feedlots on high grain diets will feed up to 48 mg/kg of monensin sodium.

Thus it is not surprising that tags vary so much in their ionophore concentration and that producers are confused when sorting through them. In order to understand what level of an ionophore you need in your supplement, it is necessary to do a similar calculation as we did with trace minerals. If the ionophore is listed at 400 mg/kg of supplement and you are feeding three quarters of a pound (.34 kg) a day of the supplement, you are feeding (400 x .34) 136 mg of the ionophore. If the animal is consuming 13 pounds or six kilograms of DM, the diet concentration is 22 mg/kg of diet (i.e. 136/6), a level suitable for coccidiosis control but not feed efficiency. To target improved feed efficiency (33 mg/kg), the supplement would need to contain 582 mg of the ionophore. Also remember that as the animal gets bigger and its intake increases, the amount of supplement in the diet needs to increase proportionately to maintain these concentrations.

As you can see, making your way through these various calculations can be confusing, even for those with experience. Working with your feed company and/or nutritionist can help avoid costly mistakes.

About the author

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John McKinnon is a beef cattle nutritionist at the University of Saskatchewan.

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