A successful mineral feeding program for dairy cows should involve:
1. Determination of animal requirements and feed intake. There are tabulated data to determine requirements, but information on feed ingestion would be best if measured on site and if cows are eating feeds that will actually be supplemented with mineral mix. This is easier to do with TMR (total mixed rations). For grazing cows, there are indirect methods to estimate pasture intake. It is important to remember that dairy cows' requirements change with a number of characteristics, particularly milk production, body weight, and stage of lactation.
2. Determination of feed quality. Forages and grains vary widely in nutrient content according to season, plant maturity, plant species, soil fertility, soil type, and level of fertilization, among other variables. Feed samples that accurately represent the array of feeds available at the operation should be sent to a reputable laboratory for quality analyses. Macrominerals (calcium, phosphorus, potassium, magnesium, and sulfur) and trace minerals (cobalt, copper, iodine, iron, manganese, molybdenum, selenium, and zinc) should be evaluated. For instance, certain soils may contain high levels of potassium, resulting in high content of potassium in forages, thus requiring lower supplementation of potassium in a dairy cow's ration. Wet chemistry should be requested for mineral analyses. Near Infrared Reflectance Spectroscopy (NIRS) analyses are commonly offered by laboratories; however, while they are considered adequate for some major nutrients (dry matter, crude protein, fibers), mineral determination using NIRS remains unreliable.
3. Estimation of supplement needs. Supplementation is required when animal requirements exceed mineral supply from feed ingredients in the ration. In practice, trace minerals contained in forages and grains are not considered and supplemented integrally in the mineral mix.
4. Evaluation of mineral sources that best complete the ration's deficiencies at the particular dairy operation. Keep in mind that mineral bioavailability can vary among different sources. In other words, not all mineral in a given source is completely available for absorption and utilization by the cow. The NRC (2001) suggests that phosphorus from mineral sources has higher bioavailability than phosphorus present in forages. So-called chelated minerals have greater bioavailability but are usually more expensive than inorganic sources. On the other hand, cows may not be able to absorb enough minerals from cheaper sources. Remember that excess mineral supplementation can be toxic and that certain mineral elements can influence the utilization of others in complicated ways. For instance, the upper limits of selenium supplementation are even regulated by law. Because of the complexity of some aspects discussed above, for best results it is recommended to consult an experienced nutritionist to evaluate the mineral feeding program of the cows.

Browse related FAQs by tag: dairy cattle