Meeting Mineral Requirements at Pasture
One of the initiatives I am working on as a nutritional technique is an educational campaign regarding the proper use of trace-mineralized salt (TM Salt) and complete mineral premixes on pasture. I think we all agree that complete minerals are expensive, as are their constituent ingredients; of greater interest is the increasing amount of data showing cattle do not need much of what is in it, especially on pasture. For a starting point, let us accept all cattle in Ontario need some supplementation as this Province's soils are selenium (Se) deficient. We need a selenium source, so 'no supplement' is not an option! Next, fresh grass is far higher in vitamins A and E than any reasonable premix, and vitamin D is synthesized under exposure to the sun, so not one of these is needed in a pasture premix. Considering the cost of vitamin E over the last year, if nothing else, a summer pasture program should lose this ingredient as the #1, no-consequence cost-saving measure! Dr. Kendall Swanson, a beef researcher at the University of Guelph comments that "typical average to good quality pastures in Ontario may not need supplementation of most minerals and vitamins, but there likely are some quite low quality pastures that do." How do you know where your pastures fit in? Read on.
Table 1. Macro and micro-mineral recommendations for
cow herds and backgrounded cattle assuming highest level of requirement
within that class, as adapted from Nutrient Requirements of Beef Cattle,
7th Revised Edition, 1996.
* - in total ration or as reported on forage test assuming 100% pasture
intake. Ppm or mg/kg are the same unit of measure, both measuring number
of units per million units.
The key to determining what level your animals need to be supplemented at is a forage test. Table 1 illustrates the levels of various minerals I would recommend in cow and backgrounder forages (fresh perennial forages). The upper section are standard minerals reported on, the next two are optional, and then trace minerals which cannot easily be tested for, so should be assumed as deficient. These values are based on requirements for critical stages such as late pregnancy/lactation for replacement heifers, and then extrapolated to cows. It is a 'worst case scenario' for the cow herd for each of the mineral parameters, as those heifer requirements are higher than for cows at any stage of production. Similarly, the same has been done for a grass steer gaining just over 2lbs per day.
A farm should build an inventory of forage tests over time to account for seasonal and weather variations on mineral uptake by the pasture. If, over time, the forage test is above the levels in Table 1, then no further action is needed on that nutrient. The rightmost column is what ingredient typically might be used to elevate that parameter (ie used in a customer formulation). In doing this many people farming on high fertility soils will realize there is no need to routinely supplement calcium, phosphorus, potassium, and perhaps other minerals. High phosphorus (P) minerals (1:1 and even 2:1 Ca:P ratio) are typically overkill for P levels, because of the high manure or fertilizer levels in parts of the province that have been farmed for several decades. The only way to be sure is a forage test for minerals. So, this is where the use of trace mineralized (TM) salt may become economical. All cattle in Ontario need Se, and if that can be done with a TM salt, then perhaps that is all a herd on a given farm needs. Some of you on very low P soils may need a source of that macro-mineral, which is absent in TM salt.
Getting Minerals into Cattle
The only way to determine if the mineral premix intake is according to specifications is to read the label of the product as to what intake should be attained per head per day on any product! That said, 100 to 150 g per head per day is pretty typical, and in turn, a 25 kg bag of mineral premix should last 167 to 250 cow-days per bag. This calculation must also be done for TM salt. Since Se deficiency is a big deal in Ontario, and if you are considering a TM salt product, look for TM salt that is 120 mg/kg selenium or formulated for higher intake. There are a few add-ons you may consider with TM salt such as adding a coccidiostat for cocci control in calves, or a TM salt plus mineral ingredients the farm is low on. For example a TM salt + magnesium oxide ('mag-ox') for pasture forages low in magnesium may be practical.
Bottom Line on Minerals at Pasture
The only way to really tell what you need is a forage test, and to accept Ontario is selenium (Se) deficient. Once you have done these two things you can figure out whether you really need a complete premix or a trace-mineralize (TM) salt to meet the mineral needs of your cattle at pasture. And remember, at pasture all of the vitamins A, D, and E cattle could ever need are there for free. Get it while you can!
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