HOW important is it to balance a ration for the actual intake for the group being fed? Dairy producers constantly pose this question to their nutritionists. The conversation may go something like this: “My high-producing cows are eating 65 pounds, and our high ration is only balanced for 60 pounds. Is this a problem?” Alternatively, during a heat-stress period, the question may come across as more concerning: Our high groups are down to 55 pounds and that is only 90% of the ration. Should I be worried?” The ultimate question is, “Should we reformulate to get intakes closer to 100%?”
It usually boils down to two main, and valid, concerns for the producer. First is the potential of wasting feed cost. Are we feeding too much of the expensive stuff? Second, and most common during periods of heat stress, is wondering if we need to concentrate the ration to get the nutrients supplied at reduced intakes.
Put ratio back in ration
Let’s first remember that since these diets are called rations, the word “ratio” is implicit in this topic. Most nutrients targeted for certain supply goals are expressed as ratios; numerator and denominator. For feeding cows, the numerator is usually pounds or grams of the nutrient, such as pounds of fiber, grams (g) of calcium, milligrams (mg) of copper, or international units (IU) of vitamins. Where the entire conversation gets tricky is deciding on the right denominator. In most cases, many of the nutrients in the vitamin, mineral, and trace mineral space are supplied to the cow in a blended product and are thus set in a fixed ratio to each other. Therein lies much of the confusion and complication when it comes to the amount that should be fed.
What denominators are most common when we are feeding dairy cows? The most common two are amounts of intake and one day. An example would be grams of calcium in a certain dry matter intake (DMI) creating a nutrient that is percent calcium. Using one day as a denominator is not uncommon, but has less relevance as a mature Holstein at 1,600 pounds of body weight (BW) or a Jersey cow at 950 pounds do not need the same amount of anything.
Since pounds of intake is mostly linear with pounds of BW, we can serve the big and small cow effectively using pounds of DMI as a key denominator. This is the main way dairy diets are built, but this approach leaves a lot on the table when it comes to real fine-tuned feeding programs.
A more nuanced denominator to consider is milk production. Though you may rarely see pounds of milk as a denominator for a dietary nutrient, the influence of level of production is implicit in how we build diets and what amounts go into the diet.
Restricted quantities
Governmental regulations have an outsized influence on how nutritionists build the ingredients that usually contain the minerals, trace minerals, vitamins, and various additives. First among these is selenium and the maximum level is 0.30 parts per million (ppm) in the ration. Selenium is the nutrient most commonly used to determine the inclusion of mineral blends. Since the selenium directives are a ratio (ppm), the ingredient supplying the added selenium must stay at a constant ratio to the DMI of the diet. In other words, if a mineral- type ingredient is designed to be fed at 1 pound per cow per day for 55 pounds of DMI, this ratio is fixed. If the cows eat more or less, as they will, the mineral ingredient must move up and down accordingly. If other nutrients in that same ingredient have a different type of ratio determining their correct inclusion, this can’t be accommodated unless you change the formulation of that ingredient every time the cow’s intake changes. Much of this can be solved by utilizing a micro-ingredient machine on-farm where these individual low-inclusion ingredients can be moved up or down as individual ingredients as opposed to in a fixed blend.
There are a few other nutrients that also have the attention of regulatory agencies. The first is iodine. Much of the same thought process driving the selenium regulations also applies to iodine. Additionally, iodine has a direct human health implication due to potential increased levels in milk, especially for people with thyroid disease. This is not to be ignored.
Another area to discuss as we try and build mineral-type ingredients to supply correct levels of micro ingredients in rations with various animal weights and intake levels are medicated ingredients, including monensin and fly control products. These dosage rates are linear with intake, can be in a fixed ratio, and can often cooperate nicely with selenium. A potential challenge of this flexibility of using one formula for different body weights is monensin. Used as a common ingredient to control coccidiosis in young heifers, it must not exceed the maximum inclusion rate when the same ingredient is used in older heifers. This is a good example of where fixed nutrient ratios can’t fit every ration.
Vitamins stand out as one of the few nutrients that have a suggested amount per day for different ages. These levels tend to be supplied as units per day regardless of intake. This can be difficult or even impossible if these vitamins are included in a mineral-type ingredient that also includes selenium or monensin. At times, we need to find creative ways to meet the unique vitamin requirements in some rations.
The last ingredients that have recently entered this discussion are branded methanogens that have minimum feed rates to qualify for carbon credit creation. If a single mineral-type ingredient is being used across multiple rations, keeping things in perfect relationship is difficult.
Not an easy answer
How did we get into the area of trace minerals, the FDA, vitamins, medicated feed additives, and even carbon credits when we were trying to see if a particular ration is mixed at the right spot for the 100% intake level? Well, the answer is that it is complicated. Unless you put these in a micro ingredient machine allowing them to be fed at differing ratios, you will never get it just right. Careful formulation strategies and diligent tracking of actual DMI of various rations must be routine. When a limited number of mineral ingredients are used, as on most farms, a skilled nutritionist will find the best approach to supply needed micronutrients and follow rules and regulations as intakes go up and down.
The nutritionist must be sure that the tension between nutrients and ingredients with differing rules for ration inclusion all stay in order. Thank goodness we don’t have to do this math in our heads!
