Most cattle producers are primarily concerned about meeting the minimum nutrient requirements for the cow herd. In many parts of the country, given the dry conditions, most producers are concerned about being able to provide a minimum amount of forage to allow them to hold on to the cow herds and maintain an acceptable level of production. The same is true because of high fertilizer, fuel and feed costs. At this point, overfeeding anything is not necessarily a concern.
While all these points are true, it is also true that overfeeding some feeds or nutrients can be a problem to animal performance – reproduction, health, weight gain. The concerns of providing minimum supplies of various nutrients are significant this year, especially as producers search for deals or opportunities on forage, feeds and byproducts. But it is possible, even probable, that whatever “deals” may be out there may also come with a caution sign.
Let’s look at some potential nutritional problems that may be encountered when specific nutrients are overfed.
Protein
Protein is a cornerstone nutrient. It is a primary building block for rumen function and for overall animal physiological function. It is the primary component of muscle, blood, enzyme systems, bone growth, connective tissue, hide, hair, hooves, etc. Virtually every system in the animal’s body has a protein requirement. As such, every animal, young and old, has a minimum protein requirement. This varies depending on age, growth, production status, etc.
It is not uncommon to overfeed protein, especially when small-grain or winter-annual pastures are fed. It can also occur if high levels of alfalfa (hay or pasture) and if certain higher-protein feeds or byproducts are overfed. An example of this might be overfeeding of dried distillers grains (DDGs). Currently due to supply and cost issues, overfeeding a byproduct like DDGs is unlikely.
Keep in mind, the part of the protein molecule that makes it unique is the presence of nitrogen. When fermented in the rumen, the degradable portion proteins are broken into their component parts, with the nitrogen largely taken up by the bacteria and formed into bacterial protein, which is later digested by the animal. For a fuller description of the process, go online (Cattle Today - Proper protein feeding important to herd health).
As mentioned, small grains or winter pastures, especially if heavily fertilized, can provide excessive protein levels. A client of mine had an intensive rotational grazing program using heavily fertilized ryegrass pastures (see Figure 1).
We analyzed the protein contents of the grass several times. The crude protein of this grass ranged from 28% to 32%, much higher than the needs of the cows. Indicators of excessive dietary protein are blood urea nitrogen or milk urea nitrogen levels in lactating cows. Your vet can help analyze for either of these. Also, a very common sign of high dietary protein is very thin manure with a score of 1 to 2 (see Figure 2).
It is important to understand that when protein levels are excessive, the animal’s body is working overtime to help clear the extra nitrogen in its system. A primary result is depressed reproduction (conceptions) in cows and heifers during these periods. Feeding a supplement that is higher in starch or soluble fiber (soybean hulls, beet pulp) can help with the nitrogen uptake in the rumen.
Starch
Starch from grains such as corn or grain sorghum is a primary source of energy in many cattle diets, either as the primary source such as in feedyard cattle or a supplemental source for cattle on pastures, particularly growing cattle. Feedyard cattle are fed high levels of starch to promote high rates of feed-efficient gain. However, they must be adapted to these high rates over time. The microbes in the rumen that break down fiber when the animal is on grass and those that break down starch when they are on full feed are different.
When moving cattle from pasture onto full feed, the rumen must be adapted to this feed change by using different rations that gradually change from high fiber, low starch to low fiber, high starch over time to prevent significant digestive upsets that result in conditions like acidosis or bloat. This is a common process in every feedyard.
This can become more of a “balancing act” when supplementing cows or growing steers and heifers on pasture. It is common that the condition of the pastures or forages may be inadequate to provide for the energy needs to either maintain the body condition of the cow or provide for adequate, cost-effective growth of stocker or backgrounding calves. In many cases, the producer may choose to supplement with grain (starch) feeding to help with the energy shortage. This can become a problem if too much grain is fed or if it is fed in the wrong manner.
When high levels of grain are fed, such as a processed corn (ground, cracked, flaked; see Figure 3), it can be fermented very rapidly in the rumen.
This can lead to a significant drop in rumen pH which, if extreme enough, can lead to acidosis or bloat. It also depresses the growth, reproduction and overall activity of the fiber-digesting microbial populations, important for the digestion of the fiber in the animal’s diet, which still makes up a sizable portion. The result, in addition to the potential for metabolic problems, is a decrease in normal fiber digestion and the nutrients grasses or hay might yield. The end result is: The animal does not perform as expected despite being fed the grain supplement, plus it can result in digestive upsets that can be more problematic and expensive.
Additionally, care should be taken as to how grain should be fed. Feeding too much at one point can lead to the problems described above. Often, producers will attempt to provide supplements every other day or every three days (twice per week). This often leads to overfeeding on those days and contributes to the problems listed above. If higher rates of grain need to be fed, regular, smaller feedings need to be arranged to prevent problems. A rule of thumb for mature cows is to never feed more than about 8 pounds of a grain-based feed or supplement at a time. Depending on the formulation (i.e., heavy on processed corn), even this amount can create problems.
Mineral
Almost everyone has seen the mineral interaction figure that shows how various minerals can interact with one another, potentially depressing the absorption of one mineral or another. It is well known that high potassium levels coupled with low phosphorus can negatively affect magnesium absorption. This is commonly seen in more mature cattle grazing winter annuals.
Likewise, high sulfur and molybdenum can bind with copper in the rumen, creating insoluble complexes where the copper is unavailable to the animal. High zinc or iron levels can also interfere with copper absorption. These interactions are known as antagonism and can cause significant problems with health and reproduction. Awareness of forage and feed mineral values are important as well as familiarity with the large variety of mineral sources available. This topic was discussed in the April issue of Progressive Dairy (progressivedairy.com/topics/feed-nutrition/a-practical-understanding-of-trace-mineral-sources). Proper formulation and use of well-designed mineral sources (Figure 4) reduce antagonism and promote proper mineral absorption in all production groups. Also, overfeeding of any of the trace minerals can cause health or other problems, even toxicities.
Conclusions
It is always important to provide adequate levels of as many of the required nutrients as possible to support animal health and performance. But be aware: Overfeeding nutrients can be a problem as well. Imbalances in the diet (deficiencies or excesses) can reduce performance significantly, lead to health issues and be very expensive. Take the time to understand what the right nutrition program is for your operation. There are numerous feed company and independent nutritionists around who can be helpful in designing or fine-tuning your program.
