Filling in the Gaps

The perfect forage for cow/calf production doesn’t exist. Even when we do a good job insuring that our cows have the best possible forage available to them there remain nutrient gaps—differences between what the forage provides and the cow requires—that, when ignored, can impact productivity.

Timing is Everything
Of course, if we provide the highest quality grazed forage (the early part of the growing season) to cows that are at their lowest requirements during the year (right after we wean the cow’s calf) then we will meet almost all of the cow’s requirements, including most minerals. The problem is that the cow’s production schedule is not in sync with the forage resource and we are wasting good quality forage on a cow with relatively low nutrient requirements. When she calves later in the season, when the forage is of a lower quality and incapable of meeting her now higher requirements, her productivity will suffer. Cows calving just prior to or at the beginning of the availability of high quality, early growth forage are generally the most productive and efficient. Calving too early, two or three months before the availability of your high quality grazed forage, requires that we feed higher-cost processed feeds or suffer significant losses of body condition in the cows.  
Know the Score
Even if your calving season aligns the cow’s higher nutrient requirements (early lactation) to when the forage available to her is the highest quality (early vegetative), nutrient gaps exist. Cows with relatively high milking ability almost always experience an energy gap. Trying to fill that gap with supplemental feed is expensive and unnecessary, if the cow calved with a body condition score (BCS) of five or higher. The cow has the ability to mobilize energy from fat stores to produce milk during early lactation and then replace that fat later during late lactation when her nutrient requirements are lower or after the calf is weaned. After weaning, the cow’s nutrient requirements are at their lowest and it easier for her to regain body condition. Therefore we do not concern ourselves with a short-term energy gap during early lactation because we have managed the energy flow using her body stores. If the cow’s BCS is low—four our less¬—then she has less body fat stores to mobilize and fill the energy gap. Low body condition at calving can result in lower peak milk production and delayed breeding, possibly failing to rebreed within the confines of the breeding season. We simply manage the inevitable early lactation energy gap by insuring that cows calve in a BCS of 5 or higher.
Protein gaps occur occasionally during the year. These acute conditions most often occur when either the cow’s requirements for protein are very high (during lactation) or when the protein content of the forage is very low (very mature or dormant). If both of these conditions occur simultaneously and last for an extended period, which is exactly what happens during a drought early in the growing season, the cow’s condition and productivity will decline rapidly. 
Most green growing forage is sufficient in protein to meet the cow’s requirements during lactation. However, that same lactating cow grazing very mature forage is likely suffering a deficiency in protein. When forage is dormant, that cow is most certainly deficient. Even after her calf is weaned, the mid-gestation cow’s lower protein requirements might be higher than dormant forage can provide. Any forage with less than seven percent protein is considered deficient in providing sufficient protein to support optimal rumen function, which will negatively impact forage digestibility and the amount of energy the cow will receive from that forage. These protein gaps are most easily filled with a highly concentrated (30% CP or higher) source of protein. The objective with high concentration, low intake protein supplementation is to maximize the microbial crude protein in the rumen given the available carbohydrates, increasing forage digestibility and thus the energy available to the cow.
Mineral – the Biggest Concern
The nutrient gaps of most concern, not only during lactation, but the entire year are with mineral. We have sampled thousands of forages from all over North America in support of our nutrition consulting business and to support the development of our strategic supplementation programs. We have yet to find any forage capable of providing all of the critical mineral nutrients the cow needs.
Characteristically there are several macro minerals and an even higher number of micro minerals deficient in all forages. Of course, the number and extent of these deficiencies varies by region, even so all are of sufficient magnitude to inhibit productivity.
Many of North America’s grazed forages are deficient at some time during the year in the macro minerals phosphorus, magnesium, potassium, sodium and occasionally, albeit not often, sulfur. The most common deficiencies occur with phosphorus and sodium. The others occur during particular times of the year and under specific conditions; magnesium during the early spring and potassium when forage is dormant.
A recent article in Feedstuffs (Guiroy and McMurry, 2008) reviewing the phosphorus requirements of beef cows indicates that a cow’s requirement for phosphorus is slightly lower than previously believed. The reduction is about ten percent or 2 – 3 grams per day. We have adjusted our mineral requirement model in our forage assessment tool, the Right Now® Mineral Analyzer, to reflect this reduction and then reevaluated the phosphorus gaps in non supplemented cattle. With the very high quality early spring forages the gaps remain relatively small, 1 – 2 grams per day for a short period of time, but increased to about five grams per day by the middle of the growing season. The middle of the growing season is generally when we are trying to get cows rebred and phosphorus is a critical reproductive element, so gaps during this time can be costly.
Micro mineral deficiencies occur in every region of the U.S. and are generally believed to result in reduced cow productivity. Most all of the forages we test are critically low in copper, zinc, cobalt, selenium and iodine. The vast majority of the forages we analyze and evaluate using our Right Now® Mineral Analyzer are deficient in the above micro minerals. In many cases the levels of these trace minerals is less than fifty percent of the cow’s requirements. Grazing these forages without providing a high quality mineral supplement capable of filling those trace mineral gaps can negatively impact performance. When we fill those gaps we generally see an increase in weaning weights, reproductive rate and cow body condition.
When in Doubt, Test
There are always geographically specific exceptions, driven by soil composition, to the general statements regarding trace mineral deficiencies. Testing forages quickly bears this out. For example, forages in southwest South Dakota and specific areas of eastern Oregon can contain excessive levels of selenium. Many types of forage in Arizona are very high in cobalt. These are exceptions and require special consideration when designing a program to fill the nutrient gaps. As a general rule though, copper, zinc, cobalt, selenium and iodine are insufficient in most forage; enough to hamper productivity.
Our best defense against experiencing the negative ramifications of these potential nutrient gaps is in understanding the nutrient content of the forage provided to the cow through forage testing. After we have the results from our analysis and estimate the cow’s intake we can calculate the amount of any nutrient that the cow is receiving in the diet. A comparison of that value to the cow’s requirement for that nutrient will tell us if we have a gap that needs filling. Fillings those gaps requires that we quantify the needs in absolute metrics, e.g. pounds of protein or TDN, grams of phosphorus or milligrams of copper. Only then can we begin our search for the most valued source of supplementation to fill the gaps.
The perfect forage for cattle, one capable of meeting all of her nutrient requirements, is yet to be discovered. However, there is a process for filling the gaps and balancing the forage available to the cows to create the near-perfect diet.