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The Role of Protein Supplementation on Extending Forage Quality

By Dr. Hebbie Purvis, Senior Ruminant Nutritionist for Ralco

Utilization of pasture, range, and harvested forages has long been an advantage of beef production. The ability to utilize the most common carbohydrate source on the planet (cellulose), gives them a unique advantage over monogastric animals which cannot effectively utilize this source of potential energy. Ruminants have a distinct advantage in which microorganisms within the rumen can effectively digest forages and release nutrients that can be utilized by the animal, allowing them to survive and thrive on an allforage diet. Cattlemen take great care to manage their forage resources in a responsible and sustainable manner. However, improvements in genetic potential have exceeded the forage’s ability to supply sufficient nutrients to support the animal to its fullest potential. This short fall in the amounts of protein, energy, minerals, or vitamins can hinder cattle production and, likewise, economic returns. Supplementation makes it possible to maximize cattle performance, but only when the supplementation successfully targets the proper amounts, types, and ratios of vital nutrients lacking in forage.

Ask a rancher, “What drives dollars to your bottom line?” In most cases you will hear, “Pounds of calves sold!” While this is true for gross revenue, the real answer is the efficiency of converting our most basic resource, forage, into sellable weight. That conversion is dependent on forage quality and quantity coupled with the efficiency of those two components into sellable product. Two important components within the forage really hold the keys to enhancing performance – energy and protein.

Within the beef cow/calf and stocker cattle arena, total digestible nutrients (TDN) is commonly used to measure the amount of energy in roughage sources. TDN is expressed as a percentage and considers potential energy supplied by digestible fiber, carbohydrates, crude protein, and fat. TDN values differ between grass species and fluctuate throughout the year. Grasses have the highest TDN values in early to mid-summer and then trend downward through winter. In general, the more mature the forage, the higher stem:leaf ratios, and more dead plant tissue equates to lower TDN values along with lower digestibility in the rumen (Figure 1).

In most cases, forage protein values follow the same trend. However, peak crude protein (CP) values often occur in late spring ahead of peak TDN values. While TDN is the fuel source for biological functions; protein is the building blocks for growth and performance. Just as with TDN, protein values decrease with the maturity of the forage, higher stem:leaf ratios, and more dead plant tissue. Protein also is a crucial nutrient for the rumen microbes and low values will impact their ability to break down forage and extract nutrients for use by the animal.

When the CP percentage of forages is less than 7% of dry matter, there may be inadequate protein to supply the needs of rumen bacteria and forage intake may be decreased (Figure 2).

The rumen microbes are only able to break down a portion of the crude protein supplied in the diet and this portion is called rumen degradable protein (RDP). The microbes break down RDP into precursors such as ammonia-N and peptides. As degradable proteins are broken down by rumen microbes, ammonia-nitrogen is released, supporting an increase of microbial activity and population. A benefit to increasing both activity and population is a more rapid and extensive digestion of forage. This leads to more energy and microbial protein, resulting in better performance. This also enhances and stimulates improved intakes which advances body condition, milk production, and more efficient gains (Figure 3).

Like everything in nature, balance is needed to maintain optimal performance; energy and protein are no different. For example: if there are sufficient building blocks (protein) but an energy deficit; the building blocks cannot not be mobilized to benefit performance. Likewise, if there is ample energy but a lack of building block, maintenance and growth activities will be stalled.

Figure 3. Impact of increasing levels of soybean meal on dry matter intake and digestibility of low-quality prairie hay (Guthrie 1984)

One way to evaluate the dietary balance of energy and protein is to look at the ratio of TDN to CP. This is simply calculated by dividing the TDN of the diet by the CP of the diet. The optimal ratio is 8:1 (often referred to as 8 with the 1 being assumed) and a target range of 7 to 9. Looking at a forage analysis where the TDN is 56 and CP of 7 and using the above calculation; the resulting TDN:CP ratio is 8:1 or 8 (as the 1 is assumed).

The next question is, “What if the ratio is not between 7 and 9 target range?” A ratio below 7 implies a lack of energy and the available protein is not utilized effectively. In this case, supplements with low protein and high digestible fiber have the greatest benefits.

However, if the ratio is closer to 5 or below, high energy supplements such as small to moderate quantities of grain or those high in digestible fats work best. If the ratio is greater than 9, then there is in sufficient RDP protein to support the microbial population. This results in the forage be under-utilized and potential nutrients being left on the table along with performance. This is the scenario where Summit Extender works best.

Summit Extender is formulated to supply the needed RDP, in the form of ammonia, to the rumen microbes. However, not all ammonia sources are created equal. Summit Extender uses Biuret which is defined in the Federal Code of Regulations and by The Association of American Feed Control Official as a feed ingredient for ruminants. While it is classified as non-protein nitrogen; Biuret is not urea or an encapsulated non-protein nitrogen (NPN) product. By its chemical nature, it dissolves slowly and is degraded by unique rumen microbial enzymes into ammonia. Biuret’s ammonia release pattern mimics that of vegetable proteins specifically that of soybean meal and therefore is much safer than urea.

Ammonia is a critical nutrient for fiber-digesting microbes, insufficient rumen ammonia dramatically limits fiber digestion which reduces forage energy and feed intake. Because of this, ammonia-N is typically the most critical factor limiting the performance of cattle consuming either winter pastures, coarse, or low protein forages. Biuret’s ability to release ammonia into the rumen over an extended period of time is important when providing supplements that are consumed or fed once a day to grazing cattle. This continuous supply of ammonia to the rumen microflora enhances their ability to break down forage while cattle are grazing or ruminating.

Research from Kansas State and Montana State looked at the benefits of Biuret in grazing scenarios. Loest and coworkers at Kansas State University evaluated the effects of Biuret had on intake and digestion of steers on prairie hay. Their results showed a 22% increase in forage intake and 52% increase in digested organic matter compared to non-supplement steers. In a winter feeding scenario at Montana State University, researchers concluded that cows on a control supplement of 18% CP lost 62 pounds and ½ body condition score. While cows receiving a supplement containing Biuret maintained both weight and condition.

In summary, Summit Extender while being a complete mineral supplement also provides enough protein (80%) to allow cattle to fully utilize the forage base to productive ends. The can all be accomplished in a very safe, economical, and convenient method. Summit Extender can meet both the mineral and protein needs of cattle grazing low quality (i.e., TDN:CP greater than 8 with an intake level between .33-.50 lb./hd/day) and be supplied in a free choice format minimizing the labor and equipment costs of supplementation. It’s worth noting that in most cases the actual non-feed costs of supplementation are greater than the feed cost. Summit Extender effectively extends the grazing season without the time or labor burden of having to deliver protein supplements on a daily basis.

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