Science and Production Know Before You Feed – The Value of Testing Forages by Kristin Thompson, Ruminant Nutritionist with New Life Mills
Forage quality has a direct impact on a producers’ profitability through influencing production performance, milk yields and reproductive efficiency. The quality of a forage is determined by the amount and availability of nutrients it contains. And when forages are the main component in beef cattle rations, this quality is important to evaluate in order to develop an effective feeding strategy. This is where analytical testing comes into play which allows us to formulate rations to meet the animals’ nutrient requirements and offer a prediction on animal performance. Three of the main forage quality components are protein, fiber and energy. Forage Quality Weather conditions and forage maturity are the main factors impacting forage quality in a hay stand or pasture. When adequate rain and limited environmental stressors are present, plants continue to grow throughout the growing season leading to a high leaf to stem ratio. However, rainfall during harvest can lead to mold growth, leaf loss and nutrient leaching. In contrast, hot, dry weather, particularly at the start of the growing season, will result in stunted plant growth and increased plant lignification. With increasing plant lignin content, the fiber component increases which corresponds to a reduction in fiber digestibility.
forage should be tested for moisture or dry matter (DM), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF) and an estimation of the energy content (Total Digestible Nutrient (TDN); Net Energy for Maintenance (NEm) or Net Energy for Gain (NEg)). The macromineral content of the forage can also be tested and depending on the different farm situations, other nutritional parameters could also be chosen for analysis to cover the requirements. For example, a farm that has previous issues with copper deficiency, might want to evaluate the molybdenum levels in forages, as molybdenum is a known copper antagonist. Figure 1 shows an example of a Certificate of Analysis. Protein The crude protein value on a forage analysis report represents the total nitrogen (true protein and non-protein nitrogen (NPN)) in the feed. The crude protein level can be further fractionated based on the rate of ruminal breakdown into soluble protein (rapidly available in the rumen), Neutral Detergent Insoluble Crude Protein (ADICP) and Acid Detergent Insoluble Crude Protein (NDICP). The NDICP value represents the portion of
protein that is slowly degraded in the rumen and consists of a large portion of the ruminally undegraded protein. The portion of protein that is undigested and thus, unavailable to the animal, is reported as ADICP. Unless the forage has heatdamage, the ADICP level should be below 12%. Some forage analysis reports will include an Adjusted Crude Protein value. This value is the CP% adjusted to remove the ADICP and should be the value used in ration formulation. It should be noted that the CP value is typically not adjusted until ADICP is 10% or higher as a percent of CP. Research has shown that when a feed tests below 7% CP, microbial fermentation is reduced. This can result in reduced feed intake and rumen passage rate. When this type of low-quality forage is being fed, a high-quality protein supplement such as by product feeds (distillers’ grains, canola meal) or high-quality legume forage, should also be included in the ration to improve nutrient utilization. Non-protein nitrogen sources can be a cheap option for inclusion in rations when protein is limiting. Urea, a common NPN source, is often also included in commercial protein supplements.
The forage quality can be further impacted by harvest and storage conditions after cutting. The longer a forage remains in storage, the more potential there is for nutrient breakdown and leaching, particularly if the forage is stored outdoors with little to no weather protection. In this situation, the outer layers of the forage become less palatable and have reduced digestibility. Analytical laboratories will typically offer a number of different analysis packages that can be grouped by sample type or livestock category. At a minimum,
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Figure 1: Example Certificate of Analysis
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NOVEMBER 2020
