By: Don Meyer, President and Owner
Feed and forage sample analysis has one key goal: an accurate depiction of the feedstuff nutrient and energy content. Accurate analytical results are chiefly important to our customers, and the end users. They are necessary to create efficient rations and maintain the health and productivity of the animals - consequently with the farmer’s livelihood hanging in the balance. So, as you can imagine, we take the accuracy of our analysis – the root of all these things – very serious. And because of this, our mantra always has been and always will be continual research of the scientific methods we implement to reach the end goal of accurate analysis.
One of the first methods we employ in feedstuff analysis is the dry matter (DM) assay. First, we should consider, what is dry matter? It is the actual nutrient (including volatile alcohols and fermentation acids) and ash content of a feed - excluding water. There are two approaches to determine dry matter content: 1) determine actual water (H2O) concentration, or 2) assess weight lost upon drying, and making assumptions that weight lost represents water (only). The first approach is the gold standard, yet is difficult to achieve quickly and cost effectively. Thus, option two is typically employed by research and commercial laboratories.
The technique used for dry matter analysis can vary among agricultural analysis labs as the National Forage Testing Association (NFTA) recognizes both forced-air and microwave oven drying as appropriate techniques for use in DM determination and sample preparation. Both determine DM as weight lost upon drying (approach two). Essentially, a portion of the sample is weighed, dried using heat, then weighed again, to determine the DM concentration of that feedstuff. As we all know, accurate DM is pertinent information for on-farm application – be it for mixing the TMR and ensuring the correct ratio for the ration, or various other components.
While both drying via microwave and forced-air ovens are accepted by the governing body of our industry, both have limitations as do all methods that utilize heat to dry a sample. As discussed earlier, on-farm application drives us, and because of this, results still need to be timely. Ideally, the most accurate means of measuring DM is implementing the Karl Fischer method or utilizing Toluene Distillation (approach one). These methods, unfortunately, take far too long (among other caveats) for applications within agricultural analysis laboratories that need to provide accurate information quickly for farm implementation as described prior.
In our efforts toward continual research of the methodology we employ, we have found some interesting results. We presented, “Samples dried with commercial DM techniques differ in volatile compound components” at the 2015 American Dairy Science Association and American Society of Animal Science Joint Annual Meeting. I’ve linked to the poster here. Our objective with that research was to evaluate whether feeds, dried using commercially adopted DM techniques, differ in retained total volatile compound contents. In other words, we were looking to assess if drying techniques differ in non-water volatile losses post drying, which would then equate to a dry matter measure error if we assumed only water was driven off. What we found was that utilizing forced-air oven drying techniques drove off significantly more non-water volatiles than a microwave oven. Our results agree with those reported by McDonald and Dewar (1960), nearly 60 years ago, who observed that between two and nine units of non-water losses occur during electric oven drying. The authors commented that the dry matter result should be corrected for these non-water losses - yet this isn’t done at commercial or academic laboratories today, and represents a dry matter measure inaccuracy with forced-air ovens. Back to our research abstract published in 2015, we observed that microwave ovens evaporate less non-water volatile compounds which could equate to a more accurate dry matter.
Our team of experts and laboratory technicians are rooted in science, passionate about what they do, and continually looking to explore and find better ways to do things for the agricultural community. Part of that passion is research to better our methodology. As agricultural laboratories, we commit ourselves to research progress and scientific integrity, and the agriculture industry depends on – and looks to us - for this. We’ll continue to work hard to improve methodologies and lead the industry peer-reviewed research, making clear the language for forage analyses.
