Characteristics of Alfalfa Hay Quality Grades Based on the Relative Feed Value Index

Leaf yield and quality are of interest for alfalfa, especially if stems are used to produce electricity through a gasification process, and this makes additional leaves available for animal feed. Quality of alfalfa and grass hay is evaluated by the relative feed value (RFV) index. Hays ranked by RFV are assigned to a quality standard grade ranging from prime through decreasing quality grades one, two, three, four, and five. The objective of this study was to determine how leafand stem fractions varied in quantity and quality across hay quality grades. Alfalfa hay samples were collected from four commercial hay auctions. Samples were separated into stem, crude leaf, pure leaf, and weed material. Ratio of total leaf to stem material was greatest in the prime quality hay and declined as hay quality grade declined. Fiber components increased and in vitro digestible dry matter (IVDDM) decreased in quality grades from prime to grade five in stem, and crude and pure leaf material. Increases in RFV were positively correlated with increases in leaf material and leaf to stem ratio, in addition to increases in IVDDM. Commercial hay ranked as either prime or grade one would be the best choice of hay to be processed and fed for leaves. Research QuestionIn the search for value-added uses for crops, the concept of energy production from biomass has been of interest both to provide new markets and to deal with the problem of global climate change. A project is underway in Minnesota to produce electricity from alfalfa stems separated from hay. This process will yield alfalfa leaf meal as a co-product. Because the economic success of the project depends on the value both of the electricity and the leaf meal, knowledge of the quality and quantity of leaves that can be separated from commercial hays is critical. Relative feed value (RFV) is an index commonly used in the upper Midwest to characterize alfalfa hay quality. Our objective was to determine how leaf and stem fractions of commercially produced alfalfa hay varied in quantity and quality across the RFV quality grades and to determine which hay grade would be best suited for producing leaf material for animal feed. Literature SummaryWhile there is an extensive literature base available on the quality of dehydrated alfalfa hay products, the alfalfa industry has limited experience with the separation of hay into leaf and stem fractions. More importantly, there is no published information on the quality of leaf and stem fractions from commercial hays or the yield of leaf material from hay. There is extensive knowledge of the decline in stem quality of alfalfa with maturation of the crop, although leaves are considered to retain their quality better. Leaf loss due to plant maturation in the field and harvest losses are well known in alfalfa. While the impacts of these changes in alfalfa hay composition on RFV are well known in the research setting, their practical impact on commercial hay where farmers are trying to avoid maturity and harvesting declines in quality have not been investigated. Study DescriptionCommercially produced alfalfa hay was sampled at four auctions in Minnesota. Hay lots were tested by near-infrared spectroscopy for quality and one individual small (~50 lb.) rectangular bale was purchased from a total of 38 hay lots representing the six quality grades of the RFV index. Based on subsequent laboratory analyses of the hays there were five prime, six Grade one, nine Grade two, 12 Grade three, three Grade four, and four Grade five bales. Hay bales were separated into leaf, stem, and weed (non-alfalfa plant material) fractions by sieving through a series of screens. Forage quality parameters measured on the hay fractions included crude protein, neutral and acid detergent fiber, acid detergent lignin, ether extract, ash, and in vitro digestible dry matter. Applied QuestionsDoes the RFV index provide a useful measure of leaf and stem quality for commercial hays? Quality of both leaf and stem fractions separated from alfalfa hay declined (decreasing protein, increasing fiber, decreasing digestibility) with decreasing hay quality grade. Contamination of alfalfa hay with grasses and other weedy materials increased with decreasing quality grade, which contributed to the declining quality of the alfalfa leaf fraction. Can RFV be used to accurately predict leaf meal yield obtained by separation of alfalfa hay into leaf and stem fractions? RecommendationThe correlation of leaf to stem ratio with RFV was limited (r = 0.49). This result indicates that RFV will be a poor predictor of leaf meal yield from alfalfa hay processing. Declining quality of the alfalfa stems and increasing weed content of lower quality grade hays contributed to this poor correlation. The RFV index can be used to categorize commercial alfalfa hay for quality of leaf meal that may be obtained by separation, but prediction of leaf content of the hay will require development of a new measurement index. To produce a high quality alfalfa leaf meal (high protein, low fiber, high digestibility) use of prime and grade one hays would be preferable.