Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: May 1, 2012
Publication Date: May 15, 2012
Citation: Samac, D.A., Lamb, J.F., Jung, H.G., Schnurr, J.A. 2012. Alfalfa for maximum livestock nutrition and forage yield. Forage Focus. May 2012. p. 19-20. Technical Abstract: A key to successful development of a more digestible cultivar is focus on altering digestibility of alfalfa stems. As the alfalfa plant matures, the herbage becomes less digestible. Even when harvested at bud stage, a large amount of the forage is difficult to digest, and from 50 to 70% of more mature forage is poorly digested. While cell walls of alfalfa leaves are easily digested, most of the cell walls in the stem are difficult for rumen microbes to digest. Previous attempts to select alfalfa simply for increased disappearance of total forage dry matter by rumen microbes led to an increase in the leaf fraction without changes in stem digestibility. The breeding and selection program by Plant Science Research Unit scientists focuses on identifying the developmental processes that cause poor digestion in stems and selection for stem traits that result in greater digestibility. A wide range of alfalfa germplasm was surveyed for differences in stem digestibility, and a significant amount of variation was found in forage quality traits among the unimproved germplasm tested, indicating that selection could be used to improve forage quality. A series of studies were done using microscopy to identify the stem cell walls that were digested rapidly and those that were digested slowly and then to determine the composition of both types of cells. The study concluded that improving fiber digestibility should target genes that reduce total cell wall concentration, perhaps by reducing the rate of xylem formation, or reduce the amount of lignin, and genes that increase the amount of pectin to improve the amount of easily digestible carbohydrate. A new near-infrared reflectance spectroscopy calibration was developed to aid in selecting plants with increased neutral detergent fiber (NDF) digestibility. Two cycles of selection were completed with the goal of increasing digestibility at later maturity stages. Multi-location field trials are being established with the latest generation of materials. The forage harvested will be tested for NDF digestibility from early bud stage through flowering and seed set. Based on the final results of these trials, forage at specific growth stages will be harvested from larger plots and used in animal feeding trials in collaboration with scientists at the U.S. Dairy Forage Research Center in Madison, Wisconsin.