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Diurnal variations of nonstructural carbohydrates and nutritive value in alfalfa

Morin, C., Bélanger, G., Tremblay, G.F., Bertrand, A., Castonguay, Y., Drapeau, R., Michaud, R., Berthiaume, R., Allard, G. (2011). Diurnal variations of nonstructural carbohydrates and nutritive value in alfalfa, 51(3), 1297-1306. http://dx.doi.org/10.2135/cropsci2010.07.0406

Abstract

Increasing the nonstructural carbohydrate (NSC) concentration of forages improves N use efficiency by dairy cows. We studied the diurnal variations of NSC concentration and other nutritive value attributes in alfalfa (Medicago sativa L.) to determine the best time during the day to cut alfalfa for maximizing NSC concentration. Field-grown alfalfa was cut every 2 h between 0600 and 2000 h on six different days around the early flower stage of development during spring growth and summer re growth at two sites in eastern Canada. Concentrations of NSC [soluble carbohydrates (SC) plus starch], neutral detergent fiber (NDF), acid detergent fiber (ADF), and N, along with in vitro true digestibility (IVTD) of dry matter (DM) and in vitro digestibility of NDF were determined. The NSC concentration increased during the day in all growth cycles and sites due mostly to an increase in starch concentration. The diurnal increase of NSC concentration, however, varied with growth cycles and sites from 15.5 to 41.9 g kg-1 DM, and it was accompanied by a decrease of 1 to 2 g kg-11 DM in N concentration. At the site where the increase in alfalfa NSC concentration was greater than 30 g kg-1 DM, concentrations of ADF and NDF also decreased by 9 to 27 g kg-1 DM while IVTD increased by 3 to 16 g kg-1 DM. Greatest NSC concentrations were reached between 11 and 13 h after sunrise and the best time during the day to cut alfalfa for maximizing NSC concentration in eastern Canada is between 1600 and 1800 h. © Crop Science Society of America.

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