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Malate, Citrate, and Amino Acids in Tall Fescue Cultivars

Relationship to Animal Preference

^a USDA-ARS, Northwest Irrigation & Soils Res. Lab., 3793 N. 3600 E., Kimberly, ID 83341-5076 USA
^b Dep. of Animal and Dairy Science, Univ. of Georgia, Athens, GA 30602-2771 USA
^c AgResearch, CRI, Grasslands Res. Ctr., Palmerston North, New Zealand

mayland{at}kimberly.ars.pn.usbr.gov

Grazing animals depend on little-understood chemical and physical cues when selecting forage diets. This study determined malate, citrate, and amino acid concentrations in endophyte-free tall fescue (Festuca arundinacea Schreb.) and related those concentrations to cultivar, harvest time, and grazing-animal preference. `Barcel', `Kenhy', `Kentucky-31', `Missouri-96', `Mozark', `Stargrazer', and the two accessions C1 and HiMag were established in three replicates within each of three pastures. Organic acids were determined on regrowth within each plot during four seasons and two years; amino acids were determined on regrowth of four cultivars across three replicates during both spring and fall seasons in one year. Malate and citrate were extracted with boiling water and quantified by high-performance liquid chromatography (HPLC) with an organic acid column. Amino acids were hydrolyzed, separated by ion-exchange HPLC, and quantified as their ninhydrin derivatives. Both malate and citrate concentrations differed between years. During one year only, malate concentrations were higher in Kenhy (68 g kg^-1 dry matter [DM], most preferred) than in Mozark (54 g kg^-1 DM, least preferred). Citrate concentrations (13 g kg^-1 DM) were not different among cultivars. Eighteen amino acids (including tryptophan) accounted for 75% of total N. Thus, tissue N data were used as covariates to amino acid data in the ANOVA. Kenhy contained higher concentrations of eight amino acids than did other cultivars. These differences may reflect presence of Lolium genes in Kenhy. Cattle (Bos taurus L.) grazing preference (0 = not eaten; 10 = completely eaten) was not related to malate, citrate, or amino acid concentrations among cultivars.

Abbreviations: EAA, essential amino acid • cyst(e)ine, cystine or its reduction product, cysteine • HPLC, high-performance liquid chromatography • NEAA, nonessential amino acid • TAA, total amino acid [measured in this study]

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