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Incorporation of ¹⁴C from Labeled Alfalfa into Rumen Bacterial and Volatile Fatty Acid Carbon and Rumen Removal Rate of Fiber and Soluble Fractions¹

Kansas State University, Manhattan

Abstract

¹⁴Carbon-labeled alfalfa harvested at prebud, bloom and seed stages of maturity was fed in separate trials to a fistulated cow. Peak ¹⁴C activity in rumen VFA, bacteria and bacterial protein occurred at 6, 3 and 3 hr., respectively, after feeding. There was no evidence of bursts of fermentation activity any time during the decline of activity after the peak. Samples of alfalfa hay and rumen dry matter were fractioned into acid-detergent fiber (ADF), neutral detergent fiber (NDF), cellulose and neutral detergent solubles (NDS). Removal rates of the labeled fractions were logarithmic. Stage of maturity had no effect on rate of rumen removal of NDS. Dry matter, cellulose, ADF and NDF were removed from alfalfa in the prebud stage faster than from bloom or seed stages. No differences in removal rates were found between alfalfa in bloom and seed stages. A comparison of relative removal rates from one maturity stage indicates that the NDS fraction is removed faster than the dry matter, cellulose, ADF or NDF fractions. Removal rates of the last four did not differ. Lack of significant differences suggests a close association of all nutrients. Peak ¹⁴C activity occurred in fecal NDS, cellulose, ADF and NDF fractions at ca. 30, 48, 48 and 45 hr., respectively. Little activity was found in feces before 18 hr. or after 120 hr. post feeding. True digestibility of ¹⁴C of prebud alfalfa was higher than that of bloom and seed stages.

¹ Contribution No. 720, Department of Dairy and Poultry Sciences, Kansas Agricultural Experiment Station, Manhattan. Data are in part from a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree in Animal Nutrition.

² Present address: Nutrena Mills, Cargill Building, Minneapolis, Minnesota.