Technical note: labeling of forages with 13C for nutrition and metabolism studies

• Published in: Journal of animal science Vol. 71; no. 5; p. 1320
• Main Authors: Svejcar, T.J. (Eastern Oregon Agriculture Research Center, ARS, USDA, Burns), Judkins, M.B, Boutton, T.W
• Format: Journal Article
• Language: English
• Published: United States 01.05.1993
• Subjects: ALFALFA; Animal Feed; Animal Nutritional Physiological Phenomena; Animals; Breath Tests; BREBIS; Carbon Isotopes; CARBONE; CARBONO; Dietary Fiber - metabolism; DIOXIDO DE CARBONO; DIOXYDE DE CARBONE; FECES; Feces - chemistry; Female; HECES; Isotope Labeling - veterinary; ISOTOPE RADIOACTIF; LUZERNE; Medicago sativa; METABOLISME; METABOLISMO; OVEJA; RADIOISOTOPOS; RUMEN; SERUM SANGUIN; Sheep - metabolism; SUERO SANGUINEO; TECHNIQUE ANALYTIQUE; TECHNIQUE DES TRACEURS; TECNICAS ANALITICAS; TECNICAS DE TRAZADORES
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/1993.7151320x

Alfalfa was labeled in the field with 99 atom % 13CO2 and cut either the same day (C1) or 30 d after labeling (C30). The C1 alfalfa contained 84% of the 13C label in cell contents, whereas C30 alfalfa contained 47% of the 13C label in cell contents. In two separate trials, C1 and C30 alfalfa were dosed to two or four Suffolk ewes fed natural abundance alfalfa diets. Carbon isotope ratios (13C/12C, expressed as delta 13C[parts per thousand] vs Pee Dee Belemnite standard) were determined for breath, feces, blood, and blood serum from ewes fed C1 alfalfa and blood and feces from ewes fed C30 alfalfa. In the C1 trial, carbon isotope ratios of respired C2 peaked 4 h after feeding, then declined to baseline levels by 40 h after the dose. Fecal samples increased in 13C only slightly from 12 to 40 h after the meal. Blood serum values increased by approximately.5 per thousand from 0 to 4 h after the dose and remained relatively constant thereafter. In both trials, carbon isotope values from whole blood were constant. In the C30 trial, fecal samples peaked in carbon isotope value approximately 30 to 36 h after dosing, then declined; the time of this peak corresponded closely to that from a concurrent study that used a pulse dose of Yb-labeled alfalfa hay. Thus, when incorporated into cell wall material, the excretion pattern of 13C in feces was similar to that of Yb-labeled hay, but little 13C enrichment in feces was found when 13C was primarily in cell contents of the labeled forage. When the soluble cell contents were enriched in 13C, the marker was detected in respired CO2 soon after feeding, which is consistent with the results of previous marker studies. These results demonstrate the feasibility of using forage labeled with the stable isotope 13C in nutrition and metabolism studies. Carbon-13, not subject to the regulatory constraints associated with 14C, provides a useful alternative when a carbon tracer is desired