Use of naturally enriched mixed food in 13 C breath tests applied in young sucking calves

Abstract

Utilization of three milk diets including cream, casein or whey, each naturally labelled with 13 C (1 mmol 13 C excess) from C 4 sources, by six young male calves of the Deutsche Fleckvieh breed was investigated in a Latin-square split-plot design. Each milk diet was examined under resting conditions and during a short period of physical exercise on a treadmill. δ 13 C values (‰) in carbon dioxide in expired air were measured at intervals of about 1 h during 6·5 h after food intake. Expired air samples for CO 2 isolation, subsequent isotopic analysis, measurement of CO 2 production and respiratory quotient were taken at about hourly intervals and 13 C recovery rates over 6·5 h were calculated. Feeding milk containing enriched milk casein, cream, or whey resulted in maximal significant 13 C enrichments over background (δ 13 C) in CO 2 of +1, +2·4 and +2·2‰, and recovery rates of 3·6, 9·9 and 12·2% respectively. This comparison shows the different kinetic behaviour of the main nutrients during the oxidation in tissues. The short exercise period (5 min at 1 J/s per kg body-weight + 5 min at 2 J/s per kg body-weight) did not influence the recovery rates significantly. However, after 10 min of muscular exercise there was a brief decrease in δ 13 C value of expired air which disappeared within the first 5 min of rest. These experiments demonstrate for the first time the applicability of the 13 C breath test with naturally enriched diets in animal nutrition research and that quantitative results may be obtained.