Passage kinetics of concentrates in dairy cows measured with carbon stable isotopes

Abstract

Fractional passage rates form a fundamental element within modern feed evaluation systems for ruminants, but knowledge on feed-specific fractional passage is largely lacking. Commonly applied tracer techniques based on externally applied markers, such as chromium-mordanted neutral detergent fibre (Cr-NDF), have been criticised for behaving differently to feed particles. This study describes the use of the carbon stable isotope ratio ( 13 C : 12 C) as an internal digesta marker to quantify the fractional passage rate of concentrates through the digestive tract of dairy cows. In a crossover study, five dairy cows were fed low (24.6%) and high (52.6%) levels of concentrates (dry matter (DM) basis) and received a pulse-dosed Cr-NDF and 13 C isotopes. The latter was administered orally by exchanging part of the dietary concentrates of low 13 C natural abundance with a pulse dose of maize bran-based concentrates of high 13 C natural abundance. Fractional passage rates from the rumen ( K 1 ) and from the large intestine ( K 2 ) were determined from faecal marker concentrations of Cr-NDF and of 13 C in the DM ( 13 C-DM), NDF ( 13 C-NDF) and neutral detergent soluble ( 13 C-NDS). No differences in K 1 estimates were found for the two concentrate levels fed but significant differences between markers ( P < 0.001) were observed. Faecal Cr-NDF excretions gave lower K 1 estimates (0.037-0.039/h) than 13 C-DM (0.054-0.056/h) and 13 C-NDF (0.061-0.063/h). The 13 C-NDS was calculated by the difference of 13 C in the DM and NDF, and K 1 values (0.039-0.043/h) were comparable to Cr-NDF. Total mean retention time was considerably higher for Cr-NDF (40.9-42.0 h) as compared to 13 C-DM and 13 C-NDF (32.0-33.5 h; P < 0.001). The accuracy of the curve fits for Cr-NDF and 13 C-DM and 13 C-NDF was overall good (mean prediction error of 9.9-13.9%). Fractional passage rate of Cr-NDF was comparable to studies where this marker was assumed to represent the fractional passage of roughages. However, K 1 estimates based on the 13 C : 12 C ratio varied considerably from studies based on external markers. Our results suggest that the use of 13 C isotopes as digesta passage markers can provide feed component-specific K 1 estimates for concentrates and provides new insight into passage kinetics of NDF from technologically treated compound feed.

Passage of stable isotope-labeled grass silage fiber and fiber-bound protein through the gastrointestinal tract of dairy cows

“…Curve fit accuracy based on the MPE was in the range of previous studies using δ 13 Clabeled forage (Pellikaan et al, 2013;Warner et al, 2013a) but MPE values were almost double compared with those reported for δ 13 C-labeled concentrates pulse dosed at high amounts (9 kg; Warner et al, 2013b). Interestingly, curve fit accuracy for Cr-NDF based on fecal sampling was considerably better than that for stable isotopes, but accuracy considerably declined for Cr-NDF with omasal digesta sampling and was even slightly worse than that of δ 15 N. These findings suggest that the small ruminal pulse dose size of stable isotopes probably affected its curve fit accuracy, and that omasal sampling provided somewhat less reliable results than fecal sampling.…”

“…Incubations (0,2,4,8,24,48, and 72 h) started with the 72-h incubation bags according to the all-out procedure at 80 h after marker administration to ensure similar conditions of degradation and passage rates. Previous studies showed that fecal marker concentrations were close to baseline concentrations after 4 d (Warner et al, 2013b). Fractional rumen degradation rates were related to fractional rumen passage rates to test a potential relationship.…”

Effects of solid feed level and roughage-to-concentrate ratio on ruminal drinking and passage kinetics of milk replacer, concentrates, and roughage in veal calves

“…The absence of an effect of R:C ratio on passage rates of concentrate (Poore et al, 1990;Warner et al, 2013) and roughage (Poore et al, 1990;Rotger et al, 2005) has been demonstrated before, as reviewed by Offer and Dixon (2000) for cattle. A negative effect of concentrate proportion on rumen volume, as observed in adult ruminants (Owens and Goetsch, 1986), was absent in our study.…”

Stable isotope‐labelled feed nutrients to assess nutrient‐specific feed passage kinetics in ruminants

“…the C/C ratio) may be constant between the moment of marker administration and the time of collection in the undigested faecal matter. Recent studies have shown that microbial fermentation did not affect the C/C ratio in apparent undigested material in vitro and in vivo (Ferreira LMM, unpublished) and that the 13 C/ 12 C ratio remained constant over time. Hence digestion of the labelled nutrient did not alter the isotopic ratio and its FPR in those studies.…”

“…However, data based on such markers are scarce. Isotopically labelled feed has been applied in early ruminant metabolic studies but was only recently applied in ruminant digestion studies or specifically to quantify passage kinetics . Here we provide an overview of recent digesta passage research and discuss opportunities and limitations of using the isotopic signature ( δ ) of dietary components as a potential novel marker to quantify FPR in ruminants.…”