A new liquid marker, cobalt-ethylenediamine tetraacetic acid (EDTA), and two solid markers, chromium (Cr) and cerium (Ce) mordanted plant cell walls, were investigated. Synthesis and methods of analysis are described for the markers. The Cr-and Ce-cell wall complexes were tested for stability to EDTA, hydrochloric acid and rumen microorganisms. Plant cell walls were rendered indigestible by mordanting with Cr and 9 8 9 i of the marker remained on the fibre after a simulated sequence (ill vitro) of digestion. Ce-mordanted cell walls were 35% digestible in vitvo using a rumen culture, and 567; of the marker could be washed off the remaining fibre. Treatment with EDTA removed all Ce and 159; of the Cr. Hydrochloric acid (0.01~) had a negligible effect on the removal of Cr from the cell walls, whereas 0 . 1~ acid removed, on average, lo:/, of the marker. Losses of Cr from the mordant may be related to the quality of the preparation. Co-EDTA was found to be comparable to Cr-E:DTA. The urinary excretion of Cr and Co was 2-37; in most animals except in rabbits, which excreted as much as 30% of the liquid markers in the urine. 42
1. Digesta passage and retention were measured in heifers, sheep, goats, equines and rabbits of varying body-weights when given timothy (Phleum pratense) hay.2. Two passage markers were compared, cobalt (111) ethylene diamine tetraacetate (CoEDTA) and chromiummordanted timothy fibre for liquid and solid phase respectively. Both markers were injected into the rumen of the ruminants and into the caecum of the equines and rabbits.3. In ruminants, two different sets of rate constants (k, and k,) were derived from a two-pool model tor marker passage, using a graphical approach and a computer-based non-linear least-squares curve-fitting technique. 4. Retention times, due to unidirectional Row through the gastrointestinal tract (transit time) and due to pool effects (mean retention time, MRT), were calculated.5. Curve titting was only successful for the excretion of liquids in ruminants. The two-pool model was not applicable to the passage of solids.6. Apparent retention of liquid was always shorter than for solids in all species, except in rabbits. However, absorption of CoEDTA was too large in the rabbits to determine liquid retentian accurately. Times for first appearance of the two markers were similar within animal groups. 8. Liquid retention seemed to decrease somewhat with increasing body-weight in the ruminants. Solids retention decreased with decreasing body-weight in the ruminants, but sheep had longer retention times than goats of similar size. Equines exhibited large individual variation in retention of the liquid or solid markers, seemingly unrelated to size. No effect of size was seen in the retention of solids in the rabbits.Digesta rate of passage in the herbivore is of great importance to the nutrition and feeding strategy of the animal. There is reason to believe that the small herbivore wilI have a more rapid rate of passage than the large herbivore, due to a higher food intake relative to body-weight and gut volume (Parra, 1978). It appears that the ruminant gut architecture imposes more restrictions to the passage of digesta than is found in the non-ruminant herbivore, affecting the relative ability of the ruminant to consume large quantities of fibrous feeds.A previous paper (UdCn & Van Soest, 1982) reported the digestive efficiencies of ruminants, equines and rabbits to utilize the fibre components of timothy (Phleumpratense) hay.The objectives of these experiments were to: (a) study the effects of gut architecture and body size on the retention of digesta (liquid and solid), (b) compare the retention and passage of liquids and solids and (c) compare different techniques for calculating the rate of passage and retention times. E X P E R I M E N T A L
Effects of full-fat crushed rapeseed (0, 1, or 2 kg/d) on rumen and total digestion, rumen biohydrogenation, and rumen microbial protein synthesis were studied in lactating cows. Rumen digestibilities (%) of DM, NDF, and cellulose were 52.1, 46.1, and 51.8, respectively, for control. Rapeseed decreased rumen and total DM digestibilities and proportion of DM digested in the rumen. Rumen digestibility of cellulose was decreased by rapeseed, but this was apparently compensated by hindgut fermentation. Dry matter, NDF, and hemicellulose digestibilities were compensated at 1 kg but not at 2 kg/d. Biohydrogenation of 18:1 fatty acids increased with increasing dietary fat, whereas that of 18:2 and 18:3 was 85% on all diets. Fatty acid digestibility was not different among diets. Microbial nitrogen in the duodenum increased from 142 g/d for control to 191 g/d for 1 and 2 kg/d. Efficiency of microbial protein synthesis (grams of microbial nitrogen per kilogram organic matter apparently digested in the rumen) was 17.3, 24.8, and 26.6 for 0, 1, and 2 kg/d. Slow release of fat from crushed rapeseed minimized negative effects on rumen metabolism; 1 to 2 kg/d of full-fat crushed rapeseed may be fed to lactating cows without detrimental metabolic effects.
Rates and extents of ruminal protein degradation for casein, solvent soybean meal (SSBM), expeller soybean meal (ESBM), and alfalfa hay were estimated from net appearance of NH3 and total amino acids in in vitro media containing 1 mM hydrazine and 30 mg/L of chloramphenicol. Protein was added at 0.13 mg of N/mL of medium, and incubations were conducted for 4 to 6 h, usually with hourly sampling. Inocula were obtained from ruminally cannulated donor cows fed diets of grass silage or alfalfa and corn silages plus concentrates. Preincubation or dialysis of inocula was used to suppress background NH3 and total amino acids; however, preincubation yielded more rapid degradation rates for casein and SSBM and was used in subsequent incubations. Preincubation with added vitamins, VFA, hemin, or N did not alter protein degradation. Protein degradation rates estimated for SSBM, ESBM, and alfalfa were not different when computed from total N release or N release in NH3 plus total amino acids, regardless of whether amino acids were quantified using ninhydrin colorimetry or o-phthalaldehyde fluorescence. Accounting for the release of peptide-N also did not affect estimated degradation. However, casein degradation rates were more rapid when using total N release or accounting for peptide-N, indicating significant accumulation of small peptides during its breakdown. Rates also were more rapid with inocula from lactating cows versus nonlactating cows with lower feed intake. Protein degradation rates were different due to time after feeding: casein rate was more rapid, but SSBM and ESBM rates were slower with inocula obtained after feeding. Several characteristics of ruminal inoculum that influenced breakdown of the rapidly degraded protein casein did not appear to have direct effects on degradation of protein in soybean meal.
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