The effects of diffusion and viscosity on ruminant faecal excretion of markers in a simple compartmental model.

Using equations obtained in a previous analysis, results are computed numerically which illustrate the effects of diffusion and viscosity on faecal excretion patterns of markers in ruminants. Results are first given for plug flow, a velocity gradient produced by viscosity, and diffusion, each mechanism operating alone. Plug flow gives a period during which no marker appears in the faeces, then a sharp increase in faeces marker concentration, followed by rapid washout.

A non-linear compartmental model to describe forage degradation kinetics during incubation in polyester bags in the rumen.

A new model for describing forage degradation kinetics during incubation in the rumen using polyester bags is presented. Attention is given to dealing with the problem of deviations from exponential behaviour in the early stages of degradation by devising a function capable of representing exponential or sigmoidal trends. This is achieved by allowing part of the fractional degradation rate to vary with time of incubation, thus enabling responses other than those expected under simple first-order kinetics to be described.

On incorporating diffusion and viscosity concepts into compartmental models for analysing faecal marker excretion patterns in ruminants.

Deterministic mathematical equations are derived to describe the pattern of marker excretion in the faeces of ruminants under steady-state conditions when diffusion and viscosity concepts are introduced into a simple two-compartment scheme of the gastrointestinal tract. The basic scheme comprises a pure-mixing pool obeying first-order kinetics and a second compartment exhibiting streamline flow. Introduction of a velocity gradient, longitudinal diffusion or both into the second compartment, even with various simplifying assumptions, yields analytically insoluble equations.

Adaptation of compartmental schemes for interpreting isotope dilution data on volatile fatty acid metabolism in the rumen to the non-steady state and for single-dose injection.

A unifying mathematical analysis of the one-pool and three-pool schemes for estimating acetate, propionate and butyrate production in the rumen from isotope dilution data is presented. Emphasis is given to non-steady-state conditions and to the administration of isotope as a single injection. The single-pool representation is also derived as a special case of the three-pool representation by assuming that the external fluxes are directly proportional to their concentrations in the rumen.

A unifying mathematical analysis of methods to estimate rumen volume using digesta markers and intraruminal sampling.

A theoretical exposition of methods for estimating the quantity of digesta in the rumen using digesta-flow markers and intraruminal sampling is given, with emphasis on the kinetic assumptions underlying each method. Single- and dual-marker approaches to estimating volume in steady and non-steady-state are presented.

On the two-compartment model for estimating the rate and extent of feed degradation in the rumen.

An analysis of the compartmental scheme used to determine the rate and extent of ruminal degradation of feeds is presented. Attention is given to the kinetic representation of the degradation of the potentially degradable fraction. Changing the kinetic order of the rate, and introducing indigestible substrate inhibition and microbial activity into its representation, are investigated.

On using a double-exponential model for describing faecal marker concentration curves.

A mathematical and numerical appraisal of the double-exponential model is presented, with particular reference to its ability to reproduce preset values of biological measures such as rumen and whole-tract mean retention times and faecal production rate. A complete, formal mathematical derivation is provided, with consideration given to a solution to the model when the two smallest rate constants are equal. It is concluded that any error introduced by using an approximation in deriving the double-exponential form is negligible in practice, and that the double exponential in logarithmic form is able to determine the relevant biological measures quite satisfactorily and speedily.

Estimating the production of faeces by ruminants from faecal marker concentration curves.

The use of faecal marker concentration curves, in conjunction with compartmental analysis, is examined as a method for predicting faecal output in ruminants. Formulae for faecal production are derived for the various multicompartment models currently used to interpret marker concentration data. A comparison of observed and model-derived estimates of faecal dry matter production using three different markers is given for sheep consuming hay or a mixed diet.

Metabolism of lactic acid isomers in the rumen of silage-fed sheep.

1. Four mature sheep were offered perennial ryegrass (Lolium perenne, cv. S23) silage (885 g dry matter/d) at hourly intervals.

Estimation of the degradability of dietary protein in the sheep rumen by in vivo and in vitro procedures.

Estimates of degradability of nitrogen in the sheep rumen for a basal hay diet and for soya-bean meal (SBM), groundnut meal (GNM) and fish meal (FM), when given together with the hay, were determined from measurements of duodenal N flow, ammonia kinetics and rumen N disappearance from polyester bags and rumen outflow rate. The ability of various in vitro procedures to predict in vivo N degradability was also examined. Four sheep were given a basal hay diet (800 g dry matter (DM) and 19 g N/d) either alone or supplemented with isonitrogenous amounts (15 g N/d) of SBM, GNM or FM.

Ytterbium acetate as a particulate-phase digesta-flow marker.

The ability of ytterbium acetabe (Yb acetate) to fulfil the requirements of a particulate-phase digesta-flow marker in a dual-phase marker system, and of the indigestible acid-detergent-fibre fraction of the feed (IADF) to act as a digesta flow marker, were examined using six mature wether sheep given a diet of dried grass (1 kg dry matter (DM)/d). CrEDTA was continuously infused (240 mg chromium/d) into the rumen of all sheep and Yb acetate was also continuously infused (100 mg Yb/d) into the rumen of three of the sheep. At this level of infusion the equilibrium concentration of Yb in rumen, duodenal and ileal digesta and in faeces could be reliably measured by atomic absorption spectrometry.

Nitrogen digestion and metabolism in sheep consuming diets containing contrasting forms and levels of N.

Nitrogen kinetics were studied in six sheep (45-55 kg live weight) consuming either a high-N grass silage or a low-N dried grass made from swards of perennial ryegrass (Lolium perenne). The diets were fed hourly at a level of 600 g dry matter/d and supplied 19.5 and 11.

A multicompartmental model to describe marker excretion patterns in ruminant faeces.

A multicompartmental model, which assumes first-order kinetics, is proposed to describe digesta flow along the gastrointestinal tract of ruminants. Solution of the model yields a multiplicative equation, containing a single-exponential term and a double-exponential term, for describing faecal outflow rate. The logarithmic transformation of the equation was fitted to eighty-two excretion curves obtained after the administration of marker into the rumen of cattle and sheep, and compared with other published models.

On the mathematics of digesta flow kinetics.

A unifying mathematical analysis of the use of compartmental models with and without time lags is given, with particular reference to the use of such models for digesta movement along the gastro-intestinal tract of the ruminant. First the generalized compartmental model without time lags is developed, and then it is shown how discrete time lags may be incorporated into this formalism. The important relationship between distributed lags, especially the gamma-distributed time lags, and the equivalent compartmental scheme, is emphasized.

The effect of formaldehyde or glutaraldehyde application to lucerne before ensiling on silage fermentation and silage N digestion in sheep.

The primary growth of lucerne (Medicago sativa) was ensiled after treatment with either formic acid alone (4.1 litres/t; silage F) or with formic acid and either formaldehyde (30.5 g/kg crude protein (nitrogen X 6.

A comparison of methods for the estimation of microbial nitrogen in duodenal digesta of sheep.

1. Six sheep, each fitted with a rumen cannula and re-entrant cannulas in the proximal duodenum and distal ileum, were given two diets (600 g dry matter (DM)/d) consisting of either grass silage (32.1 g nitrogen/kg DM) or dried grass (18.

Glutathione peroxidase activity and erythrocyte stability in calves differing in selenium and vitamin E status.

1. Glutatione peroxidase activity (EC 1.11.

The effect of formaldehyde treatment before ensiling on the digestion of wilted grass silage by sheep.

1. Wilted perennial ryegrass (Lolium perenne L. cv.

Sparing effect of folic acid deficiency on the development of vitamin B12 deficiency in baboons fed a vitamin B12 deficient diet.

The effect of a vitamin B12 and folic acid deficient diet on juvenile and adolescent baboons (Papio cynocephalus anubis) was studied. The baboons developed clinical and hematological signs characteristics of folacin deficiency, although they were less severe in juvenile baboons. The signs disappeared when folic acid was replaced in the diet.

Effect of vitamin B12 status on the occurrence of branched-chain and odd-numbered fatty acids in the liver lipids of the baboon.

Branched chain fatty acids of the anteiso series and others with methyl substitution nearer to the carboxyl group were found, together with odd numbered, straight chain fatty acids, in very small proportions in baboon liver lipids. The proportions were increased in vitamin B12-depleted animals, especially after administration of a B12 analogue.

Vitamin B12 nutrition and metabolism in the baboon (Papio cynocephalus).

1. Measurement of the vitamin B12 content of baboon tissues showed that the liver contained the highest concentration, followed by the pituitary, kidney, heart, spleen and pancreas. 2.