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M S Dhanoa

Publications and source records attributed to M S Dhanoa.

At least 19 recordsLinked to original sources
PubMed2000

Estimating the extent of degradation of ruminant feeds from a description of their gas production profiles observed in vitro: comparison of models.

An evaluation of general models that describe gas production profiles is presented. The models are derived from first principles by considering a simple three-pool scheme and permit the extent of ruminal degradation to be calculated, as described in the companion paper. The models evaluated were the generalized Mitscherlich, simple Mitscherlich, generalized Michaelis-Menten, simple Michaelis-Menten, Gompertz, and logistic. Five sets of gas production data consisting of 216 curves, obtained using a wide range of feeds (including straw, hay, silage, grain and various byproducts), were analysed to study the performance of these gas production models. Application of the non-sigmoidal models (simple Mitscherlich and Michaelis-Menten) to the data resulted in convergence problems and these models were found to be inadequate in many cases. Based on results of a pairwise comparison between models (variance ratio test), ranking of residual mean squares, lack-of-fit test, and of analyses of residuals, the generalized Mitscherlich and the generalized Michaelis-Menten models seemed particularly suited because of their flexibility to encompass sigmoidal and non-sigmoidal shapes of gas production profiles, whether symmetrical or not.

Animal Feed↗
PubMed2000

Estimating the extent of degradation of ruminant feeds from a description of their gas production profiles observed in vitro: derivation of models and other mathematical considerations.

Equations to describe gas production profiles, obtained using manual or automated systems for in vitro fermentation of ruminant feeds, were derived from first principles by considering a simple three-pool scheme. The pools represented were the potentially degradable and undegradable feed fractions, and accumulated gases. The equations derived and investigated mathematically were the generalized Mitscherlich, generalized Michaelis-Menten, Gompertz, and logistic. They were obtained by allowing the fractional rate of degradation to vary with time. The equations permit the extent of ruminal degradation (hence the supply of microbial protein to the duodenum) to be evaluated, thus linking the gas production technique to animal production.

Animal Feed↗
PubMed1999

Correcting the calculation of extent of degradation to account for particulate matter loss at zero time when applying the polyester bag method.

The established calculation of ruminal extent of degradation using the polyester bag method overestimates extent. The wash fraction, at least in part, is subject to losses from the rumen due to passage. Four formulae are proposed to minimize this risk of overestimation. Four options are considered: 1) passage losses for particulate matter escaping from the bag at zero time are according to the particulate fractional passage rate, 2) the liquid rate, and 3) the average of the two, and additionally 4) there is no instantly degradable fraction. The established and proposed formulae were examined using polyester bag data for six forages: grass silage, fresh ryegrass, fresh white clover, alfalfa hay, mixed grasses hay, and hay from a permanent mountain meadow. The established formula gave appreciably higher estimates of extent of degradation in all cases. Overestimation was at least 6.9, 4.9, 2.9, 2.1, 2.4, and 4.5%, respectively, for the six forages.

Animal Feed↗
PubMed1999

Comparison of mathematical models to describe disappearance curves obtained using the polyester bag technique for incubating feeds in the rumen.

Different nonlinear models were evaluated as candidates to describe ruminal degradation kinetics of forages from data obtained by the incubation of the feeds in the rumen using polyester bags. Nine models were used: segmented model with three straight lines (Mod0); simple Mitscherlich or exponential (Mod1); inverse polynomial (Mod2); compartmental model with two exponential terms (Mod3); generalized Mitscherlich (Mod4); generalized Michaelis-Menten (Mod5); logistic (Mod6); Gompertz (Mod7); and generalized Von Bertalanffy (Mod8). All these models can be represented in the general form D = W + S0 x phi(t), where D is in situ disappearance at incubation time t, W and S0 are positive scalars, and phi is a positive monotonically increasing function unique to each of the models studied. Based on first principles, a general formula for calculating the extent of degradation of feeds in the rumen has been derived that is applicable to all the models. The disappearance curves of different feed components (DM, N, and NDF) of 87 Mediterranean forages (i.e., a total of 261 curves) were fitted to all the models. A comparative study was carried out based on the mathematical, statistical, and biological characteristics of the models. Flexible models that can accommodate both diminishing returns and sigmoidal behavior were more appropriate in describing the curves. A discrete-lag parameter was introduced into Mod0, Mod1, and Mod2 to describe the initial stage of the disappearance curve, and this parameter considerably improved the fit of experimental data. Based on statistical criteria, models Mod1, Mod4, Mod5, and Mod8 were better than the others for most statistical tests and disappearance curves, but differences among these four models were not consistent. The estimates of degradation parameters to quantify the rate (half-life, fractional degradation rate), and extent (undegradable fraction, effective degradability) of ruminal degradation of feeds were also used as a means to discriminate between models, although in most cases all of the models gave similar values of the degradation parameters. In particular, when the extent of degradation was calculated for each forage and feed component, differences between the estimates obtained with the different models were of little nutritional significance for the animal.

Animal Feed↗
PubMed1997

A model to describe growth patterns of the mammary gland during pregnancy and lactation.

Extensive proliferation and death of cells in the mammary gland occur during pregnancy and lactation. In this study, a mechanistic model was developed that yielded a single equation to describe the pattern of mammary growth of mammals throughout pregnancy and lactation. The model contains a single pool, which is the cell population of the mammary gland; one influx, representing cell proliferation; and one efflux, representing cell death. The parameters of the equation lend themselves to direct physiological interpretation. The model fitted data on mammary gland DNA adequately and can be related to current knowledge on factors and inhibitors of mammary gland growth. A unique definition of the parameters of the model can be difficult because of the high degree of variation among animals, an improper number of observations, or timing, as indicated by analyses of simulated data. The model can also be applied to the study of the entire lactation curve. The widely applied gamma equation and the equation that was developed in this study were compared using weekly production data from dairy cows. The new model performed well, particularly when a sharp peak in milk production occurred. The model has the advantage of providing, for the first time, a simple biological description of the lactation curve that can be used to discriminate changes in lactational performance that are associated with experimental treatments.

Animals↗
PubMed1996

A simple but flexible growth function.

The functional form W(t) = Wf - (Wf - Wo) exp[-k infinite (t - T) + 2c(root of t - root of T)] where Wf, Wo, k infinite, c and T are constants, is derived as a growth equation and evaluated using commonly applied growth functions such as the Gompertz, logistic, monomolecular and Richards. Further evaluation is made with reference to sets of observations on growth in a number of animal species ranging from mice to horses. The new function provides a flexible growth equation capable of describing sigmoidal and diminishing returns behaviour. It appears adept at describing sigmoidal patterns exhibiting faster early growth and a fairly low but variable point of inflexion, and can therefore be perceived as a generalised Gompertz equation. The function also has the ability to describe a wide range of hyperbolic shapes when there is no point of inflexion. The analysis described suggests that this simple equation is a worthwhile addition to the corpus of growth functions.

Animals↗
PubMed1995

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 velocity gradient gives a more gradual appearance of marker in the faeces followed by a slower washout. Diffusion alone (although not realistic for ruminant marker kinetics) can give early appearance of marker followed by slow washout. Combining diffusion with a velocity gradient produced by viscosity can give a range of behaviour, depending on the effective diffusion coefficient, D'; an approximate method is used to compute these solutions. Because plug flow with no velocity gradient plus diffusion gives results similar to convective flow with a velocity gradient plus diffusion, we believe it will not be possible to determine the main mechanisms defining marker outflow patterns from observations of marker kinetics alone, and more detailed investigations will be needed. Although estimates of quantities such as mean transit time are unaffected by detailed mechanism, the interpretations of measures such as sigmoidicity, sharpness of the faecal marker concentration v. time curve, and length and nature of the washout tail are highly dependent on mechanism.

Animals↗
PubMed1995

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. Seven sets of data consisting of 620 curves were analysed to study the performance of the new model compared with a commonly used exponential model. The proportion of significantly better fits varied from set to set. The new model deals successfully with sigmoidal behaviour and, thus, provides a means of analysing the degradation profiles of low-quality forage feeds.

Animal Feed↗
PubMed1994

Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation.

The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE 5) d (Expt 1; post-peak, 4.51 (SE 0.26) kg milk/d) and at 180 (SE 6) d (Expt 2; late, 2.36 (SE 0.16) kg milk/d) of lactation during non-primed, continuous (Expt 1, 12 h; Expt 2, 16 h) intravenous infusions of mixtures of L-[1-13C]leucine and L-[1-13C]phenylalanine with either L-[1-13C]valine (Expt 1) or L-[5-13C]methionine (Expt 2). The 13C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6-8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the casein-bound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.

Amino Acids↗
PubMed1993

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. The impact of these mechanisms is to be investigated numerically rather than analytically in future work.

Animals↗
PubMed1993

Examination of energy utilization in cattle offered a forage diet at near- and sub-maintenance levels of feeding.

Eight Friesian calves were reared from birth to the start of the experiment at a predetermined growth rate of 1.0 kg/d. Four calves (group 1) commenced the experiment at 22 weeks of age and the remainder (group 2) at 34 weeks, and feed intake was calculated to provide sufficient metabolizable energy to sustain zero energy balance (Em). Between experimental days 30 and 56 at maintenance levels of feeding, respiratory exchange measurements were made using open-circuit calorimetry to provide indirect estimates of heat production (H) simultaneous with measurements of faecal and urinary excretion of energy and N. A datum point for Em and H was established for each animal giving mean values for Em of 491 and 537 and for H of 476 and 511 kJ/kg live weight (LW)0.75 per d for groups 1 and 2 respectively. Treatment levels calculated as 0.25, 0.5, 0.75 and 1.25 of dry matter intake required to sustain the measured Em, were imposed on individual animals after day 56 and further measurements of H and faecal/urinary balance were made between days 72 and 84 followed by measurements of fasting heat production (FHP) during days 86-90 from the two animals in each group which had received the 0.75 and 1.25 levels of intake. Regression analysis of the treatment levels indicated separate linear models which predicted Em at 419 and 473 kJ/kg LW0.75 per d for groups 1 and 2 respectively. The incorporation of FHP with partitioning of faecal and urinary energy losses measured during fasting altered the relationship but not the predicted Em. Overall predicted Em (days 72-84) from all models were 406 and 478 kJ/kg LW0.75 per d for groups 1 and 2 respectively which were significantly lower (P < 0.05) than Em measured during days 30-56.

Animals↗
PubMed1992

Studies of method of conserving grass herbage and frequency of feeding in cattle. 1. Voluntary feed intake, digestion and rate of passage.

The effect of method of conserving grass herbage and the frequency of feeding on digestion in and passage from the rumen was studied in growing cattle. A single sward of perennial ryegrass (Lolium perenne cv. Endura) was cut on 1 d and conserved as silage or hay. These forages were offered as the only feed to twelve rumen-cannulated Friesian steers (average initial live weight (LW) 128 kg) either at a restricted level of intake (20 g dry matter (DM)/kg LW; Expt 1) or ad lib. (Expt 2). In Expt 1 the forages were offered either once or eight times daily. When fed once or eight times daily, in vivo digestibility of DM was very similar for hay and silage (0.771 and 0.783 respectively), while the fractional rate of digestion measured by incubation in Dacron bags was significantly (P less than 0.05) higher for silage (0.069) than hay (0.057). The rate of passage of mordanted feed out of the rumen was significantly (P less than 0.01) faster for silage when determined from concentrations of marker in the rumen (0.034 v. 0.028/h). The volume of liquid in the rumen was lower (P less than 0.01) for animals consuming silage (27.51) compared with hay (37.11), while the fractional rate of passage of liquid from the rumen was higher (0.141 v. 0.098/h, P less than 0.05). The volume of liquid in the rumen was also lower (P less than 0.05) in steers offered feed eight times daily (29.5 l), compared with once daily (35.1 l), but frequency of feeding had no significant effect either on total digestibility or on rate of digestion in the rumen. The ad lib. intake of silage was significantly (P less than 0.01) lower than that of hay (4.53 v. 5.16 kg DM/d) in Expt 2.

Animal Feed↗
PubMed1991

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.

Acetates↗
PubMed1991

Rumen fill and digesta kinetics in lactating Friesian cows given two levels of concentrates with two types of grass silage ad lib.

Four lactating Friesian cows with permanent cannulas in the rumen and proximal duodenum were given early (EC)- or late (LC)-cut grass silage ad lib., each with either 3 or 9 kg concentrate dry matter (DM)/d in a 4 x 4 Latin square design starting about 10 weeks after calving. Feed was offered twice daily at 08.30 hours and 15.30 hours. Periods lasted 5 weeks and measurements were made in the last 15 d. The higher amount of concentrates increased total DM intake but reduced silage DM intake and the fractional rate of degradation of silage-fibre DM. Later cutting date of silage had no effect on DM intake or the fractional rate of degradation of silage-fibre DM but reduced potential degradability of silage fibre. Dilution rate of CoEDTA in rumen fluid was greater during the day (eating period) than during the night (resting period). Dilution rates measured at the duodenum were lower than those measured in the rumen, but neither was affected by diet. Silage-particle passage rates were measured by use of ytterbium-labelled silage fibre (Yb-fibre) and chromium-mordanted faecal particles (Cr-faeces) and samples were taken at the duodenum and in the faeces. Values for slower rate constant (k1) and transit time were higher and for faster rate constant (k2) were lower for Yb-fibre than for Cr-faeces, but differences in total mean retention time were inconsistent. Values for k1 for both markers and k2 for Yb-fibre only were similar at both sampling sites, but values for k2 for Cr-faeces were lower in the faeces. No diet effects were established with Yb-fibre but, with Cr-faeces, k1 was reduced by more concentrates and EC-silage. Daily mean weights of wet digesta, liquid, neutral-detergent fibre (NDF) and indigestible NDF in the rumen were greater with LC-silage but were unaffected by the amount of concentrates whereas weight of rumen DM was increased by the amount of concentrates only. Maximum rumen fill occurred at 18.00 hours with all diets. Particle-size distribution of rumen contents did not vary markedly during the day. Mean particle size was generally greater with LC-silage than EC-silage. Very small particles, passing through the 0.3 mm screen, constituted about half the rumen DM. It is concluded that rumen fill could have limited intake of LC-silage but not EC-silage.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

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. This leads to response functions such as the Gompertz and logistic for describing the cumulative disappearance of potentially degradable substrate during in-sacco and in-vitro incubation.

Animals↗