The artificial fibre bag technique was evaluated for assessing the proportions of dietary D. M. and N which disappear in the rumen. The most important factor determining the variability in disappearance from bags incubated together was the sample size in relation to bag size. For incubation of 5 g air dry feed, a bag size of 17 ✗ 9 cm was found to be adequate. There were also variations in substrate disappearance between animals and between days of incubation. It was estimated that three sheep and the measurement of substrate disappearance twice were necessary in order to obtain acceptable repeatability.The technique was found to be satisfactory as a simple and rapid guide for measuring nutrients disappearance in the rumen such as protein degradation and carbohydrate fermentation. It has been used in subsequent work to measure the effect of features of the rumen environment, such as pH and NH3 concentration, on rate of fermentation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0021859600037321

A study of artificial fibre bag technique for determining the dig estibility of feeds in the rumen

An automated technique has been developed for estimating NH4+ in Kjeldahl digests of crops, using the salicylate-dichloroisocyanurate reaction in the presence of nitroprusside. The method gives reproducible results in close agreement with those from conventional distillation and titration, and there is a marked improvement in output.

Determination of ammonium in Kjeldahl digests of crops by an automated procedure

1. Four sheep were fed from automatic continuous feeders on whole barley fortified with graded levels of a urea solution. This approach was to a large extent successful in maintaining relatively steady states of rumen ammonia concentration. 2. Rates of barley fermentation in the rumen at various rumen NH3 concentrations were assessed by measuring the disappearance of barley dry matter from polyester bags suspended in the rumen of these sheep. 3. The minimal NH3 concentration for maximal rate of fermentation was estimated as 235 mg/l rumen fluid.

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Rates of rumen fermentation in relation to ammonia concentration

A series of four nitrogen-balance experiments was carried out with growing pigs to determine the optimum balance amongst the amino acids in the diet. The reduction in N retention when 20 % of a single amino acid was removed from the diet was used to calculate a dietary amino acid pattern in which each amino acid would he equally limiting. A mixture of amino acids simulating the amino acid pattern of casein was used with the same efficiency as casein. From two successive deletion experiments an optimum balance amongst the essential amino acids was derived. Expressed relative to lysine = 100 this had threonine 72, valine 75, methionine + cystine 63, isoleucine 60, leucine 110, phenylalanine + tryosine 120, tryptophan 18. No estimate was made for histidine. Essential amino acids in this pattern were mixed with non-essential amino acids in ratios of 36:64 up to 57:43. The highest efficiency of N retention was achieved with diets having a ratio of at least 45:55. This included (g/16 g N) lysine 6 5, threonine 4.7, valine 4 9, methionine + cystine 4.1, isoleucine 3 9, leucine 7.2, phenylalanine + tyrosine 7.8, tryptophan 12. The N of diets with this amino acid pattern was utilized significantly better than when the pattern proposed by the Agricultural Research Council (1981) was used. The flow of amino acids past the terminal ileum of pigs given the semi-synthetic diet with this amino acid pattern was no greater than that observed with protein-free diets. The proposed pattern thus describes the intrinsic requirements of the growing pig for absorbed amino acids.

/pdf/the-optimum-dietary-amino-acid-pattern-for-growing-pigs-1-36zlxpq7lc.pdf

The optimum dietary amino acid pattern for growing pigs. 1. Experiments by amino acid deletion.

Two experiments were carried out to determine endogenous excretion of purine derivatives in steers and lambs, and to investigate the relationship between microbial nucleic acid input and urinary excretion of purine nitrogen. The endogenous excretion of allantoin after conversion of hypoxanthine, xanthine and uric acid to allantoin, was calculated to be 72 and 26 mg/kg W 0·75 per day in steers and lambs, respectively, when the dietary protein contained no nucleic acid nitrogen. The excretion of purine derivatives increased linearly with increasing microbial nucleic acid input in lambs. The excretion of purine derivatives in excess of endogenous contribution was closely related to the theoretically expected values. The average recovery was calculated as 0·96 for one sheep and 1·0 for the other.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0021859600080916

The effect of protein infusion on urinary excretion of purine derivatives in ruminants nourished by intragastric nutrition

An account is given of the development of a system making maximum use of automated equipment in the routine determination of nitrogen in biological samples when the desired order of precision is better than 1 per cent. and the expected number of analyses is greater than 100 per day.An automatic digestion unit made by Technicon Instruments Company Ltd. tested for liquids did not achieve the accuracy desired. Results for biological fluids with this digestor tended to be low on occasion by up to 5 per cent. Recovery of nitrogen from solutions of the pure compounds creatine and arginine was as low as 70 per cent. and alterations in the digestion mixture and digestor heating conditions did not materially improve recovery. For this reason all samples were subsequently digested by a standard Kjeldahl method before automated determination of ammonia in the diluted digests.Studies were made of the indophenol-blue reaction used in the automated system for determining ammonia in aqueous solution. Conditions were most stable when the reaction coil was maintained at 22°± 1° C and dwell time in the coil was about 3 minutes. Effects of mineral content of test solutions, sampling rate and sampler cam irregularities on the reliability of results were investigated.Results for nitrogen determined in acid digests by the automated procedure and by a standard distillation method showed close agreement.The use of an I.B.M. 1130 computer allowed calculation of results to be carried out in half the time taken when using an electronic desk calculator.

J. Mathieson

Papers

The use of automation in determining nitrogen by the Kjeldahl method, with final calculations by computer