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Biomedical subjects

E R Orskov

Publications and source records attributed to E R Orskov.

At least 55 records · Page 3Linked to original sources
PubMed1984

The nutritive value of rumen micro-organisms in ruminants. 4. The limiting amino acids of microbial protein in growing sheep determined by a new approach.

Four experiments were carried out to identify and quantify the limiting amino acids (AA) in rumen microbial protein (RMP). A method was developed which involved first, an assessment of the efficiency of utilization of absorbed AA-nitrogen (U) of RMP, defined as the retention of AA-N from RMP absorbed from the small intestine, and second, addition of a mixture of AA similar to the absorbed AA profile in a quantity defined by the U of RMP and equal to (1-U)/U. Third, it involved removal of each AA in turn and measurement of the resultant N retention. Using this approach it was possible to calculate both the order and extent of AA limitations in RMP. Apart from methionine which was found to be the most limiting AA, only lysine, arginine and histidine reduced N retention when omitted, and accordingly only these AA were limiting in RMP. The method is discussed in detail and the amount of supplementary AA required to utilize RMP fully is calculated.

Amino Acids↗
PubMed1983

Investigation of nitrogen balance in dairy cows and steers nourished by intragastric infusion. Effects of submaintenance energy input with or without protein.

Two dairy cows were maintained by intragastric infusion of volatile fatty acids and casein. Except when fasting, the casein-nitrogen was held constant, while total gross energy supply was varied from zero during fasting to 650 kJ/kg body-weight (W)0 . 75. One cow was estimated to attain zero N balance at an energy intake of 255 kJ/kg W0 . 75 and the other at 307 kJ/kg W0 . 75, which was calculated to be substantially below the estimated energy required for zero energy balance. When the cows were later given an N-free infusion for a period preceding the trial, N balance occurred at 98 kJ/kg W0 . 75 for one cow and 115 kJ/kg W0 . 75 for the other. Four steers were similarly nourished by intragastric infusion and the energy nutrient increased from 0 at fasting to 450 kJ/kg W0 . 75. The protein was held constant at 1 g N/kg W0 . 75 except at fasting. The energy level at which N balance occurred was 154 (SE 38) kJ/kg W0 . 75 or approximately equal to the energy content of the protein. The practical implications of these findings are discussed.

Animal Nutritional Physiological Phenomena↗
PubMed1983

Basal urinary nitrogen excretion and growth response to supplemental protein by lambs close to energy equilibrium.

Two experiments are reported. In Expt 1, five male lambs of 26-33 kg were used to measure basal nitrogen excretion when the lambs were entirely sustained by an intraruminal infusion of 450 kJ/kg body-weight 0.75 per d of volatile fatty acid (VFA) and were receiving no protein. In Expt 2, which was a conventional growth trial, the response to fish meal (66 or 132 g dry matter/d) of lambs given a control diet of sodium-hydroxide-treated barley straw was measured. In Expt 1 the mean basal N excretion of the lambs was 429 (SE 21) mg N/kg body-weight 0.75 per d. This exceeds current UK standards for the amino acid N of microbial origin which would be made available to the normally-fed host animal at a maintenance level of metabolizable energy intake. In Expt 2 there was a clear growth response to the fish meal, which was greater (P less than 0.05, single-tailed test) than that to be predicted from the energy content of the fish meal. There was no effect of fish meal on the voluntary intake of the basal diet, but there was a suggestion that the digestibility of the basal diet was improved. It is concluded from Expt 1 that the basal requirement for amino acid N by lambs is three- to fourfold that currently recommended in the UK. This higher basal N requirement should have resulted in a marked response to supplemental protein in Expt 2. The fact that the growth response in Expt 2 was less than anticipated may have been due to a combination of a slightly lower basal N excretion than that found in Expt 1, a higher yield of amino acids of microbial origin than current UK standards predict, and possibly to a change in the body composition of the lambs.

Animals↗
PubMed1983

The effect of changes in the amount of energy infused as volatile fatty acids on the nitrogen retention and creatinine excretion of lambs wholly nourished by intragastric infusion.

The nitrogen balance and creatinine excretion of wether lambs of 30-48 kg, wholly nourished by the intragastric infusion of nutrients, were measured in two experiments. Four lambs were used in each experiment. In Expt 1 a constant amount of casein was infused into the abomasum (640 mg N/kg body-weight (W)0.75 per d) and the amount of volatile fatty acids (VFA) infused into the rumen ranged from 0 to 670 kJ/kg W0.75 per d as six increments. Expt 2 was of similar design but two levels of casein were infused (530 and 1060 mg N/kg W0.75 per d) and, with each level of casein, VFA infused ranged from 0 to 700 kJ/kg W0.75 per d as seven increments. Daily creatinine excretion was not constant, but varied between 2-d means with standard deviations of between 7.1 and 16.5% (average 13.1%) of the over-all means. There was an apparent correlation between creatinine excretion and the amount of energy infused in six out of eight lambs. There was no effect of the amount of casein infused. In both experiments N balance was negative only when the amount of energy infused was substantially below published values for energy maintenance. In Expt 1, N equilibrium was calculated to be achieved at a gross (VFA plus protein) energy infusion level of 162 (SE 29) kJ/kg W0.75 per d. In Expt 2 it was observed that, at a given level of energy infusion, N retention was greater when the amount of energy had been increased from the previous level, than when it had been decreased. It is concluded that the animal appears to allocate available amino acids to protein synthesis, rather than to oxidation, even when in negative energy balance. It is also concluded that enhanced N retention observed when the amount of energy infused had been increased represented compensation after a period of energy restriction.

Animals↗
PubMed1983

The nutritive value of rumen micro-organisms in ruminants. 1. Large-scale isolation and chemical composition of rumen micro-organisms.

A method is described whereby a large quantity of rumen microbial dry matter of high purity was isolated from whole rumen contents obtained from abattoirs, by means of a continuous process of one filtration through four sieves followed by three differential centrifugations. The contents of ash, carbohydrate, lipid, nitrogen, RNA, DNA and individual amino acids of the three centrifugal fractions are given and compared with values summarized from more than sixty published reports on the chemical composition of rumen micro-organisms isolated from both whole rumen contents and pure cultures. The amino acid composition of isolated rumen micro-organisms, in particular that of the bacteria, was found to be remarkably constant.

Amino Acids↗
PubMed1983

The nutritive value of rumen micro-organisms in ruminants. 2. The apparent digestibility and net utilization of microbial N for growing lambs.

Four experiments were conducted with eighteen lambs sustained entirely by intragastric nutrition at gross energy inputs varying from 430 to 860 kJ/kg live weight0.75 (W0.75). Isolated rumen micro-organisms (RMO) were infused into the abomasum in quantities varying from 0 to 2 g digestible N/kg W0.75 to assess the increase in N balance as a result of increasing RMO input when N was limiting. The over-all utilization of N from RMO (RMO-N) could be described by the equation y = 0.543 X -0.457, residual SD = 0.037, where y is the N balance and X is the abomasal input of RMO-N, both expressed in g/kg W0.75. Thus the coefficient of efficiency of utilization of infused RMO-N was 0.543 (SE 0.008). The coefficient of efficiency of utilization of RMO-N truly digested (i.e. the biological value) was 0.659 (SE 0.015). The RMO-N input (mean with SE) at N equilibrium was 0.843 (0.009) g/kg W0.75. The true digestibility of RMO-N was 0.813 (0.004). The urinary N excretion when no N was infused was 0.329 (0.008) g/kg W0.75 and the N excreted via the faeces with zero N input was 0.036 (0.009) g/kg W0.75.

Amino Acids↗
PubMed1983

The nutritive value of rumen micro-organisms in ruminants. 3. The digestion of microbial amino and nucleic acids in, and losses of endogenous nitrogen from, the small intestine of sheep.

An experiment was conducted with three sheep maintained entirely by intragastric nutrition to estimate the digestibility of isolated individual constituents and amino acids (AA) of rumen micro-organisms (RMO) in the small intestine. Five levels of RMO were infused into the abomasum. The apparent and true disappearance of the individual components were measured by regression of abomasal input on the passage at the ileum. The true digestibility values of N, AA-N, DNA and RNA were 0.82, 0.85, 0.81 and 0.87, respectively. The digestibility of individual AA varied between 0.80 and 0.88, the only exceptions being diaminopimelic acid (0.37), histidine (0.68) and cystine (0.73), which were significantly lower than the average (0.847). The endogenous components in the ileal fluid in sheep given protein-free infusions, expressed in mg/kg live weight0.75 per d, were total N 42 and AA-N 20.

Amino Acids↗
PubMed1982

Intragastric infusion of nutrients in cattle.

1. A method of continuous alimentation of cattle by total infusion of nutrients has been developed. Friesian steers within the weight range 100-400 kg live weight and dairy cows were used. 2. A multi-channel peristaltic pump was used to infuse solutions of volatile fatty acids (VFA), minerals, and buffer through a cannula in the rumen and a casein-vitamin solution into the abomasum. 3. The method described was successfully used with two cows and four steers in a series of trials over intervals of approximately 2 months. The levels of infusion were up to twice maintenance and with various relative proportions of VFA and protein. Blood metabolite levels, rumen osmotic pressure and pH were monitored and effectively controlled.

Abomasum↗
PubMed1982

The determination of the minimal nitrogen excretion in steers and dairy cows and its physiological and practical implications.

1. Cattle were maintained by intragastric infusion to see how much nitrogen was excreted on protein-free diets. 2. Minimal N excretion was estimated with two dairy cows in three periods, i.e. when they were non-pregnant and non-lactating, when they were between 117 and 133 d pregnant and when they were between 220 and 233 d pregnant. The minimal N excretion was also estimated on two occasions with two steers when their average live weights were 200 and 350 kg. 3. Average urinary N excretion without protein infusion was 298, 305 and 283 mg/kg metabolic live weight (W0.75) for the non-pregnant cows and for cows during the first and second periods of pregnancy respectively; total N excretion including the faecal N was 340, 329 and 319 g/kg W0.75. 4. For steers the urinary N values were 403 and 295 mg/kg W0.75 at 200 and 350 kg live weight respectively and total N excretion including faecal N was 408 and 320 mg/kg W0.75. 5. Urinary excretion of creatinine was the same for animals given casein via the abomasum as a source of protein or given no protein with mean values for the cows of 13.6 and 14.9 g/d for the first and second stages of pregnancy respectively. Mean values for the steers were 6.5 and 7.6 g creatinine/d at 200 and 350 kg live weight respectively. 6. It is suggested that the so-called metabolic faecal N in ruminants, estimated with N-free diets, is mainly, endogenous N derived from tissue breakdown of protein but incorporated in microbial debris and excreted in the faeces.

Animals↗
PubMed1981

The effects of protein degradability and food intake on milk yield and composition in cows in early lactation.

1. In two experiments measurements were made of food intake, live-weight change, milk yield and milk composition in early lactation when dairy cows were given diets containing varying proportions of protein as fish meal (low rumen degradability) or as groundnut meal (high rumen degradability). In a preliminary trial measurements were also made with cows given supplements of either fish meal or barley and fed at a restricted level of feeding. 2. When metabolizable energy (ME) intake exceeded 160 MJ/d there was no evidence of responses to changes in protein degradability, ut at ME intakes below 135 MJ/d increases in the supply of undegradable protein led to increases in fat-corrected milk yield, protein content and live-weight loss. 3. The interaction between energy intake and protein degradability is unexpected because net protein:net energy requirement increases as milk yield increases, but may be explained in terms of differential effects of changing rumen outflow rates on degradabilities.

Animals↗
PubMed1979

An independent microbial flora of the epithelium and its role in the ecomicrobiology of the rumen.

IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations-the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ(1). Until now, studies of the 'epithelial' population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora(2-5). A recently developed technique(6) for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall(7-9).

Journal Article↗
PubMed1979

Efficiency of utilization of volatile fatty acids for maintenance and energy retention by sheep.

1. Two experiments were conducted with lambs sustained entirely by intragastric infusion of volatile fatty acids (VFA), protein, minerals and vitamins. 2. In the first experiment to determine the effects of VFA on nitrogen retention four mixtures of VFA (B, C, D and E) were used containing acetic, propionic and butyric acid in the following molar proportions respectively: 45, 45 and 10; 55, 35 and 10; 65, 25 and 10; 75, 15 and 10. The level of infusion was 836 kJ/live weight0.75 per d and the design was a 4 X 4 Latin square with 14 d periods. There were no significant differences in the N balance between the different mixtures of VFA though mixture B tended to give the highest N retention. 3. Thirty-two lambs were used in the second experiment for measurements of heat production in closed-circuit respiration chambers. Six mixtures of VFA were used. These included mixtures B-E from Expt 1 and in addition two mixtures (A and F) containing acetic, propionic and butyric acid in the following molar proportions respectively: 35, 55 and 10; 85, 5 and 10. The heat production was measured both at 450 and 900 kJ/W0.75 per d, except for mixture F, where it was not possible to achieve a rate of infusion in excess of 675 kJ/W0.75 per d. 4. The energy required for maintenance was determined to be 0.45 +/- 0.02 MJ/kg live weight0.75 per d regardless of the mixture used. 5. The efficiency of utilization for fattening (kf) values for the six mixtures were 0.78, 0.64, 0.57, 0.61, 0.61 and 0.59 for mixtures A, B, C, D, E and F respectively. Only mixture A was significantly better utilized than the other mixtures. This mixture also gave the most efficient N utilization. 6. It is concluded from this evidence that differences in kf for diets normally given to ruminants cannot be attributed to differences in utilization of volatile fatty acids.

Animals↗