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Title: Intragastric infusion and its use in the investigation of nitrogen and glucose metabolism in ruminants
Author: Girdler, Clive P.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1986
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1. Current techniques used for measurements of the composition of feeds given to ruminants and of the subsequent utilization of nutrients by these animals were reviewed. Intragastric infusion, an alternative technique for the precise control of nutrient supply under experimental conditions, was introduced and its use for the investigation of nutrient utilization was discussed. 2. Experiments were undertaken to develop the intragastric infusion technique for use at the HRI for investigations into the effects of propionate supply on N utilization in ruminants. 3. In the first experiment propionate was isoenergetically withdrawn from 'control' infusions given to a cow which were designed to provide an above-maintenance supply of energy together with adequate protein to sustain zero N retention (420mg N/kgW 0.75 per d). The quantity of N excreted by the cow was increased from 47 to 54g/d (15%) in response to propionate withdrawal. The animal maintained its homeostasis, as judged by its plasma glucose concentration, and was able to derive 2.37g glucose/kgW 0.75 per d from the protein that was catabolised. In view of the types of glucose-precursor supplied to the animal, this quantity of glucose was equivalent to the animal's minimum requirement. 4. A more extensive study of the effects of propionate supply on N utilization was conducted with a larger group of animals and this was most conveniently achieved using sheep. Propionate was isoenergetically withdrawn from 'control' infusions and N excretion was increased by 2.64g/d (27%). From this a minimum glucose requirement of 2.44g/kgW 0.75 per d was calculated and proportions of this requirement were used to supplement isoenergetic propionate-free infusions in subsequent treatments. When glucose was reintroduced in quantities equivalent to the minimum requirement, a positive retention of N of 0.06g/kgW 0.75 per d was measured, despite there being no change in the 480mg casein N/kgW 0.75 per d provided by the infusions. When glucose was again isoenergetically withdrawn from the infusions the quantity of N excreted by the animals was 13% lower than in the identical treatment initially imposed. It appeared that restriction of glucose-precursor supply was associated with increased efficiency of utilization of N and/or a reduction in glucose utilization. The effects of the treatments on the plasma concentrations of certain metabolites and amino acids suggested glucose sparing could have occurred and that non-essential amino acids were major contributors to gluconeogenesis. This despite the provision of ME in quantities calculated to allow positive energy retention. 5. In a third experiment, after an initial 'control' period (P1), propionate was withdrawn from the infusions (P2) and then reintroduced at 50% of the quantities given in (P1) for a prolonged period (P3, 32d). Finally propionate was fully reintroduced (P4). Blood analyses were made to provide information on the time scale and nature of the metabolic response. In P2 there was an increase in N excretion from 0.41 to 0.59g/kgW 0.75 per d (43%) despite a constant supply of 413mg Casein N/kgW 0.75 per d throughout the experiment. In P3 and P4, 0.38 and 0.36g N/kgW 0.75 per d were excreted respectively. P3 was intended to perpetuate the adaptive response initiated in P2 but, judging by the quantities of N excreted and the changes in the blood plasma constituents that were measured, the adaptive response had not been perpetuated and there was little difference in the effects of restricting propionate by 50% (P3) or not restricting propionate supply at all (P1 and P4). 6. A more severe perturbation of glucose-precursor supply was imposed on the animals. Following an initial 'control' period (P1), propionate was isoenergetically withdrawn from the infusions (P2) for as long as was practicable for the animals to avoid clinical hypoglycaemia. Propionate was then reintroduced to the infusions (P3) in the same quantities as given in P1. The N excreted by the animals during the 3 treatments was 0.47, 0.64 and 0.46g/kgW 0.75 per d respectively despite the provision of 473mg casein N/kgW 0.75 per d throughout the experiment. Analysis of the N data from P2 showed there to be a tendency for N excretion to fall after the first 5 days of the treatment. This change in N excretion was not, however, associated with any changes in the constitutents of blood plasma that were measured.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available