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Title: The effect of nutrition on the pathophysiology of trypanosomiasis in Scottish Blackface sheep
Author: Wassink, Geert Jan
ISNI:       0000 0001 3563 7843
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1997
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In a series of experiments the relationship between nutrition and trypanosomiasis was investigated in sheep with special emphasis on changes in digestive function. Scottish Blackface lambs were used since these animals had shown to be relatively resistant to trypanosomiasis and the results would therefore be more comparable to the results found in related experiments with trypanotolerant animals conducted in The Gambia and Burkina Faso. The control lambs used in the experiments were pair-fed to the infected lambs in order to distinguish between the direct effects of infection and the effects of anorexia during infection. In the first experiment the effects of a poor quality and a high quality roughage were compared. Different amounts of concentrate and roughage were fed to the lambs in the second and third experiments. The diets used in these last two experiments contained similar levels of dietary energy and protein. In the fourth experiment the effects of non-protein nitrogen supplementation in the form of urea were investigated. An extra experiment was conducted looking at the effects of an arginine-free diet on a trypanosome infection in mice. In all the experiments Trypanosoma congolense was used, except in the third experiment in which a strain of Trypanosoma vivax was used. Some of the traits measured were feed intake, body weight, diet digestibility coefficients, nitrogen balance and mean retention time of the roughage through the digestive tract using chromium as a marker. Some blood haematological and biochemical parameters were also measured. In general the trypanosome infections led to a reduction in feed intake in Scottish Blackface sheep. The digestibility coefficients of organic matter and gross energy were slightly decreased during trypanosome infections but the changes were relatively small and appeared to be independent of the type of diet and pathogenicity of the trypanosome infection. The fibre (NDF and ADF) digestibility coefficients were unaffected by trypanosome infections. The trypanosome infections resulted in a small decrease in the digestibility coefficient of nitrogen independent of the type of diet offered to the lambs and the pathogenicity of the infection. In general the mean retention time of the roughage through the digestive tract was significantly longer in trypanosome-infected Scottish Blackface sheep compared with their pair-fed controls. The longer mean retention time appeared to be affected by the level of lower quality roughage intake but was independent of the pathogenicity of the disease. The effect of trypanosome infections on the nitrogen balance appeared to be dependent upon the level of feeding and the pathogenicity of the disease. A higher content of digestible undegraded protein in the diet reduced nitrogen losses in the urine during the T.vivax infection, leading to a more positive nitrogen balance. Supplementation of the diet with urea did not prove to be beneficial to trypanosome-infected Scottish Blackface sheep. The anaemia observed in the trypanosome-infected Scottish Blackface sheep was relatively mild. The anaemia was independent of the type of diet but was more severe in sheep infected with the more pathogenic strain of T.vivax than in the milder strain of T.cotigolctise. The erythropoietic response to the anaemia appeared to be inhibited in the T.vivax infected Iambs by a low intake of dietary protein. Plasma cholesterol levels were significantly reduced in trypanosome-infected lambs irrespective of the type of diet or infection. There was evidence of a relationship between plasma cholesterol levels and the parasitaemia. The reduction in plasma albumin levels was greater in the T.vivax infected sheep than in the T.congolense infected sheep. Plasma nitric oxide concentrations were significantly increased in lambs displaying a high parasitaemia at the time of sampling. Dietary L-arginine was found to play an important role in the host's defence mechanism against a trypanosome infection, at least in mice. It was concluded that the effects of trypanosome infections on the diet digestibility coefficients were relatively small and hardly affected by the pathogenicity of the infection and the type of diet fed to the Scottish Blackface lambs. The mean retention time of the roughage through the digestive tract was affected by the trypanosome infections and appeared to be longer in infected lambs with a higher intake of poor quality roughage. The mean retention time was unaffected by the pathogenicity of the disease. In contrast, the nitrogen balance was affected by the pathogenicity of the disease. A higher level of digestible undegraded protein in the diet of T.vivax infected lambs decreased urinary nitrogen losses which led to a more positive nitrogen balance. These results indicate that strategic feeding of ruminants at risk from trypanosome infection with diets high in digestible undegraded protein, such as legumes, may increase their ability to withstand the effects of the infection.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Veterinary sciences & veterinary medicine