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    The rat as a model animal for digestion in the dog : a thesis presented in partial fulfilment of the requirement for the degree of Master of Science in Nutrition at Massey University
    (Massey University, 1998) Sritharan, Kugappiriyai
    The suitability of the laboratory rat as a model animal for studying protein digestion in the dog was investigated. The work was conducted in two experiments. In the first study ileal and faecal endogenous excretion of amino acids and nitrogen was measured in adult rats and dogs. Two groups of five adult dogs (two females and three males) and two groups of six adult rats (three males and three females) were fed either a protein-free (PF) or enzyme hydrolysed casein (EHC)-based diet, containing Cr O as an indigestible marker. After an 8-10 d equilibration period, 4½ h after the start of hourly feeding, the animals were euthanased and the ileal content was collected from the terminal 20 cm of the ileum and freeze-dried. Faecal digesta samples of the rats and dogs fed the PF diet were obtained one day before digesta sampling from the terminal ileum. The freeze-dried digesta collected from the EHC fed animals were ultrafiltrated before analysis. The amount of endogenous amino acids and nitrogen excreted per gram of dry matter intake at the end of the ileum for the PF and EHC fed animals and over the entire digestive tract for the PF fed animals were determined. Data were analysed using ANOVA with species, diet and the interaction between species and diet as variables. There was no interaction between species and diet on the endogenous ileal excretions of any of the amino acids or nitrogen. Significant (P < 0.05) higher endogenous amino acid and nitrogen excretions were found in the dogs compare to the rats when fed the PF and EHC-based diet. Faecal endogenous excretions were higher than ileal endogenous excretion in both species for all amino acid. The pattern of endogenous amino acid excretions was similar in both species with the endogenous excretions of amino acids measured by the ultrafiltration method significantly (P < 0.05) higher than the PF method in both species. In the second experiment the digestibility of a commercial dry dog food was compared between the rat and the dog. A group of five adult dogs (three females and two males) and six adult rats (three females and three males) were fed a commercial dry dog food, containing Cr O as an indigestible marker for 10 and 8 days, respectively. On the final day, 4½ h after the start of hourly feeding, the animals were euthanased and the ileal content was collected and freeze-dried. A faecal sample was collected from each animal one day before ileal digesta sampling. The diet and digesta samples were analysed for amino acids, nitrogen, organic matter and the apparent digestibility of dry matter, organic matter, nitrogen and amino acids were determined at a faecal and ileal level. The true ileal digestibility of nitrogen and amino acids were calculated and all the data were analysed using ANOVA. In the dog, the apparent faecal digestibility of aspartic acid, threonine, serine, proline, glycine and total nitrogen was significantly (P < 0.05) higher than the apparent ileal digestibility values whereas for methionine the apparent ileal digestibility value was significantly (P < 0.05) higher than the apparent faecal digestibility value. Apparent and true ileal digestibility for most amino acids were significantly (P < 0.05) higher in the dog when compared to the rat. Regression analysis showed that there was a significant (P < 0.001) linear relationship between the apparent and true ileal digestibility of amino acids between the rat and the dog. Ileal digestibility of amino acids in the dog (Y) could be predicted from respective rat values (X). The following equations were obtained for apparent digestibility: Y = 0.32 + 0.65 X and true digestibility: Y = 0.45 + 0.53 X. The present study showed that the rat may be a useful model for studying protein digestion in the dog. However, to make a more general conclusion regarding the use of the rat as a model animal to study protein digestion in the dog, a wider range of dog foods need to be investigated to determine the "strengths" of the regression equation shown above.
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    Research into causes of diarrhoea associated with the Hill's prescription diet Canine Z/D® Ultra Allergen Free : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2003) Hekman, Margreet
    The history, manufacture, physical and immunological characteristics, nutritional adequacy, formulation, taste and digestibility of protein hydrolysates were reviewed. Studies were then undertaken to investigate the cause of the diarrhoea reported to occur in dogs fed an early formulation of Hill's Prescription Diet Canine z/d® ULTRA Allergen Free. It was hypothesised that the digestibility of Canine z/d® ULTRA Allergen Free was poor and therefore contributing to the diarrhoea. To test this hypothesis a study was designed to assess the apparent ileal digestibility of the Canine z/d® ULTRA Allergen Free diet using a rat model of apparent ileal digestibility. The results of this study showed the apparent ileal digestibility of the Canine z/d® ULTRA Allergen Free diet was high and it was concluded that the digestibility of the diet does not predispose dogs to diarrhoea. The reported high osmolarity of protein hydrolysate diets was considered a potential contributing cause to the diarrhoea. To test this hypothesis, the osmolarity of the Canine z/d® ULTRA Allergen Free diet was compared to a standard maintenance diet and to a diet formulated for the treatment of diarrhoea. The osmolarity of the Canine z/d® ULTRA Allergen Free diet was approximately twice that of the osmolarities of the other two diets. This difference was statistically significant (p<0.05), and the data from this study suggest that the hydrolysate diet was sufficiently hyperosmolar to be capable of damaging the mucosa. Although of interest, these observations do not, however, allow a conclusion that the reported diarrhoea is due to hyperosmolarity. Lastly, breath hydrogen tests were performed to investigate whether carbohydrate malabsorption, abnormal orocolic transit times or small intestinal bacterial overgrowth played a role in the cause of the reported diarrhoea. The breath hydrogen concentrations of dogs fed the hydrolysate diet remained within reference intervals confirming the high carbohydrate digestibility observed in the rat model of apparent ileal digestibility and providing no support for abnormal orocolic transit or bacterial overgrowth of the small intestine as causes for the reported diarrhoea. In conclusion, the results of the studies in this thesis do not provide a clear explanation for the cause of the diarrhoea reported to occur with the Canine z/d® ULTRA Allergen Free diet.