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Balanced nutrition ensuring adequate intakes of energy, protein, minerals and vitamins is essential for the optimal development of young dogs. An adequate energy supply of growing dogs is critical in controlling the growth rate. Research in rodents indicates that dietary vitamin A impacts energy utilisation; the potential impact on the energy metabolism in dogs and consequently on the energy intake, body composition and growth velocity in growing dogs however remains unclear.
The literature survey in Chapter 2 indicates that the definition of healthy growth is difficult and controversial. The assessment of ideal body condition of growing dogs is more difficult compared to adult animals because increased energy intake results in increased growth rate, but not necessarily in increased body fat mass. Guidance values for energy intake and body weight development do exist, however considerable variability can be observed between breeds. The overview of studies investigating breed and age related changes in haematological and blood chemical values during growth clearly shows that prominent changes occur. Therefore results obtained from puppies have to be interpreted with care to correctly assess the health status as values may deviate from values found in adult dogs.
Chapter 3 explains the main aims and hypotheses of this thesis. The main work of the current thesis consists of two published manuscripts summarized in Chapter 4 and 5. In the first manuscript the possible effects of different dietary vitamin A concentrations on energy intake, growth rate and body composition in Labrador Retriever and Miniature Schnauzer puppies have been evaluated. However, based on the well-documented high tolerance of dogs to dietary vitamin A levels up to 104.8 μmol retinol (100 000 IU vitamin)/4184 kJ (1000 kcal) it was hypothesized that energy intake and accumulation of body fat would be unaffected (Chapter 4). This was confirmed by the results of our study.
Given the findings of Morris et al (2012), vitamin A was not considered as a factor in the evaluation of the haematological and biochemical data in the second manuscript (Chapter 5). The main interest of the second manuscript was to increase the knowledge on breed, sex and age effects and their interaction during the first year of life. The evaluation shows
that age and breed-related changes in haematological and blood chemical test results are evident in young Labrador Retriever and Miniature Schnauzer dogs. The results confirm the need for age-specific reference ranges for the interpretation of clinical data obtained from young puppies.
The potential effects of dietary vitamin A as well as growth related alterations in body tissue and metabolism are discussed in Chapter 6 together with the results obtained from this study. In conclusion, the results of the current study suggest that unlike to rodents dietary vitamin A does not affect energy utilization, growth rate or body composition in dogs. The underlying biochemical mechanisms however remain unclear and require further clarification. With regards to haematological and blood chemical parameters the study showed marked age and breed related changes illustrating growth related alterations in body tissue and metabolism during the first year of life. The early growth phase clearly appears to be most critical and needs to be investigated in more depth to ease interpretation of clinical data obtained from young puppies.