The current study was part of a larger investigation of two breeds of growing dogs (Dobenecker, 2002). The apparent digestibility of protein, fat, nitrogen-free extract (N-free extract) and organic matter as well as energy of a tripe and rice-based diet supplemented either with normal calcium [~1.1% dry matter (DM), normal calcium (NC)] or excess calcium [~3.6% DM, high calcium (HC)] was determined in two breeds of growing dogs of different sizes, including 30 Beagles and 44 Foxhound-Boxer-Ingelheim Labrador crossbred dogs (FBIs), at the ages of 12, 18 and 24 weeks. Apparent energy digestibility was significantly impaired by excess of calcium in both dog breeds, and the effect was stronger in FBIs than in Beagles (NC vs. HC in FBIs: 88.3 ± 2.6% vs. 84.7 ± 3.7%; NC vs. HC in Beagles: 89.0 ± 2.4% vs. 86.6 ± 3.4%; p < 0.05 in both FBIs and Beagles). The same was true for organic matter, N-free extract, crude protein and fat. The decrease in protein and fat digestibility was significant in FBIs, but not in Beagles. By contrast, the apparent digestibility of ash was lower in FBIs than in Beagles. Taken together, the results of the current study suggest that excess dietary calcium may be associated with systematic differences in nutrient digestibility by different breeds of dogs.
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