Influence of age and body size on the digestibility of a dry expanded diet in dogs

The objectives of the study were (i) to evaluate the effects of age and body size on the apparent digestibility of a dry expanded diet and (ii) to determine whether poor faecal quality could be related to lower nutrient utilization. Four breeds of dogs were used: six Miniature Poodles (MP), six Medium Schnauzers (MS), six Giant Schnauzers (GS) and six Great Danes (GD). Digestive trials were performed at 11, 21, 35 and 60 weeks of age. Faecal moisture and scoring were recorded at the same periods. Digestibility coefficients of all macronutrients increased significantly (p < 0.05) with age in all four breeds. Organic matter digestibility increased from 80.2 +/- 1.5 to 85.5 +/- 1.5% in MP; from 80.2 +/- 0.9 to 86.3 +/- 0.5% in MS; from 79.6 +/- 4.2 to 88.9 +/- 0.5% in GS and from 85.7 +/- 1.5 to 88.4 +/- 0.8% in GD. Crude protein digestibility increased from 74.5 +/- 4.0 to 81.5 +/- 1.9% in MP; from 74.3 +/- 3.9 to 82.6 +/- 0.9% in MS; from 71.8 +/- 6.0 to 85.9 +/- 0.9% in GS and from 80.8 +/- 4.6 to 84.8 +/- 1.3% in GD between 11 and 60 weeks of age, respectively. Mean faecal moisture also increased over the growth, except in GS. Nutrient digestibility was significantly higher in large dogs at all age periods. However, larger dogs showed lower faecal scores and increased faecal moisture. In conclusion, these results show (i) an effect of age and body size on nutrients digestibility and (ii) that the lower faecal quality observed in healthy large breed dogs does not appear related to lower nutrient utilization.