The dietary fat concentration and fatty acid profile can influence various aspects of the feline organism. This study examined their effects on the urine composition, apparent nutrient digestibility, and selected blood variables. Methods: Ten healthy adult cats (46.6 ± 14.1 months old, initial body weight 4.99 ± 0.91 kg) received a low-fat basic diet with or without the addition of sunflower oil, fish oil, or lard in a randomized crossover design. The oil and lard were added to the daily amount of food at 0.5 or 1 g/kg body weight of the cats. At the end of each 3-week feeding period, urine, feces, and fasting blood samples were collected. Results: The results demonstrated only small effects of the dietary fat concentration and source on the urine composition of the cats. In addition, the apparent nutrient digestibility was unaffected by the dietary treatments. The supplementation with fish oil, but not sunflower oil or lard, lowered the triglycerides and increased the total and low-density lipoprotein cholesterol concentrations in the plasma of the cats (p < 0.05). However, these blood values were within the physiological reference ranges among all groups. Conclusions: It can be concluded that the dietary fat content and fatty acid profile did not adversely affect the urine composition or nutrient digestibility in healthy adult cats. The lipid metabolism of the animals was modulated by the supplementation with fish oil, a relevant source of n-3 fatty acids. The observed triglyceride-lowering effect should be further investigated in clinical studies.
