Study Examines the Impact of Carbohydrate Sources on Protein and Amino Acid Digestibility in Domestic Cats

Domestic cats are obligate carnivores that require high protein in their diets, whereas carbohydrates play a functional role in extruded dry foods. This study aimed to determine whether specific protein and carbohydrate sources influence the apparent total tract digestibility (ATTD) of nutrients and amino acids in domestic cats. A total of 117 Korean short-haired domestic cats participated in a two-week adaptation before a digestibility evaluation.

The study formulated twelve diets to assess six protein sources (chicken, duck, salmon, pollock, beef, and cricket) with rice as a carbohydrate reference source, and six carbohydrate sources (rice, corn, potato, tapioca, sweet potato, and wheat) with chicken as a protein reference. Each source's ATTD of nutrients and amino acids were recorded, as well as an exploratory efficiency ratio (ER) indicating the relationship between crude protein ATTD and carbohydrate digestibility.

Among protein sources, duck, chicken, and salmon had the highest protein digestibility rates of 86.36%, 85.72%, and 83.05%, respectively, whereas beef and cricket had lower rates of 74.77% and 74.97%. For carbohydrate sources, rice and corn exhibited higher digestibility rates (85.72% and 76.82%) compared to wheat, tapioca, potato, and sweet potato, which had lower values ranging from 72.04% to 75.23%. Although rice had the lowest carbohydrate digestibility (7.71%), it yielded the highest ER (11.12), indicating substantial crude protein ATTD in comparison to carbohydrate digestibility.

Seven amino acids (Ala, Ser, Val, Thr, His, Phe, and Ile) demonstrated a strong correlation with crude protein ATTD across both source types. Regression analyses reflected positive associations between ER and selected amino acid ATTD values, notably for Phe, Ala, and Ile.

The findings suggest a connection between carbohydrate source and protein and amino acid digestibility within the specified feline diets. However, the efficiency ratio should be interpreted as a preliminary chemical measure requiring further validation rather than an absolute indicator of protein bioavailability or amino acid utilization.