Effects of Two Commercial Diets on Skin Hydration, Sebum Content, Transepidermal Water Loss, and Coat Quality in Cats: A 12-Week Feeding Trial

Background: Nutrition is a key determinant of skin barrier function and coat quality in cats, but controlled studies comparing commercial diets are limited. Methods: Eighteen healthy adult cats (3.44 ± 0.69 years) were randomly assigned to receive either a standard commercial chicken-based diet (ORI, Instinct Petfood, Visalia, CA, USA, n = 9) or a nutrient-enriched formula designed for skin and coat health (ULT, Instinct Petfood, Little Falls, MN, USA, n = 9) for 12 weeks. Body weight (BW) and body condition score (BCS) were recorded weekly. Visual coat scoring, quantitative descriptive analysis (QDA), and skin biophysical parameters (hydration, sebum, transepidermal water loss) were assessed on days 0, 21, 42, 63 and 84. Results: Both diets maintained stable BW and BCS. Visual scoring showed skin and hair remained within the normal healthy ranges in both groups throughout the study. QDA revealed significant improvements in coat glossiness, softness, and overall scores over time in both diet groups (p < 0.05). Back hydration increased over time, and in the ORI group, values at days 42, 63, and 84 were higher than baseline (44.96, 43.10, and 41.26 vs. 33.85; p < 0.05). Ear hydration showed a significant time × group interaction (p < 0.05). In the ULT group, ear hydration was higher at days 21, 42, 63, and 84 than at baseline (24.17, 35.21, 28.69, and 34.19 vs. 17.87; p < 0.05). Ear TEWL also showed a significant time × group interaction (p < 0.05) and displayed a biphasic pattern in the ULT group, with values at days 63 and 84 higher than at day 42 (15.51 and 14.48 vs. 11.77 g/m2/h; p < 0.05). Compared with the ORI group, the ULT group showed a smaller change in ear TEWL from baseline at day 42 (−2.54 vs. 2.98 g/m2/h; p < 0.05) and a greater increase in ear hydration from baseline at day 84 (16.32 vs. 9.31; p < 0.05). Conclusions: These findings indicate that both diets supported healthy skin and coat conditions in cats, while the nutrient-enriched formula may provide additional benefits for skin hydration.