Comparative Analysis of Signature Lipid Structures in Canine and Feline Milk Compared with Bovine and Caprine Milk

This study systematically compared the lipidomes of canine, feline, bovine, and caprine milk. Feline milk contained the highest total lipid content (110.83 mg/mL), significantly exceeding that of canine (81.52 mg/mL), caprine (40.27 mg/mL), and bovine milk (36.25 mg/mL). The phospholipid content in both canine (0.97 mg/mL) and feline milk (0.90 mg/mL) was approximately three times higher than that in bovine and caprine milk (approximately 0.30 mg/mL). Compared to bovine and caprine milk (approximately 30%), canine and feline milk had markedly higher proportions of unsaturated fatty acids (approximately 70%) and were enriched with functional long-chain polyunsaturated fatty acids, including arachidonic acid and docosahexaenoic acid. A distinctive feature was that over 60% of palmitic acid was esterified at the sn−2 position of triacylglycerols in canine and feline milk, a structural similarity shared with human milk. Lipidomic analysis identified 2708 lipid molecules across the four milk types, revealing several triacylglycerol species as potential species-specific biomarkers. These findings provide a concrete scientific basis for developing precisely formulated milk replacers that meet the specific nutritional requirements of puppies and kittens.