Department of Animal Science, Texas A&M University, College Station, TX, 77843, USA.
Adv Exp Med Biol. 2024;1446:135-154. doi: 10.1007/978-3-031-54192-6_6.
The hair and skin of domestic cats or dogs account for 2% and 12-24% of their body weight, respectively, depending on breed and age. These connective tissues contain protein as the major constituent and provide the first line of defense against external pathogens and toxins. Maintenance of the skin and hair in smooth and elastic states requires special nutritional support, particularly an adequate provision of amino acids (AAs). Keratin (rich in cysteine, serine and glycine) is the major protein both in the epidermis of the skin and in the hair. Filaggrin [rich in some AAs (e.g., serine, glutamate, glutamine, glycine, arginine, and histidine)] is another physiologically important protein in the epidermis of the skin. Collagen and elastin (rich in glycine and proline plus 4-hydroxyproline) are the predominant proteins in the dermis and hypodermis of the skin. Taurine and 4-hydroxyproline are abundant free AAs in the skin of dogs and cats, and 4-hydroxyproline is also an abundant free AA in their hair. The epidermis of the skin synthesizes melanin (the pigment in the skin and hair) from tyrosine and produces trans-urocanate from histidine. Qualitative requirements for proteinogenic AAs are similar between cats and dogs but not identical. Both animal species require the same AAs to nourish the hair and skin but the amounts differ. Other factors (e.g., breeds, coat color, and age) may affect the requirements of cats or dogs for nutrients. The development of a healthy coat, especially a black coat, as well as healthy skin critically depends on AAs [particularly arginine, glycine, histidine, proline, 4-hydroxyproline, and serine, sulfur AAs (methionine, cysteine, and taurine), phenylalanine, and tyrosine] and creatine. Although there are a myriad of studies on AA nutrition in cats and dogs, there is still much to learn about how each AA affects the growth, development and maintenance of the hair and skin. Animal-sourced foodstuffs (e.g., feather meal and poultry by-product meal) are excellent sources of the AAs that are crucial to maintain the normal structure and health of the skin and hair in dogs and cats.
家猫或家犬的毛发和皮肤分别占其体重的 2%和 12-24%，具体取决于品种和年龄。这些结缔组织的主要成分是蛋白质，为抵御外来病原体和毒素提供了第一道防线。保持皮肤和毛发处于光滑和有弹性的状态需要特殊的营养支持，特别是充足的氨基酸（AA）供应。角蛋白（富含半胱氨酸、丝氨酸和甘氨酸）既是皮肤表皮的主要蛋白质，也是毛发的主要蛋白质。角层丝聚蛋白（富含一些 AA，如丝氨酸、谷氨酸、谷氨酰胺、甘氨酸、精氨酸和组氨酸）是皮肤表皮中另一种重要的生理蛋白。胶原蛋白和弹性蛋白（富含甘氨酸和脯氨酸加 4-羟脯氨酸）是皮肤真皮和皮下组织的主要蛋白质。牛磺酸和 4-羟脯氨酸是犬猫皮肤中丰富的游离氨基酸，4-羟脯氨酸也是其毛发中丰富的游离氨基酸。皮肤表皮从酪氨酸合成黑色素（皮肤和毛发中的色素），并从组氨酸产生反尿刊酸。猫和犬的蛋白质 AA 定性需求相似，但不完全相同。这两种动物物种都需要相同的 AA 来滋养毛发和皮肤，但数量不同。其他因素（例如品种、毛色和年龄）可能会影响猫或犬对营养物质的需求。健康被毛的发育，尤其是黑色被毛的发育，以及皮肤的健康，都严重依赖于 AA（特别是精氨酸、甘氨酸、组氨酸、脯氨酸、4-羟脯氨酸和丝氨酸、含硫 AA（蛋氨酸、半胱氨酸和牛磺酸）、苯丙氨酸和酪氨酸）和肌酸。尽管有大量关于猫和犬 AA 营养的研究，但仍有许多关于每种 AA 如何影响毛发和皮肤的生长、发育和维持的知识需要了解。动物源性食品（如羽毛粉和禽副产品粉）是维持犬猫皮肤和毛发正常结构和健康所必需的 AA 的极好来源。
