Invited Review: Formation of Keratins in the Bovine Claw: Roles of Hormones, Minerals, and Vitamins in Functional Claw Integrity

Abstract

Keratins are the characteristic structural proteins of the highly cornified epidermis of the skin, feathers, and hoof. Keratin proteins provide the structural basis for the unique properties of the biomaterial horn and its protective function against a wide range of environmental factors. Hoof horn is produced through a complex process of differentiation (keratinization) of epidermal cells. Formation and biochemical binding of keratin proteins and synthesis and exocytosis of intercellular cementing substance (ICS) are the hallmarks of keratinization. It is finalized by the programmed death of the living epidermal cells, i.e., cornification, that turns the living epidermal cells into dead horn cells. The latter become connected by the intercellular cementing substance. The functional integrity of hoof horn essentially depends on a proper differentiation, i.e., keratinization of hoof epidermal cells. Keratinization of hoof epidermis is controlled and modulated by a variety of bioactive molecules and hormones. This process is dependent on an appropriate supply of nutrients, including vitamins, minerals, and trace elements. Regulation and control of differentiation and nutrient flow to the epidermal cells play a central role in determining the quality and, consequently, the functional integrity of hoof horn. Decreasing nutrient supply to keratinizing epidermal cells leads to horn production of inferior quality and increased susceptibility to chemical, physical, or microbial damage from the environment. A growing body of evidence suggests that hormones, vitamins, minerals, and trace elements play critical roles in the normal development of claw horn and correct keratin formation.

SEVERE HOOF DISEASE IN FREE-RANGING ROOSEVELT ELK (CERVUS ELAPHUS ROOSEVELTI) IN SOUTHWESTERN WASHINGTON, USA

“…Copper is a vital component of keratin, and deficiency may lead to abnormal sulfur cross-linking, resulting in defective hoof keratin, but generally also defective antlers and hair coat (Gogan et al 1989;Johnson et al 2007), which was not identified in this study or in affected elk in this region in general. Copper deficiency in cattle is associated with increased incidence of infectious hoof disease, heel cracks, and sole ulcers thought to be due to weak, fragile hoof and sole keratin (Tomlinson et al 2004). A population of Alaskan moose was described with lameness and severe overgrowth of the hooves (Flynn et al 1977), and the cause of this lesion, called ''slipper foot,'' was speculated to be copper deficiency.…”

Histopathology of dairy cows' hooves with signs of naturally acquired laminitis

“…The dermis is responsible for providing the nutrients which are required for the epidermal keratinization process. In the absence of an appropriate blood supply, a low quality corneum tissue is formed increasing the susceptibility of the animal to chemical, physical or biological damages to the environment (Tomlinson et al 2004). In addition, dermal fibroblasts play a modulating role in the keratinocyte growth.…”

Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration

“…8a and b): stratum basale, stratum spinosum, stratum granulosum and stratum corneum. Cells in the first three layers are differentiating keratinocytes while the outermost stratum corneum is composed of dead keratin-filled corneocytes [81]. The stratum basale is about one cell thick and rests on the basement membrane (BM in Fig.…”

“…Keratinous materials are formed by intracellularly synthesized keratins [81] through epidermal cells which build up at the outermost layer of skin. Keratinization replaces the cytoplasmic content by filamentous proteins, and is part of the cellular differentiation that transforms living and functional cells into cornified, structurally stable dead cells [82,83].…”