In poultry, there is an oil gland located dorsally to the stumpy tail of the bird. The oil is distributed when the feathers are kept in order as the bird preens itself. Pigmentation Pigment cells or melanocytes are located in the deepest layers of the epidermis or in the underlying dermis. Melanin is a pigment formed in organelles called melanosomes . Melanin is passed from melanocytes to skin cells by cytocrine secretion.
Melanin is formed from the oxidation of tyrosine by tyrosinase.
Absence of this enzyme results in an albino animal. Variation in the color of farm animals is caused by variations in the amount and distribution of melanin. Melanin may be extracted with an aqueous solution of sodium hydroxide and then recovered by acidification. Melanin is a polymer based on indole monomers, but there is also a protein component involved that makes precise determination of its structure difficult. The distribution of melanin over the animals' skin is determined prenatally by an interaction between the migration patterns of melanocytes and the diffusion patterns of the messenger substances that either activate or suppress the synthesis of melanin.