The incidence of melanin in the bovine pineal gland was studied in 880 glands. Spectrophotometric analysis and chemical and cytochemical methods identified the black pigment present in the bovine pineal gland as melanin. No melanin was found in bulls 4 and 5 years of age nor in heifers of about 18 months. In pregnant cows over 5 years of age melanin was found in 5.4% of the pineal glands. Non-pregnant cows of the same age exhibited melanin in 8.5% of the pineal glands. Castrated male cattle between 18 and 24 months of age showed 49.6% of the pineal glands with macroscopical signs of melanization. As much as 67% of the pineal glands of steers from some herds contained melanin. In intact cattle melanin in the pineal appears to be mainly an aging phenomenon. The fact that castration in male cattle causes hypertrophy of the pineal gland followed by a degenerative process in which melanin is involved seems to give strong evidence of a pineal gonadal interrelationship. The possible role of the hormones in the phenomenon of melanin formation is discussed.
