Melanizing activity of rabbit semen was reported by Beatty (1956). The activity—colour reaction when semen is supplied with dihydroxyphenylalanine—varied between males with different pelt colours : black rabbits showed intense melanizing activity and albinos none. It was further observed that the pale colour of semen was a characteristic of dark pelted bucks, and that the colour of the semen was, in some way, related to its melanizing activity. Mukherjee (1964) studied the melanizing activity of the semen of bulls, goats and rams, and observed that the activity varied between animals and between ejaculates from the same animal. Although there was no appreciable relationship between the coat colour of these animals and the melanizing activity of the semen, the yellow semen samples showed stronger melanizing activity than the non-yellow ones. The proportion of 'live' (unstained in eosin-nigrosin) spermatozoa was uniformly less in strongly melanizing semen samples than in weakly melanizing
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