FOLLICULOGENESIS, ONSET OF PUBERTY AND FECUNDITY OF MINK (MUSTELA VISION SCHREB.) SELECTIVELY BRED FOR DOCILITY OR AGGRESSIVENESS

It has been suggested that selective breeding of animals for docile be havior is correlated with early onset of puberty and improved fertilit y. We wished to test the hypothesis that mink bred for docility would show earlier onset of puberty and greater fecundity than mink bred for aggressiveness. We used farm-raised 7-mo-old mink females that had be en selectively bred for 7 to 10 generations on the basis of behavior t owards humans. Onset of puberty was estimated once (between 15 and 20 December) by vaginal smears and was said to start with preponderance o f cornified epithelial cells in the cytological specimen. Fecundity wa s measured by litter size and rate of folliculogenesis, with and witho ut hCG stimulation, by histomorphometric examination of ovaries and ut eri. A total of 43/100 (43%) docile females achieved proestrus and est rus as compared to 16/136 (12%) of the aggressive ones. Overall pregna ncy rate, survival to 5 d after whelping and litter size did not diffe r between the docile and aggressive females. Docile females showed sig nificantly higher numbers (P<0.05 and <0.001) of growing, maturing and atretic follicles than the aggressive ones, however the latter showed a highly significant (P<0.001) folliculogenic response to hCG. The re sponse of the ovary of aggressive females to hCG is particularly drama tic because in most aggressive females the ovaries contained none or o nly few follicles of any kind. The inhibition of folliculogenesis in a ggressive mink is similar to that reported in Silverblue and Sapphire mink homozygous for the Stuart factor. The paradoxical response to hCG may be an indication that selective breeding for aggression may be co rrelated with the disturbance at the early stages of folliculogenesis which creates a deficiency of follicles that are sensitive to LH-type stimulation. (C) 1998 by Elsevier Science Inc.