The Effect of Daylength on Pituitary FSH and LH and Gonadal Development of Snowshoe Hares1

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Abstract
The effect of daylength on gonadal development and pituitary LH and FSH in snowshoe hares collected in the field and maintained on simulated natural light was studied. Snowshoe hares were live trapped near Rochester, Alberta, Canada, and either were returned to the University of Wisconsin, Madison, or were killed in the field where pituitary glands, reproductive tracts, and serum were collected. In nature, prior to the breeding season, gonads develop as a function of daylength. The relationship is significantly less with the onset of breeding season as the testes approach their maximal size. After the summer solstice, the gonads begin a seasonal regression as a function of decreasing daylength. In both field-captured and laboratory-maintained hares pituitary gonadotropins as measured by using modifications of Parlow OAAD and Steelman and Pohley HCG augmentation method for LH and FSH, respectively, were positively correlated with gonadal development. Animals maintained on long day photoperiod from the summer solstice through September 1 maintained gonadal development and high pituitary hormone levels. It was therefore concluded that in the showshoe hare, gonadal development and therefore the breeding season is primarily controlled by gonadotropins which, in turn, are regulated by photoperiod.

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