Semen quality of Merino rams. 2. The effects of seasonal changes in day length on semen quality

Abstract

Two groups of five medium Wool Peppin Merino rams were individually penned in an animal house for 18 months. During this time the normal seasonal pattern of changes in day length was reversed for one group of rams (treatment). The control group of rams received normal daylight at Trangie (32¦S). From late September 1960, semen was collected once every 14 days from all rams by electro-ejaculation and semen quality was assessed. Significant treatment X months of year interactions found for most semen characteristics. The semen of treated rams had a lower pH during October 1960, and a higher proportion of normal sperm and number of sperm per ejaculate during November 1960, than the semen of control rams. During the period February to June 1961 the semen of treated rams was of a lower quality than the semen of control rams. During November- December 1961 and January to March 1963, the semen of treated rams had a significantly lower proportion of live sperm (P<0.005) than the semen of control rams. From these results it was not possible to determine if the daily photoperiod exerted a direct or indirect effect on the semen quality of Merino rams.