It is generally accepted that in cattle the conception rate depends upon the time of insemination in relation to the time of ovulation, considering the unequal life-span of the gametes and the time necessary for sperm transport and capacitation (Asdell, 1955). Accordingly, practical recommendations have been put forward as to the time during oestrus when insemination will result in the optimum conception rate (Salisbury & VanDemark, 1961).
Studies made in ewes gave variable results, with the optimum time for insemination coinciding with the first half of oestrus (Sinclair, 1957; Morrant & Dun, 1960; Restall, 1963; Jones, Martin & Lapwood, 1968; Mattner & Braden, 1969), mid-oestrus (Kardymovic, Marsakova & Pavljucek, 1934; Carbonero-Bravo, 1955) or the later stages of oestrus (Anderson, 1941; Restall, 1961; Schindler, Eyal & Volcani, 1961; Steklenev, 1961).
In view of the potential
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