When we collect ram semen to freeze (we use Triladyl), we usually find that the first collection each day does not freeze as well as the later collection, even though semen quality is apparently the same. So..we often discard the first collection on principle, and freeze the subsequent collections.
Not sure what cause this this variability, perhaps differences in seminal plasma?
Is this a common, or reasonable policy. Or are we throwing out good semen?