The number of spermatozoa per straw used in AI protocols
has been also explored, and the results are variable
(De la Vega, 1996; Bravo et al., 1999). In one study,
the pregnancy rate at 30 days (61%) was obtained using
8–12 million spermatozoa per straw. By contrast, a 53% fertility
rate was found when 4 million spermatozoa per straw
were used. In a subsequent study, there was no difference in
fertility when using 4–12 million spermatozoa (De la Vega,
1996).