Insemination of mares with raw, untreated semen is not usually carried out, or advised, unless the indication for insemination is due to physical complications in either the mare or the stallion which preclude natural covering. In order to obtain acceptable results, insemination with raw semen should be carried out between 30 s and 1 h after collection.
Insemination with raw semen provides none of the advantages of AI. Even the division of raw semen to allow the insemination of a number of mares with a single ejaculate is less successful than if the division of the sample occurs after the addition of an extender. The use of an extender is, therefore, recommended (Varner, 1986).
Many of the extenders appropriate for use with fresh semen have been reviewed in the previous section. Pregnancy rates of 75% have been reported with the use of fresh semen, comparing very favourably with fertilization rates to natural service (Pickett, 1993b). Similar conception rates for fresh semen extended with Kenney extender (73.7%) were reported by Silva Filho et al. (1994). These were better than the conception rates reported for raw semen (64.8%) in the same experiment. Extended semen can be stored quite successfully at room temperature (15-20°C), ideally in the dark, for 12-24 h without a significant drop in spermatozoan viability (Coulter and Foote, 1977; Francl et al., 1987; Varner and Schumacher, 1991).
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