Frequency of Collection

The effect of frequency of collection on semen quality has already been discussed in some detail (section 4.3.2). The frequency of collection that a stallion can tolerate without detrimentally affecting semen quality is highly variable. Evidence would suggest that instead of a single collection per day regularly over the breeding season, double collections (1 h apart) give better results. As might be expected, the first ejaculate in double collections taken on alternate days is reported to produce the best quality semen. However, pooling of these two samples resulted on average in samples with higher spermatozoan motility, a lower incidence of spermatozoan abnormalities and a higher percentage of live spermatozoa before and after freezing than single daily collections. This was at the expense of ejaculate volume, which suffered in the alternate-day collection regime (Arras, 1994). Work by Magistrini et al. (1987) showed a similar effect comparing daily collections with collection on alternate days (three times per week). This work noted a decrease in ejaculate volume and in spermatozoan concentration, along with a slight increase in spermatozoan motility when collections were made at the higher frequency. It also assessed the effect that season might have on spermatozoan quality for use with AI. Semen collected during the winter tended to be lower in volume, of both the gel and gel-free fractions, but higher in spermatozoan concentration and with lower spermatozoan motility (Magistrini et al., 1987). For AI, it is generally considered that a stallion may be collected from once per day, thus allowing monitoring of the quantity produced and any adaptation in management. For stallions in less demand, collection three times per week is often practised (J.M. Parlevliet, The Netherlands, 1998, personal communication).

The standard procedure normally used for assessing a stallion for inclusion in an AI programme is either two ejaculates taken 1 h apart, followed 3 days later by a single ejaculate for evaluation, or two ejaculates taken 1 h apart and followed by daily collection of samples for evaluation for 6-7 days (Pickett and Voss, 1972; Kenney, 1975; Sullivan and Pickett, 1975; Swierstra et al., 1975; J.M. Parlevliet, The Netherlands, 1998, personal communication). The second system, though more laborious, also allows the stallion's daily spermatozoan output to be estimated, indicating the number of mares that he can cover or the number of AI doses that can be obtained.

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