Reliable estimates of boar fertility potential from semen evaluation could be a valuable tool for boar selection. The aim of this study was to investigate the morphology and the detailed motility parameters of diluted boar semen and to relate these to their predictive value concerning conception and farrowing rate, litter size and the number of live born piglets. In addition, the optimal time for evaluation of the motility of preserved semen with respect to its predictive effect on fertility was determined. One hundred ejaculates from 38 boars were evaluated morphologically by eosin-nigrosin staining and different motility characteristics were assessed using Computer Assisted Semen Analysis (CASA). The motility was determined at 15, 45 and 120 minutes after incubation at 37 degrees C. The conception rate, farrowing rate, litter size and number of live born piglets were registered from 276 sows inseminated with these ejaculates. Different regression models were used to evaluate the predictive value of the semen characteristics on these fertility parameters, taking into account the effect of herd, parity and weaning to estrus interval.
The motility characteristics of the spermatozoa varied significantly during the 15 to 120 minutes of incubation. The longer the incubation time, the more the velocity parameters along the actual cell path decreased, while the parameters of straightforward movement increased. The predictive value of individual semen parameters on conception and farrowing rate was very small. The predictive value of certain associations of different semen parameters, on the other hand, was significant.
The percentage of motile spermatozoa had a significant (P<0.05) and positive effect on the total number of piglets born (litter size) and on the number of live born piglets, independent of the time of measurement (X-2 0.38-1.00 and 0.41-1.00, respectively). Accurate evaluation of the motility of a semen dose is therefore imperative for estimating its predictive value relating to fertility.
In conclusion, since the time of evaluation after warming the samples significantly influences the motility parameters, CASA measurement should be done when the cells are completely acclimatized to 37 degrees C. On the basis of the available data, a 45 min incubation period appeared to be sufficient. The percentage of motile spermatozoa, as assessed by CASA on diluted semen, offers detailed predictive information regarding litter size, irrespective of the time of measurement
