OBJECTIVELY MEASURED BOAR SPERM MOTILITY PARAMETERS CORRELATE WITH THE OUTCOMES OF ON-FARM INSEMINATIONS - RESULTS OF 2 FERTILITY TRIALS

Two fertility trials were undertaken to evaluate the relationship betw een boar semen quality and fertility (conception rate and litter size) after on-farm artificial insemination (AI), Trial 1 included 98 ejacu lates from 27 boars, and trial 2 included 72 ejaculates from 26 boars. The semen quality was measured by computer-assisted semen analysis (C ASA) using the Hobson Sperm Tracker. Boar semen was diluted in a stand ard extender (Beltsville Thawing Solution, BTS), dispensed into 75 ml aliquots each containing 1.5 x 10(9) spermatozoa and dispatched to far ms by overnight mail for use by their normal Al procedures. Randomly s elected 75 ml aliquots of semen from each boar were also sent to the i nstitute of Zoology for CASA measurement. Prior to CASA analysis, the spermatozoa were recovered from the BTS using Percoll gradients, resus pended in tris-buffered saline media containing 40 mM Ca++, and incuba ted at 39 degrees C. Parameters of sperm motion were measured after 0, 2, 4, and 6 hours of incubation. Various multiple regression models b ased on measured motion parameters could account for up to 24% of the variation in litter size. Using logistic regression, highly significan t (P < 0.0001) models explaining conception rate in terms of sperm mot ion were derived for trial 2 only. The change in sperm velocity during the first 2 hours of incubation and the magnitude of the velocity par ameters after 2 hours were identified as the most consistent indicator s of fertility. Other attributes of sperm quality, i.e., frequency of spontaneous acrosome reactions (AR) and ARs induced by ionophore A2318 7 or solubilized pig zona pellucida, were also examined. When the ''wi thin-trial'' median litter size was used as a way of allocating ejacul ates to ''high'' or ''low'' litter-size groups, higher litter size was associated with lower frequency of both spontaneous and induced AR. T hese results demonstrate that fertility information can be derived fro m the CASA analysis of boar semen provided it is combined with a perio d of incubation in capacitating conditions.