dl-Aspartic acid administration improves semen quality in rabbit bucks

Recently, d-aspartic acid (d-Asp) has been suggested as being involved in mechanisms regulating reproduction activity in animals and human. In this study we analyzed the effects of dl-Asp oral administration on sperm production in the rabbit. Bucks from 60, bred in a genetic centre and used for semen production, were divided in 2 subgroups of 6 individuals. The treated group was fed with a concentrate containing dl-Asp which assured a daily administration of 1.3 g dl-Asp/head; the control group was fed with the same concentrate without dl-Asp. The treatment was carried out for 2 wk and animals were monitored weekly, from 1 wk before the start of the treatment to 3 wk after the end of the treatment. Through the experimental period there were no significant variations in semen volume between the two groups. A significant increase in both sperm concentration and kinetic parameters, i.e., the overall percentage of motile spermatozoa, the average path velocity, the percentage of progressively motile spermatozoa, etc., was found in the supplemented group. l-Asp values in blood serum and seminal plasma did not vary through the experimental period. d-Asp concentration in blood serum increased more than 4-fold than baseline (P < 0.01) at the end of the treatment and was maintained at higher than baseline values for up to 3 wk after the end of the treatment. d-Asp concentration in seminal plasma was higher than in blood serum before the start of the treatment (13.7 ± 1.6 nM vs 3.5 ± 3.3 nM; P < 0.01) which suggests an elective storage of d-Asp in the male genital tract. Baseline values of d-Asp concentration in seminal plasma significantly increased following treatment and were back to initial values 1 wk after the end of the treatment. In conclusion, dl-Asp administration improved sperm quality in bucks and the high d-Asp content in seminal plasma suggests a primary role for this d-amino acid in regulatory mechanisms of reproductive activity.