Effect of indole-3-acetic acid (plant auxin) on the preservation at 15 degrees C of boar semen for artificial insemination.

In order to extend the duration of boar sperm survival at 15 degrees C for artificial insemination, we tested the effect of indole-3-acetic acid (IAA), which appeared to be the main sperm protective substance present in the Coco nucifera endosperm (coconut water). Two IAA concentrations (10 and 100 ng/mL) in Beltsville extender (BTS) were studied for their in vitro effects. The motility, the percentage of motile spermatozoa and the acrosome morphology of sperm were recorded each day over 13 days of storage at 15 degrees C, after 5 min and 3 h of incubation at 39 degrees C. The IAA effect on sperm preservation was also studied in vivo at a concentration of 10 ng/mL in BTS by inseminating groups of females twice at 24 h intervals either at D0 (day of sperm collection) and D1 (D0/1) or at D5 and D6 (D5/6). At D0/1, the two groups of females (control and IAA) were inseminated with a total of 6.3 x 10(9) spermatozoa (3.15 x 10(9) at D0 and the same dose at D1) whereas at D5/6, on IAA group was inseminated with a total of 6.3 x 10(9) spermatozoa and another one with 12.6 x 10(9) spermatozoa. The animals in the D5/6 control group were inseminated each with a total of 12.6 x 10(9) spermatozoa. For each group of females (n = 106-140), fertility rate (% farrowing) and prolificacy rate (litter size) were recorded. No effect of IAA in vitro on the motility rate and on the percentage of motile spermatozoa was observed over a 13 day storage. However, IAA (10 ng/mL) had a significant positive effect on the percentage of living spermatozoa with intact acrosomes after 13 days (66 vs 54%, P < 0.05). The fertility and prolificacy rates after 5-6 days of sperm preservation in BTS extender alone did not differ significantly between D5/6 and D0/1 but the total number of inseminated spermatozoa was 12.6 x 10(9) at D5/6 instead of 6.3 x 10(9) at D0/1. When the spermatozoa were stored in the presence of 10 ng/mL IAA for 5-6 days at 15 degrees C, the fertility and prolificacy of the females inseminated with only 6.3 x 10(9) spermatozoa were identical to those of the females inseminated with an equal number of spermatozoa at D0/1 in the presence or absence of IAA.