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

Abstract

In order to extend the duration of boar sperm survival at 15°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°C, after 5 min and 3 h of incubation at 39°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 DO (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 109 spermatozoa (3.15 x 109 at DO and the same dose at D1) whereas at D5/6, one IAA group was inseminated with a total of 6.3 x 109 spermatozoa and another one with 12.6 x 109 spermatozoa. The animals in the D5/6 control group were inseminated each with a total of 12.6 x 109 spermatozoa. For each group of females In = 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 109 at D5/6 instead of 6.3 x 109 at D0/1. When the spermatozoa were stored in the presence of 10 ng/mL IAA for 5-6 days at 15°C, the fertility and prolificacy of the females inseminated with only 6.3 x 109 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.