Sperm Aldose Reductase B1 is not a predictor of bull in vivo fertility outcomes

Abstract

Uncovering fertility biomarkers has become a major challenge for the dairy industry, where the fertility decline leads to important economic losses. In swine, seminal aldose reductase B1 (AKR1B1), a NADPH-dependent enzyme, positively influenced fertility outcomes, probably through modulation of sperm fertilizing competence. In cattle, this protein has also been reported to be involved in epididymal sperm maturation. Against this background, the present work aimed to evaluate the potential relationship between the levels of AKR1B1 in bovine sperm and in vivo fertility outcomes. Thus, a total of 15 bulls were used to inseminate 577 heifers; in vivo fertility outcomes were calculated as 90-day non-return rates (NRR). In parallel, three ejaculates per bull were pooled and centrifuged for sperm AKR1B1 analysis with immunoblotting assay. Considering that a specific two-band pattern at 36 kDa and ~80 kDa was observed, two different ratios were calculated: 36 kDa form/total AKR1B1 and ~80 kDa form/total AKR1B1 (the total amount of AKR1B1 corresponded to the sum of the intensities of the two bands). There was no correlation(P > 0.05) between the levels of sperm AKR1B1 (36 kDa/total and /~80 kDa/total ratios) and NRR). Therefore, the 15 bulls were divided into high and low fertility groups using the NRR median value (high fertility group, 41.61 ± 1.19; and low fertility group, 36.22 ± 1.58), and the two AKR1B1 ratio levels were compared between those groups. There were no differences between NRR groups (P > 0.05) in the levels of sperm AKR1B1. These findings suggested that AKR1B1 may not be a good in vivo fertility predictor in bovine in terms of NRR. Yet, it cannot be discarded of the potential for an effect of this protein on other fertility indicators such as oocyte fertilisation or even embryo development.