Relationship between insulin-like growth factor-1 and semen quality in Asian elephants (elephas maximus)

Abstract

Evidence has been increasingly suggested that insulin-like growth factor-1 (IGF-1) is related to steroidogenesis and spermatogenesis. This may be conducive to find the causes of poor sperm quality in Asian elephants (Elephas maximus). The present study aimed to investigate whether correlations among serum IGF-1 concentration, serum testosterone level and semen variables exist in elephants. A total of 17 ejaculates (1–3 ejaculates/bull) were collected by performing transrectal massage. Before each ejaculate, blood samples were obtained (n = 17). Subsequently, semen characteristics of each ejaculate were evaluated. Assessments of precision (calculations of the intra- and inter-assay coefficient of variation, CV) and accuracy (tests of linearity and spike-recovery) were performed for ELISA validation. An increase of serum IGF-1 concentration was found to correlate with the percentages of spermatozoa with intact acrosome (r = 0.53, P < 0.05) and normal head morphology (r = 0.48, P < 0.05). The serum IGF-1 concentration was positively correlated with serum testosterone level (r = 0.73, P = 0.004). The results of validation demonstrated the CV was 1.6–6.4% for intra-assay variability and 4.7–6.9% for inter-assay variability. Linearity under serial dilutions of a known serum concentration was confirmed (R2 = 0.99) with an acceptable recovery rate of each dilution (mean 114.7 ± 19%, ranging from 100 to 143%). Additionally, the mean percentage of recovery of spiked IGF-1 was 107.2 ± 21% (ranging from 80.8 to 136.9%). In summary, this commercial ELISA kit can be used to determine serum IGF-1 concentration in Asian elephants. Moreover, our findings suggest the increased IGF-1 may be relate to good sperm quality and that the relationship between serum IGF-1 and testosterone concentration indicates a crucial role in the fertility of male elephants. Further works are interesting to investigate the exact mechanism by which IGF-1 affects semen quality in elephants.