Testosterone levels and the genetic variation of sex hormone-binding globulin gene of Bubalus bubalis, bulls in Egypt.

Testosterone is themain plasma androgen produced and secreted by male testis. To be bioactive, it binds to sex hormonebinding globulin (SHBG), i.e. the major transporter protein of sex steroids in the blood of mammals and other vertebrate species.Firstly, this study aimed to determine the levels of testosterone in different-age groups of buffalo bulls (Bubalus bubalis) in Egypt, and secondly to screen the genetic polymorphisms in their SHBG gene and to investigatewhether these polymorphisms are associated with the level of the circulating serum testosterone. Blood samples were collected from 67 Egyptian buffalo bulls representing four different age-groups and testosterone concentration was measured by radioimmunoassay. Selected DNA samples from different age-groups were sequenced for the full length of theirSHBGgene.Asignificant increase in the concentration of serum testosterone in buffalo bulls was recorded with the advancement of age from 12/18 to 24/36 months. Based on the number of polymorphisms in SHBG gene, the current study reveals the presence of three bull genotypes, of which one is likely to be associated with low testosterone concentration, while other is likely to be associated with an increased testosterone concentration. Such genetic associations can provide a good tool for the selection of bull genotypes with higher testosterone concentrations, which are indispensible for breeding purposes.