الفهرس 
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Abstract
This study aimed first to determine the levels of testosterone in different-age groups of buffalo bulls (Bubalus bubalis) in Egypt, and second to screen the genetic polymorphisms in their sex hormone-binding globulin (SHBG) gene and investigate whether these polymorphisms are associated with the level of the circulating serum testosterone. Blood samples were collected from 67 Egyptian buffalo bulls representing 4 different age-groups, and testosterone concentration was measured by radioimmunoassay. selected DNA samples from different age-groups were sequenced for the full length of their SHBG gene. A significant increase in the concentration of serum testosterone in buffalo bulls was recorded with the advancement of age from 12/18 to 24 to 36 months of age. Based on the number of polymorphisms in SHBG gene, the current study reveals the presence of 3 bull genotypes, one of which is likely to be associated with low testosterone concentration, while another is likely 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.