the effect of diffrent factors on x- and y bearing sperm in bull semen

Background: newborn gender ratio is one of the most important factors in livestock industry. this ratio has affected on economic condition and controls sex-linked genetically transferred diseases. offspring sex ratio is affected by such various factors. one of these factors is the y to x bearing sperm ratio in normal semen that is called primary sex ratio, season and individual differences are important factors that can have an effect on primary sex ratio. objectives: the objective of this study was to investigate two main effective factors, individual difference and season, on proportion of sperms containing y-chromosomes to sperms containing x-chromosomes in bull semen. methods: semens were collected from 16 bulls during summer (jul-aug) and winter (dec. to jun). after sperm analysis, dnas were extracted and real-time pcr performed using three sets of primers to study sry (y-chromosome specific sequence), plp (x-chromosome specific sequence) and par (housekeeping) genes. results: the results showed that the sex ratio of sperms in normal ejaculation was not equal in different bulls. moreover, season can affect primary sex ratio. y-bearing sperm increase in summer. conclusions: we concluded that the primary sex ratio is affected by individual differences and season. we also suggested using northern blotting on pcr products to confirm results.