Objective: Male broiler breeders are exposed to feed restrictions to reach the appropriate weight, which preserves sperm production (quality and quantity). Due to genetic potential, too much feeding, consumption of females feed, etc. some roosters become obese and the elimination of them from the farm is recommended. On the other hand, naturally, with increasing age, the quality of sperm decreases that this causes a decline in fertilized eggs and hatching rates and reduction of farm profits,finally. Therefore, one of the important issues in breeder broiler flocks is the decline of fertility due to age-related obesity.Materials & Methods: In the first phase, the data of eliminated roosters at different ages were collected from ۶ breeder broiler farms, which, based on the obtained data, determined that ۲۵% greater than the standard weight, could represent the obese roosters in the present research. The experimental phase was carried out as a factorial design with ۴۰ chicks of ۱۸ to ۵۶ weeks old with two treatments in twenty replications and one rooster in each experimental unit. By a greater distribution of feed, the obese group was achieved to ۲۵% more than the standard weight after ۱۲ weeks. During the breeding period, the roosters were weighed weekly and effort was made that weight of birds not to exceed or less than ۲۵% in the obese group compared to the standard weight.From the age of ۳۰ weeks, to determine of qualitative and quantitative parameters of sperm, semenwas collected biweekly and blood testosterone concentrations were measured monthly until ۵۶weeks of age and the artificial insemination was performed at the end of the experiment to evaluatethe fertility potential.Results & Conclusion: The applied obesity had no significant effects on qualitative and quantitative parameters of semen and blood testosterone concentration between groups (P>۰.۰۵). Testosterone
concentration, membrane integrity, total motility, and progressive motility had a decreasing trend; and seminal MDA concentration showed an incremental trend in both groups with aging. Artificial insemination
at ۵۶ weeks of age revealed no significant differences in fertility and hatching percentages between the two groups (P>۰.۰۵). These results showed that applied obesity (۲۵% greater than the standard weight) in male breeder broilers had no negative effect on sperm quality and fertility rate. The decline of fertility in obese roosters can be attributed to imbalance and incorrect mating which defect can be improved by developing artificial insemination in broiler breeds.