The effect of birds’ duration of administration (duration of exposure) to exogenous Testosterone propionate on total weight gain (TWG) and agonistic behaviours (ABs) were evaluated in the Teaching and Research farm of the University of Ibadan, in Southwestern Nigeria. Testosterone propionate (TP) was administered once weekly, to Yaffa breed cockerels in T1,T2,T3,T4,T5 (for 8,12,16,18 and 20 weeks respectively).Birds in T6,received no testosterone propionate.ABs were evaluated twice daily, on a scale of 1-4,where 1 stood for ‘least agonistic’ and 4 stood for ‘very agonistic’. Agonistic acts like Head and feather pecks,kicks,chases and pushes were visually evaluated TP-administered birds had significantly (p<0.05) higher ABs and TWGs than the birds in the Control. Higher ABs however did not affect TWG and other growth parameters negatively Keywords: Cockerels, Testosterone propionate, Growth, Agonistic behaviour
