Question:  query regarding oestrous of a 1 1/2 year old heifer 
Answer:  puberty is not the sexual maturity , the follicle release at first circle may not capable for fgertilization , several cycle are required to pass for fertilization to get a mature ova which are capable for fertilization , it depent upon the management ,nutritional status & reproductive health ,it is also not uncommon to get a mature ova from female gonad under proper management at the age of 1 1/2 year