Heifers of pure exotic breeds should give birth by 24 months from the day they were born. This means they should have been pregnant by 15 months of age. Older cows should get pregnant by 85 days after the previous calving if the cows are to give you a calf every year and maximise on milk yield.
To achieve this, the farmer has to invest in confirming that each of her heifers and cows will attain these targets by first ensuring the animals are fed with the recommended balanced diets and secondly ensure the animals are free of conditions that can interfere with heat signs (cycling) and conception.