The probability distribution of the number of failures preceding conception in Holstein Friesian herd maintained at Indian Veterinary Research Institute, Izatnagar was investigated. The data showed best fit to Neyman distribution closely followed by Geometric distribution, as the agreement between theory and observation was good. The graduation of observed frequencies of number of failures preceding conception to these distributions revealed that probability of conception of a cow at first oestrus cycle differed from if she is conceived at subsequent oestrus cycles. These distributions indicated 91.72 and 90.30 percent conception respectively during first three oestrus cycles in a large herd of Holstein Friesian cows. Thereafter at subsequent oestrus cycles, these distributions revealed low chances of conception under normal conditions. Therefore, the cows those failed to conceive during first three oestrus cycles need critical evaluation for their management, feeding and reproductive disorder before any further attempt of inseminations in the welfare of animal's health. The cows those failed to conceive during first four oestrus cycles of inseminations had rare chance of conception and such cows should be culled to improve conception and lifetime production of calf and milk of Holstein Friesian herd.
