Heat synchronization in dairy cows

Dairy cows were heat synchronized with two injections of cloprostenol (PG1/PG2) with an interval of 13 days and inseminated 72 hours after PG2. The total pregnancy rate obtained was 42% The probability of achieving luteal phase at PG2, the probability of undergoing luteolysis after PG2 and the probability of achieving pregnancy were all equal whether the cows were in luteal phase, follicular phase, had follicular cysts or small ovaries at PG1. Close correlations were found between the signs of heat at the insemination and the interval from calving to PG1 to the pregnancy rates.