Fertility of dairycattle is generally decreasing. Overall estrus detection efficiency in lactatingdairy cattle is low, as expression of estrus is often compromised. Consequently,undetected estrus, low AI-submission rates, and long inter-breeding intervalsare the main contributors to poor reproductive efficiency. Although failureto become pregnant is the most common reason for culling dairy cattle, pregnancyrates could be improved by increasing the AI-submission rate through increasedestrus detection efficiency, timed insemination (Timed-AI), or timed embryotransfer (Timed-ET). In these protocols, ovarian follicular development andluteolysis are controlled, culminating in synchronous ovulation in most cows.There are several modifications to improve pregnancy rates in Timed-AI protocols,e.g. presynchronization with 2 doses of PGF2a 14 d apart, and startingthe Ovsynch protocol 12 d after the 2nd PGF2a. Timed-AIprograms ensure a timely first breeding; this should be followed with earlypregnancy diagnosis to identify nonpregnant cows, and prompt re-insemination.However, in a recent field study involving 23 dairy herds, the mean intervalbetween 1st and 2nd breeding was 42 d; only 28% of the cows were rebred within24 d after 1st breeding. Fortunately, there are several resynchronization protocolsto reduce inter-breeding intervals. Anestrus cows, or those with cystic ovarianfollicles, have a good chance of conceiving when subjected to synchronizationof ovulation and Timed-AI. Furthermore, Timed-ET is a practical and viable optionfor synchronizing and selecting recipient cattle for embryo transfers. In summary,systematic and judicious use of Timed-AI and Timed-ET protocols can greatlyenhance reproductive performance, and improve herd productivity.
