AI is time consuming and expensive so getting the best results will benefit your herd and your income.
The majority of dairy cows will resume ovulation around 42 days after calving. A suckler cow will be much slower as the bond with her calf delays the oestrous cycle.
Keeping excellent records will give you a good idea which cows are due to come into heat.
Close observation will inform you of which cows are in heat. Signs of heat include skittishness, disinterest in food, hoof marks on her back from other cows mounting, clear mucous discharge, standing to be mounted. If you see vulval blood discharge and you have not noticed her in heat, it may be too late, make a note of the date and be ready 17-20 days later.
The more often you check your herd for signs of heat, the better your detection rate will be. Ideally you would check the herd at least three times daily, as this will maximise the chances of spotting heat.
Oestrous Synchronisation programs can help to bring large herds into line, but they are expensive and do not have a blanket reliability. For example, heifers will have a much lower fertility rate than older cows as they divert energy into growing their bodies while undergoing their first lactation. They require a more nutritious diet if balance is to be achieved. Teagasc have an online guide to OS here.
Often the cause of failed AI is poor straw management. Semen is very easily killed during storage and extraction. Here are some tips on handling semen, courtesy of New Mexico State University:
Minimise time spent removing semen from the canister. If your target straw is not found within 10 seconds, lower the cannister back into the liquid nitrogen for 10-15 seconds to completely cool its contents.
Thaw semen in water of between 32-35 degrees Celsius for a minimum of 40 seconds for maximum survival rate. Dry straw completely afterwards, as water is deadly to semen. Never thaw straws in your pocket or in the cow as thaw rates will be too slow.
Warm the AI gun before loading to prevent cold shock. This can be done by rubbing it with a paper towel or with your sleeve.