During artificial insemination, sperm collected from a bull are artificially introduced into the reproductive tract of the cow. Currently 80 per cent of all dairy females in the United States are bred by AI, with a much lower percentage of beef cows breeding through AI. The use of superior bulls through AI improves the genetics of the calves and breeding herd. However, there are some disadvantages. AI often requires more labour, money, equipment and facilities than natural mating.
During AI, a disposable catheter containing bull semen is inserted into the cow's vagina. The catheter is guided into the cervix and the semen is deposited into the cervix and uterus. During this process, a gloved hand and arm inside the cow's rectum assists the procedure. A cattle handling facility to safely restrain the cow is necessary. The procedure takes training, practice and skill. It requires much more labour than turning a bull into a group of cows for natural mating.
The semen is usually collected using an artificial vagina. A solution is added to the semen to extend the fluid. Fresh semen is stored for one to four days. Containers of frozen semen are stored indefinitely in liquid nitrogen tanks. Collecting and processing the semen requires training and specialised equipment. Frozen semen is available for purchase. Storage of purchased semen requires a vacuum-sealed metal container with liquid nitrogen providing a temperature of -160 degrees C.
Time to Breed
Cows show signs of oestrus or heat every 18 to 24 days. Cows remain in heat for approximately one day. If a cow is in oestrus in the morning, she is bred in the afternoon. If the cow shows signs of heat in the afternoon, she is usually bred the next morning. Trained personnel must be readily available if AI is used.
Oestrus detection requires human observation. Cows are observed for at least 30 minutes in the early morning and 30 minutes near sunset. The cow's behaviour indicates oestrus. Under the best of circumstances, only 80 to 85 per cent of the cows in oestrus are detected by observation. Careful record keeping is essential to determine which cows might be in heat. Oestrus detection in dairy cows is usually easier than in a beef cattle herd. Dairy cows are brought to the milking barn two or three times per day and are easier to observe. Beef cows are not handled on such a regular basis.
A realistic goal for AI is a first service conception rate of 55 per cent or more. This means 45 per cent of cows bred by AI will not conceive during the first breeding. An average of 1.8 services per conception is common.