An experienced livestock veterinarian offers a primer on artificial insemination in cattle.
Aftificial insemination in cattle has at least two advantages: it saves you the cost and trouble of keeping a bull, and it enables a bull with desirable traits to mate thousands of cows.
Artificial insemination (AI)—the process of collecting live sperm from a male and introducing them into a female's reproductive tract at the proper time to produce offspring—was first researched back in 1783 by a man named Lazzaro Spallanzani, who conducted experiments with dogs in order to perfect the technique.
The first commercial AI organization in this country didn't begin operation until 1938—many years after the practice was instigated in Europe—but today, artificial insemination in cattle is responsible for the conception of more than a third of all dairy calves. Goats, dogs, pigs, and horses are also bred by AI, though not so extensively as are cattle.
AI can be your best bet, too, whether your herd is large or small. For instance, besides profiting from the relatively low cost involved (compared to the expense of feeding and maintaining a bull), the would-be breeder can pick a sire from the best of stock without having to consider how far away the male animal may actually be. Furthermore, many diseases associated with the reproduction process can be controlled, and often eliminated, by using AI.
Perhaps its greatest advantage, though, is that AI extends the use of service by superior bulls. A sire that's proved capable of transmitting desirable traits to his offspring can thus be mated to thousands of cows.
The semen is selected by using an artificial vagina (a rigid tube with an inner rubber sleeve that's been warmed with water and lubricated). The bull is tricked into mounting a "teaser" animal—usually a steer—and an attendant directs the bull's penis into the tube and traps the ejaculate. Sperm is gathered once or twice a week, depending on the weather and the bull's disposition.
A healthy, vigorous bull will produce from 300 million to two billion sperm cells in each milliliter of a normal five- to six-milliliter ejaculate. Ten million active sperm cells are considered an adequate number for one insemination, and, generally speaking, 70% of the sperm cells in a healthy ejaculate will be motile.
Immediately after collection, both the number of sperm and their motility are evaluated. Then, depending on the count of healthy sperm per milliliter, the ejaculate is diluted to produce the desired concentration of sperm cells. The diluted semen is placed in small ampules or straws and is quick-frozen for later use. Special metal canisters are necessary for storage, since the semen is kept in a liquid nitrogen refrigerant at temperatures far below freezing (-320°F ). You might be surprised to learn that calves have been born from sperm which has been stored this way for over nine years.
When a cow comes into heat, an inseminator (call your county extension agent for information on available AI service) will visit the farm and introduce the bull semen into the cow's uterus. He or she will locate the correct placement by inserting a gloved hand into the animal's rectum and manipulating the cervix until a catheter can be gently moved into place through the vagina. Once the catheter is in position, the operator pushes the plunger on a syringe to deposit the sperm.
The success rate of AI averages about 70%. This ratio of conceptions to inseminations will vary according to the bull used and the health of the cow's reproductive tract.
Have your vet stop by between 45 and 60 days after the insemination to palpate the cow for pregnancy ... and—at the same time—recommend a good vaccine and parasite-control program for your herd.
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