Fall 2008

Know How

How to get a cow pregnant

Milk and motherhood go hand-in-hand. In order to produce milk, dairy cows have to give birth, which means they have to get pregnant every year. You might think that would be a simple birds-and-bees thing–put a cow and a bull in a paddock and give them some privacy. But in fact, it’s one of the most sophisticated and difficult parts of modern herd management (and that’s saying something).

Collect the semen. In modern agriculture, bulls and cows rarely meet. Farmers order semen from genetics firms that “mate” top-quality bulls with artificial cows to collect semen.

Freeze and ship. The bull’s semen is divided and packed into plastic straws, each containing about 20 million sperm, along with nutrients and glycerol to help it survive freezing. Straws are shipped out to farms in liquid nitrogen.

Timing is everything. In the old days, farmers watched their cows closely for signs of estrus, indicating that she was ovulating and receptive to breeding. But because of their fast metabolism rates, today’s high-producing dairy cows may be in estrus for as little as three hours. Many farms now use synchronization treatments, which cause cows to ovulate on schedule.

The dirty part. The actual insemination relies on some manual dexterity. After thawing semen in a warm water bath, a farmer (or a specialized technician) inserts a syringe-like inseminator through the cow’s cervix and vagina to reach her uterus. At the same time, he or she inserts a gloved hand through the cow’s rectum to manipulate the uterus through the rectal wall.

Cross your fingers. Old timers would be astounded by today’s reproductive technology, but they’d also be amazed at the challenges. As milk production has increased, the fertility of dairy cows has decreased, dropping a few percentage points each year. The reasons aren’t clear, but finding solutions is a central focus of modern reproductive physiologists.

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