Keeping dairy cows productive means keeping them pregnant, a fact of life that sometimes escapes consumers. A cow's best milk production occurs in the two months after she delivers a calf.

A new device called the Bovine Beacon is helping dairymen determine when each member of the herd is ready for breeding. Any time a cow misses an opportunity to be bred -- a task usually accomplished by artificial insemination -- production efficiency suffers.

The beacon is affixed to the cow's rump. The device includes a light stick that emits light for 18 to 24 hours or more after the stick is broken.

How it gets broken is another fact of dairy life that most milk and cheese consumers typically do not consciously consider. A bull will detect a cow's willingness to mate, no matter how subtle the indications. When he mounts the female, his weight breaks the light stick, lighting the beacon and signaling the dairyman that the time has arrived to inseminate the cow, just in case the bull didn't accomplish his task.

However, other cows in the herd have the same ability to detect a correct breeding time, and they tend to mount a female in heat as readily as a bull. Either way, the beacon lights alerting the dairyman that breeding time has arrived.

Dairymen attach the beacon when the calendar says a particular cow should be ready for breeding, but members of the herd make the final decision with the help of the beacon.

The Bovine Beacon was developed by an Idaho dairy owner/veterinarian named Kevin Herriot. If the last name has a familiar ring, it is because he is a distant relative of the English veterinarian James Herriot who wrote "All Creatures Great and Small." The book became the subject of a TV series about a veterinarian's adventures and was shown in Great Britain and on public television in America.

Kevin's parents were experiencing missed heats with their 300-cow herd -- what he calls "the worst trouble you have." His awareness of the light sticks used in the military led to the idea of packaging them in plastic bubbles to be glued to cows' backsides.

The device was patented in the mid-'90s, introduced to California dairymen at the California Farm Equipment show in 1997, and has been a big hit since.

Other methods of detecting cows' breeding seasons have been used for many years. Chalking a cow's tail was an early method of prediction-the chalk wearing off signaled mounting activity. However, the beacon has become the most reliable and user-friendly method.