This is the VOA Special English Agriculture Report.

Dominette, a Hereford cow whose genetic material was used in the study

Researchers from twenty-five countries now have a full genetic map of a cow. Understanding what makes a cow a cow could lead to better milk and meat production.

It could also help drug companies. The cow genome is more similar to humans than to mice or rats. Mice and rats are commonly used to test new medicines. Project scientist Harris Lewin from the University of Illinois at Urbana-Champaign predicts there will be more laboratory cows in the future.

The Bovine Genome Sequencing Project found that the cattle genome contains at least twenty-two thousand genes. Most of these are shared among humans as well as mice, rats and other mammals used for comparison in the study.

More than three hundred researchers studied a female Hereford cow from the American state of Montana. The genome took six years to complete.

A genome is not just a map of the order of genes. It contains information about every position including spaces on the chromosomes on which genes are grouped.

The findings are in the journal Science. A related report looked at genetic changes in cattle over time. The bovine family tree divided into two major groups more than two hundred fifty thousand years ago.

Taurine cattle have no hump on their back. They are mostly found in Europe, Africa and East and West Asia, as well as the Americas. Indicine cattle have a hump and are found in India, South and West Asia and East Africa.

Humans started to domesticate wild cows about eight to ten thousand years ago. Scientists examined several breeds and say the cow genome appears to show evidence of this selective reproduction.

Today more than eight hundred breeds of cattle are raised for different qualities. But some people are concerned that intensive breeding has reduced genetic differences among cattle. This could make it easier for disorders to affect a large number of animals.

The scientists say the current level of diversity within cattle breeds is at least as great as within humans. They also say the new genome will make it possible to better protect genetic diversity.

Yet there may be more questions to settle about what makes a cow a cow. A team led by Steven Salzberg at the University of Maryland also published a cow genome last month in the journal Genome Biology. That team disagreed on some points with the findings published in Science.