The study was published in a recent issue of the Proceedings of the National Academy of Sciences.

Researchers note that making milk uses a lot of land, energy and feed.

However, rBST can reduce the carbon hoofprint by easing energy, land and nutritional inputs necessary to sustain milk production at levels to meet market demand.

The research showed that giving rBST to one million cows would enable the same amount of milk to be produced 157,000 fewer cows.

The nutrient savings would be 491,000 tonnes of corn, 158,000t of soybeans, and total feedstuffs would be reduced by 2.3mt.

And producers could reduce cropland use by 480,000 acres and cut soil erosion by 2.3mt annually.

Those are big numbers from a single technology available to dairy farmers for the past 15 years.

In a statement announcing the research results, Judith L. Capper said: "Supplementing cows with rBST on an industry-wide scale would improve sustainability and redcue the dairy indsutry's contribution to water acidification, algal growth and global warming."

Ms Capper is a post-doctoral research and the lead author of the report.

Capper was joined in the research by Dale E. Bauman, Cornell professor of animal science and the corresponding author; Euridice Castaneda-Gutierrez, former Cornel post-doctoral researcher; and Roger A. Cady, Monsanto. Cornell funded the research.

At a time when the dairy industry is forcing farmers to stop using the product in their herds, Bauman notes that the study "demonstrates that use of rBST markedly improves the efficiency of milk production, mitigates environmental impact including greenhouse gas emissions and reduces natural resource requirements such as fossil fuel, water and land use".