THE ENVIRONMENTAL-IMPACT OF BOVINE SOMATOTROPIN USE IN DAIRY-CATTLE

The environmental impact of bovine somatotropin (bST) use in dairy cattle (Bos taurus) was analyzed with the following assumptions: base herd (1989) of 10.1 x 10(6) cows, milk production 6475 kg of 3.5% fat per 305 d; bST herd of 8.96 x 10(6) cows, 3.8 kg/d increase during 215 d treatment period; 100% adoption rate, 60 d dry period, 40% replacement rate; all formulated diets from: alfalfa (Medicago sativa L.) hay, corn (Zea mays L.) silage, cracked corn, soybean [Glycine max (L.) Merr.] meal, and supplement to satisfy level of production. Using these assumptions, the analysis indicates that the current U.S. milk supply could be produced by 11% fewer cows fed 9% less feed produced on 6% less land, and soil loss would be 5% less. Fossil fuel requirements would be 6% less and irrigation water use would be reduced by 9%. Output of the greenhouse gas methane would be decreased 9%; manure production and outputs of N and P declined by 10, 8, and 10%, respectively.