This study used data from existing reports and databases and required no approval from an animal care
and use committee. Environmental impact was assessed
using a deterministic model based on animal nutrition
and metabolism and founded on life cycle assessment
(LCA) principles. The model was designed to compare
the environmental impact of milk production from 4
populations, each containing either Holstein or Jersey
cows, with and without rbST supplementation.
The system boundaries extended from the production
of feed and forage crops (including crop input manufacture) through and including milk harvest. It did not
include milk transportation, off-farm processing, packaging, or consumption. The functional unit by which