There are disagreements about how bST works. No receptor sites evidently occur in mammary tissue, but some believe the effect is indirect, that bST stimulates other tissues' production of somatomedins and those hormones influence the uptake of nutrients to udder cells. Until the early 1980s, most bST research was done with pituitary-derived extract from abbatoirs, but after the bST gene was isolated, technology meant recombinant bST could be genetically engineered in limitless quantities. Industry drooled like a stud bull confronted with a paddock of hot heifers. Ingested, most bST apparently breaks down into amino acids.
Undigested traces are supposedly biologically inactive in humans.
But bST-injected cows are more susceptible to mastitis, necessitating antibiotics. Critics say any milk produced this way should be clearly labelled and some U.S. states require that. The Canadian Medical Association has not yet taken a position on the issue. Chris Basudde, Shiv Chopra, Margaret Haydon, Gerard Lambert, Rajinder Sharma and Arnost Vilim complained through the Professional Institute of the Public Service that they were threatened and intimidated. New Democratic Party health critic Judy Wasylycia-Jones champions the scientists' cause.