Infection rate of S. aureus and E. coli infused into mammary glands of five transgenic and five non-transgenic lactating cows.

During each challenge experiment each gland was infused with S. aureus, E. coli or PBS, the fourth gland remained untreated. Infection was defined by the presence of viable S. aureus or E. coli in two consecutive milk samples. None of transgenic or nontransgenic glands infused with PBS became infected, so were the untreated transgenic and nontransgenic gland.*Transgenic cows or non-transgenic cows were challenged three times at interval of two months during their natural lactation period.†(Number of glands infected)/(number of glands infused).