Detection of recombinant maize DNA in rumen contents of dairy cows and in mixed ruminal cultures.

The fate of transgenic plant DNA fragments in the gastro-intestinal tract of mammals is not completely known. This experiment was designed to compare the persistence of transgenic maize DNA in the bovine rumen and in vitro mixed ruminal cultures. The persistence of maize invertase gene fragment (226 bp) and of CryIA(b) transgene fragment (211 bp) was monitored by PCR in 2 rumen cannulated cows. Animals were fed for 2 weeks a diet containing Bt176 maize (10% of dry matter intake). Samples of whole rumen contents were collected at 0, 30 min, 2, 4, 6, 8, 10, 12, 16, 24, 36, 48 and 72 h after removing the transgenic maize from the diet. An in vitro experiment was performed using rumen fluid from the same cows. Fourteen ml of inoculum (mixed 1:4 with buffer) were added to 175 mg of ground Bt176 maize, incubated at 39 °C in triplicate vials for each sampling time according to the in vivo protocol. Bacterial DNA was detected in all in vivo and in vitro samples. The invertase fragment was detected at all incubation times in the in vitro study and in most in vivo samples. The CryIA(b) fragment was detected up to 2 h in the in vitro trial and found in rumen contents in one case only (at 2 h in one cow). Detection of single-copy genes originating from transgenic feed is difficult in the complex rumen ecosystem. Caution is needed when extrapolating results from in vitro to in vivo studies.