Degradation and possible carry over of feed DNA monitored in pigs and poultry

Abstract.

A possible carry over of foreign food DNA into the body after consumption was examined. After feeding pigs with conventional and recombinant (Bt-) maize, different body samples were investigated using DNA-extraction followed by PCR procedures to detect chloroplast genes of different length (199 bp and 532 bp), a maize-specific gene (zein) and a specific transgene present in Bt-maize (cryIa). Initially, a time-dependent degradation of feed DNA in the gastrointestinal tract of pigs was analysed within the juices from stomach and three parts of the small intestine (duodenum, jejunum, ileum). Subsequently, a possible transfer of residual chloroplast specific DNA as well as recombinant Bt-maize DNA fragments into different pig organs (blood, muscle, liver, spleen and lymph nodes) was examined. The suitability of the introduced DNA extraction procedure was verified through amplification of a universal gene (ubiquitin) demonstrating the successful PCR analysis within a range of 189–417 bp long DNA. Short chloroplast DNA fragments (199 bp) could be successfully amplified from the intestinal juices of pigs up to 12 h after the last feeding. In contrast, chloroplast-specific DNA was not found in any pig organ investigated so far. Specific gene fragments from the transgene maize (Bt-maize) were never detected in any pig sample.

A field study examining supermarket poultry samples (leg, breast and wing muscle, stomach) led to frequent detections of the short chloroplast DNA fragment (199 bp). Furthermore, faint signals for the maize specific zein gene fragment were detected in these poultry tissues. Additional PCR examinations using unhatched chicken embryos provided the first indication that neither chloroplast nor maize genes are present endogenously within the wild-type poultry genome. Therefore, a transient transfer of short forage DNA into most poultry organs can be suspected.