Antimicrobial residue detection in chicken yolk samples following administration to egg-producing chickens and effects of residue detection on competitive exclusion culture (PREEMPT) establishment

Competitive exclusion (CE) cultures may offer alternatives to antimicrobial agents for disease prophylaxis in poultry. To avoid potential transfer of antibiotic resistance, safe and effective CE cultures must, by necessity, b e highly sensitive to antimicrobial residues. The following studies evaluat ed the effect of maternal administration of selected antibiotics on the est ablishment of a licensed CE culture, PREEMPT. Selected antibiotics were adm inistered to actively laying hens for a period of 7 days (experiment 1) or 9 days (experiment 2) in drinking water [sulfadimethoxine (0.05%), enroflox acin (0.005%)], and tylosin tartrate (0.05%)1 or feed (sulfadimethoxine wit h ormetoprim, 250 ppm). In experiment 1, fertile eggs were collected daily and subjected to bioassay for detectable antimicrobial residues in yolk. An timicrobial residues were not detected during the 7 days of treatment or th e subsequent 3 days following cessation of treatment in the control, sulfad imethoxine, sulfadimethoxine with ormetoprim, or tylosin treatment groups. However, detectable residues were observed in eggs derived from enrofloxaci n-treated hens on days 6 and 7 during antibiotic administration and also on days 2 and 3 post-antibiotic administration. In experiment 2, antimicrobia l residues were also only detected in yolks from hens treated with enroflox acin. Residue detection occurred on days 2-6 of antibiotic administration, on day 9 of antibiotic administration, on days 1-3 post-antibiotic administ ration, and also on day 7 postantibiotic administration. A subset of eggs f rom each experimental group, corresponding to days 2-6 of antibiotic admini stration, days 4-6 post-antibiotic administration, and days 14-16 postantib iotic administration, were pooled for incubation, and chicks hatched from t hese pools of fertile eggs were treated with PREEMPT at hatch. When 48-h ce cal propionate concentrations were used as an index of culture establishmen t, reduced (P < 0.05) efficacy was observed only in chicks derived from enr ofloxacin-treated hens at either collection period. Although several antibi otics do not appear to produce detectable egg residues or interfere with CE culture establishment, these data suggest that chicks derived from enroflo xacin-treated hens may not be candidates for safe and effective CE culture treatment.