Influence of cephalosporins on the coagulation time of yogurt made from ewes' milk

Ceftiofur and cephalexin were independently added to ewes' milk at three different concentrations 50, 100 and 150 mu g/kg. Spiked milk was used to produce yogurt and the acidification of the yogurt during incubation was then studied. Ceftiofur showed significant delays in the pH decrease rate at all concentrations assayed, but no significant delays occurred with cephalexin. When these antibiotics were administered intramuscularly to lactating ewes, from which the milk was used to make yogurt immediately after the corresponding withdrawal periods, absence of residues and pH delays were not observed during the yogurt fermentation in the presence of any antibiotic.