Effects of antimicrobial feed additives on gut microbiology and blood parameters of weaned piglets

In a feeding trial involving 120 weaned piglets (8kg initial body weight) two feed additives (essential oils blend derived from oregano, anise and citrus peels vs. Avilamycin) were compared with a negative control group. After 50 days of feeding essential oils improved numerically weight gain, feed intake and feed to gain ratio (+5 %, +3 % and -1 %), whereas Avilamycin effects were less pronounced (+1 %, -1 % and -2 %). At experimental day 22 twelve representative animals from each treatment group were slaughtered and blood samples as well as chyme samples from ileum, caecum, and colon were retrieved. Both feed additives did not affect blood analysis but reduced contents of anaerobic and aerobic germs, volatile fatty acids, and ammonia in chyme of ileum, caecum and colon as well as contents of biogenic amines in caecal chyme. The pH value and dry matter (DM) contents in chyme of the respective intestinal segments remained unchanged except for an increased colonic DM content due to essential oils. These results indicate that essential oils tested in the present study exert an antimicrobial activity in vivo similar to Avilamycin.