July 11, 2016

New interpretive summary from July Animal Frontiers

By Lucy Schroeder, ASAS Communications Intern

July 11, 2016 – For over sixty years, it has been known that treating livestock with low doses of antibiotics can increase growth rate. In recent years, using antibiotics in this way has become a controversial topic, with critics concerned about the effect it may have on the development of antibiotic-resistant bacteria important in human medicine. As a result, it is important to understand how the microbiota play a role in digestion so we better understand how to achieve efficient weight gain in livestock.

Dr. Laura M. Cox of Brigham and Women’s Hospital and Harvard Medical School examined the effects of antibiotic use on gut microbes and weight gain in different species. She has observed that the effectiveness of low-dose antibiotic use in animals can be influenced by what age the animal receives the treatment, the variety of the animal’s diet, and the length of the animal’s growth cycle.

Cox used a mouse model comparing antibiotic treatment combined with a diet lacking in complex proteins (simple protein diet) to experiments with antibiotics and a diet of complex proteins. The mice showed weight loss on the simple protein diet, while those given complex proteins experienced weight gain when compared to the controls.

Additional experimentation demonstrated that mice that received antibiotics from birth until weaning experienced significant weight gain when compared to those that did not receive antibiotics. Furthermore, mice that received treatment after weaning did not demonstrate greater weight gain than the mice that ended antibiotic treatment once they were weaned. Both mice that ended treatment before weaning and those that had continued treatment post-weaning showed increased lean mass until middle age, then experienced increased fat mass.

Cox contends that these studies demonstrate some important considerations when using antibiotics, which can have implications for both animal production and human health. To dissuade concerns of antibiotic use in livestock, Cox suggests that alternative approaches may be considered to promote digestive health and thereby increase growth.

Read more about this research in the July 2016 issue of Animal Frontiers.