The adult gastrointestinal microbiome is remarkably stable, although several factors influence gut microbial steady states starting at the time of birth. The infant microbiome is derived from maternal and environmental organisms and develops under selective pressure in the gut. Diet, drug administration, and disease states impact the intestinal microbiome, leading to transient or persistent dysbiosis, depending on the nature of the insult and its duration.
Reference:
J Vet Intern Med. 2018 Jan-Feb; 32(1): 9–25. Published online 2017 Nov 24. doi: 10.1111/jvim.14875