Direct-Fed Microbials for Dairy Calves: Gut Microbial Diversity and Host Health

Abstract

Direct-fed microbial (DFM) might provide young calves with healthy supplements to promote gut microbial diversity and host health if calves are appropriately managed. The possible usefulness of DFM, however, should not be overstated. The main objective of this review article was to investigate whether DFM is practically workable in preventing digestive tract disorders, namely diarrhea. Another objective was to delineate the possible effectiveness of such products in promoting calf health and performance. Protecting newborn calves against infectious diseases and improving their health and growth in early life is closely related to herd economics and sustainability. Diarrhea is the most prevalent contagious diseasecausing calf morbidity and mortality worldwide. Supplementing dairy calf diets (milk or starter) with beneficial microorganisms such as bacteria and yeast has been an attempt to improve the gut microbial ecosystem and optimize nutrient assimilation. However, infectious diarrhea is still a problem in many dairy and beef farms. Since diarrhea has a multifactorial nature, it seems that the possible efficacy of DFM depends on the environmental and management conditions in which the calves are raised. The rearing system (individual vs. group housing), diet, environmental microbial load, and other management factors are involved in the incidence of diarrhea. Therefore, probiotic products may interact with such factors, thus influencing their effectiveness and likely causing inconsistencies concerning probiotics' usefulness in commercial dairy farms. Thus, animal responses to dietary DFM supplementation and their usefulness are practically dependent on management conditions.