Effects of probiotics on growth performance in young calves: A meta-analysis of randomized controlled trials

Growth of calves during their first few weeks of life is one of the most important factors affecting their performance during subsequent rearing, and it can be modified by disease, especially gastrointestinal infections. Use of lactic acid bacteria (LAB) is a tool which may maintain the intestinal microbial balance, prevent diarrhea and improve growth. However, a consensus has not been reached as to whether probiotics are effective in improving growth of calves. The objective of this meta-analysis was to assess effects of probiotics on the growth of calves (i.e., body weight gain (BWG), feed efficiency). PubMed and Scopus databases were searched from 1980 to 2010, unrestricted by language. The inclusion criteria were: randomized and controlled experiments using calves less than 5d of age without apparent disease and with passive immunity, and published in peer reviewed journals. Twenty-one and 14 studies were included to assess probiotic effects on BWG and feed efficiency, respectively. LAB supplementation increased BWG (standardized mean differences (SMD)=0.22822, 95% confidence interval (CI) 0.1006–0.4638) and improve feed efficiency (SMD=−0.8141, 95% CI −1.2222 to −0.4059), considering the source of heterogeneity and publication biases. Growth of calves was not affected when the LAB was added to whole milk, but beneficial effects occurred when LAB was added to milk replacer. The probiotic effect was not related to the number of LAB strains in the inoculum. The number of calves in the experiments had an impact on the results and conclusions. Probiotics may be an alternative to the antibiotics commonly used as growth promoters in calves.