Effects of probiotic supplementation on growth performance and feed intake of dairy calves: A meta-analysis

The objective of this systematic review and meta-analysis was to evaluate the effect of probiotic supplementation on ADG, feed intake, and feed efficiency (FE) of dairy calves. A secondary objective was to assess outcomes stratified by probiotic type. Our study included quasirandomized and randomized controlled trials written in English, Spanish, or Portuguese that assessed the effects of probiotic supplementation on the growth of dairy calves. No restrictions were placed on the publication year. A total of 5,480 records were initially identified after conducting searches in Biosis, CAB Abstracts, Medline, Scopus, and the Dissertations and Theses Database. After applying inclusion criteria, 55 studies (56 trials) were included in the analysis. Multilevel random-effects models were fitted for a single dataset combining all trials regardless of probiotic type and for 4 datasets stratified by 4 probiotic types (Bacillus, Lactobacillus, Saccharomyces, and multiple genera probiotics). Meta-analyses showed that probiotic supplementation did not result in significant difference in FE compared with the control group (no treatment or placebo). Probiotic supplementation improved total DMI, starter intake, and ADG and tended to decrease milk intake. A meta-regression analysis indicated a significant association between starter intake and probiotic type and the duration of probiotic supplementation. Analyses by probiotic type revealed no significant effects on DMI or FE for Lactobacillus spp., Saccharomyces spp., or multiple genera probiotics, whereas Bacillus spp. showed no effect on DMI but a tendency to improve FE. Supplementation with Lactobacillus spp. and multiple genera probiotics tended to increase starter intake. Supplementation with Bacillus spp. and Lactobacillus spp. increased the ADG of calves, whereas Saccharomyces spp. and multiple genera probiotic supplementation did not yield significant differences. Substantial and significant heterogeneity was observed for most outcomes; thus, results must be interpreted carefully. Probiotics may be beneficial for enhancing DMI, starter intake, and ADG in dairy calves; however, current evidence remains limited due to high heterogeneity. Results of analyses by probiotic type should be interpreted carefully due to the limited number of studies per category. To develop appropriate recommendations, additional research is required to address the sources of heterogeneity in existing studies.