Characterization of controlled trials on probiotic supplementation to dairy calves: A scoping review.

The objective of this scoping review was to identify, describe, and characterize the literature on probiotic supplementation in dairy calves. Eligible studies were nonrandomized, quasi-randomized and randomized controlled trials in English, Spanish, or Portuguese that evaluated the effect of probiotic supplementation on growth and health of dairy calves. The search strategies were based on a modification of the PICO (Population, Intervention, Comparator, Outcome) framework and used synonyms and words related to "dairy calves" (population), "probiotics" (intervention), and "growth and health measurements" (outcomes). No restrictions for publication year or language were applied. Searches were conducted in Biosis, CAB Abstracts, Medline, Scopus, and the Dissertations and Theses Database. In total, the search identified 4,467 records, of which 103 studies (110 controlled trials) met the inclusion criteria. The studies were published between 1980 and 2021 and originated from 28 countries. Trials were randomized (80.0%), nonrandomized (16.4%), and quasi-randomized (3.6%), ranging in sample size from 5 to 1,801 dairy calves (mode = 24; average = 64). Enrolled calves were frequently Holstein (74.5%), males (43.6%), and younger than 15 d at the beginning of probiotic supplementation (71.8%). Often, trials were conducted in research facilities (47.3%). Trials evaluated probiotics with single or multiple species of the same genus: Lactobacillus (26.4%), Saccharomyces (15.4%), Bacillus (10.0%), Enterococcus (3.6%), or multiple species of various genera (31.8%). Eight trials did not report the probiotic species used. Lactobacillus acidophilus and Enterococcus faecium were the species most supplemented to calves. The duration of probiotic supplementation ranged from 1 to 462 d (mode = 56; average = 50). In trials with a constant dose, it ranged from 4.0 × 106 to 3.7 × 1011 cfu/calf per day. Most probiotics were administered mixed solely into feed (88.5%; whole milk, milk replacer, starter, or total mixed ration) and less frequently orally as a drench or oral paste (7.9%). Most trials evaluated weight gain (88.2%) as a growth indicator and fecal consistency score (64.5%) as a health indicator. Our scoping review summarizes the breadth of controlled trials evaluating probiotic supplementation in dairy calves. Differences in intervention design (mode of probiotic administration, dose, and duration of probiotic supplementation) and outcomes evaluation (type and methods) justify future efforts toward standardized guidelines in clinical trials.

Use of antimicrobials in the treatment of calf diarrhea: a systematic review.

The objective of this study was to conduct a systematic review of the scientific literature evaluating the efficacy and comparative efficacy of antimicrobials (AMs) for the treatment of diarrhea in calves. Eligible studies were non- and randomized controlled trials evaluating an AM intervention against a positive and negative control, with at least one of the following outcomes: fecal consistency score, fever, dehydration, appetite, attitude, weight gain, and mortality. Four electronic databases were searched. Titles and abstracts (three reviewers) and full texts (two reviewers) were screened. A total of 2899 studies were retrieved; 11 studies met the inclusion criteria. The risk of bias was assessed. Most studies had incomplete reporting of trial design and results. Eight studies compared AMs to a negative control (placebo or no treatment). Among eligible studies, the most common outcomes reported were diarrhea severity (n = 6) and mortality (n = 6). Eligible studies evaluated very different interventions and outcomes; thus, a meta-analysis was not performed. The risk of bias assessment revealed concerns with reporting of key trial features, including disease and outcome definitions. Insufficient evidence is available in the scientific literature to assess the efficacy of AMs in treating calf diarrhea.