Effects of Saccharomyces cerevisiae supplementation on growth performance, plasma metabolites and hormones, and rumen fermentation in Holstein calves during pre- and post-weaning periods

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.

Influence of Yeast Products on Modulating Metabolism and Immunity in Cattle and Swine

Nutritional supplementation has been used by livestock producers for many years in order to increase animal performance, improve animal health, and reduce negative effects associated with enteric and/or respiratory pathogens. Supplements such as yeast and yeast-based products have broad applications across many livestock production systems, including poultry, aquaculture, cattle, and swine and have been shown to benefit animal production at various stages. These benefits include improvement in milk production, weight gain and feed conversion, as well as immune function. Initial research into the mode of action for these effects has focused on stimulation of the immune system by the β-glucan fractions of yeast. However, emerging studies have revealed that some of the beneficial effects of yeast products may stem from altering metabolism, including the availability of glucose and fatty acids. These changes in metabolism, and potentially energy availability, may partially explain differences in immune function observed in yeast-supplemented livestock, as the energy demands of an activated immune system are extremely high. Thus, this paper explores the influence of yeast products on metabolism in cattle and swine, and how changes in metabolism and energy availability may contribute to improvements in immune function in supplemented animals.

Systematic review of an intervention: the use of probiotics to improve health and productivity of calves

The aims of this study were to undertake a systematic review and meta-analysis of the types of probiotic formulations that are commercially available and to critically appraise the available evidence for the effectiveness of probiotics in improving the health and productivity of calves. Relevant papers were identified to answer the question: 'In calves aged between birth to one year, is the use of probiotics associated with changes in haematological or biochemical parameters, faecal bacteria counts, average daily live weight gain, dry matter intake, or feed conversion ratio?' The search of the literature yielded 67 studies that fit the primary screening criteria. Included studies were assessed for bias and confounding using a predefined risk assessment tool adapted from the Cochrane Collaboration's tool for assessing risk of bias in randomised trials and GRADE guidelines. Meta-analysis was performed using Review Manager and R. Random sequence generation was low in more than 59 % of studies. Risk of allocation concealment and performance bias were largely unclear in over 68 % of studies. Calves fed probiotics had increased average daily live weight gains (ADG) from birth to weaning (mean difference [MD] = 83.14 g/d 95 % CI = 58.36-107.91, P < 0.001) compared with calves on a control diet. Calf age reduced the level of heterogeneity of the effect of probiotics on ADG for calves between one to three weeks of age (τ² = 73.15; I² = 4%; P = 0.40) but not for calves older than three weeks of age (τ² = 2892.91; I² = 73 %; P < 0.001). Feed conversion ratio (FCR) was lower for calves on probiotics (MD = -0.13 kg of dry matter intake (DMI) to kg of live weight (LW) gain, 95 % CI = -0.17 to -0.09, P < 0.001), and the heterogeneity of effect was large in younger aged calves (τ² = 0.05; I² = 78 %; P = 0.03). The risk of bias regarding the methodology in the included studies was high. The quality of evidence for each outcome was categorised as moderate. There is sufficient data to support the effectiveness of probiotic use in some applications such as for the improvement of performance and productivity parameters of calves. However, the evidence is weak for other potential probiotic uses in calves such as improved health and reduced risk of disease. Therefore, the existing data are inconclusive and do not support the use of probiotics as an alternative to antimicrobials to improve calf health and productivity.