Systematic review and meta-analysis of probiotic use on inflammatory biomarkers and disease prevention in cattle.

The aim of this study was to appraise the available evidence on the effectiveness of probiotic treatment on mature cattle immunity, inflammation, and disease prevention. A systematic review with meta-analysis was conducted to analyse studies that were eligible to answer the following research question: "in cattle of at least 6-months of age, is the use of probiotics associated with immunomodulatory and inflammatory responses, and clinical disease outcomes?" Our literature search yielded 25 studies that fit the inclusion criteria. From these studies, only 19 were suitable for inclusion in the meta-analysis due to data limitations and differences in study population characteristics. Included studies were assessed for bias using a risk assessment tool adapted from the Cochrane Collaboration's tool for assessing risk of bias in randomised trials. GRADE guidelines were used to assess the quality of the body of evidence at the outcome level. The meta-analysis was performed using Review Manager and R. The overall quality of evidence at the outcome level was assessed as being very low. On average, the treatment effect on immunoglobulin G (IgG), serum amyloid A (SAA), haptoglobin (Hp) and ß-hydroxybutyrate (BoHB) for cows receiving probiotics did not differ from control cows. Exposure to probiotics was not associated with reduced risk of reproductive disorders (pooled RR = 1.02 95 % CI = 0.81-1.27, P = 0.88). There is insufficient evidence to support any significant positive effects of probiotics on cattle immunity and disease prevention. This lack of consistent evidence could be due to dissimilarities in the design of the included studies such as differences in dosage, dose schedule, diet composition and/or physiological state of the host at the time of treatment.

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.