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

https://doi.org/10.1016/j.anifeedsci.2011.06.009Get rights and content

Abstract

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 5 d 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.

Introduction

Lactic acid bacteria (LAB) are in the normal intestinal microbiota of animals and humans (Schneider et al., 2004, Soto et al., 2010), and have been identified as controllers of pathogens such as Salmonella spp. (Gill et al., 2001) and Escherichia coli (Shu and Gill, 2002). These pathogens are the etiologic agent of calf diarrheas during the first weeks of life, and diarrhea is the main cause of morbidity and mortality in the early life of calves (Timmerman et al., 2005).

It is very important to reduce the prevalence of gastrointestinal infections in young calves, because when animals are ill at this stage, their subsequent growth is delayed thereby affecting productivity (Rosmini et al., 2004). The high incidence of intestinal disease is especially high in intensive rearing systems where exposure to pathogens is increased due to confinement of large numbers of animals in small areas (Callaway et al., 2002).

Use of LAB to reduce pathogenic bacteria in the gut has been termed a probiotic strategy, with an overall goal of promoting colonization of protective bacteria in calves during the first weeks of life to compete with pathogenic bacteria. Additionally, LAB can stimulate development of the immune response against pathogenic bacteria and counteract negative effects of illnesses (Frizzo et al., 2010).

To prevent and control intestinal infections, a current practice is to use antibiotics, a strategy which could increase the emergence and spread of antibiotic-resistant bacteria in meat and dairy products. In addition, residual antibiotics in those foods are unacceptable for human consumption. To overcome these problems, use of LAB has been suggested as a feed additive to promote beneficial effects to the host by favoring the balance of the intestinal microbiota (Abu-Tarboush et al., 1996).

Reports of LAB fed to young calves are inconclusive. Many authors reported beneficial effects of probiotic preparations on animal growth (Abe et al., 1995, Meyer et al., 2001, Timmerman et al., 2005, Frizzo et al., 2008, Frizzo et al., 2010), while others (Jenny et al., 1991, Higginbotham and Bath, 1993, Abu-Tarboush et al., 1996, Cruywagen et al., 1996, Goncalves et al., 2000) reported no effects.

Systematic review consists of a scientific technique of reviewing available literature using explicit methods to identify, select and critically evaluate studies which are relevant to the stated objective (Faria Filho et al., 2006). A consistent review of studies of probiotics added to calves diets and published to date can be completed using meta-analyses. As the use of probiotics in the diet of young calves may improve their growth performance, the objective of this meta-analysis was to assess effects of probiotic supplementation on growth performance (e.g., body weight gain (BWG), feed efficiency) in young calves.

Section snippets

Criteria for study selection

The studies included in the meta-analysis were selected based on the criteria: randomized and controlled experiments, studies which used calves <10 d of age, without diseases and with passive immunity, and published in peer-reviewed journals. Controlled experiments were defined to include use of a placebo. LAB could be added in whole milk, pasteurized whole milk, or milk replacer and with or without inclusion of a calf starter as a solid diet. All feeds used must have been free of added

Overview of included studies

The literature search yielded 66 scientific papers on probiotics and calves. Twenty one of the 66 screened articles met all inclusion criteria to assess the probiotic effect on BWG, but only 14 articles were included in the evaluation of the probiotic impact on feed efficiency.

Within the studies included to assess the probiotic effect on BWG in young calves, only one study was conducted before 1990, with most between 1991 and 2000 (11) and after 2001 (9). Holstein calves were used in the most

Discussion

This quantitative meta-analysis of data from several randomized controlled experiments showed that probiotic supplementation increased BWG and feed efficiency in young calves.

Conclusions

This meta-analysis included a large number of experiments which assessed growth performance of calves and showed that supplementation with LAB is effective in improving BWG and feed efficiency, especially during the first 60 d of rearing in calves fed milk replacer. The probiotic effect was not related to supplementation with monostrain or multistrain inocula. A beneficial effect on feed efficiency was associated with experiments which used >20 calves, while the effect on BWG was identified with

Acknowledgments

Laureano S. Frizzo and Lorena P. Soto are posdoctoral fellows and Marcelo L. Signorini is a Research Career Member from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina). María V. Zbrun is doctoral fellow from the Universidad Nacional del Litoral (Argentina).

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