J Dairy Sci. 2023 Nov 8:S0022-0302(23)00790-7. doi: 10.3168/jds.2023-23831. Online ahead of print.
The gastrointestinal microbial consortium in dairy cattle is critical to determining the energetic status of the dairy cow, from birth through her final lactation. The ruminant's microbial community can degrade a wide variety of feedstuffs which can impact growth, production rate and efficiency on the farm; but can also impact food safety, animal health, and environmental impacts of dairy production. Gut microbial diversity and density are powerful tools that can be harnessed to benefit both producers and consumers. The incentives in the US to develop Alternatives to Antibiotics for use in food animal production have been largely driven by the Veterinary Feed Directive and has led to an increased use of probiotic approaches to alter the gastrointestinal microbial community composition, resulting in improved heifer growth, milk production and efficiency, and animal health. However, the efficacy of Direct Fed Microbials (DFM) or probiotics in dairy cattle has been highly variable due to specific microbial ecological factors within the host gut of and its native microflora. Interactions (both synergistic and antagonistic) between the microbial ecosystem and the host animal physiology (including epithelial cells, immune system, hormones, enzyme activities, and epigenetics) are critical to understanding why some probiotics work but others do not. Increasing availability of Next Generation Sequencing (NGS) approaches provides novel insights into how probiotic approaches change the microbial community composition in the gut that can potentially impact animal health (e.g., diarrhea/scours, gut integrity, foodborne pathogens), as well as animal performance (e.g., growth, reproductive, productivity) and fermentation parameters (e.g., pH, short chain fatty acids [SCFA], methane production, and microbial profiles) of cattle. However, it remains clear that all DFM are not created equal and their efficacy remains highly variable and dependent on stage of production and farm environment. Collectively, data have demonstrated that probiotic impacts are not limited to the simple mechanisms that have been traditionally hypothesized, but instead are part of a complex cascade of microbial ecological and host animal physiological effects that ultimately impact dairy production and profitability.
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