PSVIII-15 Inoculating suckling beef calves with a bovine-derived blend of <i>Lactobacillus spp.</i> exhibited psychobiotic potential for stress mitigation

Abstract The term “psychobiotics” refers to beneficial microbiota, such as Lactobacillus spp., which positively influence the hypothalamic-pituitary-adrenal axis, immune response, and inflammation via the gut-brain axis. While these bacteria are recognized for benefiting their host, research on their application in cattle is limited. Therefore, this study evaluated the impacts of administering a bovine-derived mixture of Lactobacillus spp. during early life to beef calves as a strategy to modulate long-term gut microbiota and potentially alleviate weaning stress. Crossbred beef calves [n = 32; 66 ± 11 kg of body weight (BW); 60 ± 6 d of age] were stratified by age and sex and randomly assigned to receive either two doses of an orally-administrated Lactobacillus cocktail (n = 16; 10^9 CFU; LAB) or saline solution (n = 16; CON) 3-d apart. After first inoculation (d 0), cow-calf pairs were allocated to four different paddocks (two/treatment) for 15 d, and then, both treatments were placed in a single pen until weaning, at ~202 d of age. After weaning, calves from both treatments were housed in a single pen. Body weight was recorded, and blood samples were collected on d 0, 3, weaning, and 3- and 14-d post-weaning (PW). Data was analyzed as a completely randomized design. Plasma concentrations of phenylalanine (P = 0.04) were greater, while tyrosine (P = 0.09) and lysine (P = 0.07) tended to be greater in LAB compared with CON calves. Furthermore, LAB calves had reduced plasma concentrations of heat shock proteins 70 (P = 0.04; 0.02 vs. 0.13 ng/mL) and cortisol (P = 0.03; 108.1 vs. 121.1 ng/mL). A tendency for a treatment × day interaction was detected (P ≤ 0.07) for white blood cells (WBC), where CON calves had decreased WBC and lymphocytes (P = 0.05) on d 0 compared with LAB. Treatment did not impact average daily gain and final BW (P ≥ 0.26). Regardless of treatment, weaning stress increased plasma concentrations of haptoglobin (P &amp;lt; 0.01), serotonin (P = 0.06), and the counts and percentages of monocyte, eosinophils, and basophils (P &amp;lt; 0.01), whereas gamma-aminobutyric acid, aspartate, and insulin-like growth factor-1 concentrations decreased (P &amp;lt; 0.01) on d 3 PW. In conclusion, early life inoculation of suckling beef calves with a Lactobacillus spp. mixture presents promising effects on mitigating some physiological stress indicators, as indicated by decreased cortisol and heat shock protein concentrations and greater concentrations of amino acids precursor of central catecholamines. These preliminary results suggest that psychobiotics could offer a promising avenue for stress management in beef calves, potentially with long-term effects. This emphasizes the importance of future research on other physiological and behavioral indicators of weaning and other stressors to fully elucidate the potential benefits of psychobiotic inoculation in livestock management.