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Impact of heat stress and OmniGen-AF on performance and immunity of mid-lactation dairy cows.

T. N. Marins




Impact of heat stress and OmniGen-AF on performance and immunity of mid-lactation dairy cows.
T. N. Marins*1, J. Gao1, Q. Yang1, R. M. Binda1, C. M. B. Pessoa1, R. M. Orellana1, J. K. Bernard1, M. Garcia2, D. J. McLean2, J. D. Chapman2, D. J. Kirk2, S. Tao1. 1University of Georgia Tifton, GA, 2Phibro Animal Health Corp Teaneck, NJ.

This study aimed to evaluate the impact of OmniGen-AF (OG; Phibro Animal Health) supplementation and deprivation of evaporative cooling on performance and peripheral blood mononuclear cells (PBMC) proliferation of mid-lactation Holstein cows during summer. Multiparous cows (n = 60) were blocked by parity (2.5) and DIM (189 d), and randomly assigned to 4 treatments (TRT) in a 2 � 2 factorial arrangement with 2 environments (E): cooled (CL) using fans and misters or non-cooled (NC), and 2 top-dressed feed additives (D, 56 g/d): OG or AB20 (Phibro Animal Health) as control (CON). Cows were cooled and fed respective diets for 60 d before experiment. Temperature-humidity index averaged 78 during the 8 wk trial. Dry matter intake (DMI) was recorded daily and milk yield (MY) 3x/d. Vaginal temperatures (VT) were recorded every 5 min for 4 d/wk. Blood was drawn on d 1, 3, 5, 7, 15, 28, 44, and 56 to analyze cortisol (COR), prolactin (PRL), tumor necrosis factor (TNF)-α and interleukin (IL) 10. PBMC were isolated on d 3, 14, and 42 (n = 8 cows/TRT) and cultured with hydrocortisone, PRL, lipopolysaccharides (LPS), or their combinations to assess proliferation and cytokine production. NC cows had higher VT, lower DMI and MY (E: P < 0.01), and greater blood COR at d 1 and 5 than CL (E � Time: P < 0.01). NC did not alter COR levels in OG cows but NC-CON cows had higher COR than CL-CON (E � D: P = 0.02). NC did not alter TNF-α levels in OG cows but NC-CON cows tended to have lower TNF-α than CL-CON (E � D, P = 0.07). LPS+hydrocortisone-stimulated PBMC from OG cows tended (P = 0.09) to proliferate more than CON. Deprivation of cooling tended to increased proliferation of LPS- and LPS+PRL-stimulated PBMC from OG cows, but not CON cows (E � D: P ≤ 0.108). Relative to CL, PBMC supernatant of NC cows had greater (P ≤ 0.01) TNF-α concentration stimulated by LPS or LPS+PRL, and tended (P = 0.09) to have greater IL10 stimulated by LPS, and those were not affected by diet. In conclusion, NC impaired performance and promoted COR release, but OG supplementation prevented COR release, maintained TNF-α secretion and promoted PBMC proliferation after deprivation of cooling.

Keywords: heat stress, OmniGen, immunity.