Please cite this article in press as: Abdelfattah, E.M., et al., Acute phase cytokines, TAC1, and toll-like recep- tor4 mRNA expression and health associated with group size in veal calves. Vet. Immunol. Immunopathol. (2015), http://dx.doi.org/10.1016/j.vetimm.2015.01.008 ARTICLE IN PRESS G Model VETIMM-9309; No. of Pages 9 Veterinary Immunology and Immunopathology xxx (2015) xxx–xxx Contents lists available at ScienceDirect Veterinary Immunology and Immunopathology j ourna l h omepa ge: www.elsevier.com/locate/vetimm Research paper Acute phase cytokines, TAC1, and toll-like receptor4 mRNA expression and health associated with group size in veal calves E.M. Abdelfattah a , M.M. Karousa a , M.M. Schutz b , D.C. Lay Jr. c , J.N. Marchant-Forde c , S.D. Eicher c,∗ a Department of Animal Hygiene, Behavior and Management, Faculty of Veterinary Medicine, Benha University, Qalyubia, Moshtohor 13736, Egypt b Purdue University, Department of Animal Sciences, West Lafayette, IN 47907, USA c USDA-ARS, Livestock Behavior Research Unit, West Lafayette, IN 47907, USA a r t i c l e i n f o Article history: Received 17 January 2014 Received in revised form 27 January 2015 Accepted 30 January 2015 Keywords: Group size Health Immune status Stress Veal calf a b s t r a c t Chronic stressors are a major health and well-being issue in animals. Immune status of animals under chronic stress is compromised, thus reducing disease resistance and compro- mising well-being of the animal. The objective of this study was to determine the influence of group size of veal calves on immune status and leukocyte mRNA expression of acute phase cytokines, toll-like receptor 4 (TLR4) and tachykinin 1 (TAC1) over a five-month fin- ishing period. Holstein bull calves (n = 168), 44 ± 3 days of age were assigned to one of three treatments; 2, 4, or 8 calves/pen (pen space allowance of 1.82 m 2 /calf). Jugular blood samples were collected at the day of grouping and then monthly for 4 months. The differ- ential leukocyte counts were determined and mRNA was extracted from the leukocytes. Reverse transcription-qPCR was used to measure the gene expression of interleukin-1 (IL- 1), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor (TNF-), TLR4, and TAC1 in leukocytes. Health was evaluated before grouping and monthly for 4 months. On the 1st month after grouping, veal calves that were housed in groups of 8 have greater expres- sion of IL-1 mRNA than calves housed in groups of 4 or 2 (treatment × month, P = 0.04). Also at 1 month, groups of 8 had greater TAC1 expression (P < 0.05) than calves housed in groups of 4 or 2. However, the expression of IL-1Ra, TNF-, and TLR4 were not influenced by group size. In the first month of the trial, calves in groups of 8 coughed more (P < 0.05) than calves in groups of 2 and coughed more than calves in groups of 4 and 2 during the 2nd month (treatment × month, P = 0.03). Calves housed in groups of 8 tended to have greater neutrophil percentage (P = 0.09), neutrophil to lymphocyte ratio (P = 0.06), and had lower lymphocyte percentage (P = 0.06) than those housed in groups of 4 or 2. In conclusion, the number of veal calves in a group, given the same space during the finishing period did not alter IL-1Ra, TNF-, and TLR4 mRNA expression. However, housing of calves in groups of 8 was associated with greater expression of IL-1 and TAC1 mRNA in peripheral blood leukocytes, and coughing during the first 2 months after grouping. Therefore, housing of veal calves in larger groups may lead to greater susceptibility to respiratory disease and stress. Published by Elsevier B.V. Abbreviations: mRNA, messenger RNA; N/L ratio, neutrophil to lymphocyte ratio; RT-qPCR, quantitative reverse transcription PCR; TAC1, tachykinin 1; TLR4, toll-like receptor 4. ∗ Corresponding author. Present address: USDA-ARS, Purdue University, 125 S. Russell Street, 216 Poultry Building, West Lafayette, IN 47907, USA. Tel.: +1 7654963665; fax: +1 7654961993. E-mail address: Susan.Eicher@ars.usda.gov (S.D. Eicher) . http://dx.doi.org/10.1016/j.vetimm.2015.01.008 0165-2427/Published by Elsevier B.V.