Location: Livestock Behavior ResearchTitle: Acute brief heat stress in late gestation alters neonatal calf innate immune functions Author
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2015
Publication Date: 10/16/2015
Citation: Strong, R.A., Silva, E.B., Cheng, H., Eicher, S.D. 2015. Acute brief heat stress in late gestation alters neonatal calf innate immune functions. Journal of Dairy Science. 98:7771-7783. doi.org/10.3168/jds.2015-9591. Interpretive Summary: Heat stress is an environmental stressor that not only affects the dairy cow, but recent evidence supports an impact on calves born after heat stress during the last months of gestation. Cows were maintained in a control or heat stress environment for 7 days. Although the heat stress was only mild, the cows had greater respiration rates and body temperatures during the heat stress. They also tended to stand more when under heat stress. These data showed that an acute, mild heat stress was achieved. Calves born to these cows had altered acute phase cytokines (immune communication molecules). The white blood cells of those calves had more adhesion molecules, suggesting activation. The phagocytic cells of the calves, which are essential for their protection during the first weeks of life were greater in the calves from the heat stressed cows and also indicative of an acute response. The alterations of the immune functions of these calves suggests that their immune responses are altered, and that they may already have increased susceptibility to disease. This work provides evidence that dairymen need to alleviate even mild heat-stress to reduce impact on upcoming generations of livestock. This will ultimately improve survivability and thriftiness of the neonate born after or during warmer weather.
Technical Abstract: Heat stress (HS), as one of the environmental stressors affecting the dairy industry, compromises the cow's milk production, immune function, and reproductive system. However, few studies have looked at how prenatal HS affects the offspring. The objective of this study was to evaluate the effect of HS during late gestation on calf immunity. Calves were born to cows exposed to evaporative cooling (CT) or heat stress (HS; cyclic 23-35°C) 3 wk before calving. Both bull and heifer calves (CT, n=10; HS, n=10) were housed in similar environmental temperatures after birth. Both CT and HS calves received 3.78 L of pooled colostrum within 12 h after birth and were fed the same diet throughout the study. In addition to tumor necrosis factor alpha (TNF-a), interleukin 1 beta (IL-1ß), interleukin 1 receptor antagonist (IL-RA), and toll-like receptor 2 (TLR2), and 4 (TLR4) mRNA expression, the expression of CD14+, CD18+, and DEC205 were determined in whole blood samples at d 0, 3, 7, 14, 21, and 28. The neutrophil to lymphocyte (N/L) ratio, differential cell counts, and the hematocrit (HCT) were also determined. During late gestation, the HS cows had greater respiration rates (P < 0.0001), rectal temperatures (P < 0.0001), and tended to spend more time standing compared to the CT cows (P = 0.09). The HS calves had less expression of TNF-a and TLR2 and greater levels of IL-1ß, IL-RA, and TLR4 compared to CT calves (P < 0.05). The HS calves also had a greater percentage of CD18+ compared to the CT calves (P < 0.05). Additionally, a greater percentage of PMN and less lymphocytes were in the HS calves compared to the CT calves (P < 0.05). The results indicate that biomarkers of calf immunity are affected by HS in the dam during late gestation and those calves may be slower to respond to pathogens that they encounter.