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Using a rapid blood test to study the impact of heat stress on the immune status of first-time pregnant heifers and their calves.

Q. T. Huo

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06-23-2020

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Abstract:

T21
Using a rapid blood test to study the impact of heat stress on the immune status of first-time pregnant heifers and their calves.
Q. T. Huo*1, I. Toledo2, B. Davidson2, G. Dahl2, J. Laporta2. 1University of Central Florida Orlando, FL, 2University of Florida Gainesville, FL.

This study was to evaluate the impact of late-gestation environmental heat stress on the immune status of first-time pregnant Holstein heifers during the peri-parturition period and their newborn calves using a rapid blood immunity test. The test uses gold nanoparticles that act as pseudo pathogens to probe the immune activity in blood samples. Upon mixing the nanoparticle with a blood serum, proteins from the humoral immune system including antibodies and complement proteins react with the nanoparticles, leading to an aggregate formation that is detected using dynamic light scattering. The test score is positively correlated to the humoral immune activity in the blood. Pregnant heifers were assigned randomly to 1 of 2 treatments: heat stress (shade, HT; n = 16) or cooling (shade, fans, and soakers, CL; n = 15) for the final 60 d of pregnancy (d −60). Weekly blood samples were collected from heifers (from d −60 to one week after calving) and bi-weekly from their calves (n = 13 per treatment) after colostrum feeding (d 0 14, 28, 42 and 56). Serum samples were analyzed in the laboratory. Student t-test was used to analyze the difference between sample groups. This study found that the humoral immunity of pregnant heifers decreased as they approach parturition, reaching the lowest level around the day of calving. Heifers under HT have lower immunity score compared with CL heifers on the day of calving (P = 0.03). Newborn calves show similar immunity test scores as dams on d 0, due to passive immunity transfer through colostrum feeding. No statistically significant difference was found from calves born from HT dams versus calves born from CL dams. Regardless of the treatment, there was a gradual decline of humoral immunity in neonatal calves from d 0, reaching the lowest level between d 14 and d 21. Afterward, the immunity test score of the calves increase gradually likely due to the development of calf's own immune system. In summary, this study finds that heat stress negatively impacts the immune status of late-pregnant heifers at the day of calving, but the impact on their newborn calves is not significant.

Keywords: immunity, pregnancy, heat stress.