Prenatal heat load effect on calf health, and in vitro calf innate immune response to Salmonella serovars
Abstract
A study was conducted to investigate the effects of prenatal heat load on bacterial levels and innate immunity in the neonatal calves. The study was undertaken in spring and summer of 2010 on two commercial dairies. Fifty-three neonatal Holstein calves were used, 27 born in spring (SP) and 26 born in summer (SU). Bacterial populations were determined on hide and udder swabs taken from the dams, and nasal and rectal swabs taken from the calves. RNA expression of toll-like receptor 4 (TLR4) and tumor necrosis factor-alpha (TNF-α) was determined in calf blood leukocytes. Also, Colostrum samples from dams were collected to determine bacterial population and IgG concentration. The results show that prenatal heat load affects bacterial populations in the neonatal calves, increasing the concentrations of total aerobes. Moreover, it was shown that prenatal heat stress decreased TNF-α expression of neonatal calves. The observed increased bacterial load and immune suppression may affect calf morbidity and mortality. A second study was conducted with the objective of determining the innate immune response of bovine leukocytes against ex vivo exposure with Salmonella enterica serovars Dublin (SD), Typhimurium (ST), and Enteritidis (SE). Jugular blood from ten Holstein heifers at approximately three weeks of age was collected. Blood leukocyte were isolated and exposed ex vivo to nonopsonized or serum-opsonized SD, ST, and SE for two hours. Leukocyte phagocytosis and oxidative burst, cell surface expression of cluster of differentiation (CD) 14 and CD18 were analyzed using flow cytometry. Leukocyte mRNA expression of interleukin-8 (IL-8), IL-12, TNF-α, and TLR4 was determined using real-time RT-PCR. The results suggest that, compared to ST and SE, bovine-host-adapted SD enhances its internalization by bovine phagocytic immune cells. Moreover, SD and ST suppressed the oxidative burst in phagocytes, which may benefit their survival, replication, and dissemination within the host. In contrast, SE did not induce uptake by phagocytes and showed no oxidative burst suppressing effect. Thus, SE infection in cattle is likely to be restrained within the gastrointestinal tract, and eliminated at the early stage of the infection. In conclusion, the innate immunity of neonatal calves was affected by prenatal heat load, and exposure with different Salmonella serovars elicited different innate immune responses in calf blood leukocytes.
Degree
M.S.
Advisors
Ebner, Purdue University.
Subject Area
Microbiology|Animal sciences|Immunology
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