Effect of Shiga toxoid vaccination and vitamin E supplementation on shedding of Shiga toxin-producing Escherichia coli, immunological, health and performance parameters in male Holstein calves

Cattle are considered the main reservoir for Shiga toxin (Stx)-producing Escherichia coli (E. coli), abbreviated as STEC, as well as for human-pathogenic enterohemorrhagic E. coli (EHEC), a subset of STEC. Humans become infected with EHEC via the fecal-oral route by contact with ruminants, their feces or their environment as well as consumption of contaminated and raw or insufficiently heated food products. Vaccination of cattle is a promising approach to inhibit intestinal STEC colonization and to lower fecal STEC excretion in cattle and thereby to minimize human EHEC infection risk. The principal virulence factor of STEC, the eponymous Stx, modulates cellular immune responses in cattle. Vitamin E, an essential antioxidant for maintaining the stability of biological membranes and the function of the immune system, is considered to support adaptive immune responses and performance in cattle. The overall objective of the study was to investigate the effects of Shiga toxoid (rStx1MUT/rStx2MUT) vaccinations and vit E supplementation as well as its interactions on immunological parameters and STEC shedding in growing calves as proof-of-concept under field-like-conditions. A group of 24 calves was passively (colostrum from rStxMUT immunized cows) and actively (intra-muscularly at 5th and 8th week of life) vaccinated. Twenty-four calves served as unvaccinated controls (fed with low anti-Stx colostrum, placebo injected). For each vaccination group, data was analyzed according to the level of vitamin E supplementation offered by milk replacer (188 IU all-rac-α-tocopheryl acetate daily [moderately] versus 354 IU [high]). An increase by 79 % in daily vit E supplementation led to slightly higher serum α-tocopherol level and earlier concentrate intake at the beginning of the experiment, without significant differences in live weight gain, hematology, blood chemistry parameters and percentage of peripheral CD4+ and CD8+ T cell sub-populations. The effective transfer of Stx-neutralizing antibodies from dams to calves via colostrum was confirmed by Vero cell assay. Serum antibody titers in calves differed significantly between the vaccinated and the control group until the 16th week of life. Using the expression of activation marker CD25 on CD4+CD45RO+ cells and CD8αhiCD45RO+ cells as flow cytometry based read-out, cells from vaccinated animals responded more pronounced than those of control calves to lysates of STEC and E. coli strains isolated from the farm as well as to rStx2MUT in the 16th week. rStxMUT vaccination modulated the CD4+/CD8+ ratio in peripheral blood. Additive effects of vitamin E supplementation and rStxMUT immunization on the immune response were not detected. Summarized for the entire observation period, less fecal samples from vaccinated calves were stx1 and/or stx2 positive than samples from control animals when calves were fed a moderate amount of vitamin E. In conclusion, this study provides evidence, that the maternal transfer of Stx-neutralizing antibodies to young calves and the active Shiga toxoid vaccination offers the opportunity to reduce the incidence of stx-positive fecal samples in a calf cohort. In order to maximize the rStxMUT immunization effect and to elicit a quantitative effect on STEC shedding, the immunogenic capacity (dose), the vaccine formulation, and the time and route of application have to be optimized.