The impact of zinc on growth and barrier function during administration of a coccidial vacccine

Catalina Troche, Purdue University

Abstract

A series of studies were designed to investigate the ameloriative effect of supplemental Zn on coccidiosis. Broiler growth, jejunal barrier function, and immune function were evaluated in each experiment. Zinc trafficking during coccidiosis was of particular interest; therefore Zn transporter expression was determined in jejunal mucosa and cecal tonsils in Experiments 2 and 3. Dietary treatments for the initial experiment (Experiment 1) were formulated as corn/SBM diets and supplemented with one of three premixes: 90 mg/kg of Zn from Zn-Sulfate (90ZnSO4), a 90 mg/kg blended supplement of ZnSO4 and Availa®-Zn (90BS), or a 130 mg/kg blended supplement of ZnSO4 and Availa®-Zn of a Blended Supplement (130BS). Blended supplements were included in order to evaluate the impact of chelated minerals, which are thought to have improved availability over mineral salts. It was hypothesized that birds consuming the blended supplements would have improved growth, barrier function, and immune response over birds consuming ZnSO4. Dietary treatments were fed to broilers raised on used litter through 21 days of age. Body weight gain was not influenced by dietary treatment. However, 90BS improved epithelial resistance over birds consuming 90ZnSO4. A challenge model was created by administering a live coccidiosis vaccine at five times the recommended level (5XCV). While there was no effect of dietary treatment, phagocytic capacity and intracellular free Zn were increased by 3 and 40% (respectively) in broilers exposed to 5XCV. Zinc is typically sequestered with the cell, but can act as a secondary messenger when released from the endoplasmic reticulum/golgi complex. Therefore, intracellular free Zn was thought to be indicative of increased cell response to challenge. A significant treatment by challenge interaction occurred when IL1β and IL10 expression was evaluated in cecal tonsils. Birds consuming Zn in the form 90ZnSO4 had reduced IL10 expression with challenge compared to blended Zn regimens suggesting that blended Zn regimens had improved resolution of infection. Experiments 2 and 3 were designed to investigate how dietary Zn concentration impacted coccidial challenge. Therefore in Experiment 2, Zn was provided from the basal diet alone (no supplemental Zn) or from supplemental regimens which provided 90 mg/kg total dietary Zn. As in Experiment 1, Zn regimens were either soley ZnSO4 or a blend of ZnSO4 and Availa® -Zn. Experiment 3 was identical to Experiment 2 with the exception of additional increments of supplental Zn between basal and 90 mg/kg. The challenge model for Experiments 2 and 3 differed from Experiment 1 in concentration and frequency of administration. Experiments 2 and 3 used a 10X dose of live coccidial vaccine which was administered weekly, as opposed to a 5X dose which was administered once Experiment 1. In comparison to broilers consuming basal diets, supplemental Zn improved body weight gain (BWG) and feed intake (FI) by 12 and 11%, respectively (Experiment 2). In Experiment 2, exposure to 10XCV suppressed BWG and FI by 8 and 7%, respectively. The addition of Zn was not able to overcome the growth depression due to 10XCV. Exposure to 10XCV in Experiment 2 had no impact on BWG or FI. However, the introduction of additional supplemental concentrations resulted in a 9% linear increase when dietary Zn increased from 45 to 70 mg Zn per kg diet. In Experiment 2, proximal jejunal tissues from 10XCV broilers consuming supplemental Zn had a refractory short circuit current (ISC) response to a buffer addition of ZnSO4. Tissues from 10XCV broilers consuming the blended Zn source had negligible ISC response when exposed to carbachol, a cholinergic agonist which stimulates Cl- secretion. These findings suggest that a blended Zn regimen may improve anaphylactic response to coccidia. AAA Interestingly 10XCV intracellular free Zn was decreased in jejunal (Experiment 2) and cecal tonsil cells (Experiment 3) by 58 and 27% respectively. Phagocytic capacity decreased (5%) in jejunal tissue (Experiment 2) and increased (2%) in cecal tonsils cells (Experiment 3). As seen in Experiment 1, neither intracellular free Zn nor phagocytic capacity was influenced by dietary treatment. These results were contrary to our hypothesis that coccidiosis would increase intracellular free Zn and phagocytic capacity. The difference between Experiment 1 and Experiments 2 and 3 may have resulted from the time post administration of coccidial vaccine. The differences in intracellular free Zn and phagocytic capacity may have reflected a shift in cell populations between the experiments. AAA Zinc trafficking is mediated by Zn solute carriers. Zinc transporters (ZnT) mediate movement of Zn out of the cytoplasm and ZRT, IRT-like proteins (ZIP) traffick Zn into the cytoplasm. Four transporter sequences specific to Gallus gallus were evaluated in both jejunum and cecal tonsils; ZnT5, ZnT7, ZIP9, and ZIP13. All transporters have been associated with the endoplasmic reticulum (ER)/golgi complex. Based on the infiltration of immune cells, which use intracellular free Zn during coccidiosis, it was hypothesized that the overall ratio of ZIP:ZnT expression would increase with challenge. The ratio of ZIP:ZnT in jejunal and cecal cells increased by 2.5 and 13 fold, respectively. Given the directionality of Zn transporters (ZIPs into cytosol, ZnTs out of cytosol) this pattern of expression would be expected to increase intracellular free Zn. However, Experiments 2 and 3 reported decreased intracellular free Zn with 10XCV. One explanation is that Zn from ZIP transporters became incorporated into cytosolic proteins, e.g. MT or other metal-regulatory protein. Alternatively, the cell may have upregulated exporters in an effort to recover depleted Zn during coccidiosis. Overall coccidial vaccine exposure had the largest impact on immune status and intracellular free Zn concentration. However, Zn improved BWG and FI in unchallenged birds. Supplemental Zn also improved jejunal barrier function (Experiment 1 and Experiment 3). Blended Zn regimens improved baseline intestinal resistance and ameliorated anaphylactic response (i.e. chloride secretion) during coccidial vaccine challenge.

Degree

Ph.D.

Advisors

Applegate, Purdue University.

Subject Area

Nutrition|Immunology

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