197 Effects of dietary zinc supplementation strategy on immune response, bacterial load and disease severity in growing gilts infected with Mycoplasma hyopneumoniae.
Authors: Carpenter Corey B , Urriola Pedro E , Shurson Gerald C , Pieters Maria , Johnston Lee J , Schweer Wesley , Rodrigues Lucas 
Published: May 2024

Abstract
The objective of this study was to assess impacts of dietary zinc (Zn) supplementation strategy on immune response, bacterial clearance, and disease severity in growing gilts infected with Mycoplasma hyopneumoniae. Weaned gilts [n = 96; 21-d old; initial body weight (BW) = 6.94 kg], were used in a 63-d experiment which consisted of a pre- (d 0-35) and post- (d 35-63) M. hyopneumoniae challenge. On d 0 (-35 d post-inoculation; dpi), gilts were confirmed negative for M. hyopneumoniae and PRRSv and assigned randomly to 1 of 2 dietary treatments with 8 pens/treatment and 6 gilts/pen. Treatments were: 1) Control; 125 mg/kg Zn from ZnSO4, and 2) Zn-blend; 125 mg/kg Zn with 50 mg/kg Zn from Zn-amino acid complex (ZnAA) and 75 mg/kg Zn from ZnSO4. Dietary treatments were fed in 4-phases with pharmacological levels of zinc oxide included in the first 2 phases. Phase 1 (d 0) control and Zn-blend diets contained 3,121 and 3,256 mg/kg total Zn, respectively. Phase 2 (d 0-14) control and Zn-blend diets contained 3,657 and 3,593 mg/kg total Zn, respectively. Phases 3 (d 14-35) and 4 (d 35-63) control and Zn-blend diets contained 213 and 193 mg/kg and 229 and 212 mg/kg total Zn, respectively. At 0 and 1 dpi, all gilts were inoculated intratracheally with 10 mL of a lung homogenate containing 1×105 CCU/mL of M. hyopneumoniae strain 232. Blood and tracheal secretions were collected on -35, 0, 7, 14, 21, 28 dpi. Blood samples were evaluated for antibody detection, and tracheal secretions were analyzed by PCR. Number of coughs were recorded daily from 7 to 28 dpi. At 28 dpi, gilts were humanely euthanized, and bronchoalveolar lavage fluid (BALF) and macroscopic lung lesion observations were collected. Gross lung lesions were scored, and lung tissues were fixed for histopathology. Normally distributed data were analyzed in a generalized linear model with the fixed effect of diet and repeated measures for days post-inoculation. Non-normal data were analyzed using a Mann Whitney U Test using the NPAR1WAY procedure of SAS with a fixed effect of diet or a Chi-square test. Gilts consuming control diets tended (21.68 vs. 20.90 Ct, P = 0.08) to have less relative bacterial load than those consuming Zn-blend diets, over time. No differences in mean sample-to-positive ratio or proportion of gilt seroconversion (P &gt; 0.05) were detected between treatments. There were no differences in mean concentrations of IL-1α, IL-1β, IL-6, IL-8, IL-10 (P &gt; 0.05) in BALF for gilts consuming control or Zn-blend diets. There were no differences in mean macroscopic (P = 0.73) or microscopic (P = 0.67) lung scores, and coughing index score (P = 0.25) over the entire period between gilts consuming the different dietary Zn supplementation strategies. In conclusion, growing gilts consuming diets containing different Zn sources exhibited similar signs of infection during the acute phase of a M. hyopneumoniae infection.