Establishing an experimental challenge model in broiler chickens exposed to multiple mild stressors of cyclic elevated ambient temperature, feed withdrawal, and coccidiosis infection.

Abstract

Broilers routinely experience environmental and immunological stressors in commercial production settings; however, there is limited literature evaluating their combined effects. Therefore, our objective was to assess the synergistic effects of elevated ambient temperature, feed withdrawal, and coccidiosis infection on broiler growth performance, carcass characteristics, and health. The 43-d study (starter d 0-15, grower d 15-29, finisher d 29-43) was conducted in a 2 &#xd7; 2 &#xd7; 3 factorial arrangement with factors including 1) environmental status (thermoneutral or cyclically elevated brooder temperature), 2) feed withdrawal status (0- or 12-h withdrawal prior to vaccine challenge), and 3) coccidiosis vaccine challenge on d 16 [0 &#xd7; (non-challenged), 3 &#xd7;, or 5 &#xd7; challenge). Therefore, 360 male Ross 708 chicks were assigned to 1 of 12 treatments with 6 birds allotted to each of 5 replicate cages per treatment (n = 5). Day of inoculation was designated as 0 d post-inoculation (DPI). A 1-way ANOVA was used for the starter growth phase, whereas a 3-way ANOVA was utilized for the grower growth phase, liver weights, and carcass characteristics. No statistical analyses were applied to finisher performance data. Birds that received a 3 &#xd7; or 5 &#xd7; Eimeria challenge had a lower (P < 0.05) body weight gain (BWG) and feed intake (FI) during the grower phase compared with sham-inoculated birds. Additionally, on 6 DPI, birds that received a 3 &#xd7; or 5 &#xd7; challenge had higher (P < 0.05) relative liver weights compared with sham-inoculated birds. On 6 DPI, there was a 2-way interaction (P < 0.05) between vaccine challenge dose and feed withdrawal status where birds that received a 3 &#xd7; vaccine dose and underwent a 12-h feed withdrawal had similar fluorescein isothiocyanate-dextran (FITC-d) serum concentrations compared with birds challenged with a 5 &#xd7; vaccine dose. Overall, these results suggest that the combination of cyclically elevated temperatures, a 12-h feed withdrawal period prior to Eimeria inoculation, and a 5 &#xd7; vaccine dose elicited a practical experimental challenge in broilers.