Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2005
Publication Date: 5/1/2005
Citation: Huff, G.R., Huff, W.E., Balog, J.M., Rath, N.C., Anthony, N.B., Nestor, K.E. 2005. Stress response differences and disease susceptibility reflected by heterophil/lymphocyte ratio in turkeys selected for increased body weight. Poultry Science. 84:709-717. Interpretive Summary: Three genetic lines of turkeys were compared for their responses to bacterial challenge in two stress models, 1.Bacterial injection following treatment with a compound that mimics stress or 2. Bacterial injection 8 days before being transported in a truck for 12 hours. The turkey lines were a slow growing line selected for increased egg production (Egg-line), a fast growing line selected for increased body weight (F-line), and a fast growing commercial line (Comm-line). All treated birds and untreated control birds were bled at the same time, which was 1 day after transport and 9 days after challenge with E. coli. The total numbers of white blood cells (WBC), which are known to be involved with prevention of disease, was the same for all 3 lines, however the percentages of each type of white blood cell changed differently in the fast-growing lines. The ratio between two types of WBC, heterophils and lymphocytes (H/L ratio) is known to increase when birds are under stress. The H/L ratio was lower in the slow growing Egg-Line birds than in the two faster growing lines and was increased more by stress in the fast-growing lines compared with the Egg-line. Death, disease and loss of body weight were greatest in the fastest-growing Comm-line which also had the highest H/L ratio. The differences between these lines in their disease resistance and blood cell responses to stress, in two different stress models, suggests that increasing selection for body weight of turkeys is accompanied by changes in the stress response that causes an increase in bacterial disease.
Technical Abstract: Three genetic lines of turkeys were compared for their responses to Escherichia coli challenge following dexamethasone injection (Dex) or E. coli challenge preceeding transport stress (Transport). The turkey lines were a slow growing line selected for increased egg produc-tion (Egg-line), a fast growing line selected for increased 16 wk BW (F-line), and a commercial line (Comm-line). At 14 wks of age, the Dex group was treated with 3 injections of 2mg Dex/kg BW followed by airsac challenge with 100 cfu of E. coli. The Transport group was given the same E. coli challenge at 1x10**4 cfu/bird without Dex treatment, and was subjected to transport stress, including 12 hours of holding time in a transport vehicle, 8 days after the challenge. All treated birds and untreated control birds were bled at the same time, which was 1 day after transport and 9 days after challenge with E. coli. The main effect mean (MEM) total leukocyte counts (WBC) and the percentages of eosinophils (Eos) and basophils (Baso) were the same for all 3 lines, however the MEM percentages of heterophils (Het) and monocytes (Mono) and the heterophil/lymphocyte ratio (H/L) were lower and the percentage of lymphocytes (Lym) was higher in the Egg-line as compared to the two fast-growing lines. Both stress treatments increased WBC, Het, and H/L and decreased Lym in all three lines, however these effects were significantly greater in both fast growing lines as compared to the Egg-line. Sixteen week BW was unaffected by either treatment in the Egg-line and was decreased by both treatments in the Comm-line and by the Dex treatment in the F-line. Main effect mean airsacculitis score (AS) was not affected by line and was significantly increased by both Transport and Dex treatments. Neither treatment affected AS of the Egg-line birds, while Dex treatment increased AS of the F-line and both Dex and Transport increased AS of the Comm-line. Mortality was significantly higher in the Comm-line as compared to the Egg-line and was intermediate in the F-line. The differences between these lines in their disease resistance and physiological response to stress in two different stress models suggests that increasing selection for body weight of turkeys is accompanied by changes in the stress response resulting in increased susceptibility to opportunistic bacterial infection.