Response of White Leghorn chicks fed ascorbic acid and challenged with Escherichia coli or with corticosterone

Ascorbic Acid Differentially Affects Stress Response and Resistance to Colibacillosis in Turkeys from Genetic Lines Differing in Growth Rate

Genetic selection for fast growth can affect the ability of male turkeys to cope with stressors, resulting in decreased immunity to opportunistic bacterial infection. The purpose of the current study was to compare the effects of ascorbic acid (AA) on the stress response and resistance to Escherichia coli challenge of birds selected for increased 16-wk body weight (BW; F-line) with their random-bred parent line (RBC2). Male turkeys were raised in duplicate floor pens in a two line×two AA treatment×two stress challenge (SC) design. At 5 wk of age, AA (1200 ppm) was provided in drinking water for a 24-hr period, during which all birds were weighed. After AA treatment, the SC group was subjected to a transport stress protocol. Six hours after the start of transport, SC birds were also inoculated in the thoracic air sac with 1×10(4) colony-forming units of E. coli. The following morning four birds from each pen were bled, and all birds were weighed and necropsied 2 days later. BW and gain after SC were decreased in the F-line but not the RBC2 line, and there were no AA effects on BW. The weight of the bursa of Fabricius relative to BW was higher in the RBC2 line than in the F-line, was decreased by SC, and was not affected by AA. The heterophil∶lymphocyte ratio was higher in the SC F-line as compared to the SC RBC2 and was decreased by AA only in the SC F-line. Corticosterone (C) levels were increased by SC only in the F-line, and AA decreased C levels only in the RBC2 line. Airsacculitis scores were increased in the F-line SC birds. The challenge strain of E. coli was only detected in the air sac and liver of the AA-treated F-line SC birds and in the liver of the no-AA F-line birds. These results suggest that SC at 5 wk of age had a more deleterious effect on the fast-growing F-line than on its parent line and that AA may have increased susceptibility to colibacillosis in the SC F-line birds.

Dexamethasone triggers lameness associated with necrosis of the proximal tibial head and proximal femoral head in broilers

Bacterial chondronecrosis with osteomyelitis (BCO) and turkey osteomyelitis complex (TOC) are characterized by bacterial infection and necrotic degeneration within the tibiae and femora. Stress and immunosuppression have been implicated in the pathogenesis of BCO and TOC. Immunosuppressive doses of dexamethasone (DEX) trigger high incidences of TOC in turkey poults. The present study was conducted to determine if DEX injections or heat stress can trigger BCO and lameness in broilers. In 3 independent experiments, broilers were weighed and either remained uninjected or received repeated injections of 0.9% saline or DEX dissolved in saline (0.45 to 1.5 mg of DEX/kg of BW). Across all 3 experiments, the incidences of lameness were 0% for uninjected controls, 0 to 8% in saline-injected groups, and 24 to 68% in groups injected with 0.9 to 1.5 mg of DEX/kg of BW. Growth was inhibited by DEX injections regardless of whether the birds became lame or survived. When compared with saline-injected groups, DEX injections consistently increased the incidence of severe proximal tibial head necrosis in lame birds as well as in survivors. The DEX injections also triggered a subset of lesions that are not considered pathognomonic for BCO (for example, avascular femoral head necrosis and fatty necrosis of the tibiae). In a fourth experiment, repeated episodes of heat stress did not trigger lameness, although the subclinical incidence of tibial head necrosis was substantially higher at 28 and 35 d of age in heat-stressed broilers when compared with broilers reared under thermoneutral conditions. Accordingly, stress and immunosuppression must be considered contributing factors in the pathogenesis of tibial and femoral lesions associated with lameness in broilers. A subset of the lesions triggered by repeated DEX injections did not precisely mimic the pathogenesis of BCO in broilers, and DEX consistently inhibited growth whereas BCO is associated with rapid growth. These caveats must be acknowledged when DEX is used to trigger lameness in broilers.

The effect of vitamin C on the non-specific immune response of the juvenile soft-shelled turtle (Trionyx sinensis)

The study was conducted to determine the effect of supplementation vitamin C in dietary non-specific immunity in juvenile soft-shelled turtles. The soft-shelled turtles were fed with vitamin C supplementation at dosages of 0, 250, 500, 2500, 5000 and 10000 mg/kg diets, respectively, for 4 weeks. The results showed that there were no differences in the phagocytosis of blood cells, serum bacteriolytic activity and bactericidal activity among soft-shelled turtles fed with vitamin C supplementation in 0-500 mg/kg diets. However, firm indicators were significantly enhanced in soft-shelled turtles fed with vitamin C supplementation at 2500 mg/kg diets compared with those fed at 0 and 250 mg/kg diets. The soft-shelled turtles fed with 5000 mg/kg diets had only significantly higher bactericidal activity than those fed vitamin C-deficient diets. The vitamin C supplementation in 10000 mg/kg diets had no notable effects on the phagocytosis, bacteriolytic activity and bactericidal activity. These results suggest that vitamin C seems have an upper and lower threshold for improving non-specific immune function, and the optimum dose was 2500 mg/kg.

Sex-related differences of hepatic microsomal mixed function oxidase system and antibody production in broilers implanted with corticosterone and/or fed ascorbic acid

1. Most of the components of the mixed function oxidase (MFO) in hepatic microsomes were reduced by corticosterone implants, and the degree of the reduction in females and at an older age was greater than those in males and at a younger age. 2. Ascorbic acid (AA) prevented the reduction in the MFO caused by corticosterone implants. 3. The activities of aniline hydroxylase and aminopyrine N-demethylase were enhanced by corticosterone implants regardless of AA supplementation. 4. The activity of NADPH-cytochrome c reductase in male broiler was greater than that in females under normal conditions. 5. Corticosterone implants and dietary AA had less influence on the antibody production, especially to T-cell dependent antigen.

Glucocorticoid effects on natural and humoral immunity in mallards

Two studies were conducted to determine the effects of dexamethasone (DEX) on immune function in mallard ducks. Each day ducks were injected intramuscularly with DEX at doses ranging from 0.2-4.0 mg/kg for 28-30 days. Physiologic effects consistent with high dose glucocorticoid (GC) treatment were observed at the 4 mg/kg dose, and included significant body weight loss, lowered hematocrit, and elevated alanine aminotransferase (ALT) activity. At all doses, effects of DEX on the immune system were observed. When DEX was given at 0.2 mg/kg/day, significant suppression of primary IgG antibody titers to sheep erythrocytes (SRBC) was observed. At 1 mg/kg/day, primary IgM and secondary IgM and IgG titers were suppressed as well. These doses of DEX also produced significant elevation in natural killer cell (NKC) activity of peripheral blood mononuclear cells (PBMNC). Removal of adherent cells from the PBMNC prior to NKC assay eliminated the enhancement in NKC activity. Based on these results, it was postulated that the elevation in NKC activity may be due to suppression by DEX of monocyte production of prostaglandin-E2 (PGE-2) resulting in the release of NKC activity from the inhibitory effects of PGE-2. This hypothesis was supported by a measured decrease in PGE-2 production during the NKC assay by cells from DEX-treated birds. Furthermore, an enhanced NKC activity could be reproduced in vitro with the addition of indomethacin or DEX to NKC cultures containing adherent cells from PBMNC. Direct effects of DEX on nonadherent cell NKC activity and lymphocyte viability were only observed at high concentrations (10(-4) M) of DEX, while the phagocytic activity of adhered blood monocytes was inhibited at 10(-6) M DEX. The suppressed phagocytic activity may contribute to the suppressed antibody responses observed in DEX-treated birds. Together, these results support an indirect immunomodulatory effect of DEX on NKC activity and perhaps antibody responses in vivo via altered monocyte function in mallard ducks.

Effect of cold stress on performance and immune responses of Bedouin and White Leghorn hens

1. Bedouin chickens are kept in deserts mainly for eggs and are well adapted to arid conditions. However, deserts are also characterised by relatively cold winter nights. As a consequence of cold stress there is an involution of lymphoid organs and a depression of immunological function. We compared the performance and immunological responses of Bedouin and White Leghorn hens kept in outdoor pens in the Negev Desert during the winter. 2. Initial mean body mass was similar for the two breeds: 1525 g for Bedouin hens and 1542 g for White Leghorn hens. White Leghorns lost 7.74 g/d, compared with 0.60 g/d for Bedouin hens and produced 0.36 eggs/d, compared with 0.54 eggs/day for Bedouin hens. 3. The heterophil/lymphocyte ratio for Bedouin hens was 0.28, which was lower than the 0.44 for White Leghorn hens. Phagocytic index was higher in Bedouin hens than in White Leghorns. Furthermore, wattle index measured 24, 48 and 72 h after PHA injections and anti-SRBC antibody titres determined 10 d after challenge were also higher in Bedouin hens than in White Leghorns. 4. We concluded that the Bedouin hens were less stressed by the cold than were the White Leghorn hens.