Genetic variation of physiological response to aflatoxin in Gallus domesticus

Aflatoxicosis, infectious bursal disease and immune response to Newcastle disease vaccination in rural chickens

To investigate the immunosuppressive effects of infectious bursal disease virus (IBDV) and aflatoxin in indigenous chickens of Uganda, Newcastle disease (ND) seronegative chicks were randomly allocated to two treatment groups. Group A chicks were injected intramuscularly at the age of 3 weeks every 2 days up to four times with 0.250 mg aflatoxin B1 per bird, group B was infected occulo-nasally with IBDV 3 days prior to vaccination, while group C was left as a control group. All the chicks from the three groups were then vaccinated with Hitchner B1 vaccine at 21 days of age followed by a secondary vaccination with La Sota vaccine 3 weeks later. Humoral and cell-mediated immune responses were assessed by measuring antibody levels and delayed hypersensitivity reaction post vaccination. Growth performance in the three groups was assessed by weekly body weights while evidence of excretion of vaccinal ND virus was detected by reverse transcription-polymerase chain reaction.A significant (P < 0.05) reduction in the haemagglutination inhibition of ND antibody titre following initial priming with Hitchner B1 and subsequent booster with La Sota vaccines and a delayed hypersensitivity test following sensitization with dinitrochlorobenzene showed aflatoxin to be a more potent immunosuppressant than IBDV. Aflatoxin exerted its maximum effects during primary antibody response in the second and third weeks post vaccination. Aflatoxin and IBDV did not affect growth rates (P > 0.05) but prolonged La Sota vaccine virus excretion in faeces. Under our experimental conditions, aflatoxin and IBDV do not significantly affect the immune response of rural chickens to ND vaccination.

Effects of dietary aflatoxin in aflatoxin-resistant and control lines of chickens

The resistance to a single oral dose (12 mg of aflatoxin per kg of BW) and 4 wk of dietary aflatoxin (2.5 mg per kg of feed) were investigated in chicks selected for five generations for resistance to acute aflatoxicosis (AR) and unselected control (C) chicks. The AR chicks were more resistant to a single oral dose of aflatoxin and had significantly decreased sodium pentobarbital sleeping time compared to C chicks. Four-weeks exposure to dietary aflatoxin did not result in any significant change in BW or feed conversion ratios of chicks from either the C or AR line. However, more sensitive indicators of aflatoxicosis including plasma total protein, albumin, cholesterol concentrations, and gamma glutamyl transferase activity were significantly altered in C chicks but not in AR chicks fed aflatoxin. Percentages of liver lipid and liver hyperplasia score were also significantly altered as a result of dietary aflatoxin treatment in C but not AR chicks. These data indicate that selection-associated differences exist between the C and AR lines of chickens that convey resistance to not only a single oral dose of aflatoxin but also to a more chronic dietary exposure to aflatoxin.

Selection for resistance to aflatoxin in chickens

Two populations of broiler chickens [Athens-Canadian (AC) and a commercial stock] were selected for resistance to aflatoxicosis by dosing chickens in each population with a single oral dose of aflatoxin, which resulted in 40 to 70% mortality. Chickens that did not receive aflatoxin served as the nonselected control groups. Birds surviving the aflatoxin challenge were used as breeders for subsequent generations. Rapid progress was made in the AC population for resistance to aflatoxin, but only moderate progress for this trait was attained in the commercial broiler stock. After five generations of selection in the AC population, LD50 values of 9.42 and 17.05 milligrams aflatoxin per kilogram body weight (BW) were determined for the nonselected and selected lines, respectively. After four generations of selection in the commercial broiler population, LD50 values of 6.05 and 8.02 mg aflatoxin/kg BW were determined for the nonselected and selected lines, respectively. These data demonstrate that genetic progress can be made in chickens, but the amount of progress for resistance to aflatoxin may be influenced by the population.

The relationship of certain blood parameters to aflatoxin resistance in Japanese quail

Blood chemistry profiles were obtained for two lines of Japanese quail selected for resistance to aflatoxin, and for a nonselected control line. Nine of the 18 plasma components measured in samples taken at 4 weeks of age changed as a result of selection. Plasma concentrations of total protein, albumin, cholesterol, and potassium, and the activities of lactic dehydrogenase, glutamic-oxalacetic transaminase, and cholinesterase were significantly elevated in aflatoxin-resistant quail compared with the nonselected line. The activities of beta-glucuronidase and alpha-amylase changed most dramatically; both activities were much lower in the resistant lines than in the control line. In another experiment, serum total protein, albumin, alpha-amylase, and beta-glucuronidase were tested as identifiers of aflatoxin-resistant individuals within a nonselected population of quail. Serum samples obtained from 150 nonselected quail immediately before and 24 hr after administration of an oral dose of aflatoxin were analyzed for each of the four components. The acute toxicosis decreased body weight, serum alpha-amylase activity, total protein, and albumin; whereas, serum beta-glucuronidase activity and the coefficients of variation for each parameter were increased. Correlations between measurements made prior to dosing and parameters reflecting aflatoxin susceptibility were not significant. However, postdose determinations of albumin, protein, and beta-glucuronidase were significantly related to susceptibility parameters. These data indicate that the four blood components tested cannot be utilized to identify resistant birds within a nonselected population of quail without an aflatoxin challenge; but albumin, protein, and beta-glucuronidase are correlated with resistance when measured during an aflatoxin stress.

Comparative responses of genetically resistant and nonselected Japanese quail to dietary aflatoxin

Two lines of Japanese quail (AR2.5 and AR3) selected for resistance to aflatoxin and a nonselected control line (NS) were fed diets containing 0, 10, and 20 micrograms of aflatoxin/g of feed. Line-related reductions in mortality and growth inhibition clearly demonstrated the resistance of the AR lines to dietary aflatoxin. Two-week cumulative mortality percentages for the NS, AR2.5, and AR3 lines fed the 10 micrograms/g diet were 13.9, 7.7, and 2.6%, respectively, and 44.4, 17.9, and 12.8% at 20 micrograms/g. Average growth reduction percentages resulting from feeding the 10 and 20 micrograms/g diets to the NS, AR2.5, and AR3 lines were: 17.3 and 27.5%, 10.7 and 20.1%, and 4.3 and 10.5%, respectively. In addition, AR quail were resistant in varying degrees to the following aflatoxin-induced effects: liver lipid accumulation and enlargement, hepatic protein depletion, elevated hepatic beta-glucuronidase activity, bursal regression, and hypoproteinemia. Comparisons of the AR and NS lines fed the control diet revealed no detrimental physiological or biochemical response to selection for aflatoxin resistance. Genetic resistance to aflatoxin was associated with increased relative liver weight, higher liver protein content, and elevated plasma concentrations of protein and lipid compared with NS quail. One or more of these differences may be related to the mechanism of genetic resistance to aflatoxin in AR quail.