“Stress” and its Implications in Poultry Production

Modification of the plasma cortisol response to stress in rainbow trout by selective breeding

Male and female rainbow trout were segregated into high- and low-responding individuals (HR, LR) on the basis of their plasma cortisol response to a 3-h period of confinement imposed at monthly intervals for 5 months. Consistent divergence was obtained in the responsiveness of the two groups, although the difference between LR and HR groups was greater in female fish (56 c.f. 116 ng ml(-1)) than in males (45 c.f. 69 ng ml(-1)). Progeny groups (full-sib families) were obtained from the pairing of HR males and females and LR males and females. A third progeny group (US) was obtained by random pairing of parents which were not selected as HR or LR. Poststress plasma cortisol levels in the progeny were first tested at 6 months after hatch and were significantly correlated with the response of the corresponding parental groups, HR > US > LR (178, 126, 81 ng ml(-1), respectively). The difference in responsiveness between LR and HR groups was demonstrated in all four subsequent tests over a 12-month period. There were no significant differences in baseline plasma cortisol levels in LR and HR groups prior to confinement. During a 4-h period of confinement, the differences in plasma cortisol levels between LR and HR fish were sustained throughout, indicating that the trait upon which the fish were selected was related to absolute maximum levels of circulating cortisol and not to the rate of change of cortisol levels during exposure to a stressor. A moderately high heritability (h(2)) for confinement-induced plasma cortisol of 0.41 was obtained by a parent-progeny regression. Manipulation of stress responsiveness in fish by selective breeding offers scope for optimizing performance under intensive rearing conditions but also provides a useful research tool for investigating the operation of the endocrine stress response.

Selection of Japanese quail for contrasting blood corticosterone response to immobilization

Japanese quail (Coturnix coturnix japonica) were divergently selected for 12 generations for increased (high stress, HS) and decreased (low stress, LS) blood corticosterone (B) response to unfamiliar environments. Response lines were selected initially on the basis of wild-type quail B response to albino (ALB) quail intrusion (S1 to S3) and subsequently on B response to immobilization (IMB) (S4 to S12). Using ALB intruders as stressors proved unsuccessful, therefore the practice was abandoned in favor of using IMB, which proved successful. Across nine generations of selection, using the IMB stressor, the HS line exhibited a mean serum B response that was approximately 58% greater than that of the random-bred (control stress, CS) line, whereas the LS line had a mean response approximately 23% less than that of the CS line. Selection differentials were approximately three-fold greater in the HS than in the LS line whereas realized heritabilities (h2) were approximately two-fold greater in the HS than in the LS line.

Reproductive performance of broiler breeders exposed to cycling high temperatures from 17 to 20 weeks of age

Forty male and 240 female broiler breeders were placed in cages within environmental chambers (20 males or 40 females per chamber) at 14 weeks of age. Chamber temperatures were maintained at 21.3 +/- 2.5 C, and relative humidity (RH) ranged from 40 to 50%. Ventilation rate was approximately 47.2 liters/sec per chamber, and light was provided from 0600 to 1800 hr. Feed was restricted daily according to industry recommendations, and water was provided ad libitum. From 17 to 20 weeks of age, control (C) chambers were kept at constant 21.0 +/- 1.4 C with 45 +/- 5% RH, and heat-treated (HT) chambers were cycled from 24.4 +/- 5.5 C (45 +/- 5% RH) during 1800 to 0800 hr to 36.0 +/- 2.8 C (15 +/- 5% RH) during 0800 to 1800 hr. Body weights were recorded at biweekly intervals. At 18 and 20 weeks of age, blood samples and rectal body temperatures were obtained randomly from five fasted birds per chamber at 0800 and 1400 hr. From 20 to 60 weeks of age, all birds were kept in individual cages in a conventional fan-ventilated house. Maximum temperature never exceeded 30 C, and average RH was 65.0%. Reproductive parameters were monitored and body weights were obtained at 4-week intervals. There were no significant treatment effects for body weight, body temperature, or differential leukocyte counts. Hematocrits were significantly lower for HT females than controls, and heat treatment did not result in consistent changes in plasma glucose or total proteins.(ABSTRACT TRUNCATED AT 250 WORDS)