Effects of group selection for productivity and longevity on blood concentrations of serotonin, catecholamines, and corticosterone of laying hens

Effect of selection for resistance and susceptibility to viral diseases on concentrations of dopamine and immunological parameters in six-week-old chickens

White Leghorn chickens were inbred respectively from their parent lines, which were diversely selected for resistance (line 6(3)) or susceptibility (lines 7(2) and 15I(5)) to Marek's disease and lymphoid leukosis. The differences in disease resistance may have been due to differential regulation of immune and neuroendocrine homeostasis. At 5 wk of age, chickens from the same line were randomly assigned to cages at 4 birds per cage. Blood samples were collected from the chickens at 6 wk of age (n = 10/line). Subsets of T lymphocytes (CD4+ and CD8+) and B cells were measured using flow cytometry. Concentrations of plasma IgG and dopamine were quantified with ELISA and HPLC assay, respectively. Line 6(3) chickens had a higher percentage of CD8+ cells but not CD4+ cells than the chickens of the lines 7(2) and 15I(5) (P < 0.01). In contrast, both lines 7(2) and 15I(5) had a greater percentage of B cells (P < 0.01). The concentrations of plasma IgG and dopamine were also regulated differently among the lines; both were in an order of 7(2) > 15I(5) > 6(3) (P < 0.05 and P < 0.01, respectively). These results suggested that genetic selection for disease resistance also directly or indirectly modified the corresponding genetic components that govern the immune and neuroendocrine systems. The genetic lines of chickens may be used as animal models for investigation of the cellular mechanisms of genetic-environmental interactions on disease resistance.

Effects of raclopride on aggression and stress in diversely selected chicken lines

Genetic selection for chickens of high (HGPS) and low (LGPS) group productivity and survivability, resulted in two distinct genetic lines characterized by differences in cannibalism, flightiness, and immunocompetence. Additionally, birds exhibited differences in behaviour and social stress coping strategy. HGPS birds have a superior stress coping strategy compared with birds of LGPS or Dekalb XL (DXL), a commercial strain. Line differences in stress response and behaviour could be due to selection-induced differences in expression of the dopaminergic system. The dopamine (D2) receptor, an integral part of the dopaminergic system, was hypothesized to be a key contributory factor of the stress response. We tested this hypothesis by injecting either a D2 antagonist (raclopride) or saline in the dominant individual in pair-housed birds for 10 days and examining stress coping ability. Results showed that dominant birds of all strains showed a reduced frequency of aggressive pecks on subordinates following raclopride injection. In contrast, subordinates paired with raclopride-injected birds increased pecking frequency. Two days after stopping injections, LGPS and DXL birds returned to pre-injection levels of aggressive threats, while HGPS birds maintained depressed frequency of threats. Strain differences in aggressive responsiveness coincided with increased epinephrine levels in raclopride treated LGPS birds relative to control LGPS birds, but not by HGPS and DXL birds. Our findings suggest a functional linkage between the genetic basis of stress coping ability and the dopamine regulation of aggressive responsiveness. The data further indicate that the sympathetic-adreno-medullary axis is directly involved in regulating both stress coping strategy and aggressiveness.

Altered Circulating Levels of Serotonin and Immunological Changes in Laying Hens Divergently Selected for Feather Pecking Behavior

The aim of this study was to investigate the changes in immunological parameters as well as changes with respect to plasma levels of serotonin and tryptophan in lines selected for and against feather pecking (FP) behavior [high FP (HP) line and low FP (LP) line] for 5 generations. The hens from the HP line had a higher plasma serotonin level than those from the LP line (0.059 vs. 0.037 micromol/L, F(2,27) = 0.031, P < 0.05). The plasma level of tryptophan was, on average, 67.30 micromol/L and did not differ between the lines (68.3 vs. 66.3 micromol/L, F(2,28) = 0.36, P < 0.05). The HP line had a higher response to infectious bursal disease virus vaccination after 1 wk post-vaccination compared with the control and LP lines. The number of white blood cells (P < 0.0001) and the expression of MHC class I molecules on CD4 (P < 0.02), CD8beta (P < 0.006) and on B cells (P < 0.03) were highest in the LP line compared with the control and HP lines. Selection for or against FP, therefore, changes the number of white blood cells and the expression of MHC class I molecules on T and B cells, which may influence the health status of the birds.

Divergent Selection on Feather Pecking Behavior in Laying Hens Has Caused Differences Between Lines in Egg Production, Egg Quality, and Feed Efficiency

The correlated changes in egg production, egg quality, and feed efficiency (FE) due to selection for feather pecking (FP) were investigated by analyzing the data from an experiment including 2 divergently selected lines and a control line. The experiment was conducted with hens from 42 to 46 wk (hatch 1) and 39 to 43 wk (hatch 2) of age in the fifth generation of selection. The number of FP bouts per hour in the low FP line (LFP) was lower than the high FP line (HFP; 0.38 vs. 2.01), and total plumage score in line LFP was better than in line HFP (16.9 vs. 11.6). During the 4 wk, egg number and egg mass in line LFP were higher than those in HFP (24.4 vs. 18.3 and 1,223 vs. 1,132 g, respectively). On the other hand, line HFP had greater egg weight (60.7 vs. 59.2 g), albumen height (73.0 vs. 64.9 in Haugh units), shell thickness (38.1 vs. 37.0 mm), and yolk percentage (30.6 vs. 29.5%) than the LFP line. The control line was intermediate for those traits. The residual feed consumption (RFC) was highest in line HFP, lowest in line LFP, and intermediate in line C. Partial regressions of feed consumption (FC) on BW gain and egg mass were not significantly different among the 3 lines, whereas a significant difference in regression on metabolic BW (32.6 g/d in line LFP, 38.0 g/d in control line, and 43.4 g/d in line HFP) was observed. In addition, there was a negative regression of FC per day on plumage score (-1.73 g). The adjustment for plumage score accounted for 60% of the difference between regressions on metabolic BW in lines LFP and HFP. These results indicated that selection for FP has led to a change in egg production, egg quality, and FE. The better FE in line LFP resulted from a lower requirement for maintenance energy. The later was partly accounted for by a better plumage cover.

Behavioral and physiological features of chickens diversely selected for resistance to Avian Disease. 1. Selected inbred lines differ in behavioral and physical responses to social stress

To test the hypothesis that genetic variations in response to social stress modulate susceptibility to disease in poultry, aggressive behaviors induced by social stress were measured in chickens of different inbred lines selected for disease resistance (line 63) or susceptibility (lines 72 and 15I5), as well as 2 recombinant congenic strains (B and X). At 15 wk of age, roosters from each genetic line or strain were randomly assigned to pairs for intraline male-male aggression tests (n = 8 per line). Based on the results of the intraline aggression tests, the roosters were divided into 2 groups, winners and losers. At 16 wk of age, the roosters were randomly paired as winners vs. winners and losers vs. losers for interline aggression tests, i.e., line 63 vs. 72 and 15I5; line 73 vs. line 15I5; and strain X vs. strain B. Similarly, at 17 wk of age, line 63 vs. strains X and B, and line 72 vs. strains X and B were tested. The tests were conducted in a novel cage that was similar to their home cages, to provide a neutral space for both roosters being tested. Each pair was videotaped for 15 min. Male-male interaction-induced aggressive behaviors were markedly different among the genetic lines. Compared with roosters of lines 15I5 and 72, line 63 roosters generally showed fewer aggressive behaviors, including aggressive pecks and fights, as well as durations (P < 0.05). Roosters of the recombinant congenic strains X and B, each possessing a unique random 87.5% genome of line 63, exhibited low aggressive behaviors, which were similar or equal to the level of line 63 in both intraline and interline aggression tests (P = 0.05). These results may indicate that some of the gene(s) commonly carried between strains X and B as well as line 63 likely played an important role in governing their lower levels of aggression. The present chicken lines may be used as animal models for investigation of the cellular mechanisms of genetic-environmental interactions on disease resistance and stress responses.

Chronic social stress differentially regulates neuroendocrine responses in laying hens: II. Genetic basis of adrenal responses under three different social conditions

Chicken lines were divergently selected for both high (HGPS) or low (LGPS) group productivity and survivability resulting from cannibalism and flightiness in colony cages. Each line has unique characteristics in physical indexes, domestic behavior, and physiological responsiveness to stress. The differences between the selected lines could be reflected in differing regulation of the neuroendocrine system such as the hypothalamic-pituitary-adrenal axis. Change of the adrenal function is a key initial event in response to stress in animals, which differs for this trait. Comparisons between the selected lines showed that adrenal function was stable in HGPS hens but not in LGPS hens in response to chronic social stress. Social stress-induced adrenal hypertrophy and its positive correlation with plasma corticosterone concentrations were found in the LGPS hens but not in the HGPS hens. The data demonstrated that chickens selected for variations in productivity and survivability variously altered the adrenal system in response to social stressors. The results suggest that these chicken lines could be valuable animal models for biomedical investigation of the effect of genetic-environmental interactions on the neuroendocrine function in controlling stress responses.

Endotoxin stress responses in chickens from different genetic lines. 1. Sickness, behavioral, and physical responses

Genetic variation in response to lipopolysaccharide (LPS) challenge was studied in chicken lines divergently selected for high (HGPS) and low (LGPS) group productivity and survivability resulting from cannibalism and flightiness in colony cages and in a Dekalb XL (DXL) commercial line. Six-week-old chicks were randomly assigned to control or experimental groups and were injected intravenously with Escherichia coli LPS (5 mg/kg of BW) or distilled saline (control). Sickness responses were measured at 6, 12, 24, 48, and 72 h following injection (n = 10 at each point in time for each line). Although LPS induced widespread sickness symptoms in all of the treated chicks, the reactions were in a genotypic- and phenotypic-specific manner. Compared with LGPS and DXL chicks, HGPS chicks had acute, transient behavioral and physical changes with less effect on BW gain, organ development, and core temperature, which were in the order HGPS < DXL < LGPS. The effects of heritable factors and LPS challenge on the differential responses among the present lines may reflect each line's unique adaptability to stress and resistance to infection and inflammation. The results suggested that the present chicken lines may provide a valuable animal model for investigating the effects of genetic-environmental interactions on the behavioral and physiological homeostasis in response to stress and disease.

Social stress differentially regulates neuroendocrine responses in laying hens: I. Genetic basis of dopamine responses under three different social conditions

Effects of genetic-environmental interactions on plasma dopamine (DA) concentrations were studied in White Leghorn chickens selected for both high (HGPS) or low (LGPS) group productivity and survivability resulting from cannibalism and flightiness. Plasma DA levels were measured from chickens in three social treatments: single-, two-, or ten-hen cages. The two-hen treatment consisted of paired chickens from three genetic lines: HGPS, LGPS and a commercial strain, Dekalb XL (DXL). In HGPS/DXL and LGPS/DXL pairs, the DXL hen was used as a standardized genetic competitor. The ten-hen treatment contained only hens from the same line, which is similar to the original selection condition. After 7 weeks housing in the social environments, LGPS hens in the ten-hen treatment had greater plasma DA concentrations than HGPS hens (P<0.05). Compared to levels in the ten-hen treatment from the same line, plasma DA concentrations in both HGPS and LGPS hens were significantly lower in the two-hen treatment (average mean, 0.09 vs. 0.15 ng/ml and 0.22 vs. 0.44 ng/ml, P<0.05, respectively), but significantly higher in the single-hen treatment (average mean, 0.44 vs. 0.15 ng/ml and 1.78 vs. 0.44 ng/ml, P<0.05 and P<0.01, respectively). In the single-hen treatment, LGPS hens had greater plasma DA levels than HGPS hens (P<0.05). The results provide evidence of genetically related differences in the regulation of chickens' plasma DA concentrations in response to social stress. These differences may magnify the behavioral and physiological differences observed in the lines under basal and challenged conditions. These results suggest that these chicken lines may provide a new model for investigating effects of DA on the control of behavioral, neural and endocrine responses to stress.

Social stress in laying hens: differential effect of stress on plasma dopamine concentrations and adrenal function in genetically selected chickens

Genetic selection for high or low group productivity and survivability (HGPS, LGPS) has created two phenotypically distinct chicken lines. Each line has unique characteristics in behavioral and physiological adaptability to multiple-bird cage system. The present study was designed to examine whether these differences reflect genetic variation in the control of plasma dopamine (DA) concentrations and adrenal function in response to social stress. Chickens from the HGPS and LGPS lines were randomly assigned to single- or 10-bird cages at 17 wk of age. The 10-bird cages were the same as those used in the development of the two lines. Differences in regulation of DA concentrations and adrenal function in response to different social environments were measured between the two lines when the study was conducted at 24 wk of age. In the 10-bird cages, the HGPS line had lower levels of DA (P < 0.05) and heavier adrenal glands (AG, P < 0.05) than those of the LGPS line, but concentrations of corticosterone (CORT) from the two lines were not significantly different. In the single-bird cages, DA levels in both lines were greater than in that of their siblings in the 10-bird cages, but a greater increase was found in the LGPS line (P < 0.01 and P < 0.05, 405% vs. 293%). Likewise, both lines had lower concentrations of CORT (P < 0.05) in the single- vs. 10-bird cages, but the AG were less heavy in the LGPS line but not in HGPS line in the single-bird cages (P < 0.05). The results indicated that the two strains reacted differently in terms of their stress hormone levels in the two different environments. These differences could contribute to the behavioral and physiological differences existing between the two lines.

Administration of triiodothyronine and dopamine to broiler chicks increases growth, feed conversion and visceral organ mass

The influences of triiodothyronine (T3) or dopamine (DA) administration on growth, feed conversion, and visceral weights in broiler chicks between the ages of 6 and 12 d posthatch were investigated. In Trial 1, six chicks at age 6 d were randomly administered one of the following treatments: 0.37, 0.74, 1.48, and 2.96 micromol T3/kg BW or 0.07, 0.14, 0.28, and 0.56 micromol DA/kg BW. Both T3 and DA were administered via intraperitoneal injections between the end of sternum and the ends of os pubis, with 0.9% saline as the excepient. In addition, two groups of six birds each were either not injected or injected with excepient only, as controls. Four replications were carried out with a total of 264 chicks. Heart weight as a percentage of feed-deprived body weight (FDBW) of the chicks injected with 2.96 micromol T3/kg BW was heavier than that of controls. Other variables measured were not significantly different between treatments. In trial 2, six chicks at age 6 d were randomly administered, one of the following treatments: 0.56, 1.12, 2.24, and 4.48 micromol T3/kg diet or 0.40, 0.80, 1.60, and 3.20 micromol DA/kg diet as well as a nonsupplemented control. Four replications were carried out with 216 chicks. The results in Trial 2 showed that the effects of T3 (X, micromol/kg diet) on body weight gain (Y1, g) and feed consumption (Y2, g) were linear (Y1 = 310 - 21.5X, R2 = 0.868, P < 0.001 and Y2 = 398 - 22.3X, R2 = 0.765, P < 0.001, respectively). The feed conversion ratio, the weight of liver, the weights of various intestinal segments, the lengths of the duodenum, jejunum and the ileum, as well as weight per centimeter jejunal length, gizzard weight as percentage of FDBW, and the duodenal length per kilogram FDBW all had linear responses (P < 0.05) to the level of dietary supplementation of T3. The effect of dietary supplementation of T3 on the heart weight was quadratic (Y16 = 2.58 + 0.89X - 0.17 X2, R2 = 0.526, P < 0.01). Similarly, the weights of pancreas and gizzard, the heart weight as a percentage of FDBW and the pancreas weight as a percentage of FDBW all had second-order curve responses. Dietary DA supplementation exerted no effect on the variables measured except that the regression of the heart weight as a percentage of FDBW on dietary DA supplementation (X1, micromol/kg diet) existed, namely, Z1 = 0.64 + 0.24 X1 - 0.23 X1(2) + 0.05 X1(3) (R2 = 0.868, P < 0.05).

Social stress in laying hens: differential dopamine and corticosterone responses after intermingling different genetic strains of chickens

White Leghorn chickens were genetically selected for high (HGPS) or low (LGPS) group productivity and survivability. The selection resulted in two genetic lines with marked opposite changes in cannibalism and flightiness when housed in multiple-colony battery cages without beak trimming. The objective of the study was to examine whether the genetic selection differentially affected the neuroendocrine system of chickens from different strains in response to social stress. Based on the previous studies, social stress was induced by randomly pairing 17-wk-old hens from three genetic lines, i.e., HGPS, LGPS, and Dekalb XL (DXL), to form three mixed-line combinations. At 24 wk of age, the concentrations of plasma dopamine (DA) and corticosterone (CORT) showed no differences in DXL hens housed with HGPS or LGPS hens (P > 0.05). However, different regulations of DA and adrenal function were found between HGPS and LGPS hens when paired with DXL hens. Compared to HGPS hens, LGPS hens had greater levels of DA and CORT (P < 0.01 and P < 0.05, respectively). In addition, under the HGPS-LGPS social treatment, the concentrations of DA but not CORT were greater in LGPS hens than in HGPS hens (P < 0.05 and P > 0.05, respectively). The results indicated genetic selection for production and survivability differentially altered DA and CORT systems in response to social stress. The data suggested, compared to LGPS hens, HGPS hens had a better coping capability to social stress, which might have been responsible for their higher productivity and survivability.