The role of adrenoreceptors in control of stereotyped oral behavior in restricted-fed fowls

The immunomodulatory effects of clonidine, an α-2-adrenergic agonist, in laying hens

The ability of the sympathetic nervous system to regulate chicken immune function was examined. Clonidine, an alpha-2 adrenergic receptor agonist, was administrated at 2.5, 5.0, or 10.0 mg/L in the drinking water of White Leghorn hens at 48 wk of age. The hens were randomly housed in conventional cages in pairs. Concentrations of plasma IgG (also named IgY) were detected using chicken IgG ELISA, and the percentage of subpopulations of circulating lymphocytes were analyzed using flow cytometry. Compared with controls, treated hens had higher circulating IgG levels and a greater percentage of circulating B cells (Bu-1+ cells, P < 0.01) after 1 wk of treatment. Additionally, the percentages of CD8+ cells were consistently higher (P = 0.07) in the treated hens compared with controls, whereas the percentages of CD4+ cells and the ratio of CD4+ cell to CD8+ cell were not affected by the treatment (P > 0.05). These effects of clonidine on the IgG concentrations and the proportions of B-cells and CD8+ cells were dose-related. The highest increase was found in the hens treated with 10.0 mg/L of clonidine. These results suggest that the sympathetic nervous system is directly involved in regulating the chicken immune system via regulation of alpha-2-adrenergic receptor activations.

Do low-density diets improve broiler breeder welfare during rearing and laying?

Low-density diets may improve welfare of restricted fed broiler breeders by increasing feed intake time with less frustration of feed intake behavior as a result. Moreover, low-density diets may promote satiety through a more filled gastrointestinal tract, and thus feelings of hunger may be reduced. Broiler breeders were fed 4 different diets during the rearing and laying periods. Behavioral and physiological parameters were measured at different ages as indicators of hunger and frustration of the feeding motivation. A diet of 8.4 MJ/kg as compared with a standard diet of 10.9 MJ/kg extended feeding time and reduced stereotypic object pecking at 6 and 10 wk of age. Furthermore, compensatory feed intake at 12 wk of age was reduced. During lay, differences in behavior were observed between the treatments that could be attributed to differences in feeding time. However, birds fed the diet with the lowest energy content (i.e., 9.2 MJ/kg) had higher heterophil to lymphocyte ratios (H/L) at 40 wk of age compared with the other treatments, indicating that they experienced more stress during the laying period than the other treatments. This result could have been due to the very long feeding time of this treatment group during lay, which may be stressful. In conclusion, a low-density diet of 8.4 MJ/kg may reduce hunger and frustration in the first half of the rearing period. However, for substantial improvement of broiler breeder welfare during rearing, more extreme diet modifications are required.

Influence of food restriction on dopamine receptor densities, catecholamine concentrations and dopamine turnover in chicken brain

To investigate further a putative role of dopamine in control of food restriction-induced behavioural stereotypies, chickens were fed during rearing on either a daily restricted ration recommended by a breeding company, twice the recommended restricted ration, or ad libitum food. They were killed at 60 days of age and their excised brains were dissected into six regions and homogenized. Densities of dopamine D1 and D2 receptors were assessed, after first estimating binding parameters for [3H]SCH 23390 (D1) and [3H]spiperone (D2) in chicken brain homogenates. Specific binding of both ligands was highest in basal telencephalon. Concentrations of dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were also highest in basal telencephalon, whereas noradrenaline and adrenaline levels were highest in diencephalon. Dopamine concentration in basal telencephalon and noradrenaline concentration in diencephalon were increased significantly in response to food restriction, but no effect of feeding treatment was found in dopamine turnover, adrenaline levels, or D1 and D2 receptor densities in any brain region studied. The observed changes in brain catecholamine levels are consistent with roles for dopaminergic and adrenergic mechanisms in the control of food restriction-induced behavioural stereotypies in chickens.

Is there a role for corticosterone in expression of abnormal behaviour in restricted-fed fowls?

Growing parent stock (breeders) of meat-type chickens (broilers), subjected routinely to chronic food restriction, show increased pacing before a single daily meal and increased drinking and pecking at non-food objects (oral stereotypies) afterwards. Expression of these activities is correlated positively with the level of restriction imposed, and is thought to be controlled mainly by central dopaminergic mechanisms. There is published evidence that glucocorticoids can amplify dopamine mediated behaviours, and this paper describes four experiments examining the relationship between corticosterone and behaviour in individually caged broiler breeders. In Experiment 1 (with 3 levels of food restriction), plasma corticosterone concentration was correlated positively with the level of restriction imposed when blood samples were taken in the morning, but not when they were taken in the afternoon. This may be because corticosterone level declines from morning to afternoon with mild but not severe restriction. In Experiment 2 (severe restriction only), plasma corticosterone level did not change significantly with time of day, and mean values of individual birds were not correlated with their observed times spent in oral stereotypies. In Experiment 3 (severe restriction), object pecking increased in a dose-related way after systemic injection of 1-4 mg/kg corticosterone (significant) and 7.5-30 IU/kg ACTH (not significant), and 10-40 mg/kg metyrapone (corticosterone synthesis inhibitor) had no effect. In Experiment 4 (severe restriction), 180 mg/day metyrapone administered in food for 5 days reduced the plasma corticosterone response to injection of 15 IU/kg ACTH on the fourth day, but otherwise had no effect. Significant increases in drinker directed activity after injection of ACTH on the fourth day and 4 mg/kg corticosterone on the fifth day coincided with greatly elevated plasma levels of corticosterone. It is concluded that the oral stereotypies of restricted-fed broiler breeders do respond to induced increases in plasma corticosterone concentration that are supra-physiological, but there may be only a weak association between behaviour and corticosterone within the physiological range.

mu-Opioid receptor binding in chicken brain in relation to degree of food restriction: a quantitative autoradiographic study

Quantitative receptor autoradiography was used to measure differences in [3H]DAGO binding to mu-opioid receptors in selected fore- and midbrain regions of chickens subject to varying degrees of chronic food restriction: either R (a recommended restricted ration), 2R (twice recommended restricted ration) or AL (ad libitum). A significant increase in binding of 75% was observed in the paleostriatum primitivum (a homologue of the mammalian globus pallidus) with the R treatment compared to the 2R and AL treatments. This finding concurs with results of earlier pharmacological manipulations with opioid antagonists, which indicated that activation of mu-opioid receptors plays a contributory role in reinforcement of post-feeding oral stereotypies in chickens subject to the same R treatment.