Endocrine Control of Postnatal Growth in Poultry

This paper provides an overview on the role of several endocrine factors in the regulation of the somatic growth (skeletal muscle and bone development) and body composition in meat-type poultry. The hormones of both the somatotrophic axis (GH and IGFs) and the thyrotrophic (T4, T3) axis are a prerequisite for normal growth and development. Posthatch hormone therapy does however not stimulate growth but rather to the contrary. In ovo treatment with somatotrophic hormones seems to elicit positive responses in postnatal growth and adiposity. Androgens are anabolic and their plasma levels are positively correlated with growth rate, whereas estrogens are clearly lipogenic. The androgen : estrogen activity ratio may certainly not be underestimated in growth and adiposity regulation, even in juvenile poultry. Leptin has appetite-reducing properties in chickens and hepatic leptin expression is controlled by several hormones. Finally, feed restriction as well as diet composition is used as models to illustrate how endocrine factors interact with the intermediary metabolism in a deterministic and mechanistic way

Adipose tissue and lipid metabolism

© 2015, 2000 Elsevier Inc. All rights reserved. Adipose tissue is the most variable carcass component and has traditionally been considered a rather inert storage tissue for energy in the form of lipids. Most of the fat in chickens is located in adipose depots, which are all late maturing. At the cellular level, preadipocyte differentiation and proliferation are under the control of multiple hormones and transcription factors. The growth of fat tissue is initially due to hyperplasia followed by hypertrophy of the mature adipocytes. The amount of fat deposited is controlled by numerous hormones and depends on genetic and nutritional factors.Dietary fat is transported as portomicrons to the liver, which is also the primary site of the de novo lipogenesis. The newly formed very-low-density lipoproteins (VLDLs) are distributed by the blood to the rest of the body. Lipoprotein lipase is a key enzyme in the further processing of these lipoproteins at the level of various tissues, in particular the lipoprotein metabolism in laying hens. All egg yolk lipids are synthesized mainly by the liver and transported to the ovary in special yolk-targeted VLDL (VLDLy) with an unusual apoprotein (apo) composition (only apoB and apoVLDLII).Recent research has, however, revealed that adipose tissue must now be regarded as a dynamic tissue, which secretes a considerable number of adipokines and hence plays a role in a multitude of bodily processes.status: publishe

Adipose tissue and lipid metabolism

Adipose tissue is the most variable carcass component and is traditionally being considered as a rather inert storage tissue for energy under the form of lipids. Most of the fat in chickens is located in adipose depots, which are all late maturing. At the cellular level, preadipocyte differentiation and proliferation is under the control of multiple hormones and transcription factors. The growth of fat tissue is initially due to hyperplasia followed by hypertrophy of the mature adipocytes. The amount of fat deposited is controlled by numerous hormones and depends on genetic and nutritional factors.Dietary fat is transported as portomicrons to the liver, which is also the primary site of the de novo lipogenesis. The newly formed very low density lipoproteins (VLDL) are distributed by the blood to the rest of the body. Lipoprotein lipase is a key enzyme in the further processing of these lipoproteins at the level of various tissues; The lipoprotein metabolism in laying hens is particular. All egg yolk lipids are synthesized mainly by the liver and transported to the ovary in special yolk-targeted VLDL (VLDLy) with an unusual apoprotein composition (only apoB and apoVLDLII). Recent research has however revealed that adipose tissue must now be regarded as a dynamic tissue, which secretes a considerable number of adipokines and hence plays a role in a multitude of bodily processes

Implications of dietary macronutrients for growth and metabolism in broiler chickens

In chickens, metabolism is influenced by environmental factors and of particular interest nutritional factors, such as diet quantity and composition. With respect to the dietary macronutrients, literature clearly shows that in isoenergetically formulated diets, the protein level has a pronounced effect on metabolism, whereas fat and carbohydrate concentrations play a limited role. A decreased dietary protein level results in depressed growth rates, with reduced carcass gains in both water and protein content. In spite of the lower protein retention in chickens fed low protein diets, the efficiency of utilization of dietary protein appears to be increased. This indicates an inverse relationship between protein intake and utilization, which is reflected in decreased circulating uric acid levels. In addition, feed intake is increased, at least when protein levels are slightly reduced, leading to an involuntary overconsumption of energy compared to protein. The chickens deal with this excess energy consumption by increasing de novo lipogenesis and fat deposition, which is supported by increased plasma triglyceride concentrations, and heat production is increased. In contrast to adult mammals, the dietary macronutrients have no effect on diet-induced thermogenesis, nor is there any relationship between diet-induced thermogenesis and feed intake. Plasma growth hormone levels are higher in chickens reared on a low protein diet, indicating a causal relationship between growth hormone secretion and protein efficiency. In spite of the increased growth hormone levels, plasma insulin-like growth factor concentrations are lowered in low protein reared chickens, and may be partially responsible for the reduced growth rate observed in these animals. Plasma corticosterone concentrations are augmented in chickens on low protein diets, despite a decline in the ACTH concentration. Finally, plasma T-3 and T-4 levels are well known to increase and decrease, respectively, with decreasing protein content, whereas the effects of dietary macronutrients on circulating leptin levels require more research.status: publishe

Effect of thyroid hormones on the redox balance of broiler chickens

In the present study, two trials were conducted to evaluate the effects of hyper- and hypothyroid status on the redox balance of broiler chickens. In Trial 1, 3 groups of broiler chickens were randomly subjected to one of the three treatments: subcutaneous administration of triiodothyronine (T3, 150 μg/kg BW), methimazole (MMI, 150 mg/kg BW), or saline. The blood, liver and heart were sampled at 3 h after injection. In Trial 2, three groups of 20 broiler chickens were randomly fed with one of the three diets: control, dietary supplementation of T3 (1.5 mg/kg diet) or MMI (1 g/kg diet) for 7 days. In trial 1, the plasma concentrations of T3 and T3 to thyronine ratio (T3AT4) were significantly increased by T3 injection. Plasma levels of thiobarbituric acid reacting substances (TBARS) tended to be increased (p = 0.067) by both T3 and MMI treatments while the ferric reduced/antioxidant capacity (FRAP) was increased only by MMI treatment. Acute T3 treatment had no significant effect on the activities of Superoxide dismutase (SOD) and the concentrations of FRAP and TEARS in either liver or heart tissue. In contrast, the hepatic activities of SOD were decreased (p<0.05) while the cardiac levels of FRAP were significantly increased (p<0.0001) by MMI treatment. In chronic treatments, the rectal temperature of chickens was significantly decreased (p<0.05) by MMI treatment. The circulating T3 levels were significantly increased (p<0.05) by long-term T3 treatment, and showed a trend to decrease in MMI treatment. The plasma concentrations of TEARS were significantly (p<0.05) increased by MMI treatment. All the redox parameters measured in either liver or heart were not significantly altered by either long-term T3 or MMI treatment except that the hepatic SOD activities were significantly augmented by T3 treatment. The result showed that neither acute nor long-term elevation of circulating T3 levels induced lipid peroxidation in broiler chickens. The enhanced enzymatic antioxidant system (SOD in cardiac tissue) may be involved in the protection of the bird to increased oxidative challenge. The responses of redox balance to changed thyroid state seem to be tissue specific.status: publishe

Cerulenin upregulates heat shock protein-70 gene expression in chicken muscle

Lines of evidence suggested that systems involved in the regulation of the stress responses and energy homeostasis are highly integrated. Because cerulenin, the natural antibiotic product of the fungus Cephalosporium ceruleans and a broad-spectrum fatty acid synthesis (FAS) inhibitor, has been shown to affect food intake and energy balance, and because the biomarker of stress Hsp-70 gene was found to interact directly with fatty acids, we hypothesized that cerulenin may regulate Hsp-70 gene expression. Therefore, the present study was undertaken to examine this issue. Cerulenin administration significantly (P < 0.05) decreased food intake and induced Hsp-70 mRNA levels in muscle, but not in liver or hypothalamus of 2-wk-old broiler chickens. These changes were accompanied by an unpregulation of muscle uncoupling protein and carnitine palmitoyltransferase 1 mRNA levels. This result indicated that the regulation of Hsp-70 gene expression in normal chickens, as estimated by oxidative stress indices [TBA reacting substances, ferric reducing/antioxidant power, and ceruloplasmin oxidase activity] levels, is tissue-specific. In attempt to discriminate between the effect of cerulenin and cerulenin-reduced food intake on Hsp-70 gene expression, we also evaluated the effect of food deprivation on the same cellular responses. Food deprivation for 16 h did not affect Hsp-70 gene expression in all tissues examined, indicating that the effect of cerulenin is independent of the inhibition of food intake. To ascertain whether the effect of cerulenin is direct or indirect, we carried out in vitro studies. Cerulenin treatment did not affect Hsp-70 gene expression in Leghorn male hepatoma and quail myoblast cell lines, suggesting that the observed effect in vivo may be mediated through the central nervous system.status: publishe

Chapter 3: Feed intake and regulation

peer reviewe

Further evidence for the involvement of anatomical parameters of the cardiopulmonary system in the development of ascites syndrome in broiler chickens

Eggs from a broiler line were incubated at two different altitudes and hatched. Relative heart and lung weights, volumes of the heart, lung and thoracic cavity, incidence of right ventricular hypertrophy and ascites, and related physiological parameters were followed in the day-old chickens hatched from the above eggs. Lung and heart weights as a percentage of body weight, lung and heart volumes relative to the volume of the thoracic cavity after removing the heart and lungs were higher in chickens hatched at high altitude. Additionally, embryonic triiodothyronine (T3) and thyroxine (T4) levels relative to cardiopulmonary parameters were higher in day-old chickens that hatched at high altitude as compared with chickens hatched at low altitude. This was associated with a lower incidence of right ventricular hypertrophy and ascites in chickens hatched at high altitude. Our data indicate that chronic hypoxia interacting with the endogenous functions of embryos during embryonic development at high altitude, as adaptation mechanisms, changed the developmental trajectories of cardiopulmonary parameters in postnatal chickens. This important development facilitates an increase in the gas exchange area in broiler chickens, thus lowering their susceptibility to pulmonary hypertension and ascites