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Lipid metabolism in avian species places unique demands on the liver in comparison to most mammals. The avian liver synthesizes the vast majority of fatty acids that provide energy and support cell membrane synthesis throughout the bird. Egg production intensifies demands to the liver as hepatic lipids are needed to create the yolk. The enzymatic reactions that underlie de novo lipogenesis are energetically demanding and require a precise balance of vitamins and cofactors to proceed efficiently. External stressors such as overnutrition or nutrient deficiency can disrupt this balance and compromise the liver’s ability to support metabolic needs. Heat stress is an increasingly prevalent environmental factor that impairs lipid metabolism in the avian liver. The effects of heat stress-induced oxidative stress on hepatic lipid metabolism are of particular concern in modern commercial chickens due to the threat to global poultry production. Chickens are highly vulnerable to heat stress because of their limited capacity to dissipate heat, high metabolic activity, high internal body temperature, and narrow zone of thermal tolerance. Modern lines of both broiler (meat-type) and layer (egg-type) chickens are especially sensitive to heat stress because of the high rates of mitochondrial metabolism. While this oxidative metabolism supports growth and egg production, it also yields oxidative stress that can damage mitochondria, cellular membranes and proteins, making the birds more vulnerable to other stressors in the environment. Studies to date indicate that oxidative and heat stress interact to disrupt hepatic lipid metabolism and compromise performance and well-being in both broilers and layers. The purpose of this review is to summarize the impact of heat stress-induced oxidative stress on lipid metabolism in the avian liver. Recent advances that shed light on molecular mechanisms and potential nutritional/managerial strategies to counteract the negative effects of heat stress-induced oxidative stress to the avian liver are also integrated.

Orexins are originally characterized as orexigenic hypothalamic neuropeptides in mammals. Subsequent studies found orexin to be expressed and perform pleiotropic functions in multiple tissues in mammals. In avian (non-mammalian) species, however, orexin seemed to not affect feeding behavior and its physiological roles are poorly understood. Here, we provide evidence that orexin and its related receptors are expressed in chicken hepatocytes. Double immunofluorescence staining showed that orexin is localized in the ER, Golgi, and in the lysosomes in LMH cells. Brefeldin A treatment reduced orexin levels in the culture media, but increased it in the cell lysates. Administration of recombinant orexins upregulated the expression of orexin system in the liver of 9-day old chicks, but did not affect feed intake. Recombinant orexins increased fatty acid synthase (FASN) protein levels in chicken liver, activated acetyl-CoA carboxylase (ACCα), and increased FASN, ATP citrate lyase(ACLY), and malic enzyme (ME) protein expression in LMH cells. Blockade ERK1/2 activation by PD98059 attenuated these stimulating effects of orexin on lipogenic factors. Overexpression of ERK1/2 increased the expression of lipogenic genes, and orexin treatment induced the phosphorylated levels of ERK1/2 Thr202/Tyr204 , but not that of p38 Thr180/Tyr182 or JNK1/2 Thr183/Tyr185 in chicken liver and LMH cells. Taken together, this is the first report evidencing that orexin is expressed and secreted from chicken hepatocytes, and that orexin induced hepatic lipogenesis via activation of ERK1/2 signaling pathway.

Modern broilers, selected for high growth rate, are more susceptible to heat stress (HS) as compared to their ancestral jungle fowl (JF). HS affects epithelia barrier integrity, which is associated with gut microbiota. The aim of this study was to determine the effect of HS on the cecal luminal (CeL) and cecal mucosal (CeM) microbiota in JF and three broiler populations: Athens Canadian Random Bred (ACRB), 1995 Random Bred (L1995), and Modern Random Bred (L2015). Broiler chicks were subjected to thermoneutral TN (24 °C) or chronic cyclic HS (8 h/day, 36 °C) condition from day 29 until day 56. HS affected richness in CeL microbiota in a line-dependent manner, decreasing richness in slow-growing JF and ACRB lines, while increasing richness in faster-growing L1995 and L2015. Microbiota were distinct between HS and TN conditions in CeL microbiota of all four lines and in CeM microbiota of L2015. Certain bacterial genera were also affected in a line-dependent manner, with HS tending to increase relative abundance in CeL microbiota of slow-growing lines, while decreases were common in fast-growing lines. Predictive functional analysis suggested a greater impact of HS on metabolic pathways in L2015 compared to other lines.

Heat stress (HS) is devastating to the poultry industry due to its adverse effects on animal well-being and performance. The effects of heat stress are typically measured using a portable i-STAT blood analyzer that quantifies circulatory hemoglobin concentration and other blood chemistry parameters. Here, we used diffuse reflectance spectroscopy (DRS) as a novel non-invasive method to directly determine changes in hematological parameters in the breast tissues of live heat-stressed broilers. Three-week-old male broilers were randomly subjected to two environmental conditions (thermoneutral, TN, 24 °C vs. cyclic heat stress, HS, 35 °C, 12 h/day). Optical spectra were acquired using DRS to monitor breast hemoglobin (Hb) concentration and vascular oxygen saturation (sO 2 ) at three time points: at baseline prior to heat stress, 2 days, and 21 days after initiation of HS. While i-STAT did not demonstrate a discernible change due to HS in circulatory hemoglobin, DRS found a significant decrease in breast Hb and sO 2 after exposure to chronic HS. The decrease in sO 2 was found to be due to a decrease in oxygenated hemoglobin concentration, indicating a large increase in oxygen consumption in heat-stressed broilers. Our results demonstrate that DRS could potentially be used to study the effects of HS directly in specific organs of interest, such as the breast and thigh, to improve meat quality.

Neuropeptide Y (NPY) is one of the most abundant and ubiquitously expressed neuropeptides in both the central and peripheral nervous systems, and its regulatory effects on feed intake and appetite- have been extensively studied in a wide variety of animals, including mammalian and non-mammalian species. Indeed, NPY has been shown to be involved in the regulation of feed intake and energy homeostasis by exerting stimulatory effects on appetite and feeding behavior in several species including chickens, rabbits, rats and mouse. More recent studies have shown that this neuropeptide and its receptors are expressed in various peripheral tissues, including the thyroid, heart, spleen, adrenal glands, white adipose tissue, muscle and bone. Although well researched centrally, studies investigating the distribution and function of peripherally expressed NPY in avian (non-mammalian vertebrates) species are very limited. Thus, peripherally expressed NPY merits more consideration and further in-depth exploration to fully elucidate its functions, especially in non-mammalian species. The aim of the current review is to provide an integrated synopsis of both centrally and peripherally expressed NPY, with a special focus on the distribution and function of the latter.

Bacterial Chondronecrosis with Osteomyelitis (BCO) is a specific cause of lameness in commercial fast-growing broiler (meat-type) chickens and represents significant economic, health, and wellbeing burdens. However, the molecular mechanisms underlying the pathogenesis remain poorly understood. This study represents the first comprehensive characterization of the proximal tibia proteome from healthy and BCO chickens. Among a total of 547 proteins identified, 222 were differentially expressed (DE) with 158 up- and 64 down-regulated proteins in tibia of BCO vs. normal chickens. Biological function analysis using Ingenuity Pathways showed that the DE proteins were associated with a variety of diseases including cell death, organismal injury, skeletal and muscular disorder, immunological and inflammatory diseases. Canonical pathway and protein–protein interaction network analysis indicated that these DE proteins were involved in stress response, unfolded protein response, ribosomal protein dysfunction, and actin cytoskeleton signaling. Further, we identified proteins involved in bone resorption (osteoclast-stimulating factor 1, OSFT1) and bone structural integrity (collagen alpha-2 (I) chain, COL2A1), as potential key proteins involved in bone attrition. These results provide new insights by identifying key protein candidates involved in BCO and will have significant impact in understanding BCO pathogenesis.

Abstract Heat stress (HS) is a financial and physiological burden on the poultry industry and the mitigation of the adverse effects of HS is vital to poultry production sustainability. The purpose of this study was, therefore, to determine the effects of an amino acid-chelated trace mineral supplement on growth performance, stress and inflammatory markers, and meat quality in heat-stressed broilers. One day-old Cobb 500 male broilers (n = 480) were allocated into 12 environmental chambers (24 floor pens) and divided into two groups: one group supplemented with amino acid-chelated trace mineral in drinking water and one control group. On day 28, birds were subjected to chronic heat stress (HS, 2 wk, 35 °C and 20% to 30% RH) or maintained at thermoneutral condition (TN, 24 °C) in a 2 × 2 factorial design. Feed intake (FI), water consumption, and body weight were recorded. At day 42, serum fluorescein isothiocyanate dextran (FITC-D) levels, blood gas, electrolyte, and stress markers were measured. Jejunum samples were collected to measure gene expression of stress, inflammation, and tight junction proteins. The rest of the birds were processed to evaluate carcass traits. HS resulted in an increase in core body temperature, which increased water intake and decreased FI, body weight, and feed efficiency (P < 0.05). HS reduced carcass yield and the weight of all parts (P < 0.05). HS significantly increased levels of circulating corticosterone (CORT), heat shock protein 70 (HSP70), interleukin 18 (IL-18), tumor necrosis factor alpha, C-reactive protein, and nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing 3 expression. HS significantly increased serum FITC-D levels and the expression of HSP70 and IL-18 in the jejunum. Although it did not affect the growth performance, amino acid-chelated trace mineral supplementation reversed the effect of HS by reducing CORT and FITC-D levels and the expression of stress and proinflammatory cytokines in the circulation and the jejunum. However, it upregulated these parameters in birds maintained under TN conditions. Together, these data indicate that the amino acid-chelated trace mineral might alleviate stress and inflammation and improve gut integrity in heat-stressed but not thermoneutral broilers.

Background Due to the important functions of arginine in poultry, it should be questioned whether the currently adopted dietary Arg:Lys ratios are sufficient to meet the modern broiler requirement in arginine. The present study aimed, therefore, to evaluate the effects of the dietary supplementation of L -arginine in a commercial broiler diet on productive performance, breast meat quality attributes, incidence and severity of breast muscle myopathies and foot pad dermatitis (FPD), and plasma and muscle metabolomics profile in fast-growing broilers. Results A total of 1,170 1-day-old Ross 308 male chicks was divided into two experimental groups of 9 replicates each fed either a commercial basal diet (CON, digestible Arg:Lys ratio of 1.05, 1.05, 1.06 and 1.07 in each feeding phase, respectively) or the same basal diet supplemented on-top with crystalline L -arginine (ARG, digestible Arg:Lys ratio of 1.15, 1.15, 1.16 and 1.17, respectively). Productive parameters were determined at the end of each feeding phase (12, 22, 33, 43 d). At slaughter (43 d), incidence and severity of FPD and breast myopathies were assessed, while plasma and breast muscle samples were collected and analyzed by proton nuclear magnetic resonance-spectroscopy. The dietary supplementation of arginine significantly reduced cumulative feed conversion ratio compared to the control diet at 12 d (1.352 vs. 1.401, P  < 0.05), 22 d (1.398 vs. 1.420; P  < 0.01) and 33 d (1.494 vs. 1.524; P  < 0.05), and also tended to improve it in the overall period of trial (1.646 vs. 1.675; P  = 0.09). Body weight was significantly increased in ARG compared to CON group at 33 d (1,884 vs. 1,829 g; P  < 0.05). No significant effect was observed on meat quality attributes, breast myopathies and FPD occurrence. ARG birds showed significantly higher plasma concentration of arginine and leucine, and lower of acetoacetate, glutamate, adenosine and proline. Arginine and acetate concentrations were higher, whereas acetone and inosine levels were lower in the breast of ARG birds ( P  < 0.05). Conclusions Taken together, these data showed that increased digestible Arg:Lys ratio had positive effects on feed efficiency in broiler chickens probably via modulation of metabolites that play key roles in energy and protein metabolism.

Low environmental temperatures are among the most challenging stressors in poultry industries. Although landmark studies using acute severe cold exposure have been conducted, still the molecular mechanisms underlying cold-stress responses in birds are not completely defined. In the present study we determine the effect of chronic mild cold conditioning (CMCC) on growth performances and on the expression of key metabolic-related genes in three metabolically important tissues: brain (main site for feed intake control), liver (main site for lipogenesis) and muscle (main site for thermogenesis). 80 one-day old male broiler chicks were divided into two weight-matched groups and maintained in two different temperature floor pen rooms (40 birds/room). The temperature of control room was 32°C, while the cold room temperature started at 26.7°C and gradually reduced every day (1°C/day) to reach 19.7°C at the seventh day of the experiment. At day 7, growth performances were recorded (from all birds) and blood samples and tissues were collected (n = 10). The rest of birds were maintained at the same standard environmental condition for two more weeks and growth performances were measured. Although feed intake remained unchanged, body weight gain was significantly increased in CMCC compared to the control chicks resulting in a significant low feed conversion ratio (FCR). Circulating cholesterol and creatine kinase levels were higher in CMCC chicks compared to the control group (P<0.05). CMCC significantly decreased the expression of both the hypothalamic orexigenic neuropeptide Y (NPY) and anorexigenic cocaine and amphetamine regulated transcript (CART) in chick brain which may explain the similar feed intake between the two groups. Compared to the control condition, CMCC increased the mRNA abundance of AMPKα1/α2 and decreased mTOR gene expression (P<0.05), the master energy and nutrient sensors, respectively. It also significantly decreased the expression of fatty acid synthase (FAS) gene in chick brain compared to the control. Although their roles are still unknown in avian species, adiponectin (Adpn) and its related receptors (AdipoR1 and 2) were down regulated in the brain of CMCC compared to control chicks (P<0.05). In the liver, CMCC significantly down regulated the expression of lipogenic genes namely FAS, acetyl-CoA carboxylase alpha (ACCα) and malic enzyme (ME) and their related transcription factors sterol regulatory element binding protein 1/2 (SREBP-1 and 2). Hepatic mTOR mRNA levels and phosphorylated mTOR at Ser2448 were down regulated (P<0.05), however phosphorylated ACCαSer79 (inactivation) was up regulated (P<0.05) in CMCC compared to control chicks, indicating that CMCC switch hepatic catabolism on and inhibits hepatic lipogenesis. In the muscle however, CMCC significantly up regulated the expression of carnitine palmitoyltransferase 1 (CPT-1) gene and the mRNA and phosphorylated protein levels of mTOR compared to the control chicks, indicating that CMCC enhanced muscle fatty acid β-oxidation. In conclusion, this is the first report indicating that CMCC may regulate AMPK-mTOR expression in a tissue specific manner and identifying AMPK-mTOR as a potential molecular signature that controls cellular fatty acid utilization (inhibition of hepatic lipogenesis and induction of muscle fatty acid β-oxidation) to enhance growth performance during mild cold acclimation.

Originally named for its expression in the posterior hypothalamus in rats and after the Greek word for “appetite”, hypocretin, or orexin, as it is known today, gained notoriety as a neuropeptide regulating feeding behavior, energy homeostasis, and sleep. Orexin has been proven to be involved in both central and peripheral control of neuroendocrine functions, energy balance, and metabolism. Since its discovery, its ability to increase appetite as well as regulate feeding behavior has been widely explored in mammalian food production animals such as cattle, pigs, and sheep. It is also linked to neurological disorders, leading to its intensive investigation in humans regarding narcolepsy, depression, and Alzheimer’s disease. However, in non-mammalian species, research is limited. In the case of avian species, orexin has been shown to have no central effect on feed-intake, however it was found to be involved in muscle energy metabolism and hepatic lipogenesis. This review provides current knowledge and summarizes orexin’s physiological roles in livestock and pinpoints the present lacuna to facilitate further investigations.