Leptin, a key regulator of reproductive physiology, influences various processes in vertebrates, including oocyte proliferation, embryogenesis, the onset of puberty, ovarian function, and follicle development. In mammals, leptin affects steroidogenesis, folliculogenesis, and hormonal regulation through the hypothalamic-pituitary-gonadal axis. Instead, in avian species, leptin-controlled mechanisms are poorly understood, because birds do not produce leptin in adipocytes. In birds, leptin is expressed in the brain, pituitary glands, and gonads, where it enhances ovarian function and egg-laying performance, particularly during feed deprivation. In this review, we discuss and summarize the recently discovered role of leptin in regulating ovarian function during different life stages in birds and compare it with its function in mammals.

Regulation of food intake, especially during the neonatal period, is important to ensure optimal nutrition and meet the metabolic requirements of growing and healthy animals. However, many problems associated with neonatal chicks remain unsolved. Feeding behavior during the neonatal stage is characterized by short resting periods between very brief times spent taking up food. Accordingly, neuropeptides, which take time to synthesize and release, as well as nutrients that are taken up via feeding, may be involved in feeding regulation. The present review summarizes current knowledge about the role of amino acids and their interaction with neuropeptides on the regulation of food intake in neonatal chicks with special emphasis on L-arginine metabolism and neuropeptide Y. Fasting and subsequent short-term refeeding influence amino acid metabolism in the brain. Short-term refeeding induces a rapid increase in the concentrations of several amino acids, which may contribute to satiety signals in the neonatal chick brain. The function of L-arginine is related to its metabolite, L-ornithine, which acts as an innate satiety signal in the control of food intake. Co-injection with L-ornithine attenuates the orexigenic effect of neuropeptide Y in a dose-dependent manner. This implies a potent interaction in the brain between the regulation of food intake by neuropeptide Y and acute satiety signals by L-ornithine. The roles of other amino acids in feeding and their relationship with the stress response are also discussed in this review. In conclusion, endogenous neuropeptides and endogenous and/or exogenous nutrients such as amino acids are believed to coordinate the feeding behavior of neonatal chicks.

Farm biosecurity is valuable for reducing the indiscriminate use of antimicrobials. However, its relationship with antimicrobial usage can be difficult to assess because of multiple factors. This study evaluated the impact of biosecurity practices on productivity, frequency of antimicrobial use, and development of antimicrobial resistance. Among factors related to biosecurity, mortality rate <2% within one week of age, survival rate >98%, and production index >350 in farms in which: bedding was not reused or only reused once, regular advice and biosecurity training was provided by poultry veterinarians, distinctions between clean and dirty areas were strictly enforced at all times, workers used farm biosecurity manuals, or disinfection guidelines were fully implemented, including cleaning before introducing new flocks and daily disinfection throughout growth, were significantly higher than those in farms without these measures (p < 0.05). The absence of biosecurity practices increased antimicrobial use to one (25.7%), two (39.2%), and three (25.7%) times (p < 0.05). In farms that implemented biosecurity practices, the antimicrobial administration was significantly increased to two times (44.2%) (p < 0.05), with only 17.4% of farms using antimicrobials three times. The prevalence of environmental Escherichia coli resistant to multiple cephalosporins and chloramphenicol, which are not used on broiler farms, was significantly reduced by biosecurity practices (p < 0.05). Our findings indicate that improved biosecurity practices decrease antimicrobial use, decrease the incidence of antimicrobial-resistant bacteria, and help to eliminate resistant bacteria in farm environments.

Avian gout (AG) is detrimental to the survival and production performance of poultry and effective drugs are lacking. Caulis sinomenii has shown clinical efficacy against arthritis and may have potential value in AG prevention and treatment. In the present study, the components and targets of C. sinomenii and AG-related targets were identified using relevant databases. The common targets, target interactions, and signaling pathways involved in the prevention and treatment of AG by C. sinomenii were determined using software to explore the potential mechanisms of action. Sixteen components of C. sinomenii, eight of which were active ingredients with 351 targets and 2993 AG-related targets, were identified using several databases. A total of 156 common targets were associated with 202 biological processes and 34 pathways. Toll-like receptor 4 (TLR4) and prostaglandin endoperoxide synthase 2 were core targets. These targets may exert therapeutic effects on AG through four pathways: the nucleotide-binding oligomerization domain (NOD)-like receptor, mammalian target of rapamycin, TLR, and mitogen-activated protein kinase signaling pathways. In summary, C. sinomenii has potential therapeutic efficacy against AG through multicomponent, multi-target, and multi-pathway mechanisms.

This study evaluated the impact of replacing inorganic mineral sources of Cu, Zn, and Se with chelated organic minerals (OM) on performance, nutrient and mineral utilization rates, and intestinal morphometry in growing Japanese quails (Coturnix japonica). A total of 150 nine-day-old quails were randomly assigned to receive one of the following diets over 4 weeks: CTRL (100% inorganic minerals), OM33 (replacement of 33% inorganic minerals), OM67 (replacement of 67% inorganic minerals), and OM100 (100% organic minerals). Quails fed the OM67 diet exhibited higher (P < 0.05) viability, daily weight gain, and live weight than the other groups, with no significant difference in feed intake or feed efficiency across treatments. The utilization rates of Cu and Fe were lower in the OM33 group. The CTRL group presented the lowest tibial weight (P < 0.05). Growing quails fed the OM67 diet contained the highest intestinal villi in the duodenum, jejunum, and ileum. In conclusion, the partial replacement (up to 67%) of inorganic mineral with OM in the diet of growing quails can enhance their productive performance and intestinal histological traits.

This study clarified the histological changes in the mucosal epithelium of the chicken intestine during the pre- and post-hatching stages. The duodenum, jejunum, ileum, and colorectum were collected from embryos at 15, 17, 18, 19, and 21 days of incubation and from chicks at 1 and 3 days after hatching. Paraffin sections prepared from tissue samples were stained with periodic acid-Schiff followed by alcian blue for histological analysis and to detect goblet cells. Villin and β-actin were detected using double immunofluorescence. Villi with finger-like shape were already observed in embryos after 15 days of incubation, and no obvious change in shape was observed even after hatching. Villous height increased in all intestinal regions as the developmental stage progressed, particularly a few days before and after hatching. Goblet cells first appeared in the epithelium of all intestinal regions after 18 days of incubation. The density of goblet cells rapidly increased from 18 to 21 days of incubation. Both villin and β-actin immunoreactivities were detected at the apical surface of the villous epithelium in all intestinal regions, and villin immunopositivity was stronger in the jejunum and ileum after hatching. These findings indicate that the villi and microvilli of the intestine of broiler chickens show histological changes during few days just before and after hatching. Additionally, the density of goblet cells rapidly increased for a few days before hatching.

Trehalose (Tre) is composed of two molecules of D-glucose joined by an α,α-1,1 glucosidic linkage. Because Tre is utilized by the gut microbiome and enhances gut immunity in chickens, it is used as a feed ingredient. However, taste preference and metabolic dynamics of Tre in chickens are not fully understood. Therefore, in this study, we investigated the taste preference in chickens for Tre and the metabolism of this disaccharide. In a short-term drinking test, chickens preferred low concentrations of Tre solution while avoiding high concentrations. Instead, in a conditioned taste aversion test, chickens did not show taste aversion to Tre, implying that chickens do not have a sufficient taste for Tre. The initial feed intake rate increased when 0.5% Tre was added. Respiratory gas analysis revealed that intragastric administration of 1.0 M Tre weakly increased the respiratory quotient. Furthermore, approximately 50% of Tre was metabolized in chickens. These results suggest that chickens slightly taste the sweetness of Tre. Moreover, adding Tre to feed increases the chickens’ initial appetite, and they use approximately 50% of Tre as an energy source. This information is relevant for using Tre alone or as a supplement in poultry feed.

From the perspective of animal welfare, freedom from hunger and thirst is an undeniable requirement for the poultry industry. Regulatory mechanisms underlying drinking behavior have not yet been identified in chickens; however, the regulation of osmolality and water intake appears to be closely related. This study clarified whether wet feeding affects appetite, osmolality, and stress-related gene expression in the hypothalami of chicks. In Experiment 1, the effects of different wet feed percentages on the growth of broiler chicks were examined. Wet feeds were prepared by mixing either 0.25 g (20% wet feed), 0.667 g (40% wet feed), or 1.5 g (60% wet feed) of distilled water per g of commercial feed. Then, the wet feeds were offered to 4-day-old broiler chicks until 42 d of age. Forty percent wet feed significantly increased body, breast, and leg weights. In Experiment 2, 7-day-old broiler chicks were given either commercial starter feed or 40% wet feed until 21 d of age. Again, weights of the body, breasts, and legs were significantly increased by wet feeding. The total amount of water loss in the individual waterers was significantly decreased by wet feeding. No significant changes were observed in mRNA levels of the genes encoding appetite-regulatory peptides (neuropeptide Y and α melanocyte-stimulating hormone), osmoregulatory peptides (vasotocin and mesotocin), or stress-related peptides (corticotrophin-releasing factor) in the chicken hypothalamus. Overall, 40% wet feed improved growth without inducing thirst or hunger in broiler chicks. These findings suggest that wet feeding contributes to both meat yield and animal welfare during broiler production.

Abstract: Salmonella enterica and coccidia (Eimeria spp.) are important intestinal pathogens in broiler production. Salmonella has high zoonotic potential, and coccidia are responsible for large economic losses. Live vaccines reduce shedding of Salmonella and minimize the impact of coccidial infections on broiler performance. This study investigated the interaction between both vaccines on the intestinal health of broilers. The 2 × 2 experimental design included vaccination against Salmonella Typhimurium (ST) (no vaccination or vaccination on day 14) and vaccination against coccidiosis (no vaccination or vaccination on day 1). On day 28, all groups were challenged with a ST marker strain resistant to nalidixic acid. Re-isolation of ST from the liver and ceca on day 42 indicated higher susceptibility to systemic infection with ST in birds vaccinated against coccidiosis than that in unvaccinated birds. On day 42, cecal immunoglobulin A (IgA) levels against ST decreased in the group vaccinated against ST and coccidia compared to those in all other groups. IgG antibodies in the cecal contents significantly decreased in the group vaccinated against coccidiosis compared to that of the group vaccinated against ST. There was no difference in systemic IgG levels among groups. Analysis of the cecal microbiota revealed a significant difference in beta diversity on days 28 and 42 between the groups vaccinated against coccidiosis and unvaccinated groups. Functional pathway profiling showed increased activity of pathways associated with carbohydrate and arachidonic acid metabolism in the group vaccinated against ST compared to that in other groups. Gene expression of claudin 1, claudin 4, E-cadherin, β-catenin, and zonula occludens 2 in the cecal wall differed between the groups on days 28 and 42. These findings indicated the significant influence of ST and coccidiosis vaccines on the intestinal health of broilers; however, further studies are required to clarify the implications for health and performance.

Betaine has been proposed as a low-cost source of methyl groups in poultry feed, replacing methionine and choline. The present study aimed to investigate the effect of betaine on growth performance, methionine metabolism, and methyl transfer in broilers aged 1 to 21 days fed a low-methionine diet. A total of 960 one-day-old male broilers were randomly divided into four groups: positive control (0.62% methionine in the diet), negative control (0.37% methionine in the diet), and two treatment groups (0.37% methionine in the diet plus either 1500 or 3000 mg betaine/kg diet). Chicks fed the 1500 mg betaine/kg diet had the highest feed-to-gain ratio (P < 0.05), but no significant difference in final body weight, average daily gain, average daily feed intake, or mortality. Serum S-adenosyl-L-methionine and total homocysteine were higher at 1500 mg betaine/kg diet; whereas serum S-adenosylhomocysteine exhibited the opposite trend. Except for DNA methyltransferase 1, key enzymes and metabolites involved in the hepatic single-carbon pathway showed the highest levels at 1500 mg betaine/kg diet and declined thereafter. Furthermore, betaine promoted dose-dependent mRNA and protein expression of enzymes involved in the hepatic single-carbon metabolic cycle and methyl transferase pathways in chicks fed methionine-deficient diets. In conclusion, while the addition of betaine did not significantly improve the growth performance of chicks aged 1–21 days, inclusion of 1500 mg betaine/kg diet effectively stabilized methionine metabolism and methyl transfer in methionine-deficient diets.

Freedom from thirst is an undeniable requirement of the poultry industry. However, the regulatory mechanisms underlying water intake in chicks are not yet fully understood. In humans, increased blood osmolality is probably the strongest signal for drinking. Angiotensin II, a hyperosmotic signal, induces water intake in chickens; this effect is attenuated by an opioid receptor antagonist. Vasotocin and mesotocin appear to have osmoregulatory functions in chicken. Dehydration activates brain corticotrophin-releasing factor (CRF) neurons in rats, and the central administration of CRF induces water intake in rabbits. This study aimed to clarify the effects of neuropeptides such as opioid peptides, vasotocin, mesotocin, and CRF on water intake to identify thirst-inducing neuropeptides in chicks. Eight-day-old male chicks were intracerebroventricularly injected with saline or the peptides. Water intake was measured 120 min after the injection under feed-deprived conditions. Intracerebroventricular administration of Met-enkephalin (a δ-opioid receptor agonist), β-endorphin (a δ-opioid receptor agonist), and nociception (a κ-opioid receptor and opioid receptor-like protein agonist) significantly suppressed water intake in chicks, whereas dynorphin B (a κ-opioid receptor agonist) and endomorphin-1 and 2 (μ-opioid receptor agonists) did not affect water intake. Intracerebroventricular administration of vasotocin, mesotocin, and CRF significantly suppressed water intake in chicks. Our findings suggest that none of the neuropeptides used in this study function as thirst-inducing peptides in the central nervous system of chicks.

The present study aimed to determine the inheritance and effect of dwarfism, which occurs naturally in the Nicobari chicken breed, on various growth and production traits. The dwarf character did not affect body weight for up to 4 weeks; but had a negative impact from 8 weeks onward, with body weight declining by 5.5%–9.0% in males and 9.0%–16% in females. Shank length was 22% and 27% shorter in male and female dwarf birds, respectively, than in full-size birds. The average age at first egg was 3.08% higher in dwarf hens than in their normal counterparts, and was accompanied by a non-significant decline (5.63%) in 40 weeks egg production. Egg weights were 2.23% and 2.64% lower at 32 and 40 weeks, respectively, in dwarf hens. Instead, the shape index and shell thickness were better in dwarf hens. The eggs of dwarf hens were darker and red, with less hue than those of normal hens; whereas internal egg quality was the same. Fertility and hatchability were lower in dwarf dams mated with dwarf sires than in crosses or reciprocal crosses between normal and dwarf birds. Breeding experiments and sequencing of transmembrane protein 263 ruled out the sex-linked (dw) and autosomal dwarfism (adw), as the genetic causes of dwarfism in the Nicobari breed, which instead appears to follow a novel pattern and has a unique effect on growth traits.

In this study, we aimed to identify the mechanism responsible for tissue degeneration and fibrosis in pectoral and supracoracoideus muscles. Ten chickens fed ad libitum broiler feed (Bro) were compared to 10 chickens fed breeding feed (Adj), which has lower metabolizable energy. The median body weight of Bro and Adj birds at 48 days of age was 4.9 and 0.9 kg, respectively. In Bro birds, hind legs were farther apart and tended to abduct, whereas their standing posture was often tilted forward, making them unstable. The two Bro males were heavier than the average, markedly less stable when standing or walking, and often flapped their wings vigorously to maintain balance. Myofiber damage and fibrosis were observed at the myoaponeurotic junction of the pectoralis major and supracoracoideus muscles in Bro birds. Myofiber damage and fibrosis were detected also in areas distal to the myoaponeurotic junction in the two heavier males but were otherwise less evident. By contrast, in Adj birds, almost no degeneration or fibrosis of muscle tissue was observed at the myoaponeurotic junction. In addition, the supracoracoideus muscle of one of the Bro birds showed coagulative necrosis of muscle tissue, surrounded by prominent fibrous tissue. Numerous incompletely formed blood vessels with irregular shapes and prominent branching proliferated in the fibrous tissue. These findings suggest that injury at the myoaponeurotic junction and abnormal capillary proliferation may be closely related to the formation of lesions, along with prominent fibrosis in the pectoralis major and supracoracoideus muscles.

The present study evaluated the effect of different dietary energy levels on reproductive performance in breeding pigeons, as well as growth performance and intestinal health in squabs. In total, 180 pairs of 12-month-old White King breeding pigeons were randomly assigned to five dietary treatments, each with six replicates of six pairs of birds, and fed diets containing 11.60, 11.80, 12.00, 12.20, and 12.40 MJ/kg for 46 days, respectively. Energy content beyond 12.00 MJ/kg shortened the laying interval (linear and quadratic, P<0.05), while boosting 38-day, 42-day, and 46-day laying rates (linear, P<0.05) in breeding pigeons. Except for the early stage of lactation, feed intake showed a linear and/or quadratic negative relationship with dietary energy content (P<0.05). Body weight at 1 week of age, average daily gain during the early growth stages, and serum total protein of squabs increased with increasing dietary energy content (linear, P<0.05); whereas alanine aminotransferase activity decreased (quadratic, P<0.05). Jejunal villus height and villus height to crypt depth ratio in squabs increased with increasing dietary energy levels (linear and quadratic, P<0.05), particularly in the 12.40 MJ/kg group. Higher dietary energy content increased jejunal malondialdehyde content (linear, P<0.05), total superoxide dismutase (T-SOD), and glutathione peroxidase activities (linear, P<0.05), as well as ileal T-SOD (linear and quadratic, P<0.05) and catalase (quadratic, P<0.05) activities in squabs. Hence, intakes greater than 12.00 MJ/kg altered the jejunal redox status. Finally, higher dietary energy content improved reproduction in breeding pigeons and intestinal morphology in squabs. Overall, 12.00 MJ/kg strikes the right balance as it promotes reproductive performance in breeding pigeons and intestinal health in squabs.

Endogenous water production is an important response for inducing water acquisition in birds, with proteins and lipids being major sources of endogenous water. However, the roles of protein and lipid metabolism-related gene expression in the regulation of their body fluid balance have not been investigated. This study aimed to clarify the roles of protein and lipid metabolism-related genes in osmoregulation in chicks. In Experiment 1, we examined the effects of 12 h of water deprivation on the mRNA levels of protein and lipid metabolism-related genes and feed intake in chicks. Feed intake was significantly decreased by water deprivation throughout the experimental period. The mRNA levels of vasotocin in the diencephalon were significantly increased by water deprivation. The mRNA levels of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme of mitochondrial fatty acid oxidation, were significantly increased by water deprivation in the liver, breast muscle, and diencephalon of the chicks. The mRNA levels of atrogin-1, a regulatory enzyme of the ubiquitin proteasome-system, were significantly increased by water deprivation in the breast muscle of the chicks. In contrast, the mRNA levels of fatty acid synthase, the rate-limiting enzyme of fatty acid synthesis, were significantly decreased by water deprivation in the liver of the chicks. In Experiment 2, the effects of intraperitoneal administration of hypertonic saline were examined under feed and water-deprived conditions. The mRNA levels of renal aquaporin 1, breast muscle atrogin-1, and diencephalon CPT1A were significantly increased 1 h after hypertonic saline injection. These results suggest that osmotic stress may induce protein catabolism in the skeletal muscle and fatty acid catabolism in the diencephalon of the chicks.

The current study investigated the optimal standardized ileal digestible (SID) methionine (Met) requirement for the growth performance of white Pekin ducks from hatching to 21 days of age. A total of 288 one-day-old male white Pekin ducklings were initially weighed and randomly assigned to six dietary groups, with six replicates per group. Eight ducklings were housed in each floor cage, pre-littered with rice hulls. Basal diets (corn-soybean-based) included 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, and 0.55% SID Met, representing the dietary treatment groups. Ducklings were offered unrestricted access to experimental diets and freshwater for the duration of the study. Body weight and feed intake were recorded weekly, and the average daily gain and feed conversion ratios were calculated. Overlapping linear- and quadratic-plateau regression models were employed to estimate SID Met requirements. Final body weight, average daily gain, and feed conversion ratios in white Pekin ducks exhibited significant quadratic growth with increasing dietary SID Met concentrations. In conclusion, estimated SID Met requirements for white Pekin ducks from hatching to 21 days, based on an average of linear and quadratic model responses, were determined to be 0.51% for body weight improvement, 0.51% for average daily gain, and 0.50% for feed conversion efficiency. These findings provided invaluable insight into optimized nutritional strategies for early growth performance in white Pekin ducks.

Plumage color in birds is determined by melanin, whose synthesis and transport are affected by many genes, including specific solute carriers (SLCs). The main objective of this study was to detect polymorphisms in the SLC24A5 gene of the Chinese yellow quail (Coturnix japonica) and analyze their effect on tyrosinase activity in skin tissue and melanin content in down feathers. The cDNA of the SLC24A5 gene was cloned by RT-PCR and subjected to Sanger sequencing. Potential single-nucleotide polymorphisms (SNPs) were screened using multiple sequence alignment. The screened nonsynonymous SNPs were genotyped across 265 Chinese yellow quails using the kompetitive allele-specific PCR method. The association of genotypes with tyrosinase activity in the skin and melanin content in down feathers was analyzed. The g.8884145A/G SNP was identified in exon 9 of the SLC24A5 gene, resulting in an Asp396Ala mutation. The mutant residue was predicted to be located inside the eighth transmembrane helix of the SLC24A5 protein, which is primarily responsible for recognizing Na⁺/Ca²⁺ ions. Mutant individuals had significantly lower total melanin content in the feathers and tyrosinase activity in dorsal skin, in spite of no significant difference in SLC24A5 mRNA expression in the same tissues. This study indicates that the g.8884145A/G mutation reduced tyrosinase activity by affecting the function of the SLC24A5 protein, which in turn decreased melanin content of down feathers in Chinese yellow quail.