Assessing the Influence of Guanidinoacetic Acid on Growth Performance, Body Temperature, Blood Metabolites, and Intestinal Morphometry in Broilers: A Comparative Sex-Based Experiment

It is well known that female and male broilers showcase variations in their growth performance, influenced by various physiological factors. This experiment aims to explore potential differences between female and male broilers concerning growth performance, body temperature, blood metabolites, carcass traits, and intestinal architecture in response to guanidinoacetic acid (GAA) supplementation. A total of 240 Ross 308 broiler chickens were arranged in a 3 × 2 factorial design and randomly allocated into 48 boxes, each containing 5 birds. The experiment comprised six treatments, with eight replicates per treatment. The main factors investigated were dietary GAA levels (0%, 0.06%, and 0.12%) and sex (male and female). Male broilers demonstrated superior body weight gain (BWG) and feed intake (FI) compared to females (p< 0.05). GAA supplementation at 0.12% concentration notably improved BWG and reduced FI and feed conversion ratio (FCR) across experimental phases (p < 0.05). However, interactions between sex and GAA were minimal except for reduced FI and FCR (p < 0.05) in both sexes during early growth stages. Regardless of GAA treatment, the male birds exhibited more elevated shank and head temperatures than the females. Carcass traits were largely unaffected by GAA supplementation or sex, except for higher heart yield in the males. Serum metabolite levels were not different between treatment groups at 10 and 24 days of age, except for a higher level of serum creatinine at 10 days in the female birds with 0.06% GA supplementation (p < 0.05). Intestinal morphology was significantly affected by GAA and sex, depending on the segment of intestine, in which GAA supplementation significantly increased villus height, crypt depth, villus width, surface area, and goblet cell count, while the males consistently exhibited higher values of these parameters than the females, and differences were observed between intestinal segments, especially in the ileum and duodenum, at different ages. In conclusion, the interactions between GAA and sex had minimal influences on growth performance indices. However, male broilers demonstrated a more pronounced response to GAA concerning ileal architecture. This study highlights the importance of supplementing broiler chicken diets with GAA for optimizing male broiler performance and intestinal function. The inclusion of GAA into broiler diets needs further study to reveal the underlying mechanisms driving these sex-specific responses and assess the long-term impacts of GAA supplementation on broiler health and productivity.

Dietary supplementation with ellagic acid improves the growth performance, meat quality, and metabolomics profile of yellow-feathered broiler chickens

The aim of this research was to explore the effects of ellagic acid (EA) on growth performance, meat quality, and metabolomics profile of broiler chickens. 240 healthy yellow-feathered broilers were randomly divided into 4 groups (6 replicates/group and 10 broilers /replicate): 1) a standard diet (CON); 2) CON+0.01% EA; 3) CON+0.02% EA; 4) CON+0.04% EA. Compared with the CON group, dietary 0.02% EA increased linearly and quadratically the ADG and lowered F/G ratio from 29 to 56 d and from 1 to 56 d of age (P < 0.05). The EA groups had higher spleen index and showed linear and quadratic improve thymus index (P < 0.05). A total of 0.02% EA linearly and quadratically increased the leg muscle percentage and quadratically increased the breast muscle percentage (P < 0.05). Compared to the control diet, 0.02% EA decreased quadratically the L* and increased a* of breast muscle at 45 min postslaughter (P < 0.05), and quadratically decreased (P < 0.05) the b* and increased linearly and quadratically (P < 0.05) drip loss. Additionally, EA improved linearly and quadratically (P < 0.05) serum total protein concentration and reduced linearly and quadratically (P < 0.05) serum blood urea nitrogen concentration. A total of 0.02% EA quadratically increased catalase activity and decreased malondialdehyde concentration in breast muscle compared with the control diet (P < 0.05). 0.02% and 0.04% EA could linearly and quadratically increase (P < 0.05) the concentrations of histidine, leucine and essential amino acids (EAA), 0.02% EA could linearly and quadratically increase (P < 0.05) the concentrations of threonine, glutamate, and flavored amino acids in breast muscle. 0.02% EA linearly and quadratically improved the C20:3n6, C22:6n3, polyunsaturated fatty acid (PUFA) concentrations, and the ratio of PUFA to saturated fatty acids (SFA), but reduced the C16:0 and the SFA concentrations in breast muscle than the CON group (P < 0.05). The EA diet linearly increased (P = 0.035) and quadratically tended (P = 0.068) to regulate the C18:2n6c concentration of breast muscle. Metabolomics showed that alanine metabolism, aspartate and glutamate metabolism, arginine and proline metabolism, taurine and hypotaurine metabolism, and glycerophospholipid metabolism were the most differentially abundant. These results showed that EA supported moderate positive effects on growth performance, meat quality, and metabolomics profile of broilers.

Effect of Dietary Puerarin Supplementation on Growth Performance, Immune Response, Antioxidant Capacity, and Intestinal Morphology in Domestic Pigeons (Columba livia)

Puerarin is an isoflavone extracted from Gegen (Pueraria lobata) and has been widely utilized to treat various human diseases; however, information regarding its benefits in animal production is limited. In this study, we aimed to investigate the influence of dietary puerarin supplementation on growth performance, immune organ index, immunoglobulin profile, antioxidant capacity, and intestinal morphology in pigeons. In total, 375 healthy 28-day-old White King pigeons were randomly divided into five groups, each consisting of five replicates and 15 pigeons per replicate. Each group was administered one of five dietary treatments: the basal diet, or the basal diet supplemented with 40, 80, 120, or 160 mg/kg puerarin. Treatment duration was 30 days following a 7-day acclimation period. Puerarin treatment did not significantly alter the growth performance of pigeons but afforded a significant linear enhancement in the thymus index (P < 0.05). Additionally, puerarin supplementation significantly increased serum immunoglobulin A and immunoglobulin M levels in pigeons in a linear manner (P < 0.05). Similarly, puerarin significantly and linearly increased the activities of total antioxidant capacity, superoxide dismutase, glutathione, and catalase in the serum and liver, and decreased the malondialdehyde content (P < 0.05). Moreover, the villus height (VH), crypt depth (CD), and VH/CD ratio of the small intestine (including the duodenum, jejunum, and ileum) increased linearly upon puerarin supplementation (P < 0.05). Collectively, these results indicate that puerarin supplementation could improve the immune response, antioxidant capacity, and intestinal morphology of pigeons.

Comprehensive Transcriptomic and Metabolomic Analysis Revealed the Functional Differences in Pigeon Lactation between Male and Female during the Reproductive Cycle

Lactation is a unique reproductive behavior in pigeons, with the crop serving as the organ responsible for secreting pigeon milk. Both male and female pigeons can produce crop milk and rear their offspring through a division of labor. Since the time of the secretion of pigeon crop milk is different in the process of feeding the young, whether the metabolism and formation of pigeon milk use the same mechanism is a very interesting scientific question. However, the metabolic dynamics and underlying genetic mechanisms involved in the formation of pigeon crop milk remain unclear, particularly during the incubation-feeding reproductive cycle. In this study, we integrated lactation-associated metabolism and transcriptome data from the crop tissues of both male and female pigeons during the brooding and feeding stages. We mapped the changes in metabolites related to milk formation in the crop tissues during these stages. Through metabolome profiling, we identified 1413 metabolites among 18 crop tissues. During the breeding cycles, the concentrations of estrone, L-ergothioneine, and L-histidine exhibited the most dynamic changes in females. In contrast, estrone, L-anserine, 1-methylhistidine, homovanillate, oxidized glutathione, and reducing glutathione showed the most dynamic changes in males. Gender-specific differences were observed in the metabolome, with several metabolites significantly differing between males and females, many of which were correlated with cytokine binding, immunity, and cytochrome P450 activity. Using this dataset, we constructed complex regulatory networks, enabling us to identify important metabolites and key genes involved in regulating the formation of pigeon milk in male and female pigeons, respectively. Additionally, we investigated gender-associated differences in the crop metabolites of pigeons. Our study revealed differences in the modulation of pigeon crop milk metabolism between males and females and shed light on the potential functions of male and female pigeon milk in the growth, development, and immunity of young pigeons, an area that has not been previously explored. In conclusion, our results provide new insights into the metabolic regulation of pigeon crop milk formation during the brooding and breeding stages. Furthermore, our findings lay the foundation for the accurate development of artificial pigeon milk.

Optimal dietary energy and protein levels for breeding pigeons in the winter "2 + 3" lactation pattern

The nutritional requirements of breeding pigeons depend on their physiological period, breeding pattern, and environmental conditions. Despite works on reduced litter size in winter production to combat high mortality and the poor welfare of squabs, there are few studies on the related nutritional requirements of these pigeons. A total of 432 pairs of European Mimas pigeons were randomly divided into 9 groups in which 3 crude protein (CP) levels (15, 16.5, and 18%) and 3 metabolizable energy (ME) levels (12.2 MJ/kg, 12.4 MJ/kg, and 12.6 MJ/kg) were tested to determine the optimal energy and protein requirements of breeding pigeons in the winter "2 + 3" breeding pattern. The results showed that ME and CP levels had little effect on the body weight, feed intake, and egg quality of breeding pigeons during the lactation period. An 18% CP diet significantly increased the laying rate and hatchability (P < 0.05), but there was no difference in the laying rate with 18% CP and 16.5% CP during the whole reproductive cycle (P > 0.05). There was a significant interaction between ME and CP levels, and the laying interval of breeding pigeons in group 9 (18% CP; 12.6 MJ/kg) was significantly shortened (P < 0.05). For squabs, the ME level had no effect on growth performance, slaughter performance, or meat quality. The body weight of 21-day-old squabs in the 18% CP group increased by 3.16% compared with that of the 15% CP group, but there was no difference between the 18% CP and 16.5% CP groups. Compared with other experimental groups, group 7 (18% CP; 12.2 MJ/kg) had the fastest growth rate in squabs (P < 0.05), and the corresponding slaughter weight was also the heaviest (P < 0.05). We further found that the height of the squab intestinal epithelium was significantly increased in both the 16.5% CP and 18% CP groups of squabs (P < 0.01), but male breeding pigeons showed a certain degree of oxidative stress with an increase in CP level. In conclusion, the effects of 15 to 18% CP levels and 12.2 to 12.6 MJ/kg ME levels on the reproductive metabolism of breeding pigeons and the growth and development of squabs in the "2 + 3" breeding pattern during winter are small. For economic efficiency, we suggest that the CP level can be reduced to 16.5% while the ME level should not be less than 12.2 MJ/kg in practical production.

Chemical Composition of Pigeon Crop Milk and Factors Affecting Its Production: A Review

Pigeons are important commercial poultry in addition to being ornamental birds. In 2021, more than 111 million pairs of breeding pigeons were kept in stock and 1.6 billion squabs were slaughtered for meat in China. However, in many countries, pigeons are not domestic birds; thus, it is necessary to elucidate the factors involved in their growth and feeding strategy due to their economic importance. Pigeons are altricial birds, so feedstuffs cannot be digested by squabs, which instead are fed a mediator named pigeon crop milk. During lactation, breeding pigeons (both female and male) ingest diets and generate crop milk to feed squabs. Thus, research on squab growth is more complex than that on chicken and other poultry. To date, research on the measurement of crop milk composition and estimation of the factors affecting its production has not ceased, and these results are worth reviewing to guide production. Moreover, some studies have focused on the formation mechanism of crop milk, reporting that the synthesis of crop milk is controlled by prolactin and insulin-activated pathways. Furthermore, the Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) pathway, target of rapamycin (TOR) pathway and AMP-activated protein kinase (AMPK) pathway were also reported to be involved in crop milk synthesis. Therefore, this review focuses on the chemical composition of pigeon crop milk and factors affecting its production during lactation. This work explores novel mechanisms and provides a theoretical reference for improving production in the pigeon industry, including for racing, ornamental purposes, and production of meat products.

Effects of Hydrogen Peroxide-Induced Oxidative Stress on Intestinal Morphology, Redox Status, and Related Molecules in Squabs

The purpose of this study was to evaluate the potential effect of oxidative stress on the intestine of squabs, and to explore the molecular mechanisms. A total of 360 1-day-old squabs were divided evenly into five different groups (n = 72/group): control, negative control, low, medium, and high dose groups. On the 3rd, 5th, and 7th days, squabs in the control group were not effectively treated and the negative control group were intraperitoneally injected with normal saline, whereas the H₂O₂ group was injected with H₂O₂ of 2.0, 2.5, and 3.0 mmol/kg BW respectively. On the 21st day, the serum and duodenum were collected for further analysis. The results indicated that, compared with the control group, H₂O₂ caused squabs weight loss and intestinal morphology damage, and these effects were enhanced with an increase in dose. Further examination revealed that the contents of oxidative stress markers in both the serum and duodenum of the H₂O₂ group were significantly enhanced as the dose was increased. In addition, H₂O₂ exposure also resulted in the lower mRNA expression of Occludin, ZO-1, Beclin1, Atg5, and Caspase-3, but the expression of Claudin2 and Bcl-2 was decreased in comparison to the control group. These findings suggested that duodenal oxidative damage was accompanied by weight loss, changes in intestinal morphology, redox status imbalance, apoptosis as well as autophagy of intestinal cells, with, effects of 3.0 mmol/kg BW of H₂O₂ being the most severe.

Effects of Yucca schidigera extract on serum biochemical parameters, humoral immune response, and intestinal health in young pigeons

Introduction

It is of great importance to find antibiotic alternatives that can improve poultry performance and enhance immunity. Plant-derived extracts and their concentrates are natural bioactive compounds that are widely and effectively applied as the antibiotic alternatives in animal industries. This study was conducted to investigate the effects of Yucca schidigera extract (YSE) on growth performance, serum biochemical parameters, immune function, intestinal morphology, and microbiota diversity of young pigeons.

Methods

A total of 120 healthy White King pigeons (28 days old) with similar weight were randomly assigned to 4 treatments with six replicate cages. Each of the pigeons from 4 treatments was orally administrated with 0 (control), 5, 10, and 15 mg YSE per day, respectively.

Results

The results showed that orally supplemental YSE had no significant effects (P > 0.05) on the growth performance and immune organ index of pigeons. The serum total protein and IgM contents in the 10 mg YSE group were significantly higher (P < 0.05) than those in the control group. Supplemental 10 and 15 mg YSE significantly lowered the level of serum total cholesterol (P < 0.05) and increased (P < 0.05) the villi height in the jejunum compared with the control group. Supplemental 5 and 10 mg YSE significantly decreased (P < 0.05) the level of serum alanine aminotransferase and the crypt depth in the ileum compared with the control group. The beta diversity showed a distinct difference in the ileum microbial composition between the control and the 10 mg YES group. YSE supplementation enriched the bacterial genera Sulfurospirillum, Solobacterium, Desulfovibrio, Desulfobulbus, Lactococcus, Parabacteroides, Acidaminococcus, Acetobacter, and Streptococcus. Additionally, Enterococcus genus showed a significantly negative correlation with serum alanine aminotransferase (R = -0.618, P = 0.043). Actinomyces genus showed a significantly negative correlation with cholesterol (R = -0.633, P = 0.036). Turicibacter genus showed a significantly positive correlation with villi height in the jejunum (R = 0.751, P = 0.008).

Discussion

In conclusion, orally supplemental YSE could improve serum biochemistry, immunoglobulin contents, and intestinal morphology by regulating the composition of microbial community in the ileum of young pigeons.

Nonlinear model fitting analysis of feather growth and development curves in the embryonic stages of Jilin white geese (Anser cygnoides)

Poultry is subject to varying degrees of feather loss and feather pecking during production, which seriously affects the live appearance and carcass appearance of their commercial traits and greatly reduces the production profitability of the farming enterprise. It also has an impact on down production and quality in the case of geese. In this study, mathematical models (Logistic, Gompertz, and Von Bertalanffy) were used to assess feather growth and development during the embryonic period in Jilin white geese (Anser cygnoides) predicting the weight and length of feathers from the back, chest, and belly tracts at different embryonic ages, to determine which growth model more accurately described feather growth patterns. The result first showed that the primary feather follicles of the Jilin white goose developed at E14 and secondary feather follicles at E18; primary feather follicle density increased and then decreased, whereas secondary feather follicle density increased continuously and the primary and secondary feather follicles developed independently. Secondly, the embryonic feather growth followed a slow-fast-slow pattern, with feathers growing slowly from E12 to E18, quickly from E18 to E24, and then decreasing after E24 until just before emergence (E30). In addition, before E14, feathers were concentrated in the back tracts, and no feathers were found on the head, neck, chest, abdomen, or wings. By E22, the whole body of the embryo was covered with feathers, and the back feathers were the earliest and fastest to develop. Compared to the Gompertz and von Bertalanffy models, the logistic model fit (R2 = 0.997) was the highest, while the sum of residual squares (RSS = 25661.67), Akaike's information criterion (AIC = 77.600), Bayesian information criterion (BIC = 78.191), and mean square error (MSE = 2851.296) were the lowest. Therefore, the logistic model was more suitable for describing the changes in whole-body feather growth during the embryonic period in Jilin white geese. In conclusion, using the growth curve model to explain the relationship between feather growth and embryonic age in geese will potentially speed up the process of genetic improvement in Jilin white geese (A. cygnoides) and thus provide scientific support for molecular genetic breeding.

Linoleic acid ameliorates intestinal mucosal barrier injury in early weaned pigeon squabs (Columba livia)

The study aimed to investigate whether linoleic acid could improve the intestinal barrier function of squabs under weaning stress conditions. Totally 320 7-d-old weaned squabs were randomly divided into four treatment groups, including control group (CON), 0.7% linoleic acid addition group (LA007), 1.4% linoleic acid addition group (LA014) and 2.1% linoleic acid addition group (LA021). At 21 d, eight squabs were randomly selected from each treatment group for sampling and determination. The results showed that adding linoleic acid could improve (P < 0.05) the body weight of weaned squabs, and LA014 had the best effect. With the increase of linoleic acid dosage, villi height and villi area increased linearly or quadratically (P < 0.05), and reached the maximum in LA021 or LA014, respectively. The linoleic acid supplementation could improve the intestinal tight junction of weaned squabs, and the LA014 was the most significant (P < 0.05). With the linoleic acid increasing, the levels of intestinal IL-6 and TNF-α decreased linearly (P < 0.05), while intestinal IL-10 increased quadratically (P < 0.05) and reached the maximum in LA014. Serum endotoxin and diamine oxidase levels decreased linearly (P < 0.05) and reached the lowest level in LA014. The ultrastructure of villi revealed that the length of ileal microvilli in LA014 was significantly increased (P < 0.05) and the microvilli became dense, and the mitochondria in epithelial cells returned to normal state. Further exploring the mechanism of linoleic acid alleviating intestinal injury caused by weaning stress in squabs, it was found that linoleic acid down-regulated (P < 0.05) the relative protein expression of TLR4, MyD88, phosphorylated JNK, and phosphorylated p38, reducing secretion of pro-inflammatory factors IL-6 and TNF-α. This study indicated that linoleic acid could alleviate intestinal barrier injury of early weaned squabs by down-regulating TLR4-MyD88-JNK/p38-IL6/TNF-α pathway.

Analysis of mRNA and lncRNA Expression Profiles of Breast Muscle during Pigeon (Columbalivia) Development

The breast muscle is essential for flight and determines the meat yield and quality of the meat type in pigeons. At present, studies about long non-coding RNA (lncRNA) expression profiles in skeletal muscles across the postnatal development of pigeons have not been reported. Here, we used transcriptome sequencing to examine the White-King pigeon breast muscle at four different ages (1 day, 14 days, 28 days, and 2 years old). We identified 12,918 mRNAs and 9158 lncRNAs (5492 known lncRNAs and 3666 novel lncRNAs) in the breast muscle, and 7352 mRNAs and 4494 lncRNAs were differentially expressed in the process of development. We found that highly expressed mRNAs were mainly related to cell-basic and muscle-specific functions. Differential expression and time-series analysis showed that differentially expressed genes were primarily associated with muscle development and functions, blood vessel development, cell cycle, and energy metabolism. To further predict the possible role of lncRNAs, we also conducted the WGCNA and trans/cis analyses. We found that differentially expressed lncRNAs such as lncRNA-LOC102093252, lncRNA-G12653, lncRNA-LOC110357465, lncRNA-G14790, and lncRNA-LOC110360188 might respectively target UBE2B, Pax7, AGTR2, HDAC1, Sox8 and participate in the development of the muscle. Our study provides a valuable resource for studying the lncRNAs and mRNAs of pigeon muscles and for improving the understanding of molecular mechanisms in muscle development.

Effects of in ovo feeding of methionine and/or disaccharide on post-hatching breast development, glycogen reserves, nutrients absorption parameters, and jejunum antioxidant indices in geese

We investigated the effects of in ovo injection of methionine (Met) and/or disaccharide (DS) on breast muscle and small intestine development, and the aspect of the glycogen contents, digestive enzymes activities, and jejunal antioxidant parameters in geese after incubation. A total of 600 fertilized eggs were used in this study to be employed in a 2 × 2 factorial experiment. Eggs were randomly assigned to 4 groups, 6 replicates per group, and 25 eggs per replicate. Factors in four groups included non-injection, Met injection (5 g/L Met dissolved in 7.5 g/L NaCl), DS injection (25 g/L maltose and 25 g/L sucrose dissolved in 7.5 g/L NaCl), and DS plus Met injection (25 g/L maltose, 25 g/L sucrose, and 5 g/L Met dissolved in 7.5 g/L NaCl). As a result, birth weight, relative weight of breast muscle, diameter of myofiber, glycogen contents, jejunal villus and surface area, and jejunal digestive enzymes activities improved, while liver glucose-6-phosphatase activity decreased, by DS injection. Additionally, DS administration upregulated the expression of myogenic factor-5 (Myf-5) from breast muscle and sodium/glucose cotransporter protein-1 (SGLT-1) from jejunum. In ovo delivery of DS has long-term effects on the improvement of jejunal glucose transporter-2 (GLUT-2) and sucrase-isomaltase expression. In ovo feeding of Met improved the relative weight of breast muscle and small intestine, diameter of myofiber, length of small intestine, jejunal villus width, jejunal sucrase, Na⁺/K⁺ATPase and alkaline phosphatase activities, and jejunal glutathione (GSH) concentration, and decreased the jejunal glutathione disulfide (GSSH) and the ratio of GSSG to GSH, in early-life post-hatching. The breast muscle Myf-5 and myostatin expression, jejunal villus height and surface area, jejunal glutathione peroxidase concentration, and the expression of GLUT-2 in jejunum long-term improved by in ovo delivery of Met. Moreover, in ovo feeding of DS plus Met mixture synergistically improved the diameter of myofiber, jejunal villus height and width, jejunal sucrase, and alkaline phosphatase activities in early-life post-hatching, but long-term upregulated the expression of jejunal GLUT-2. Therefore, we concluded that in ovo injection of Met plus DS is an effective way to improve the development of gosling during post-hatching stages.

Dietary Supplementation of Chitosan Oligosaccharide–Clostridium butyricum Synbiotic Relieved Early-Weaned Stress by Improving Intestinal Health on Pigeon Squabs (Columba livia)

According to a previous study, we had found that early weaning causes harm to growth performance, intestinal morphology, activity of digestive enzymes, and antioxidant status in pigeon squabs (Columba livia). Chitosan oligosaccharides (COS) and Clostridium butyricum have been reported to have great potential to improve the growth performance and intestinal health of early-weaned animals. Therefore, the aim of this study is to explore whether dietary supplementation with COS-C. butyricum synbiotic could relieve early-weaned stress by evaluating its effects on growth performance and intestinal health in pigeon squabs. A total of 160 squabs (weaned at 7 days of age) were randomly divided into 5 groups: the control group, fed with artificial crop milk; the COS supplementation group, fed with artificial crop milk + 150 mg/kg COS; and three synbiotic supplementation groups, fed with artificial crop milk + 150 mg/kg COS + 200, 300, and 400 mg/kg C. butyricum. The results showed that a diet supplemented with COS-C. butyricum synbiotic benefitted the growth performance of early-weaned squabs; even so the differences were not significant among the five groups (p > 0.05). In addition, dietary supplementation of 150 mg/kg COS + 300~400 mg/kg C. butyricum significantly improved the intestinal morphology (especially villus surface area and the ratio of villus height to crypt depth), the activity of digestive enzymes (lipase, trypsin, and leucine aminopeptidase) in duodenum contents, and the production of total short-chain fatty acids and acetic acid in ileum content (p < 0.05). Additionally, dietary supplementation of 150 mg/kg COS + 400 mg/kg C. butyricum benefitted gut health by improving the antioxidant capacity (glutathione peroxidase and total antioxidant capacity) and cytokine status (IL-4 and IL-10) (p < 0.05), as well as by improving the intestinal microbiota diversity. In conclusion, our results revealed that dietary supplementation with synbiotic (150 mg/kg COS + 300~400 mg/kg C. butyricum) could relieve early-weaned stress by maintaining intestinal health in pigeon squabs.

Research Note: Morphology and immune function development of the jejunum and ileum in squab pigeons (Columba livia)

The study was aimed to evaluate the morphology and immune function development of the jejunum and ileum in squab pigeons (Columba livia), by determining the villus ultrastructure, secretory IgA, and cytokines. Eight squabs were randomly selected and sampled on the day of hatch (DOH), d 7 (D 7), 14 (D 14), and 21 (D 21) post-hatch, respectively. The results showed that under transmission electron microscope, the enterocyte circumference in jejunum and ileum decreased with age. The tight junction involved in enterocyte circumference of jejunal villi plateaued from D 7, whereas that of ileal villi changed irregularly. The microvilli of jejunal and ileal villi was maximum at D 14. Under scanning electron microscope, the villus morphology of jejunum and ileum appeared finger-shaped at DOH. After D 7, the jejunal villi were still finger-shaped whereas the ileal villi were leaflike. The secretory IgA in jejunum was significantly increased at D 21. The TGF-β decreased linearly in jejunum and ileum. The anti-inflammatory cytokines increased linearly and proinflammatory cytokines decreased linearly in jejunum and ileum with age. In conclusion, the morphological changes of jejunal epithelium were concentrated at DOH-D 7 and ileal epithelium at DOH-D 14 mainly. The changes in mucus layer and immune-related factors of jejunum and ileum persisted for almost the entire period.

Dynamic variations in serum amino acid and the related gene expression in liver, ovary, and oviduct of pigeon during one egg-laying cycle

The present study was carried to investigate dynamic variations in serum amino acid (AA) contents and the relative mRNA abundance of the AA transporters and AA synthesis-related enzymes in liver, ovary and oviduct of pigeons during one egg-laying cycle (ELC). In experiment 1, seventy laying pigeons (American Silver King) were randomly divided into 14 groups by different days of one ELC (DELC) and arranged as a 2 × 7 factorial design, which included 2 ages (6-mo-old or 12-mo-old) and 7 DELCs. For experiment 2, 35 six-mo-old laying pigeons (American Silver King) were randomly divided into 7 groups by different DELCs and immediately treated with a 12-h fasting. Dynamic variations in serum AAs were detected during one ELC, characterized by high levels of Lys, Met, Leu, Phe, Tyr, Asp, Ser, Glu, Ala, and TAA on day 1 (D1) of one ELC (P < 0.05). Fasting caused obvious decreases in serum levels of Leu, Ile, Val, Phe, Tyr, and TAA from day 2 (D2) to day 7 (D7) (P < 0.05). Relative organ weights of ovary and oviduct increased to the peak values on day 13 (D13) (P < 0.05). Serum calcium decreased to the lowest level on day 4 (D4) (P < 0.05) and serum total triglyceride was kept in a high level on D1, D7, day 10 (D10), and D13 (P < 0.05). Relative mRNA expression of the AA synthesis genes and the AA transport genes exhibited different variation patterns in liver, ovary and oviduct, but Pearson correlation test showed the percentage of positive r values with significant differences were much higher in oviduct than those in liver or ovary. In conclusion, dynamic variations of serum AAs during one ELC were positively related with the expression of the AA transport genes and AA synthesis genes in oviduct, suggesting the upregulated serum AAs might be necessary to meet the AAs requirement for egg white formation in pigeon.

Identification and expression pattern analysis of miRNAs in pectoral muscle during pigeon (Columba livia) development

MicroRNAs (miRNAs) are a group of crucial regulators in the process of animal growth and development. However, little is known about the expression and function of miRNAs in pigeon muscles. To identify the miRNAs participating in the rapid development of pigeon pectoral muscles and quantitate their expression levels of pectoral muscles in different age stages, we performed miRNA transcriptome analysis in pigeon pectoral muscles by sequencing small RNAs over three different age stages (1-day old, 28 days old, and 2 years old). Dual-luciferase reporter assay was applied to validate the interaction between miRNA and its target gene. We identified 304 known miRNAs, 201 conserved miRNAs, and 86 novel miRNAs in pigeon pectoral muscles. 189 differentially expressed (DE) miRNAs were screened out during pigeon development. A short time-series expression miner (STEM) analysis indicated 89 DE miRNAs were significantly clustered in a progressively decreasing expression profile, and mainly enriched in biosynthesis-related GO categories and signaling pathways for MAPK and TGF-β. Dual-luciferase reporter assay indicated that a progressively down-regulated miRNA (miR-20b-5p) could directly target Krüppel-like factor 3 (KLF3) gene. To sum-up, our data expand the repertoire of pigeon miRNAs and enhance understanding of the mechanisms underlying rapid development in squabs.

Protective effect of Polygonatum sibiricum polysaccharide on cyclophosphamide-induced immunosuppression in chickens

The purpose of the study was to evaluate the protective effects of polygonatum sibiricum polysaccharide (PP), an important component of rhizome polygonatum, on cyclophosphamide (CY) induced immunosuppressed chickens. Four hundred and eighty one-day-old Erlang mountainous chickens were randomly allocated into four treatments. The main factors consisted of dietary supplement (PP at 0 or 800 mg/kg of diet) and immunosuppressive challenge (birds challenged with CY or treated with sterile saline). The results showed that PP enhanced chickens' growth performance via elevating daily weight gain (DWG), serum protein production, and decreasing feed conversion ratio (FCR). Moreover, physical measurements revealed that PP accelerated recovery of relative weights of immune organs and maintained their structure and function. Biochemical analysis indicated that PP significantly stimulated immunoglobulin and antioxidant indexes in serum, and improved the proliferation of peripheral blood T lymphocytes. In addition, PP promoted immune organs cells to enter into S and G₂/M phases as well as inhibited the apoptosis in the spleen, thymus, and bursa of Fabricius. PP up regulated the expression of IL-2, IL-6 and IFN-γ genes. Therefore, PP performs a profile in antagonizing Cy-induced immunosuppression in chickens, and it seems that PP can be used as a potential immunostimulant agent.

MicroRNA expression profiling reveals potential roles for microRNA in the liver during pigeon (Columba livia) development

The liver is the central organ for metabolism and influence the growth and development of the animals. To date, little is known about the microRNA (miRNA) in pigeon livers, particularly in different developmental stages. A comprehensive investigation into miRNA transcriptomes in livers across 3 pigeon developmental stages (1, 14, 28 d old) and an adult stage (2 y old) was performed by small RNA sequencing. We identified 312 known miRNA, 433 conserved miRNA, and 192 novel miRNA in pigeon livers. A set of differentially expressed (DE) miRNA in livers were screened out during pigeon development. This set of miRNA might be involved in hepatospecific phenotype and liver development. A Short Time-series Expression Miner analysis indicated significant expression variations in DE miRNA during liver development of pigeons. These DE miRNA with different expression patterns might play essential roles in response to growth factor, cell morphogenesis, and gland development, etc. Protein-protein interaction network and Molecular Complex Detection analysis identified several vital target genes (e.g., TNRC6B, FRS2, PTCH1, etc.) of DE miRNA, which is closely linked in liver development and enriched in PI3K cascade and regulation of growth. Our results expanded the repertoire of pigeon miRNA and may be of help in better understanding the mechanism of squab's rapid development from the perspective of liver development.

Age-Related Changes in Serum Lipid Levels, Hepatic Morphology, Antioxidant Status, Lipid Metabolism Related Gene Expression and Enzyme Activities of Domestic Pigeon Squabs (Columba livia)

The objective of this study was to evaluate the age-related changes in antioxidant status and the lipid metabolism of pigeon squabs (Columba livia), by determining the BW, antioxidant indices, serum lipid levels, lipid metabolism-related enzyme activities, lipid metabolism-related gene expression, and liver morphology in squabs. Ten squabs were randomly selected and sampled on the day of hatching (DOH), days 7 (D7), 14 (D14) and 21 (D21) post-hatch, respectively. The results showed that BW of squabs increased linearly from DOH to D21. The minimum fold of BW gain was observed in the phase from D14 to D21. Serum triglyceride and free fatty acid levels displayed linear and quadratic trends as age increased, with these maximum responses in D14. Serum low-density lipoprotein cholesterol level responded to age linearly and quadratically with the minimum in D14. Serum high-density lipoprotein cholesterol level and the ratio of high-density lipoprotein cholesterol to low-density lipoprotein cholesterol increased linearly with age, whereas the very low-density lipoprotein cholesterol level decreased linearly. The activities of glutathione peroxidase, catalase, and superoxide dismutase in liver displayed linear and quadratic trends as age increased, with these minimum responses in D14. Hepatic malondialdehyde concentration responded to age linearly and quadratically, with the maximum in D14. Activities of lipoprotein lipase, hepatic lipase, and 3-hydroxy-3-methyl glutaryl coenzyme A reductase in liver responded to age linearly and quadratically, with these minimum responses in D14. Hepatic hormone-sensitive lipase activity displayed linear and quadratic trends as age increased with the maximum in D14. Hepatic acetyl CoA carboxylase activity on D14 was significantly lower than squabs on DOH and D7. Hepatic carnitine palmitoyltransferase 1 mRNA expression responded to age linearly and quadratically, with minimum response in D14. Hepatic mRNA expression of acetyl CoA carboxylase and fatty acid synthetase increased linearly with age. Hepatic Oil-Red-O staining area displayed a quadratic trend as age increased, with the maximum response in D14. In conclusion, the phase from DOH to D14 was a crucial development stage for growth, antioxidant status and lipid metabolism in pigeon squabs. The results suggest it is better to take nutritional manipulation in squabs before D14.

The profiling of amino acids in crop milk and plasma and mRNA abundance of amino acid transporters and enzymes related to amino acid synthesis in the crop tissue of male and female pigeons during incubation and chick-rearing periods

The present study was carried out to investigate the changes in amino acid (AA) contents of crop milk and plasma and mRNA abundance of AA transporters and AA synthesis-related enzymes in the crop tissue of male and female pigeons during incubation and chick-rearing periods. Forty-two pairs of adult White King pigeons with 2 fertile eggs per pair were randomly divided into 7 groups by different breeding stages. The AA content of crop milk decreased from day 1 (R1) to day 25 (R25) of chick rearing (P < 0.05). In both male and female adult pigeons, the contents of Thr, Leu, Val, His, Asp, and Pro in plasma increased to maximum levels on R25. Parental sex effect and interaction between stage and sex were observed in the AA contents of pigeon plasma (P < 0.05). For AA transporters, the mRNA abundances of SNAT2, ASCT1, LAT1, and y+LAT2 in the male crops reached the highest value on day 17 of incubation (I17), and the peak mRNA levels of PAT-1, xCT, b0,+AT, and CAT1 were found on R7 (P < 0.05). In females, the abundances of ASCT1, B0AT1, asc-1, and CAT1 mRNA peaked on R1, whereas the maximum levels of LAT1, PAT-1, b0,+AT, and y+LAT2 were observed on R7. For enzymes involved in AA synthesis, the highest gene expressions of glutamate dehydrogenase 1, acetolactate synthase in both parent pigeons, and L-threonine 3-dehydrogenase in female pigeon crops were attained on I17. The expressions of ornithine-δ-aminotransferase, glutamic-oxal(o)acetic transaminase 1, glutamic-oxal(o)acetic transaminase 2, asparagine synthetase, serine hydroxymethyltransferase 2, and glutamic-pyruvic transaminase 2 in both sexes and argininosuccinate lyase and L-threonine 3-dehydrogenase in males were the highest on R1. In conclusion, AA used for pigeon crop milk formation may originate from plasma and intracellular synthesis. The genes involved in AA transport and synthesis varied significantly with sexual effects, indicating that other factors should be considered in future explorations of the mechanism of protein formation in crop milk.

Effects of in ovo feeding of L-lysine on hatchability, hatching time, and early post-hatch development in domestic pigeons (Columba livia)1

This study was conducted to evaluate the effects of in ovo feeding (IOF) of L-lysine (Lys) on hatchability and development in pigeon neonates. At day 13 of incubation, fertile eggs were injected with 200 μL of sterilized saline (0.75%, SC group), 1% Conc. Lys solution (Lys group, 2.11 mg Lys dissolved in 200 μL of sterilized saline), with controls not injected (NC group). The results showed that IOF of Lys decreased the hatchability (P < 0.05) compared with other groups, whereas the hatching time was not affected among groups. On day 14 of post-hatch (D14), the body weight (BW) of squabs received Lys IOF was increased relative to the NC group (P < 0.05). Squabs in Lys group exhibited higher (P < 0.05) body weight gain (BWG) than other groups from D14 to day of hatch (DOH). Meanwhile, IOF of Lys increased the brain relative weight on DOH (P < 0.05), and organ index of heart, legs, and gizzard on day 7 of post-hatch (D7) compared with other groups. In addition, the length index of duodenum, jejunum, or ileum had no difference between groups, as well as the weight index except the weight index of duodenum in Lys group was higher than that of SC group on DOH. However, squabs received Lys IOF showed lower villus height, crypt depth, and villus surface area of jejunum than NC group (P < 0.05) on DOH, and lower crypt depth than NC and SC groups on D7. The situation was improved by D14, although there was no significant difference in morphometric trait of jejunum between Lys group and NC group, squabs received Lys IOF showed higher villus height, crypt depth, and villus surface area of jejunum than NC group. In conclusion, the present study demonstrates that IOF of Lys has negative effects on hatchability and development of early post-hatch squabs, but the situation will be improved with the growth of age.

Leucine promotes the growth of squabs by increasing crop milk protein synthesis through the TOR signaling pathway in the domestic pigeon (Columba livia)

Leucine (Leu) plays a critical regulatory role in protein synthesis, however, the effects and molecular mechanisms of Leu on crop milk protein in the domestic pigeons (Columba livia) are still unknown. Therefore, the study aimed to investigate the effects of dietary Leu supplementation on crop milk protein synthesis and the growth performance of squabs and the possible underlying mechanism. A total of 240 pairs of breeding pigeons (1102.3 ± 9.5 g/pair) were randomly assigned to 1 of 5 treatments, including a positive control (PC) diet that had adequate crude protein (crude protein, CP = 18%; Leu = 1.30%), a negative control (NC) diet that was low in CP (CP = 16%, Leu = 1.30%), and NC diets supplemented with Leu at 0.15%, 0.45%, or 1.05%. Compared with the NC diet, 0.15 to 0.45% Leu supplementation decreased BW loss and increased relative crop weight, crop thickness, and protein levels in the crop tissue and milk of breeding pigeons. However, dietary supplementation with 1.05% Leu inhibited ADFI in breeding pigeons. Dietary supplementation with 0.15 to 0.45% Leu decreased the mortality rate and increased the BW, eviscerated yield, and breast muscle yield of young squabs. The protein expression levels of the target of rapamycin (TOR), ribosomal protein S6 kinase 1 (S6K1), ribosomal protein S6 kinase (S6), eukaryotic initiation factor 4E binding protein 1 (4EBP1), and eukaryotic translation initiation factor 4E (eIF4E) were upregulated in the crop tissue of breeding pigeons in PC, 0.15% and 0.45% Leu-supplemented groups. Collectively, these results indicated that 0.15 to 0.45% Leu supplementation could decrease BW loss, increase milk protein synthesis in the crop of breeding pigeons, and enhance the survival rate and growth performance of young squabs through the TOR signaling pathway.

Comparison of nonlinear models to describe the feather growth and development curve in yellow-feathered chickens

Feathers play a critical role in thermoregulation and directly influence poultry production. Poor feathering adversely affects living appearance and carcass quality, thus reducing profits. However, producers tend to ignore the importance of feather development and do not know the laws of feather growth and development. The objective of this study was to fit growth curves to describe the growth and development of feathers in yellow-feathered broilers during the embryonic and posthatching periods using different nonlinear functions (Gompertz, logistic and Bertalanffy). Feather mass and length were determined during the embryonic development and posthatching stages to identify which growth model most accurately described the feather growth pattern. The results showed that chick embryos began to grow feathers at approximately embryonic (E) day 10, and the feathers grew rapidly from E13 to E17. There was little change from E17 to the day of hatching (DOH). During the embryonic period, the Gompertz function (Y = 798.48e-203 431exp(-0.87t), Akaike's information criterion (AIC) = -0.950 × 103, Bayesian information criterion (BIC) = -0.711 × 103 and mean square error (MSE) = 559.308) provided the best fit for the feather growth curve compared with the other two functions. After hatching, feather mass and length changed little from the DOH to day (D) 14, increased rapidly from D21 to D91 and then grew slowly after D91. The first stage of feather molting occurred from 2 to 3 weeks of age when the down feathers were mostly shed and replaced with juvenile feathers, and the second stage occurred at approximately 13 to 15 weeks of age. The three nonlinear functions could overall fit the feather growth curve well, but the Bertalanffy model (Y = 116.88 × (1-0.86e-0.02t)3, AIC = 1.065 × 105, BIC = 1.077 × 105 and MSE = 11.308) showed the highest degree of fit among the models. Therefore, the Gompertz model exhibited the best goodness of fit for the feather growth curve during the embryonic development, while the Bertalanffy model was the most suitable model due to its accurate ability to predict the growth and development of feathers during the growth period, which is an important commercial characteristic of yellow-feathered chickens.

Best-fitting growth curves of the von Bertalanffy-Pütter type

Introduction: A large body of literature aims at identifying growth models that fit best to given mass-at-age data. The von Bertalanffy-Pütter differential equation is a unifying framework for the study of growth models.

Problem: The most common growth models used in poultry science literature fit into this framework, as these models correspond to different exponent-pairs (e.g., Brody, Gompertz, logistic, Richards, and von Bertalanffy models). Here, we search for the optimal exponent-pairs (a and b) amongst all possible exponent-pairs and expect a significantly better fit of the growth curve to concrete mass-at-age data.

Method: Data fitting becomes more difficult, as there is a large region of nearly optimal exponent-pairs. We therefore develop a fully automated optimization method, with computation time of about 1 to 2 wk per data-set. For the proof of principle, we applied it to literature data about 217 male meat-type chickens, Athens Canadian Random Bred, that were reared under controlled conditions and weighed 28 times during a time span of 170 D.

Results: We compared 2 methods of data fitting, least squares using the sum of squared errors (SSE), which is common in literature, and a variant using the sum of squared log-errors SSElog. For these data, the optimal exponent-pairs were (0.43, 4.06) for SSE = 2,208.6 (31% improvement over literature values for the residual standard deviation) and (0.89, 0.93) for SSElog = 0.04599. Both optimal exponents were clearly distinct from the exponent-pairs of the common models in literature. This finding was reinforced by considering the region of nearly optimal exponents.

Discussion: We explain, why we recommend using SSElog for data fitting and we discuss prognosis, where data from the first 8 wk of growth would not be enough.

Changes in hormone profiles, growth factors, and mRNA expression of the related receptors in crop tissue, relative organ weight, and serum biochemical parameters in the domestic pigeon (Columba livia) during incubation and chick-rearing periods under artificial farming conditions

The present study was conducted to determine the changes in concentrations of hormones and growth factors and their related receptor gene expressions in crop tissue, relative organ weight, and serum biochemical parameters in male and female pigeons during incubation and chick-rearing periods under artificial farming conditions. Seventy-eight pairs of 60-week-old White King pigeons with 2 fertile eggs per pair were randomly divided into 13 groups by different breeding stages. Serum prolactin and insulin-like growth factor-1 (IGF-1) concentrations in crop tissue homogenates were the highest in both male and female pigeons at 1 d of chick-rearing (R1), while epidermal growth factor (EGF) in female pigeons peaked at d 17 of incubation (I17) (P < 0.05). mRNA expression of the prolactin and EGF receptors in the crop tissue increased at the end of incubation and the early chick-rearing stage in both sexes. However, estrogen, progesterone, and growth hormone receptor expression each decreased during the early chick-rearing stage (P < 0.05). In male pigeons, IGF-1 receptor gene expression reached its peak at R7, while in female pigeons, it increased at the end of incubation. The relative weight of breast and abdominal fat in both sexes and thighs in the males was lowest at R7, and then gradually increased to the incubation period level. Serum total protein, albumin, and globulin concentrations increased to the highest levels at I17 (P < 0.05). Total cholesterol, triglyceride, and low-density lipoprotein reached their highest values at I17 in male pigeons and R25 in female pigeons (P < 0.05). In conclusion, hormones, growth factors, and their receptors potentially underlie pigeon crop tissue development. Changes in organs and serum biochemical profiles suggested their different breeding-cycle patterns with sexual effects.

Effects of in ovo feeding of l-arginine on hatchability, hatching time, early posthatch development, and carcass traits in domestic pigeons (Columba livia)

The objective of this research was to test the hypothesis that in ovo feeding of arginine (Arg) may improve hatchability and posthatch performance in domestic pigeons (). A completely randomized design ( = 3) with an Arg feeding treatment (Arg group, 1.14 mg Arg dissolved in 200 μL of 0.75% NaCl buffered saline as 1% concentration compared to total Arg in the egg), a buffered saline feeding treatment (SC group, 7.5 g NaCl dissolved in 1 L sterile distilled water as the concentration of poultry physiological saline), and a nonfeeding treatment (NC group) was used. Six squabs from each treatment were randomly sampled on day of hatch (DOH), posthatch d 7 (D7), and posthatch d 14 (D14), respectively. Hatchability, hatch time, BW, organ development, and carcass traits were examined. Results showed that in ovo feeding of the Arg solution increased ( < 0.05) the hatchability and advanced ( < 0.05) the hatching time in comparison with those of the other groups. Body weight of pigeon squabs that received Arg in ovo feeding was heavier ( < 0.05) on DOH and D14 than that of the NC group, and a greater ( < 0.05) BW gain from DOH to D14 and D7 to D14 was observed. Three clusters of 12 organs were classified according to the changes of organ indices. Squabs provided the Arg in ovo feeding treatment gained a priority in organ development. The heart index and gizzard index on D7 and the proventriculus index on D14 of squabs receiving Arg in ovo feeding were increased ( < 0.05) compared to those of the other groups. The brain index on DOH, the small intestine index and pancreas index on D7, and the liver index, pancreas index, and spleen index on D14 of squabs fed Arg were higher ( < 0.05) than those of the NC group. The spleen index on D7 and the small intestine index on D14 of squabs provided the Arg feeding treatment were enhanced ( < 0.05) compared with those of the SC group. The semieviscerated carcass weight of squabs receiving Arg was higher ( < 0.05) on D14 than that of other groups. The absolute weight of breast meat yield on D7 and breast meat yield percentage on D7 and D14 were improved ( < 0.05) in the Arg group compared with the NC group. The leg meat percentage on D7 and the carcass weight, eviscerated carcass weight, and absolute weight of breast meat yield on D14 were increased ( < 0.05) in the Arg group compared with those of the SC group. The results of this study indicate that in ovo feeding of pigeon embryos with Arg may have beneficial effects on squab hatch performance and early posthatch performance.

EAAT3 promotes amino acid transport and proliferation of porcine intestinal epithelial cells

Excitatory amino acid transporter 3 (EAAT3, encoded by SLC1A1) is an epithelial type high-affinity anionic amino acid transporter, and glutamate is the major oxidative fuel for intestinal epithelial cells. This study investigated the effects of EAAT3 on amino acid transport and cell proliferation through activation of the mammalian target of the rapamycin (mTOR) pathway in porcine jejunal epithelial cells (IPEC-J2). Anionic amino acid and cystine (Cys) transport were increased (P<0.05) by EAAT3 overexpression and decreased (P<0.05) by EAAT3 knockdown rather than other amino acids. MTT and cell counting assays suggested that IPEC-J2 cell proliferation increased (P<0.05) with EAAT3 overexpression. Phosphorylation of mTOR (Ser2448), ribosomal protein S6 kinase-1 (S6K1, Thr389) and eukaryotic initiation factor 4E-binding protein-1 (4EBP1, Thr70) was increased by EAAT3 overexpression and decreased by EAAT3 knockdown (P<0.05), as were levels of activating transcription factor 4 (ATF4) and cystine/glutamate antiporter (xCT) (P<0.05). Our results demonstrate for the first time that EAAT3 facilitates anionic amino acid transport and activates the mTOR pathway, promoting Cys transport and IPEC-J2 cell proliferation.

Di- and tripeptide transport in vertebrates: the contribution of teleost fish models

Solute Carrier 15 (SLC15) family, alias H⁺-coupled oligopeptide cotransporter family, is a group of membrane transporters known for their role in the cellular uptake of di- and tripeptides (di/tripeptides) and peptide-like molecules. Of its members, SLC15A1 (PEPT1) chiefly mediates intestinal absorption of luminal di/tripeptides from dietary protein digestion, while SLC15A2 (PEPT2) mainly allows renal tubular reabsorption of di/tripeptides from ultrafiltration, SLC15A3 (PHT2) and SLC15A4 (PHT1) possibly interact with di/tripeptides and histidine in certain immune cells, and SLC15A5 has unknown function. Our understanding of this family in vertebrates has steadily increased, also due to the surge of genomic-to-functional information from 'non-conventional' animal models, livestock, poultry, and aquaculture fish species. Here, we review the literature on the SLC15 transporters in teleost fish with emphasis on SLC15A1 (PEPT1), one of the solute carriers better studied amongst teleost fish because of its relevance in animal nutrition. We report on the operativity of the transporter, the molecular diversity, and multiplicity of structural-functional solutions of the teleost fish orthologs with respect to higher vertebrates, its relevance at the intersection of the alimentary and osmoregulative functions of the gut, its response under various physiological states and dietary solicitations, and its possible involvement in examples of total body plasticity, such as growth and compensatory growth. By a comparative approach, we also review the few studies in teleost fish on SLC15A2 (PEPT2), SLC15A4 (PHT1), and SLC15A3 (PHT2). By representing the contribution of teleost fish to the knowledge of the physiology of di/tripeptide transport and transporters, we aim to fill the gap between higher and lower vertebrates.