Probiotics are live microorganisms which, when administered in adequate amounts, confer health benefits to the host. The use of probiotics in poultry has increased steadily over the years due to higher demand for antibiotic-free poultry. The objective of this systematic review is to present and evaluate the effects of probiotics on the nutrient utilization, growth and laying performance, gut histomorphology, immunity, and gut microbiota of poultry. An electronic search was conducted using relevant keywords to include papers pertinent to the topic. Seventeen commonly used probiotic species were critically assessed for their roles in the performance and gut health of poultry under existing commercial production conditions. The results showed that probiotic supplementation could have the following effects: (1) modification of the intestinal microbiota, (2) stimulation of the immune system, (3) reduction in inflammatory reactions, (4) prevention of pathogen colonization, (5) enhancement of growth performance, (6) alteration of the ileal digestibility and total tract apparent digestibility coefficient, and (7) decrease in ammonia and urea excretion. Thus, probiotics can serve as a potential alternative to antibiotic growth promoters in poultry production. However, factors such as the intestinal health condition of birds, the probiotic inclusion level; and the incubation conditions, feedstuff, and water quality offered to birds may affect the outcome. This systematic review provides a summary of the use of probiotics in poultry production, as well as the potential role of probiotics in the nutrient utilization, growth and laying performance, and gut health of poultry.

Early growth and development of the gastrointestinal tract are of critical importance to enhance nutrients' utilization and optimize the growth of poultry. In the current production system, chicks do not have access to feed for about 48–72 h during transportation between hatchery and production farms. This lag time affects early nutrient intake, natural exposure to the microbiome, and the initiation of beneficial stimulation of the immune system of chicks. In ovo feeding can provide early nutrients and additives to embryos, stimulate gut microflora, and mitigate the adverse effects of starvation during pre-and post-hatch periods. Depending on the interests, the compounds are delivered to the embryo either around day 12 or 17 to 18 of incubation and via air sac or amnion. In ovo applications of bioactive compounds like vaccines, nutrients, antibiotics, prebiotics, probiotics, synbiotics, creatine, follistatin, L-carnitine, CpG oligodeoxynucleotide, growth hormone, polyclonal antimyostatin antibody, peptide YY, and insulin-like growth factor-1 have been studied. These compounds affect hatchability, body weight at hatch, physiological functions, immune responses, gut morphology, gut microbiome, production performance, and overall health of birds. However, the route, dose, method, and time of in ovo injection and host factors can cause variation, and thereby inconsistencies in results. Studies using this method have manifested the benefits of injection of different single bioactive compounds. But for excelling in poultry production, researchers should precisely know the proper route and time of injection, optimum dose, and effective combination of different compounds. This review paper will provide an insight into current practices and available findings related to in ovo feeding on performance and health parameters of poultry, along with challenges and future perspectives of this technique.

Heat stress in poultry is a serious concern, affecting their health and productivity. To effectively address the issue of heat stress, it is essential to include antioxidant-rich compounds in the poultry diet to ensure the proper functioning of the redox system. Microalgae (Spirulina platensis) are rich in antioxidants and have several health benefits in humans and animals. However, its role in health and production and the underlying mechanism in heat-stressed broilers are poorly understood. This study aimed to determine the effect of microalgae supplementation on the health and production of heat-stressed broilers. Cobb500 day-old chicks (N = 144) were raised in litter floor pens (6 pens/treatment and 8 birds/pen). The treatment groups were: 1) no heat stress (NHS), 2) heat stress (HS), and 3) heat stress + 3% microalgae (HS+MAG). The broilers in the HS+MAG group were fed a diet supplemented with 3% microalgae, whereas NHS and HS groups were fed a standard broiler diet. Broilers in the NHS were raised under standard temperature (20°C–24°C), while HS and HS+MAG broilers were subjected to cyclic heat stress from d 22 to 35 (32°C–33°C for 8 h). Heat stress significantly decreased the final body weight, whereas the supplementation of microalgae increased the final body weight of broilers (P < 0.05). The expressions of ileal antioxidant ( GPX3 ), immune-related ( IL4 ), and tight-junction ( CLDN2 ) genes were increased in microalgae-supplemented broilers compared to heat-stressed broilers (P < 0.05). The ileal villus height to crypt depth ratio was improved in microalgae-supplemented broilers (P < 0.05). In addition, microbial alpha, and beta diversities were higher in the HS+MAG group compared to the HS group (P < 0.05). There was an increase in volatile fatty acid-producing bacteria at the genus level, such as Ruminococcus, Ocillospira, Lactobacillus, Oscillobacter, Flavonifractor, and Colidextribacter in the group that received microalgae supplementation. In conclusion, dietary supplementation of microalgae improved the growth performances of heat-stressed broilers by improving their physiogenomics. Thus, the dietary inclusion of microalgae can potentially mitigate heat stress in broilers.

Microalgae are becoming potential sustainable feed ingredients, whereas terrestrial feedstuffs are becoming scarce and costly. They are rich in nutritional and functional values but have lower digestibility. This study evaluated the effects of microalgae with or without xylanase supplementation on growth performance and gut health of broiler chickens. A total of 162-day-old Cobb 500 chicks were raised for 35 d. Birds were fed with either 1 of the 3 dietary treatments: 1) corn-soybean meal-based diet (CON), 2) CON + 3% microalgae (MAG), and 3) MAG + xylanase (MAG+XYN) in 2 phases (starter: d 0-21 and finisher: d 22-35) in mash form. Each dietary treatment had 6 replicates, with 9 birds in each replicate. The level of significance was considered at the P value <0.05. The BW, ADG, and ADFI were significantly higher in MAG by 50%, 52.5%, and 42.4%, respectively, and MAG+XYN by 44.1%, 49.7%, and 38.6%, respectively, compared to the CON group. No significant difference was observed for FCR; however, FCR was reduced by 6.3% in both MAG and MAG+XYN groups compared to the CON group. The carcass and organ weight relative to the total body weight were not significantly different among the treatments. The expressions of Zonula occludens 1 (ZO1), Cluster of differentiation 56 (CD56), and Solute carrier family 7 member 7 (SLC7A7) were significantly modulated, for example, by 3.7, 3.9, and 3.3 folds, respectively, in the MAG group compared to CON and 0.8, 0.6, and 1.1 folds, respectively, in the MAG group compared to MAG+XYN groups on d 35. Villi surface area (VSA) of ileum tended to increase on d 3 (P = 0.0725) and d 35 (P = 0.0785) in the MAG and MAG+XYN groups, compared to the CON group. The results suggest that adding microalgae with or without xylanase to broiler's diet could promote growth performance and show a tendency to improve gut health parameters. The nutrient profile and its functional properties make microalgae a valuable resource to the poultry industry as a part substitution of corn and soybean meal and a functional feed supplement to modulate the gut health of broilers.

The effect of dietary inclusion of Moringa oleifera leaf powder (MLP) on the growth, meat quality, carcass characteristics, hematobiochemical profile, and cecal bacteria of broiler chicken was investigated in this research trial. In this study, 192-day-old Arbor Acre broiler chicks were assigned in a completely randomized design to three groups: control, antibiotic, and MLP. A standard basal diet was given to the control group, while the antibiotic group received 75 mg/kg chlortetracycline, and the MLP group received 100 mg/kg M. oleifera leaf powder supplemented basal diet. Each group was further divided into eight replicates consisting of eight birds each, and the trial ran for 35 days. Among the groups, the MLP-fed broilers achieved the highest final body weight (FBW), average daily gain (ADG), and average daily feed intake (ADFI). Notably, the FCR for the whole experimental period was lower in the MLP group, indicating a more efficient use of feed for growth. Supplementation of MLP with basal diet significantly increased (p < 0.05) the weight of thighs and drumsticks relative to live weight %, while the spleen and abdominal fat weight (% of live weight) were significantly decreased (p < 0.05). Adding MLP to the diet improved the meat quality of broilers, as indicated by the highest pH of meat at 45 min and the lowest cooking loss (%) observed in this group. MLP exhibited hypocholesterolemic and hypolipidemic effects, with the lowest total cholesterol and triglyceride levels compared to non-supplemented groups. The hematological profile revealed that the MLP group exhibited the highest RBC count and Hb level, while also showing the lowest H/L ratio. Moringa supplementation significantly (p < 0.05) modulated the cecal bacterial population, reducing pathogenic E. coli and Shigella spp. while increasing beneficial Lactobacillus spp. and the total aerobic plate count (TAPC). In conclusion, Moringa oleifera leaf powder (MLP) can be used as a natural feed supplement for promoting the growth, meat quality, healthy blood, and sound health of broilers.

Oyster mushroom stem residue, a by-product with medicinal and nutritive values, might be a prospective feed supplement in poultry nutrition. The study focused on evaluating the impact of oyster mushroom (Pleurotus ostreatus) stem residue (OMSR) powder supplementation on growth performance, carcass traits, meat quality, blood characteristics, and the cecal bacterial count in Arbor Acres broilers raised 35 d. A total of 144 day-old chicks, with an average weight of 40.27± 2.45 g, were divided into 3 groups: control (received a standard basal diet), antibiotic (basal diet + 75 mg/kg chlortetracycline), and OMSR (fed a basal diet with 300 mg/kg OMSR), where each group comprises 8 replications of 6 chicks. Supplementation of 300 mg/kg of OMSR powder in the broiler diet significantly (P < 0.05) enhanced the average daily gain (ADG) and final body weight as opposed to the control and antibiotic treatments, though the average daily feed intake was not influenced by OMSR supplementation during the whole experimental period. However, in comparison to the control and antibiotic groups, OMSR significantly reduced the postmortem breast meat drip loss percentage (P < 0.05) at 24 hours and on the seventh d. Furthermore, the OMSR group reported significantly elevated levels of Hb and RBC counts (P < 0.05), and decreased levels of serum triglyceride (TG) and total cholesterol (TC) concentrations (P < 0.05) on d 35 in comparison to broilers in the control and antibiotic groups. Additionally, the OMSR group exhibited an improved Heterophil/Lymphocytes (H/L) ratio (P < 0.05) relative to the broilers of the control and antibiotic groups. In contrast, the inclusion of OMSR in the broiler diet did not significantly (P > 0.05) influence other serum biochemical and hematological values tested. Broilers in OMSR group had reduced number (P < 0.05) of E. coli and Salmonella spp., but higher presence of Lactobacillus spp. (P < 0.05) in contrast to the control broilers. To summarize, the study's findings revealed that 300 mg of OMSR powder supplementation per kg of basal diet could be act as a natural growth promoter, and confer favorable effects on health and meat quality of broilers.