Fertile eggs were obtained from a commercial flock of Ross broiler breeders (51 weeks old) and candled to determine the presence of hairline or star cracks. Eggs (5400 total) were assigned in equal numbers to 3 treatments (hairline-cracked, star-cracked, and normal eggs) and incubated for 21 days. Upon hatching, 10 chicks per treatment were euthanized, and organ weights were measured. Compared with normal eggs, the presence of egg shell cracks (regardless of type) resulted in higher egg weight loss at the time of transfer; a decrease in hatchability, hatch of fertile eggs, chick length, yolk-free body mass (P < 0.01), and percentage of hatchling breast and liver weight (P < 0.05); and an increase in the contamination rate of eggs (P < 0.01). Weight loss in hairline-cracked eggs was significantly higher than in star-cracked eggs (P < 0.001). Percentage hatchability and body weight of chicks hatched from star-cracked eggs was higher than in chicks from hairline-cracked eggs (P < 0.001). Crack type did not have a significant effect on chick length and body weight uniformity; however, the Pasgar score as a quality indicator was higher in chicks hatched from star-cracked eggs than those from hairline-cracked eggs (P < 0.05). There were no significant differences among treatments in terms of heart and small intestine weight. The contamination rate of hairline-cracked eggs was higher than that of star-cracked (P < 0.01). A higher incidence of embryonic mortality was observed during days 1-8 of incubation for shell-cracked eggs (P < 0.001). Total embryonic mortality in hairline-cracked, star-cracked, and normal eggs was 51.1%, 36.6%, and 13.3%, respectively. This study showed that egg shell cracks reduced incubation parameters and chick quality. The negative effects of hairline cracks were more pronounced than those of star cracks.

The microbiota includes prokaryotes (archaea and bacteria) and eukaryotes. Archaea are single‐celled prokaryotes and essential part of gut microbiome. Researches on archaea in ruminants and humans are more than mono‐gastric. The low abundance of archaea in the gut depends on the method used (metagenomics or meta‐transcriptomic) and age of people or poultry. The lack of complete recognition of archaea is due to their small number and method of identifying them (16S rRNA gene primers). The uses of archaea include analytical kit, reduce oil pollution, archaeosomes or drugs production, vaccines agents, lipid carriers in the pharmaceutical industry and molybdenum extraction in the nuclear industry. The nutritional functions of methanogenic archaea including feed utilization (ruminants) and efficiency, hydrogen reducing (human), fat deposition and enhancement of energy harvesting in mice, CAZymes genes, cecal fermentation, syntrophic potential, carotenoid source and improved transit time and appetite and SCFAs production. Archaea acting as antibiotics (produce archaeocins, sulfolobicins and halocin KPS1) and as probiotics (archaeobiotics) can reduce TMAU (trimethylaminuria) disease, cardiovascular diseases (CVDs), and atherosclerosis, brain abscess, cancer, colorectal cancer, inflammatory bowel disease (IBD), constipation, obesity, food allergies, asthma and anti‐inflammation which can be prevented by using archaea, and other functions include energy homeostasis, heat shock protein (HSP) production and reducing aging.

The poultry gastrointestinal microbiome consists of more than 900 bacterial species and their metabolites; it serves as an indicator of bird health and is influenced by nutrition, medication, and other factors. Dysbiosis is a form of reduced microbial diversity, characterised by the loss of beneficial microbes, the expansion of opportunistic microbes, and the disruption of tight junctions, as well as raised pro-inflammatory cytokines (interleukin-6 and interleukin-17), tumour necrosis factor-α, and Enterobacteriaceae, and decreased short-chain fatty acids. Dysbiosis leads to various disorders, including liver disorders, metabolic disease, cardiovascular disease, and neurological problems. It also impacts several bodily systems, such as the gastrointestinal tract, kidneys, the gut-liver axis (liver disease, hepatocellular carcinoma, autoimmune liver disease, and metabolic-associated fatty liver disease), the gut-lung axis (pneumonia and chronic obstructive pulmonary disease), the gut-microbiota axis (irritable bowel syndrome, inflammatory bowel disease, and constipation or stool hardness), and the gut-islet axis (hypertension, hyperglycaemia, diabetes, and hypercreatinaemia syndrome). Many factors, including medications (antibiotics, anti-tumour, and immunosuppressants), environmental pollutants (heavy metals, pesticides, microplastics, and atmospheric particulates), high levels of nutrients (protein, fat, salt, and sugar), and others (age, disease, habits, and genes), cause and enable gastrointestinal dysbiosis to develop. Nutritional strategies such as the administration of probiotics, prebiotics, antibiotics, or phytogenic feed additives, and the consumption of a high-quality, balanced diet, as well as early detection of gut health malfunction and an emphasis on increasing bird resilience, can reduce the risk of dysbiosis, modify the gut microbial balance, and make microbial eubiosis possible.

Effects of pre-incubation upside-down positioning of eggs (from collection time at the farm until delivery to the hatchery, which can be up to 5 days) and breeder flock age on hatchability and chick quality were investigated. In this study, 5400 eggs from broiler breeder flocks were assigned to two groups (upside-down and normal position eggs as Control group). The birds were divided in three age groups (46, 73 and 107 weeks of age). Each age group had six replicates with 150 eggs per replicate. The results indicated that keeping eggs in an upside-down position reduced (P < 0.05) hatchability by 4.3% compared with the Control (normal position) group. Also, reversed egg positioning significantly increased relative intestine weight (P < 0.05) and percentage of embryo mortality between 18–19 days of incubation (P < 0.01). Flock age affected (P < 0.01) hatchability, egg shape index, chick cull percentage, infertile eggs, total embryo mortality, percentage egg weight loss and chick yield. The lowest hatchability and the highest percentage egg weight loss were observed in flocks with 107 weeks of age.