Heat stress is one of the major environmental stressors in the poultry industry resulting in substantial economic loss. Heat stress causes several physiological changes, such as oxidative stress, acid-base imbalance, and suppressed immunocompetence, which leads to increased mortality and reduced feed efficiency, body weight, feed intake, and egg production, and also affects meat and egg quality. Several strategies, with a variable degree of effectiveness, have been implemented to attenuate heat stress in poultry. Nutritional strategies, such as restricting the feed, wet or dual feeding, adding fat in diets, supplementing vitamins, minerals, osmolytes, and phytochemicals, have been widely studied and found to reduce the deleterious effects of heat stress. Furthermore, the use of naked neck (Na) and frizzle (F) genes in certain breed lines have also gained massive attention in recent times. However, only a few of these strategies have been widely used in the poultry industry. Therefore, developing heat-tolerant breed lines along with proper management and nutritional approach needs to be considered for solving this problem. Thus, this review highlights the scientific evidence regarding the effects of heat stress on poultry health and performances, and potential mitigation strategies against heat stress in broiler chickens and laying hens.

Background: The mechanism of egg formation in the oviduct of laying hens is tightly controlled; each segment of the oviduct contributes a unique component of the egg. Several genes/proteins are involved in the synthesis of a completely healthy egg. This implies a time- and tissue-specific expression of genes and proteins in the different oviductal segments. We used hens at different physiological stages and time points to understand the transcriptional regulation of egg-white (albumen) synthesis and secretion onto the eggs in the magnum of laying hens. This study used Next-Generation Sequencing and quantitative real-time PCR (qPCR) to detect the novel genes and the cognate biological pathways that regulate the major events during the albumen formation. Results: Magnum tissues collected from laying (n = 5 each at 3 h post-ovulation, p.o. and 15–20 h p.o.), non-laying (n = 4), and molting (n = 5) hens were used for differential gene expression analyses. A total of 540 genes (152 upregulated and 388 down-regulated) were differentially expressed at 3 h p.o. in the magnum of laying hens. Kyoto Encyclopedia of Genes and Genomes pathways analysis of the 152 upregulated genes revealed that glycine, serine, and threonine metabolism was the most-enriched biological pathway. Furthermore, the top two most enriched keywords for the upregulated genes were amino-acid biosynthesis and proteases. Nine candidate genes associated with albumen formation were validated with qPCR to have differential expression in laying, non-laying, and molting hens. Proteases such as TMPRSS9, CAPN2, MMP1, and MMP9 (protein maturation, ECM degradation, and angiogenesis); enzymes such as PSPH, PHGDH, and PSAT1 (amino-acid biosynthesis); RLN3, ACE, and REN (albumen synthesis, secretion and egg transport); and AVD, AvBD11, and GPX3 (antimicrobial and antioxidants) were recognized as essential molecules linked to albumen deposition in the magnum. Conclusions: This study revealed some novel genes that participate in the signaling pathways for egg-white synthesis and secretion along with some well-known functional genes. These findings help to understand the mechanisms involved in albumen biosynthesis.

The chicken oviduct is a unique organ in which ovulated yolk transforms into a complete egg. Ovarian hormones induce the cellular and biochemical changes in the oviducts during the egg formation and oviposition. Estradiol regulates the folliculogenesis, accumulation of yolk in the follicles, ovulation, and development of oviducts. Estradiol also induces glandular development and expression of the genes responsible for egg white proteins. Progesterone induces the ovulation of yolk from the ovary, and development of oviductal glands. In addition, several genes are spatiotemporally expressed in the magnum for albumen synthesis and deposition around the yolk, in the isthmus for shell membranes synthesis, and in the uterus for eggshell biomineralization. This chapter highlights the involvement of hormones, genes/proteins, and their interaction for egg formation in the oviduct of laying hens.

Heat stress (HS) poses a substantial challenge in the poultry sector, resulting in considerable economic losses as it negatively impacts the well-being and productivity of chickens. Dried plum (DP) is a rich source of minerals, vitamins, antioxidants, and phenolic compounds. Studies have indicated that DP offers various health advantages, including preserving the body's redox system, immune function, and calcium balance. In our previous study, DP supplementation improved overall growth performance and intestinal health metrics in heat-stressed broilers. Considering the beneficial effects of DP on health, we hypothesized that adding DP to the diet would mitigate the harmful impacts of heat stress in the liver of broiler chickens. Day-old unsexed broiler chicks (n = 72) were raised under standard conditions and randomly assigned to three treatment groups (n = 24/group): 1) Control, 2) heat stress with basal diet (HS), and 3) heat stress with supplement (DP). During the finisher stage, the DP group received feed containing 2.5% DP during treatment, while the other groups were given a standard finisher diet. After 21 d, birds in the HS and DP groups were subjected to cyclic heat stress conditions for 3 wk. The heat stress conditions involved exposing the birds to a temperature of 33-35°C for 8 h during the daytime. In contrast, the birds in the Control group were raised under normal conditions with temperatures ranging from 22-24°C. DP supplementation significantly increased (P < 0.05) heat shock factor 1 (HSF1) expression in the liver compared to the Control group. DP supplementation significantly increased (P < 0.05) thioredoxin (TXN), peroxiredoxin (PRDX), insulin-like growth factor 1 (IGF1), and methyl-CpG binding domain (MBD4) expression in the DP group compared to the HS group. Fructose-1,6-bisphosphatase 1 (FPB1) expression was significantly decreased (P < 0.05) in the DP group compared to the HS group. Solute Carrier Family 3 Member 1 (SLC3A1), DNA methyltransferase 1 (DNMT1), DNA methyltransferase 3 alpha (DNMT3A), ten-eleven translocation methylcytosine dioxygenase 2 (Tet2), ten-eleven translocation methylcytosine dioxygenase (Tet3), and thymine DNA glycosylase (TDG) expression were significantly increased (P < 0.05) in the DP group compared to the other treatment groups. In conclusion, post-hatch DP supplementation lessened the negative effects of HS on broiler chickens by upregulating genes related to heat shock, antioxidants, growth, nutrient transporters, and epigenetics in the liver.

In Nepal, a predominantly Hindu country, most communities consider the cow as a sacred animal leading to their special place in society. However, male calves are neglected because of their limited utility in the context of religiously restricted beef consumption. A cross-sectional survey was conducted among the dairy farmers of the Chitwan district in the central region of Nepal to understand the rearing practices of dairy calves and the associated animal welfare concerns. A majority of the producers (70%) that participated in the survey reared female calves to be replacement dairy animals, hence providing better care and management on the farm. Male calves, however, were vulnerable to indiscriminate removal following non-humane methods; 20% of calves starved by feed withdrawal, and 20% of calves chased away from the farm to live as stray animals. Therefore, the religious, sentimental, economic, and ethical analysis of the welfare situation needs to be assessed in a broader context and a sustainable policy needs to be implemented to change the overall attitude of the farmers towards male dairy calves.