JAHP_13_s1_127-135

INTRODUCTION

A major environmental problem influencing dairy cattle all over the world, especially within areas alongside high ambient temperatures, and humidity, is heat stress. Heat stress affects important physiological and reproductive processes that define the general output, and sustainability for dairy farms, therefore impacting not just simple pain however, and also other aspects for physiology. Elevated temperatures cause dairy cows to have a significant drop within reproductive efficiency, which changes hormone production, compromises ovarian function, and lowers conception rates (Menta et al., 2022). Developing mitigating methods and improving genetic resistance within dairy cattle depends upon an understanding for the molecular processes behind heat stress-induced reproductive failure given the economic, and welfare consequences. The endocrine system is one for the main physiological reactions to heat stress; specifically, gonadotropin production including luteinizing hormone (LH) and follicle - stimulating hormone (FSH) disturbs it. Essential favor follicular growth, and ovulation, these hormones have been linked to lower conception rates when their levels are disrupted during heat stress (Dahl et al., 2020). Particularly within cows alongside reduced circulating estrogen levels, past studies have shown, that heat stress reduces the pulsatility, and amplitude for gonadotropin secretion (Tao et al., 2020; Kareem et al., 2023; Aziz et al., 2023). All for which compromise reproductive performance within dairy cattle, this hormonal imbalance causes delayed ovulation, less than ideal follicular development, and decreased corpus luteum activity.

The physiological effects of heat stress lead to significant genetic and transcriptomic changes that affect dairy cows. Through modern RNA sequencing technology scientists have identified heat adaptation events in alternative splicing along with differently expressed genes (Hu et al., 2022). Scientific investigations confirmed heat-stressed animals develop major molecular expression pattern variations that control both stress reaction mechanisms and immunity and metabolic changing capacity (Garner et al., 2020; Kadhim et al., 2024; Al-Sailawi et al., 2024; Mohsen et al., 2024). Heat-stressed cells depend on RNA splicing control genes such as RBM25 and LUC7L3 to properly adapt to thermal changes according to Hu et al. (2022). Moreover, the effect for heat stress upon reproductive function differs depending upon the climatic circumstances, which emphasizes the need for environmental adaptation plans. Various researches have established that summer conceptions rates decreased by 52% to 24% compared to winter rates across multiple geographic locations (Tao et al., 2020). The long-term approach for dairy output sustainability in hot areas includes heat-tolerant genetic selection along with immediate cooling methods such as using shade and fans and water sprinklers to decrease reproductive losses (Brito et al., 2021). The main genetic along with physiological responses for dairy cows to heat stress are shown in Figure 1 where the figure links gene expression with thermotolerance and oxidative stress and metabolic adaptations.

The analysis of Figure 1 demonstrates which genes are activated in response to thermotolerance as well as oxidative stress and metabolic adaptations showing the primary genetic and physiological methods that dairy cows use to manage heat stress. The increase of thermotolerance and immune competence because of heat shock proteins (HSPA4, HSP90AB1, HSPH1, AHSA1) has been observed by Garner et al. (2020) though metabolic changes reduce acetyl-CoA synthesis and increase lipolysis which elevates plasma free fatty acids (NEFA) thus exacerbating mortality risks (Hu et al., 2022). Heat stress influences skin temperature management through BDKRB1 and BDH2 markers because these markers alter blood pressure regulation (Tao et al., 2020). The molecular changes confirm how dairy cows link their physiological heat stress responses with their genetic adaptability through complete mechanisms. This work attempts to combine environmental, genetic, and hormonal viewpoints to provide a whole picture for heat stress-induced reproductive failure within dairy cows. We want to clarify the molecular processes involved within heat stress adaptation, and find possible indicators favor raising reproductive efficiency through combining hormonal analysis alongside transcriptome profiling alongside RNA-Seq. through means for this interdisciplinary approach, we want to contribute to the creation for focused breeding programs, and management techniques improving the resilience for dairy cattle against stresses resulting coming from climate change.

MATERIALS AND METHODS

This research evaluated dairy cows’ physiological as well as hormonal together with genetic reactions to heat stress. A detailed investigation of heat stress effects on reproduction performances included environmental data collection and hormonal analysis together with gene expression monitoring. The research took place at a dairy farm situated in Erbil Province which operated under managed environmental settings.

Animal Selection and Experimental Design

We have studied lactating Holstein cows located in controlled environments. The research groups included Heat Stress (HS) animals which received testing together with Thermoneutral (TN) animals. We monitored environmental conditions especially the temperature-humidity index (THI) to define the cattle groups (Luo et al., 2021). Researchers applied a THI threshold of 68 to identify heat stress conditions while the HS group spent at least a minimum of ten consecutive days above this threshold (Yue et al., 2020).

Hormonal Profiling

Blood samples were obtained during various stages of the estrous cycle in order to study the endocrine effects of heat stress. Researchers measured estradiol along with LH and FSH in blood plasma through enzyme-linked immunosorbent assay (ELISA). A statistical analysis of LH pulse amplitude and frequency throughout the study provided data on gonadotropin secretion patterns caused by heat exposure according to Gilad et al. (1993). The effects of heat stress on pituitary functions in animals were researched through GnRH stimulation tests as described by Kim et al. (2021).

Transcriptomic Analysis

A TRIzol reagent extraction procedure was used by the researchers to obtain PBMCs RNA which underwent quality assessment testing before library construction. The Illumina sequencing system performed full transcriptomic RNA-Seq analysis through RNA-Seq while detecting gene expression differences and alternative splicing effects which led to the reported findings presented in Hu et al. (2022). The analysis performed computational bioinformatics steps involving HISAT2 alignment followed by feature counts quantification and DESeq2 differential expression discovery (Sun et al., 2022). Researchers used both Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases to discover heat stress adaptation related genes and pathways (Huang et al., 2022).

Physiological Assessments

The evaluation of heat stress physiological changes included regular measurements of rectal temperature alongside respiratory rate and drooling score assessment. Analysis of Variance (ANOVA) enabled statistical comparison between TN and HS groups along with subsequent Tukey’s post-hoc testing according to Xiong et al. (2020). Validation of key heat stress-responsive gene expression levels used quantitative real-time PCR (qRT-PCR) methodology (Daniels et al., 2021).

Significance of the Study

This study integrates multiple levels of data analysis to reveal complete understanding of heat stress mechanisms that affect dairy cow reproduction. The research results will guide the future creation of efficient management approaches and breeding initiatives for dairy cattle heat tolerance improvement (Brito et al., 2020).

RESULTS AND DISCUSSION

Effect for Heat Stress Upon Physiological Parameters

Rectal temperature, respiration rate, and drooling score were among the physiological factors greatly influenced through heat stress. Rectal temperatures (39.5 ± 0.2°C) for cows within the heat stress (HS) group are notably higher than those within the thermoneutral (TN) group (38.4 ± 0.1°C) Li et al. (2020). Comparatively, within HS circumstances, respiration rates rose significantly; average breath count within TN cows used to be 45 breaths per minute, whereas beneath HS conditions it used to be 85 breaths per minute. Another compensatory mechanism shown like improving evaporative cooling (Cheruiyot et al., 2022) used to be increased drooling. These results complement earlier studies showing how heat stress negatively affects thermoregulating reactions within dairy cows (Freitas et al., 2021).

Emphasizing the thermal strain impact of heat stress (HS) exists predominantly through thermal strain and metabolic changes for high ambient temperatures which becomes evident through the data shown in Table 1 regarding dairy cows’ essential physiological parameters. Dairy cows exposed to hot stress temperatures experienced a substantial increase in their body temperature to 39.5 ± 0.2°C when compared to their normal temperature of 38.4 ± 0.1°C (p = 0.05). Finding has documented these known thermal effects that heat stress causes in ruminants as they lead to poor thermoregulation through decreased evaporative cooling functions and greater metabolic heat production (Li et al., 2020; Hoffmann et al., 2019). The body’s core temperature deviates from stable levels thus altering metabolic efficiency along with decreased feed intake to hurt reproductive success (Cheruiyot et al., 2022; Freitas et al., 2021).

Table 1: Physiological parameters beneath heat stress and thermoneutral conditions.

Parameter	Thermoneutral (TN)	Heat Stress (HS)	P-Value
Rectal Temperature (°C)	38.4 ± 0.1	39.5 ± 0.2	<0.05
Respiration Rate (breaths/min)	45 ± 3	85 ± 5	<0.05
Drooling Score	1.2 ± 0.3	3.6 ± 0.4	<0.05

The respiration rate experienced a matching increase because the rate averaged 85 ± 5 breaths/min inside HS but was 45 ± 3 breaths/min, p = 0.05. Under heat stress conditions dairy calves increase their respiratory rate to manage extra body heat through panting according to Wang et al. (2019) and Morrell (2020). Heavily increased panting activities lead to respiratory alkalosis that disrupts blood pH parameters as well as electrolyte stability therefore worsening hormonal abnormalities and reproductive problems (Saravanan et al., 2020; Laporta et al., 2020).Furthermore, drooling ratings were much greater within heat-stressed cows (3.6 ± 0.4 vs. 1.2 ± 0.3, p = 0.05), therefore showing more salivation like a thermoregulatory response. Although this physiological reaction is meant to improve evaporative cooling, too much drooling may cause water, and electrolyte losses, therefore compromising the hydration status, and metabolic performance (Otto et al., 2019; Alhussien and Dang, 2019). Extended dehydration beneath HS circumstances lowers reproductive hormone circulation, which directly affects ovarian follicular formation, and estrous cyclicity (Mishra, 2021; Talker et al., 2022).

Effect for Heat Stress Upon Endocrine Function

Heat stress modified an array of molecular indicators which belong to metabolic and immunological categories. Heat-stressed cows had reduced adrenocorticotropic hormone (ACTH) levels, suggesting a possible adaption mechanism to protracted temperature exposure (Bohlouli et al., 2022). beneath heat stress, blood urea nitrogen (BUN), and cortisol (COR) levels were also lower, suggesting metabolic changes brought upon through higher energy consumption, and decreased feed intake (Wang et al., 2019). Upon the other hand, the HS group showed notably greater amounts for heat shock protein 70 (HSP70), and norepinephrine (NE), which reflects stronger cellular stress responses, and sympathetic nervous system activation (Laporta et al., 2020).

The findings shown within Figure 1 provide important new perspectives upon how heat stress influences dairy cow endocrine control for reproduction. Beneath heat stress, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) release showed a significant decrease coming from thermoneutral settings. These results highlight the detrimental impact for heat stress upon the hypothalamic-pituitary-gonadal (HPG) axis, which is vitally important favor controlling ovarian development, and ovulation (Morrell, 2020; Li et al., 2020) (Figure 2).

Reaching peak levels around the 4-hour mark post-injection, the LH, and FSH response to gonadotropin-releasing hormone (GnRH) responded beneath thermoneutral conditions within line alongside normal reproductive physiology (Gilad et al., 1993; Laporta et al., 2020). Beneath heat stress, nevertheless, both hormones showed a reduced response alongside lower peak concentrations, and a delayed return to baseline. Heat-induced disturbances within GnRH output coming from the hypothalamus like well like decreased responsiveness for the anterior pituitary gland to GnRH stimulation (Bohlouli et al., 2022; Otto et al., 2019) most likely explain this suppression.

The specific stress reactions of heat explain the biological mechanisms by which this suppression happens. The main physiological effect of heat stress involves elevating cortisol levels that blocks GnRH release and reduces production of FSH and LH (Wang et al., 2019; Saravanan et al., 2020). Heat stress leads to dysfunction in gonadotropin function as well as disruption of ovarian follicular development through both inflammatory responses resulting from HSPs increases and oxidative marker elevations (Freitas et al., 2021; Hoffmann et al., 2019). Moreover, heat stress is well recognized to hasten metabolic needs, and redirect energy away coming from reproduction to thermoregulating systems (Cheruiyot et al., 2022). This metabolic change might help to explain the lowered ovarian reactivity to gonadotropins, therefore affecting estradiol production, less optimum follicular maturation, and finally lower conception rates within dairy cows (Brito et al., 2021; Laporta et al., 2020).

Effect for Heat Stress Upon Biochemical Parameters

The exposure to heat stress negatively impacted multiple physiological indicators which control metabolic and immunological procedures. Heat stress exposure of cows reduced their adrenocorticotropic hormone (ACTH) levels which suggest an adaptive mechanism within prolonged periods of high temperatures according to Bohlouli et al. (2022). beneath heat stress, blood urea nitrogen (BUN), and cortisol (COR) levels were also lower, indicating metabolic adaptations resulting from elevated energy use and decreased feed consumption (Wang et al., 2019). HSP70 together with NE developed elevated levels in HS group members because cellular stress responses and sympathetic nervous system activation occurred at more prominent levels (Laporta et al., 2020).

Figure 3 presents qualitative changes in dairy cow metabolism between heat stress conditions compared to thermoneutral environments. The lower adrenocorticotropic hormone (ACTH) level amounts (p = 3.31 × 10⁻⁹ demonstrate that stress impedes hypothalamic-pituitary-adrenal (HPA) axis responses to elevated cortisol levels (p = 7.78 × 10⁻10). A rise in nervous system activity indicated by elevated norepinephrine (NE) (p = 1.20 x 10⁻15) levels results in decreased ovarian blood flow but increased stress protein HSP70 expression at (p = 2.90 x 10⁻15) aids cellular protective measures during stress. Furthermore, beneath HS, triiodothyronine (T3) levels (p = 1.29 × 10⁻⁷) were lowered, indicating a metabolic change, that gives heat dissipation first priority atop energy-intensive reproduction activities (Saravanan et al., 2020; Wang et al., 2019). Comparably, the drop within blood urea nitrogen (BUN) (p = 1.26 × 10⁻3) points to decreased protein metabolism, and food availability, which can have a deleterious effect upon follicular growth, and fertility. beneath heat stress, the inhibition for superoxide dismutase (SOD) activity (p = 2.49 × 10⁻2) emphasizes even more oxidative stress, which is a main cause for granulosa cell dysfunction, and reduced steroidogenesis (Bohlouli et al., 2022; Talker et al., 2022).

These results are highly correlated alongside the hormonal and reproductive abnormalities seen within heat-stressed dairy cows, like seen within Figure 1, where beneath HS circumstances FSH and LH output used to be considerably lowered. Together alongside changed metabolic and oxidative pathways, the disturbance within endocrine function emphasizes the requirement for genetic selection favor thermotolerance, and better management measures to preserve fertility beneath heat stress settings (Cheruiyot et al., 2022; Otto et al., 2019). Finding heat-resistant genetic markers and precision monitoring methods to minimize these impacts, and improve dairy cow reproductive efficiency within hot areas should be the main priorities for future studies.

Effect for Heat Stress Upon Gene Expression

The stressor heat condition activated considerable changes in cellular gene expressions as determined by transcriptomic assessment. Widely expressed genes were identified following heat stress exposure as members of the three biological groups that affect oxidative stress and inflammation while controlling metabolism. The thermal stress activates HSPA4 and HSPH1 proteins which protect cells from damage according to Otto et al. (2019) research. Research data indicated that Follicular development essential genes FSHR and LHCGR demonstrated reduced expression which points to ovarian function disturbances (Bohlouli et al., 2022).

Biochemical changes show significant heat stress (HS) affecting endocrine, metabolic, and oxidative stress indicators within dairy cows (Table 2). Under heat stress, a notable drop within adrenocorticotropic hormone (ACTH) levels (p < 0.05) points to a suppression for the hypothalamic-pituitary-adrenal (HPA) axis, which controls stress adaption, and reproductive function (Hoffmann et al., 2019; Morrell, 2020). Beneath HS circumstances, cortisol levels were noticeably raised (p < 0.001) even like ACTH levels dropped; this suggests an adaptive response meant to minimize cellular damage (Li et al., 2020; Freitas et al., 2021). Rising cortisol, however, is known to lower gonadotropin production, which lowers LH, and FSH pulsatility, thereby directly contributing to decrease follicular development and ovulation (Laporta et al., 2020; Cheruiyot et al., 2022).

Table 2: Biochemical markers within dairy cows beneath heat stress, and thermoneutral conditions.

Parameter	Thermoneutral (TN)	Heat Stress (HS)	P-Value
ACTH (pg/mL)	35.2 ± 3.1	25.4 ± 2.8	<0.05
BUN (mmol/L)	5.2 ± 0.6	4.1 ± 0.5	<0.01
CRP (mg/L)	3.2 ± 0.4	2.5 ± 0.3	<0.05
T3 (ng/mL)	22.5 ± 2.3	15.7 ± 1.8	<0.01
Cortisol (ng/mL)	30.4 ± 4.2	20.8 ± 3.6	<0.001
HSP70 (pg/mL)	110.3 ± 15.6	140.7 ± 18.2	<0.01
NE (ng/mL)	3.1 ± 0.5	6.2 ± 1.0	<0.001
SOD (U/mL)	125.5 ± 10.3	140.8 ± 12.4	<0.05

Re-measurement of triiodothyronine (T3) at p < 0.01 levels together with blood urea nitrogen (BUN) at p < 0.01 demonstrated clear metabolic reactions to heat stress conditions. T3 serves as the critical energy balance and metabolic rate controller thus its decreased levels during HS result in heat reduction that affects reproductive efficiency. BUN levels decreasing indicates protein metabolism changes and impaired nitrogen use efficiency that stems from reduced feed consumption and delayed ovarian follicular maturation (Saravanan et al., 2020; Wang et al., 2019). Increase within heat shock protein 70 (HSP70) expression (p < 0.01), and norepinephrine (NE) levels (p < 0.001) also showed the stress-induced inflammatory, and oxidative reactions. Key biomarketer favor heat adaptation (Talker et al., 2022; Paludan et al., 2021), HSP70 is a molecular chaperone involved within protein refolding, and cellular defense against thermal damage. Rising NE levels beneath heat stress point to increased sympathetic nervous system activation, which is linked to vasoconstriction, and decreased ovarian perfusion, hence aggravating heat-induced reproductive failure (Hoffmann et al., 2019; Alhussien and Dang, 2019).

Fascinatingly, C-reactive protein (CRP) levels dropped (p < 0.05) during heat stress, which would imply change immune system, and possible immunosuppression brought upon through long-term thermal strain. This is consistent alongside other studies showing heat stress lowers immune cell viability, and increases susceptibility to infections within dairy cows, therefore influencing fertility, and general reproductive health (Freitas et al., 2021; Park et al., 2021). beneath heat stress, superoxide dismutase (SOD) activity also rose (p < 0.05), suggesting higher oxidative stress responses, that might cause granulosa cell death, and reduced steroidogenesis, both for which are negative favor ovarian function (Bohlouli et al., 2022; Talker et al., 2022).

The drop in FSH and LH value levels in Figures 1 and 2 creates a direct connection to reproductive issues because of heat exposure in dairy cows. Dairy cows require better heat tolerance as genetic selection progresses because cortisol together with metabolic changes through oxidative stress and altered ovarian physiology affect cows as stated by Otto et al. (2019) and Cheruiyot et al. (2022). Monitoring biomarkers through real-time measurements alongside specific dietary strategies for managing animals creates essential approaches to decrease the effects of heat stress on reproductive systems (Saravanan et al., 2020; Fontoura et al., 2022). Our finding shows how much heat stress affects dairy cow reproductive ability. Morever, we validate, that heat stress disturbs endocrine control, modulates gene expression, and reduces fertility. These results highlight the necessity for focused breeding plans, and better management techniques to raise the resistance for dairy cattle within hot conditions. Future studies should concentrate upon new mitigating strategies to maintain dairy output within heat-stressed conditions, and genetic selection favor heat tolerance (Saravanan et al., 2020).

CONCLUSIONS AND RECOMMENDATIONS

This study shows that, heat stress has considerable negative effects on the efficiency of the reproductive process in dairy cows due to several physiological mechanisms. The long-term exposure to elevated ambient conditions inhibits the luteinizing hormone (LH) and follicle stimulating hormone (FSH), the hypothalamic-pituitary-gonadal (HPG) axis and the development of ovarian follicles and the rate of ovulation. The increase in levels of heat shock proteins (HSP70, HSP90), norepinephrine, and cortisol, and the change of expression patterns of genes indicate the critical changes in the metabolism. Also, a reduction in triiodothyronine (T3) and blood urea nitrogen, and an increase in the markers of oxidative stress such as super oxide dismutase activity and C-reactive protein further reduce the quality of oocytes and embryonic survival.

Integrated management must be done to combat or reduce these ugly consequences. To come up with selective breeding, genetic selection should give emphasis on heat-resistant phenotypes and thermotolerance-related genes using the genome-wide association studies. At the same time, the use of high-performance cooling systems (misting fans, shade structures, evaporative cooling), enhanced nutrition incl. antioxidants and electrolytes, and precisely targeted monitoring technologies to early detect heat stress are important management interventions. Future directions primarily include the investigation of epigenetic mechanisms, a widening parameter space (transcriptomic and metabolomic) to determine predictive biomarkers, and gut microbiota in heat tolerance. The dairy industry can only find ways of sustainable resolution in the face of thermal stress brought about by global warming through genetic selection and enhanced management principles as well as on-going molecular research.

ACKNOWLEDGEMENTS

The author is grateful to the Department of Basic Science, College of Dentistry, Al-Iraqia University, Baghdad, Iraq, which supported the study in terms of the institution, facilities, and educational opportunities. A special appreciation is given to dairy farm management and employees at Erbil Province who have cooperated in handling and collection of samples. Technical support of laboratory staff on hormonal assays and RNA extraction and animal welfare verification in the course of the study are appreciated.

NOVELTY STATEMENT

The current study is the first molecular characterization of heat stress responses including the physiological and endocrine observations and transcriptome in Middle Eastern dairy cattle. New findings are; (1) the determination of a specific gene expression signature (HSPA4, HSPH1, FSHR, LHCGR) as biomarkers of heat tolerance; (2) the definition of the relations between metabolism and reproduction under thermal conditions; (3) the identification of the markers of oxidative stress correlating with reproductive deterioration; (4) the first molecular evidence of blocking of the HPG axis in local dairies breeds. The study supplies baseline information on precision breeding schemes and weather-informed administration tactics.

AUTHOR’S CONTRIBUTIONS

Entissar Mansour Abdul Rasool: was the idea and design creator of the study, and performed all experimentations including physiological measurements, laboratory experimentation (hormonal profiling, biochemical parameters, RNA extraction), data analysis (statistical analysis, RNA-Seq bioinformatics, qRT-PCR validation) and manuscript text writing. The author assumes complete responsibility in data integrity and analysis accuracy.

Conflict of Interest

The author does not report any conflicts of interest. This study is an academic work done at Al-Iraqia University with no commercial support or money holdings with dairy industries, pharmaceutical, and biotechnology firms. The experiment was conducted with exclusive scientific motives of improving knowledge about the effects of heat stress on reproduction of dairy cattle.

REFERENCES

Alhussien MN, Dang AK (2019). Potential roles of neutrophils in maintaining the health productivity of dairy cows during various physiological and physio-pathological conditions: a review. Immunol. Res., 67: 21–38. https://doi.org/10.1007/s12026-019-9064-5

Ali AS, Kadhim NA, Rasool EMA, Al-Erjan M, Lahhob QR, Mudhafar M (2024). Harnessing CRISPR-Cas9 gene editing for the eradication of inherited retinal diseases in purebred dogs: A path to preservation and health. J. Anim. Health Prod., 12(1): 145–156.

Al-Sailawi HA, Hadi AA, Raheem HA, Mudhafar M, Dhahi SJ, Lahhob QR (2024). Impact of serratiopeptidase vs. N-acetyl cysteine (NAC) on skin grafting healing in albino male rabbits. Adv. Anim. Vet. Sci., 12(10): 1941–1947. https://doi.org/10.17582/journal.aavs/2024/12.10.1941.1947

Aziz LM, Alhachami FR, Abdullah MA, Abed AS, Hassib Ali M, Al-Yasiri RM, Lahhob QR (2023). Molecular Characterization and Antibiotic Resistance Profile of Staphylococcus haemolyticus in Pregnant Women with Urinary Tract Infections. Iran. J. Med. Microbiol., 17(3): 354–360. https://doi.org/10.30699/ijmm.17.3.354

Bohlouli M, Halli K, Yin T, Gengler N, König S (2022). Genome-wide associations for heat stress response suggest potential candidate genes underlying milk fatty acid composition in dairy cattle. J. Dairy Sci., 105: 3323–3340. https://doi.org/10.3168/jds.2021-21152

Bohlouli M, Yin T, Hammami H, Gengler N, König S (2021). Climate sensitivity of milk Production traits and milk fatty acids in genotyped Holstein dairy cows. J. Dairy Sci., 104: 6847–6860. https://doi.org/10.3168/jds.2020-19411

Brito LF, Oliveira HR, McConn B, Schinckel A, Arrazola A, Marchant-Forde J, Johnson J (2020). Large-scale phenotyping of livestock welfare in commercial Production systems: A new frontier in Animal breeding. Front. Genet., 11: 793. https://doi.org/10.3389/fgene.2020.00793

Brito LF, Bedere N, Douhard F, Oliveira HR, Arnal M, Peñagaricano F, Schinckel AP, Baes CF, Miglior F (2021). Review: Genetic selection of high-yielding dairy cattle toward sustainable farming systems in a rapidly changing world. Animals, 15: 100292. https://doi.org/10.1016/j.animal.2021.100292

Catozzi C, Ávila G, Zamarian V, Pravettoni D, Sala G, Ceciliani F (2020). In vitro effect of heat stress on bovine monocytes lifespan and polarization. Immunobiology, 225: 151888. https://doi.org/10.1016/j.imbio.2019.11.023

Cheruiyot EK, Haile-Mariam M, Cocks BG, Pryce JE (2022). Improving genomic selection for heat tolerance in dairy cattle: current opportunities and future directions. Front. Genet., 13: 894067. https://doi.org/10.3389/fgene.2022.894067

Dahl GE, Tao S, Laporta J (2020). Heat Stress Impacts Immune Status in Cows across the Life Cycle. Front. Vet. Sci., 7: 116 https://doi.org/10.3389/fvets.2020.00116.

Daniels NJ, Hershberger CE, Gu X, Schueger C, DiPasquale WM, Brick J, Saunthararajah Y, Maciejewski JP, Padgett RA (2021). Functional analyses of human LUC7-like proteins involved in splicing regulation and myeloid neoplasms. Cell Rep., 35: 108989. https://doi.org/10.1016/j.celrep.2021.108989

Fang H, Kang L, Abbas Z, Hu L, Chen Y, Tan X, Wang Y, Xu Q (2021). Identification of key Genes and Pathways Associated with Thermal Stress in Peripheral Blood Mononuclear Cells of Holstein Dairy Cattle. Front. Genet., 12: 662080. https://doi.org/10.3389/fgene.2021.662080

Fontoura BP, Javaid A, Sáinz de la Maza-Escolà V, Salandy NS, Fubini SL, Grilli E (2022). Heat stress develops with increased total-tract gut permeability, and dietary organic acid and pure botanical supplementation partly restores lactation performance in Holstein dairy cows. J. Dairy Sci., 105: 7842–7860. https://doi.org/10.3168/jds.2022-21820

Freitas PH, Wang Y, Yan P, Oliveira HR, Schenkel FS, Zhang Y (2021). Genetic diversity and signatures of selection for thermal stress in cattle and other two Bos species adapted to divergent climatic conditions. Front. Genet., 12: 102. https://doi.org/10.3389/fgene.2021.604823

Garner JB, Chamberlain AJ, Vander Jagt C, Nguyen TTT, Mason BA, Marett LC, Leury BJ, Wales WJ, Hayes BJ (2020). Gene expression of the heat stress response in bovine peripheral white blood cells and milk somatic cells in vivo. Sci. Rep., 10: 19181. https://doi.org/10.1038/s41598-020-75438-2

Gilad E, Meidan R, Berman A, Graber Y, Wolfenson D (1993). Effect of heat stress on tonic and GnRH-induced gonadotrophin secretion in relation to concentration of oestradiol in plasma of cyclic cows. Reproduction, 1993; 99(2): 315-321. https://doi.org/10.1530/jrf.0.0990315

Hoffmann G, Herbut P, Pinto S, Heinicke J, Kuhla B, Amon T (2019). Anim.-related, non-invasive indicators for determining heat stress in dairy cows. Biosyst. Eng., 188: 90–109.

Huang S, Dou J, Li Z, Hu L, Yu Y, Wang Y (2022). Analysis of Genomic Alternative Splicing Patterns in Rat under Heat Stress Based on RNA-Seq Data. Genes, 13: 358. https://doi.org/10.3390/genes13020358

Hu J, Peng P, Cao X, Wu K, Chen J, Wang K, Tang, N, Huang AL (2022). Increased immune escape of the new SARS-CoV-2 variant of concern Omicron. Cellular & Molecular Immunology, 2022; 19(2): 293–295. https://doi.org/10.1038/s41423-021-00836-z

Kadhim MM, Khadom AA, Abaies JK, Kadhum WR, Hachim, SK (2024). Performance of ginger constituents against SARS-CoV-2 virus: a therapeutic and theoretical approach. Parasite Epidemiology and Control, 2024; 25: e00347. https://doi.org/10.1016/j.parepi.2024.e00347

Kandel A, Masello M, Xiao Z, Helper CD (2021). CD4+ T cell responses to pathogens in cattle. In: Bovine Sci.-Challenges and Advances. Ed. M. Abubakar London, United Kingdom: InTech-Open. https://doi.org/10.5772/intechopen.100410

Kareem H, Jihad I, Hassan H, Znad M, Harbi M, Lahhob Q, Jasim A (2023). Biochemical and hematological variables in COVID-19 positive patients. J. Med. Pharm. Chem. Res., 5: 609.

Kim WS, Peng DQ, Jo YH, Nejad JG, Lee HG (2021). Responses of beef calves to long-term heat stress exposure by evaluating growth performance, physiological, blood and behavioral parameters. J. Therm. Biol., 100: 103033. https://doi.org/10.1016/j.jtherbio.2021.103033

Laporta J, Ferreira FC, Ouellet V, Dado-Senn B, Almeida AK, de Vries A (2020). Late-gestation heat stress impairs daughter and granddaughter lifetime performance. J. Dairy Sci., 103: 7555–7568. https://doi.org/10.3168/jds.2020-18154

Lengi AJ, Stewart JW, Makris M, Rhoads ML, Corl BA (2022). Heat stress increases mammary epithelial cells and reduces viable immune cells in milk of dairy cows. Animals, 12: 2810. https://doi.org/10.3390/ani12202810

Li G, Chen S, Chen J, Peng D, Gu X (2020). Predicting rectal temperature and respiration rate responses in lactating dairy cows exposed to heat stress. J. Dairy Sci., 103: 5466–5484. https://doi.org/10.3168/jds.2019-16411

Liu S, Yue T, Ahmad MJ, Hu X, Zhang X, Deng T, Hu Y, He C, Zhou Y, Yang L (2020). Transcriptome Analysis Reveals Potential Regulatory Genes Related to Heat Tolerance in Holstein Dairy Cattle. Genes, 11: 68. https://doi.org/10.3390/genes11010068

Luo H, Brito LF, Li X, Su G, Dou J, Xu W, Yan X, Zhang H, Guo G, Liu L (2021). Genetic parameters for rectal temperature, respiration rate, and drooling score in Holstein cattle and their relationships with various fertility, Production, body conformation, and health traits. J. Dairy Sci., 104: 4390–4403. https://doi.org/10.3168/jds.2020-19192

Menta PR, Machado VS, Piñeiro JM, Thatcher WW, Santos JEP, Vieira-Neto A (2022). Heat stress during the transition period is associated with impaired Production, reProduction, and survival in dairy cows. J. Dairy Sci., 105: 4474–4489. https://doi.org/10.3168/jds.2021-21185

Mishra SR (2021). Behavioral, physiological, neuro-endocrine and molecular responses of cattle against heat stress: an updated review. Trop. Anim. Health Prod., 53: 400. https://doi.org/10.1007/s11250-021-02790-4

Mohsen AK, Jassim SE, Alaridhi TT, Al-Erjan AM, Lahhob QR, Mudhafar M (2024). Revolutionizing infectious disease management in Anim.s through advanced phage therapy: a comprehensive strategy for the eradication of multidrug-resistant bacterial pathogens. J. Anim. Health Prod., 12(s1): 157–167. https://doi.org/10.17582/journal.jahp/2024/12.s1.157.167

Morrell JM (2020). Heat stress and bull fertility. Theriogenology, 153: 62–67. https://doi.org/10.1016/j.theriogenology.2020.05.014

Otto PI, Guimarães SEF, Verardo LL, Azevedo ALS, Vandenplas J, Sevillano CA (2019). Genome-wide association studies for heat stress response in Bos taurus×Bos indicus crossbred cattle. J. Dairy Sci., 102: 8148–8158. https://doi.org/10.3168/jds.2018-15305

Ouyang Y, Xia K, Yang X, Zhang S, Wang L, Ren S, Zhou H, Liu Y, Tang F (2021). Alternative splicing acts as an independent prognosticator in ovarian carcinoma. Sci. Rep., 11: 10413. https://doi.org/10.1038/s41598-021-89778-0

Paludan SR, Pradeu T, Masters SL, Mogensen TH (2021). Constitutive immune mechanisms: mediators of host defense and immune regulation. Nat. Rev. Immunol., 21: 137–150. https://doi.org/10.1038/s41577-020-0391-5

Panigrahi M, Harshit K, Saravanan KA, Divya R, Sonali SN, Kanika G (2022). Trajectory of livestock genomics in South Asia: a comprehensive review. Gene, 843: 146808. https://doi.org/10.1016/j.gene.2022.146808

Park DS, Gu BH, Park YJ, Joo SS, Lee SS, Kim SH (2021). Dynamic changes in blood immune cell composition and function in Holstein and Jersey steers in response to heat stress. Cell Stress Chaperones, 26: 705–720. https://doi.org/10.1007/s12192-021-01216-2

Rajawat D, Panigrahi M, Kumar H, Nayak SS, Parida S, Bhushan B (2022). Identification of important genomic footprints using eight different selection signature statistics in domestic cattle breeds. Gene, 816: 146165. https://doi.org/10.1016/j.gene.2021.146165

Sammad A, Luo H, Hu L, Zhu H, Wang Y (2022). Transcriptome Reveals Granulosa Cells Coping through Redox, Inflammatory and Metabolic Mechanisms under Acute Heat Stress. Cells, 11: 1443. https://doi.org/10.3390/cells11091443

Sammad A, Wang YJ, Umer S, Lirong H, Khan I, Khan A, Ahmad B, Wang Y (2020). Nutritional Physiology and Biochemistry of Dairy Cattle under the Influence of Heat Stress: Consequences and Opportunities. Animals, 10: 793. https://doi.org/10.3390/ani10050793

Saravanan KA, Panigrahi M, Kumar H, Bhushan B, Dutt T, Mishra BP (2020). Selection signatures in livestock genome: a review of concepts, approaches and applications. Lives. Sci., 241: 104257. https://doi.org/10.1016/j.livsci.2020.104257

Sun J, Liu Z, Quan J, Li L, Zhao G, Lu J (2022). RNA-seq Analysis Reveals Alternative Splicing under Heat Stress in Rainbow Trout (Oncorhynchus mykiss). Mar. Biotechnol., 24: 5–17. https://doi.org/10.1007/s10126-021-10082-z

Talker SC, Barut GT, Lischer HEL, Rufener R, von Münchow L, Bruggmann R (2022). Monocyte biology conserved across species: functional insights from cattle. Front. Immunol., 13: 889175. https://doi.org/10.3389/fimmu.2022.889175

Tao S, Orellana Rivas RM, Marins TN, Chen YC, Gao J, Bernard JK (2020). Impact of heat stress on lactational performance of dairy cows. Theriogenology, 150: 437–444. https://doi.org/10.1016/j.theriogenology.2020.02.048

Wang B, Wang C, Guan R, Shi K, Wei Z, Liu J, Liu H (2019). Effects of dietary rumen-protected Betaine supplementation on performance of postpartum dairy cows and immunity of newborn calves. Animals, 9: 167. https://doi.org/10.3390/ani9040167

Xiong Y, Yi H, Wu Q, Jiang Z, Wang L (2020). Effects of acute heat stress on intestinal microbiota in grow-finishing pigs, and associations with feed intake and serum profile. J. Appl. Microbiol., 128: 840–852. https://doi.org/10.1111/jam.14504

Yang Y, Zhang C, Zhu D, He H, Wei Z, Yuan Q, Li X, Gao X, Zhang B, Gao H (2022). Identifying candidate genes and patterns of heat-stress response in rice using a genome-wide association study and transcriptome analyses. The Crop J., 10: 1215–1225. https://doi.org/10.1016/j.cj.2022.02.011

Yue S, Wang Z, Wang L, Peng Q, Xue B (2020). Transcriptome Functional Analysis of Mammary Gland of Cows in Heat Stress and Thermoneutral Condition. Animals, 10: 1015. https://doi.org/10.3390/ani10061015