G. Krishnan

Toll-like receptors: Significance, ligands, signaling pathways, and functions in mammals

ABSTRACT This review attempts to cover the implication of the toll-like receptors (TLRs) in controlling immune functions with emphasis on their significance, function, regulation and expression patterns. The tripartite TLRs are type I integral transmembrane receptors that are involved in recognition and conveying of pathogens to the immune system. These paralogs are located on cell surfaces or within endosomes. The TLRs are found to be functionally involved in the recognition of self and non-self-antigens, maturation of DCs and initiation of antigen-specific adaptive immune responses as they bridge the innate and adaptive immunity. Interestingly, they also have a significant role in immunotherapy and vaccination. Signals generated by TLRs are transduced through NFκB signaling and MAP kinases pathway to recruit pro-inflammatory cytokines and co-stimulatory molecules, which promote inflammatory responses. The excess production of these cytokines leads to grave systemic disorders like tumor growth and autoimmune disorders. Hence, regulation of the TLR signaling pathway is necessary to keep the host system safe. Many molecules like LPS, SOCS1, IRAK1, NFκB, and TRAF3 are involved in modulating the TLR pathways to induce appropriate response. Though quantification of these TLRs helps in correlating the magnitude of immune response exhibited by the animal, there are several internal, external, genetic and animal factors that affect their expression patterns. So it can be concluded that any identification based on those expression profiles may lead to improper diagnosis during certain conditions.

Comparative assessment of heat stress induced changes in carcass traits, plasma leptin profile and skeletal muscle myostatin and HSP70 gene expression patterns between indigenous Osmanabadi and Salem Black goat breeds

The primary objective of the study was to compare the impact of heat stress on meat production characteristics of Osmanabadi and Salem Black breed goats based on changes in carcass characteristics, meat quality attributes, plasma leptin concentration, skeletal muscle myostatin and heat shock protein 70 (HSP70) gene expression patterns. The goats were randomly distributed into four groups: OSC (n = 6; Osmanabadi Control), OSHS (n = 6; Osmanabadi Heat Stress), SBC (n = 6; Salem Black Control) and SBHS (n = 6; Salem Black Heat Stress). The animals were slaughtered at the end of the study and their meat characteristics were assessed. This study established the impact of heat stress on a wide variety of carcass and meat quality characteristics in OS and SB goat breeds. The results from the study also provided some crucial evidence for a better resilience capacity of Salem Black breed as compared to Osmanabadi goats in maintaining the meat production during heat stress. The study also established plasma leptin and HSP70 genes to be the ideal biomarkers to reflect the impact of heat stress on meat characteristics in indigenous goats.

Summer season induced rhythmic alterations in metabolic activities to adapt to heat stress in three indigenous (Osmanabadi, Malabari and Salem Black) goat breeds

Abstract A study was conducted to assess the adaptive capability of three indigenous goat breeds to heat stress. Thirty six 10 months to one-year-old female goats of Osmanabadi, Malabari and Salem Black breeds were randomly divided into six groups, OC (n = 6; Osmanabadi control), OHS (n = 6; Osmanabadi heat stress), MC (n = 6; Malabari control), MHS (n = 6; Malabari heat stress), SBC (n = 6; Salem Black control) and SBHS (n = 6; Salem Black heat stress). Among the metabolic activity controlling hormones, the breed factor significantly (P < 0.05) influenced only plasma triiodothyronine (T3). However, heat stress significantly (P < 0.05) decreased thyroid stimulating hormone (TSH) in both MHS and SHS groups while significantly (P < 0.05) decreased the plasma T3 in MHS. The rumen metabolites such as acetate, propionate, butyrate and total volatile fatty acids (TVFAs) showed significant (P < 0.05) variation for both breed and treatment effect. The Salem Black breed did not show any significant variation for most of the rumen metabolites as compared to both Osmanabadi and Malabari breeds for the heat stress treatment. The study indicated the importance of the metabolic alterations in indigenous goat breeds to cope to the seasonal rhythms. The results indicated that on comparative basis, Salem Black breed adapted better to the heat stress challenges.

Summer season induced heat stress impact on the expression patterns of different toll-like receptor genes in Malabari goats

Abstract The study was conducted with the primary objective of establishing the impact of heat stress on the expression pattern of different toll-like-receptors (TLRs) in Malabari goats. The study was conducted for a period of 45 days using twelve Malabari goats. The goats were randomly allocated into two groups: MC (n = 6; Malabari control) and MHS (n = 6; Malabari heat stress). At the end of study, all 12 animals were slaughtered and their mesenteric lymph node (MLN) tissues were collected for gene expression. Heat stress significantly (p < 0.05) down regulated TLR1, TLR4, TLR5 and TLR6 and significantly increased (p < 0.05) TLR2 expression pattern. A negative correlation (p < 0.01) was also established between THI and different TLRs except TLR3, TLR7 and TLR10. The study indicated that TLR2 could serve as ideal immunological marker for establishing the superior thermo-tolerance ability of Malabari breed in terms of maintaining the immune status during heat stress challenges.

Diurnal variation and oscillatory patterns in physiological responses and HSP70 profile in heat stressed yaks at high altitude

ABSTRACT The present study was carried out at altitude of 3000 m above sea level (asl) to evaluate the impact of heat stress on yak adaptability. Sixteen healthy yaks of different age were randomly divided into two groups, calf (GI; n = 8) and adult (GII; n = 8). Experimental yaks were exposed to heat stress in the open paddock. THI ranged between 61.60 and 64.17 which were beyond the comfortable limit for yak. Post-exposure, rectal temperature increased (p < 0.01) by 2.97 °F and 2.42 °F in calf and adult yaks as compared to pre-exposure (100.08 ± 0.04 °F, 100.06 ± 0.05 °F). Respiration rate increased (p < 0.01) by 2.96 and 2.40 fold in calf and adult yaks with increased pulse rate on post-exposure to heat stress. The oscillatory patterns of physiological responses indicated that the level of heat stress increment was higher (p < 0.05) in calves than adult yaks. Plasma HSP70 increased (p < 0.01) by 7 fold in calf and 5 fold in adult yaks in comparison to pre-exposure level of 83.67 ± 1.11pg/ml and 80.65 ± 1.35 pg/ml. Thus, the yaks were experiencing heat stress at high altitude of 3000 m asl during the warmer months of the year and calves were more prone to heat stress as compared to adults.

Adaptation Strategies to Sustain Osmanabadi Goat Production in a Changing Climate Scenario

Small ruminants are an integral part of farming systems in the tropical, subtropical, and arid regions of the world. Goats are considered suitable animals in such regions, since they were the first domesticated animals in the hot and arid zones of the world. Goats are considered as an ideal animal model to meet the global demands for animal protein in the changing climate scenario. Understanding the multifaceted impacts of heat stress on goat production is the prerequisite for the development of appropriate strategies to sustain goat production in the face of climate change. The identification of thermo-tolerant genes can help to improve the resilience capacity of existing non-descript goat breeds through marker-assisted selection. The strategies to augment goat production during extreme climatic conditions may be broadly categorized under management and nutritional strategies. The management strategies for Osmanabadi goat production under changing climate scenario comprise of housing, environment reproductive and health management. Technological interventions such as estrus synchronization, artificial insemination, and embryo transfer protocols may help to improve the reproductive efficiency in indigenous breeds such as Osmanabadi goats. The nutritional interventions comprise of mineral, electrolyte and antioxidant supplementation, utilization of unconventional feed resources, feeding tree foliage and leaves, fat and feed additives supplementation. Efforts are also needed to understand the occurrences and epidemiology of diseases under climate change and appropriate management should be provided by health and prevention programs.

Adaptive Mechanisms of Sheep to Climate Change

Sheep rearing is the most integral part of animal production particularly in tropical regions. Climate change is observed to have devastating effects on sheep farming through constraints such as heat stress, lower grazing lands, water scarcity and higher pest and disease incidences. These environmental constraints may lead to compromised productive functions in sheep. The cumulative effects of heat, nutritional and walking stress occurring in the hotter parts of the year compromise the productive and reproductive performances of the sheep through reduced feed intake, modified endocrine profile, lower rumination and nutrient absorption and higher maintenance demands.

Adaptation Strategies to Counter Climate Change Impact on Sheep

Climate change has proved to impose potential negative effects on species survival, ecosystems stability and sustainable livestock production around the globe. Among the various environmental factors, heat stress is well known for its harmful effects on livestock and related production losses. Sheep exposed to heat stress show lower body growth and hide quality and compromised reproductive functions in both males and females. Adapting to the changing climate requires appropriate manipulations in the production system by taking into account the positive effects and attempting to diminish the negative effects of climate change. The highly adapted indigenous breeds identified by marker-assisted selection can be used as an efficient tool for developing thermotolerant breeds through improved breeding programmes. Promotion of such breeds can improve production efficiency and may lead to fewer greenhouse gas emissions. Further, the local people, especially women, are good managers of natural resources and possess excellent skills to utilize the natural resources efficiently. Hence, occasional training and a participatory research approach into the roles of women assist the tackling of climate change in the rural areas. In addition, well-organized early warning systems avoid severe damage due to unexpected disasters by providing sufficient time to prepare effective responses. Development of skilled disease surveillance supported with effective health services may effectively control the spread of climate change-related diseases in sheep. Furthermore, the production system requires improved water resource management to provide sufficient water for sheep production in the arid and semi-arid regions. Cultivation of drought-tolerant fodder varieties in extremely hot areas is an efficient adaptive strategy to ensure sufficient supply of feed during scarcity periods. Finally, strengthening extension services and building awareness through capacity-building programmes helps the livestock keepers to improve their adaptive capacities against climate change. Adaptation strategies related to cold stress include advanced cold-tolerant breeding programmes, migration in extreme winter and adoption of proper cold management practices. According to the predictions by various international bodies, the consequences of climate change will be on the rise in the future. Hence, adequate cost-effective management strategies appear to be the immediate need of the hour for adapting sheep production systems to the changing climate.

Measurement of Severity of Heat Stress in Sheep

Animals show optimum growth, health, and productivity within a range of environmental temperatures. Exposure of the sheep to higher temperature leads to heat stress, which negatively affects their well-being and productivity. In addition to ambient temperature (AT), other climatic factors like humidity (RH), wind speed (WS), and solar radiation (SR) also influence the degree of heat stress in sheep. Further, climate change caused a higher rate of temperature increase in the tropical region. Hence, there is an urgent necessity to develop a simple, reliable, and easy method to assess the degree of heat stress in sheep particularly during summer. In the mid-twentieth century, temperature-humidity index (THI) was introduced to evaluate the severity of summer stress and was extended to dairy animals as a tool to explain the welfare of the animals. Moreover, several THI equations were developed by various scientists based on prevailing AT and RH. However, the main drawback of the THI was that it did not account for other weather parameters like WS and SR, even though they also equally influenced the level of heat stress in animals. Research efforts pertain to establishing a suitable thermal index by incorporating all cardinal weather parameters. With this background, heat load index (HLI) was developed as an alternative to THI relating RH, WS, and black-globe temperature (accounts both AT and SR). The few other modern indices available to assess the severity of heat stress in sheep are black-globe temperature-humidity index (BGTHI), thermal comfort index (TCI), and global comprehension index (GCI). In addition to weather indices, some physiological indices are also used to assess heat stress in sheep. Physiological responses like rectal temperature and respiration rate are considered as good indicators of heat stress in sheep. Moreover, strong correlations between blood parameters like hemoglobin, packed cell volume, and endocrine parameters such as cortisol and thyroid hormones production are well established in sheep. Further, genomics and proteomics tools are providing advanced options to evaluate the adaptation processes of sheep. Some of the genes identified in sheep during heat stress are heat shock protein, heat shock factor-1, thyroid hormone receptor, and prolactin receptor genes. Besides, the identified thermo-tolerant genes could be used as an ideal marker for assessing the level of heat stress and may be further utilized for marker-assisted selection breeding programs to develop superior thermo-tolerant breeds.

Impact of Adverse Environmental Stress on Productive and Reproductive Performance in Osmanabadi Goats

Among the livestock species, goats have notable characteristics that make it peculiar to outshine competently in harsh tropical and subtropical environments. Osmanabadi goat breed is a dual purpose (meat and milk) hardy goat breed native to the states of Maharashtra and its adjoining states belonging to the tropical semiarid regions in India. The results from the available literatures indicate the extreme adaptive capability of Osmanabadi goats to the extreme climatic condition. It has been proved that if nutrition is not compromised, Osmanabadi goats were found to cope with heat stress (HS) challenges without compromising production. In males, HS impacts reproduction directly by reducing the semen volume, sperm motility, higher sperm defects, and reduces libido. These impacts were aggravated when feed scarcity coupled with HS. Further, the various experimental findings established that the Osmanabadi goats possessed superior adaptive capability to counter HS through their ability to alter the behavioral, physiological, endocrinological, and different thermotolerant gene expression patterns. In addition, lying time, drinking frequency, respiration rate, rectal temperature, plasma heat shock protein 70 (HSP70), and peripheral blood mononuclear cell HSP70 gene were reported to be the ideal biological markers to quantify the impact of environmental stress in Osmanabadi goats. Also, higher expression of toll-like-receptor 8 (TLR8) and TLR10 in heat-stressed Osmanabadi goats indicated that these two genes could be the immunological markers for HS in goats.