M. Bagath

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.

Summer season related heat and nutritional stresses on the adaptive capability of goats based on blood biochemical response and hepatic HSP70 gene expression

Abstract A study was conducted to assess the impact of summer season-related heat stress and nutritional stress individually as well as simultaneously on the adaptive capability of goats. Twenty four adult Osmanabadi bucks (average body weight (BW) 16.0 kg) were divided into four groups, C (n = 6; control), HS (n = 6; heat stress), NS (n = 6; nutritional stress) and CS (n = 6; combined stress). The study was conducted for a period of 45 days. The NS and CS bucks were under restricted feed to induce nutritional stress. The HS and CS bucks were exposed to summer heat stress. The animals exhibited different physiological adaptive behavior in the morning and afternoon. Further, the higher plasma cortisol (p < 0.01) and aldosterone (p < 0.05) was recorded in CS group as compared to other groups. The highest degree of degenerative changes and hyperactivity of endocrine cells was recorded in CS group liver and adrenal gland respectively. The higher expression of adrenal and hepatic Heat Shock Protein 70 (HSP70)messenger ribonucleic acid (mRNA) was reported in CS and HS goats respectively. It can be concluded from this study that plasma cortisol and adrenal HSP70 gene expression may be considered as ideal biological markers for combined stresses in Osmanabadi bucks.

Overview on Adaptation, Mitigation and Amelioration Strategies to Improve Livestock Production Under the Changing Climatic Scenario

Livestock production is thought to be adversely affected by detrimental effects of extreme climatic conditions. Consequently, adaptation, mitigation and amelioration of detrimental effects of extreme climates have played a major role in combating the climatic impact in livestock production. While measures to reduce the growth of greenhouse gas emissions are an important response to the threat of climate change, adaptation to climate change will also form a necessary part of the response. The salient adaptation strategies are developing less sensitive breeds, improving water availability, improving animal health, promoting women empowerment, developing various policy issues, establishing early warning systems and developing suitable capacity building programmes for different stakeholders. Developing adaptation strategies is therefore an important part of ensuring that countries are well prepared to deal with any negative impacts that may occur as a result of climate change. The integration of new technologies into the research and technology transfer systems potentially offers many opportunities to further the development of climate change adaptation strategies. Adapting to climate change and reducing GHG emissions may require significant changes in production technology and farming systems that could affect productivity. Many viable opportunities exist for reducing CH4 emissions from enteric fermentation in ruminant animals and from livestock manure management facilities. To be considered viable, these emission reduction strategies must be consistent with the continued economic viability of the producer and must accommodate cultural factors that affect livestock ownership and management. This chapter also elaborates on ameliorative strategies that should be given consideration to prevent economic losses incurred due to environmental stresses on livestock productivity. Reducing the impact of climatic stresses on livestock production requires multidisciplinary approaches which emphasise animal nutrition, housing and animal health. Therefore, emphasis should be given to all three aspects of adaptation, mitigation and amelioration strategies to sustain livestock production under the changing climate scenario.

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.

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.