Climate change is a long term shift in the statistics of the weather such as temperature, radiation, wind and rainfall characteristics of particular region. Climate change has a great impact on the reproductive activity of livestock species. The Intergovernmental Panel on Climate Change indicated that the developing countries tend to be more vulnerable to extreme climatic events as they largely depend on climate sensitive sectors like agriculture and forestry. India is highly vulnerable to climate change impacts and ranks among the top 10 high risk countries. The greenhouse gas emission from agriculture sector is the most important factor for global warming. The productive and reproductive performances of cattle and buffaloes are likely to be aggravated due to climate change and global warming. The ability of an animal to cope up with environmental stress could be improved through strategic management of reproduction by manipulation of folliculogenesis, hormonal alterations, selective breeding, and application of embryo transfer techniques.
Livestock play a key role in the agricultural sector in developing nations, as the livestock sector contributes 40% to the agricultural GDP. Global demand for foods of animal origin is growing and it is apparent that the livestock sector will need to expand (FAO, 2009). Livestock is adversely affected by the extreme weather. Climatic extremes and seasonal fluctuations in herbage quantity and quality will affect the well-being of livestock and will lead to declines in production and reproduction efficiency Sejian et al (2013).
Climate is one of the determining factors for production and reproduction in farm animals throughout the world. Evidence from the intergovernmental panel on climate change is now overwhelmingly convincing that climate change is real and will become worse. Globally average land and ocean surface temperature showed a warming of 0.85˚C (0.65 to 1.06) over the period of 1880 to 2012.Changes in many extreme weather and climatic events have been observed since 1950. The frequency of the heat waves has increased in large parts of Asia and numbers of heavy precipitation events have increased. Over the period of 1901 to 2010, global mean sea level rise by 0.19m. (0.17 to 0.21). The IPCC predicts that by 2100 the increase in global temperature may be between 1.8˚C and 4.0˚C. With increases of 1.5˚C to 2.5˚C, approximately 20 to 30 % of plant and animal species are expected to be at risk of extinction with severe consequences for food security in developing countries.
Direct Effects of Climate Change on Livestock
The most important direct impact of climate change on livestock production comes from the heat stress. Heat stress causes a wide range of effects on the livestock’s. The effect of heat stress is aggravated when it is accompanied by elevated environmental temperature, solar radiation and relative humidity leads to hyperthermia or heat stress. Some of these effects causes directly reduce the performance of fertility and embryonic survival in dairy cows Hansen and Arechiga (1999). These include compromised endometrial function and secretary activity, smaller follicular size and suppressed dominance of the large follicle Wolfenson et al (2000). Disturbances in hormonal balance include decreased serum estradiol concentration Wilson et al (1998), decreased plasma concentration of LH and decreased progesterone secretion. Furthermore, oocyte quality Gendelman et al (2012), embryo development and embryo survival are impaired by heat stress. These processes lead to a decrease in conception rate in the subtropical areas during the hot season at 90 and 135 days postpartum and thus, heat stress has becoming an impacting factor responsible for extensive economic losses to the dairy industry. It also affects livestock sector economically through decrease in milk production, meat production, reproductive efficiency and animal health.
Indirect Effects of Climate Change on Livestock
Most of the production and reproduction losses are incurred via indirect impacts of climate change, because of reduction or non-availability of feed and water resources. Climate change has the potential to affect the quantity and reliability of forage production, quality of forage, water demand for cultivation of forage crops, as well as large-scale rangeland vegetation patterns. Due to the wide fluctuations in distribution of rainfall in growing season in several regions of the world, the forage production will be greatly impacted. Also climate change influences the water demand, availability and quality. Changes in temperature and weather may affect the quality, quantity and distribution of rainfall, snowmelt, river flow and groundwater. The scarcity of water affects animal physiological homeostasis leading to loss of body weight, low reproductive rates and a decreased resistance to diseases Naqvi et al (2015).
Impact of Climate Change on Livestock Production
Exposure of the animal to heat stress leads to reduced feed intake and increased water intake, by which endocrine status get changed thus performance of animal is reduced Gaughan and Cawsell-Smith (2015). Environmental stressors reduce body weight, average daily gain and body condition of livestock. Thatcher (1974) and Johnson (1976) also reported decline in the milk production, it might be due to heat stress has negative effects on the secretary function of the udder Silanikove et al (1992). When a lactating Holstein cow is transferred from an air temperature of 18°C to 30°C. Milk fat, solids-not-fat, and milk protein percentage decreased by 39.7, 18.9 and 16.9% respectively McDowell et al (1976). Cow maintained under similar temperatures during the day but at 25°C at night did not decrease milk production beyond that normally expected under temperate conditions Richards et al (1985). Furthermore, Sharma et al(1983) concluded that climatic conditions appeared to have maximum influenced during the rest 60 days of lactation. Generally the higher production animals are the most commonly affected. Adaptation to prolonged stressors may be accompanied by production losses. Increasing or maintaining current production levels in an increasingly hostile environment is not a sustainable option. It may make better sense to look at using adapted animals, albeit with lower production levels (and also lower input costs) rather than try to infuse ‘stress tolerance’ genes into non-adapted breeds Gaughan et al (2015).
Effect of Climate Changes on Diseases Occurrence
The impacts of changes in ecosystems on infectious diseases depend on the ecosystems affected, the type of land-use change, disease specific transmission dynamics, and the susceptibility of the populations at risk Patz et al (2005). Climate change will affect not only those diseases that have a high sensitivity to ecological change, but there is also significant health risks associated with flooding. Variations in temperature and rainfall are the most important climatic variables affecting disease outbreaks. Warmer and wetter weather (mainly warmer winters) will increase the risk and occurrence of animal diseases, because certain species that serve as disease vectors, such as biting flies and ticks, are more likely to survive year-round. The movement of disease vectors into new areas e.g. malaria and livestock tick borne diseases (theileriosis, babesiosis and anaplasmosis), Rift Valley fever and bluetongue disease in Europe has been documented. Some of the existing parasitic diseases may also become more prevalent, or their geographical range may spread, if rainfall increases. This may favors to an increase in disease spread for livestock such as ovine chlamydiosis, caprine arthritis (CAE), equine infectious anemia (EIA), equine influenza, Marek’s disease (MD), and bovine viral diarrhea (BVD). There are numerous rapidly emerging diseases that continue to spread over large areas. Outbreaks of diseases such as foot and mouth disease or avian influenza affect very large numbers of animals and contribute to further degradation of the environment and surrounding community’s health and livelihood.
Climate Change impacts on Livestock Reproduction
Reproductive functions of livestock are vulnerable to climate changes. Reproductive processes are affected by thermal stress. In dairy cows, the conception rates may drop in 20–27% during summer. Heat stress also negatively affects reproductive function. Amundson et al (2006) such as poor expression and intensity of oestrus due to reduced oestradiol secretion from the dominant follicle developed in a low LH environment. Heat stress causes, changes in ovarian function and embryonic development by reducing the competence of oocyte to be fertilized Naqvi et al (2012). Buffaloes are more vulnerable to heat stress as compare to cattle which may be due to high thermal load in this species as a result of difficulty in heat dissipation due to unavailability of place for wallowing and lesser number of sweat glands Vaidya et al (2010).Heat stress compromises oocyte growth by altering progesterone secretion, the secretion of LH, FSH and ovarian dynamics during the oestrus cycle. Heat stress has also been associated with impairment of embryo development and increase in embryonic mortality in cattle. Heat stress during pregnancy slows growth of the foetus and can increase foetal loss. In case of males, heat stress negatively affects spermatogenesis perhaps by inhibiting the proliferation of spermatocytes.
Ameliorative Measures to Counteract Under Changing Climatic Scenario
There are different strategies available to counter the impact of climate change on livestock reproduction. It can be broadly grouped under two categories: (1) management strategies (2) advanced reproductive strategies.
The time of greatest susceptibility for livestock reproduction is immediately after the onset of
estrus and early postbreeding. One way to minimize effects of heat stress is to provide housing
that alleviates heat stress. Providing adequate shade and water to cows on pasture can help keep them cool, resulting in increased embryo survival.
Specific Nutritional Strategies
Properly balanced rations will provide adequate energy to reduce problems of herd health and reproduction associated with decreased dry matter intake (DMI) during heat stress. Preliminary research has shown fungal cultures can reduce body temperature and respiration rate and beta-carotene has been successful in increasing fertility and pregnancy rate in cows calving during the summer. Nutritional tools, such as antioxidant feeding (vit. A, selenium, zinc, etc.) and ruminant- specific live yeast can be helpful. The use of antioxidants such as vit. E, vit. A, selenium, and selenium-enriched yeast helps in reducing the impact of heat stress on the oxidant balance, resulting in improved reproductive efficiency and animal health Sejian et al (2014 ).
Advanced Reproductive Strategies
Delayed effect of heat stress on follicle quality may be overcome by mechanical removal of follicles by OPU from ovaries or by stimulating follicle turnover. FSH treatment increases the number of medium-sized follicles in the follicular waves following heat stress and induced an earlier emergence of high-quality oocytes Roth et al (2002) ; Friedman et al (2010 ). Stimulation of gonadal function by GnRH improves follicular function, as frequent follicular waves induced during fall increased follicular estradiol content in preovulatory follicles aspirated from previously heat-stressed cows Roth et al (2004 ). Synchronization with GnRH and PGF2α also
improves fertility Friedman et al (2011 ). Progesterone supplementation during early pregnancy has proven beneficial in some studies. Supplementation of exogenous progesterone during summer heat stress has the potential to improve fertility. Accessory CL may be useful in supporting the plasma progesterone which may be facilitated by the induction of ovulation from first-wave dominant follicle by treatment with GnRH agonist or hCG. In general, efficiency to increase progesterone concentration is greatest when accessory CL is induced by hCG. GnRH administration at insemination or 12 days later can improve the fertility of lactating cows during heat stress (Lopez-Gatius et al., 2006).One simple way to reduce plasma concentrations of estradiol is to remove follicles by transvaginal ultrasound-guided aspiration of follicles. Secretion of interferon (IFN) is positively associated with conceptus size Mann et al (1999); therefore, larger conceptus should be better able to block PGF synthesis and luteolysis. One possible way to stimulate conceptus growth is through the administration of bST. bST increases secretion of IGF-1, insulin, and growth hormone Bilby et al (2004 ). The elevation in the IGF-1 would protect the oocyte and embryos from damage caused by heat stress. In vitro administration of recombinant bST increased fertilization rates, hastened embryo development, and increased embryo quality Moreira et al (2002) ; Santos et al (2004) ; Ribeiro et al (2014 ).
The use of superovulation (SOV) followed by AI is a technique that generates greater numbers of embryos per donor. TAI associated with embryo transfer (ET) is a powerful tool to disseminate high-quality genetics and improve reproductive performance mainly in heat-stressed dairy cattle and repeat breeders Hansen et al (2001) ; Baruselli et al (2011).One feasible and effi cient way to escape this developmental block may be the use of embryo transfer (ET) technology, Embryos are typically transferred into recipient females when they reach the morula or blastocyst stages of development, typically at day 7 post ovulation. Thus, transferring day 6–8 embryos may escape these most thermosensitive periods, and pregnancy rate may be improved in summer. The use of ET is considered a potential strategy for minimizing the negative effects of heat stress on bovine reproduction Baruselli et al (2011). Insulin-like growth factor-1 (IGF-1) acts as a survival factor for preimplantation embryos exposed to heat stress (Hansen and Block 2004 ), and addition of IGF-1 in the culture media enhances bovine/bubaline preimplantation embryo development Sirisathein et al (2003); Chandra et al (2012) as IGF-1 and IGF-2 receptors are present in all preimplantation stage embryos Chandra et al (2011). Treatment with IGF-1 can make embryos resistant to heat shock (Jousan and Hansen 2007), and there might be variation between embryos in the degree of thermo tolerance at the blastocyst stage.
Genetic Selection and Production of Thermo tolerant Animals
Sustainable livestock production in climate change scenario may be attained through producing heat-resistant strains of animals. It has been seen that certain breeds of beef and dairy cattle are better in regulating body temperature during heat stress than others. Thus, genetic improvement in resistance to heat stress may be achieved by applying genetic selection or crossbreeding. There are wide variations in genetics in resistance to heat stress among livestock species Hayes et al (2009). Bos indicus breeds have been found to be more heat tolerant than Bos taurus . Compared with B. taurus cattle, B. indicus cattle exhibit increased total numbers of oocytes, increased oocyte viability, increased blastocyst rate, and a reduced rate of nuclear fragmentation in in vitro produced blastocyst Baruselli et al (2012).
Climate change is a global reality and contributing factors are Temperature, Rainfall, Radiation, Wind velocity, Relative humidity and Snow fall. Industrialization & anthrop activities increase the GHG that contribute to climate change. Developing countries tend more vulnerable to climatic change. Heat stress adversely affects reproductive performance. Mitigation strategies includes Cooling of animal shed, proper ventilation, Nutritional management, hormonal alterations ,Genetic Selection and production of thermo tolerant animals.
The authors are thankful for the support of ICAR-Indian Veterinary Research Institute, Izatnagar (U P.), India.