Figure 1: Schematic view of the expected outcome of climate change as a consequence of
global warming on farm animal productivity and food security (Elsa et al 2012).
| Livestock Research for Rural Development 28 (12) 2016 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Climate change is a long-term shift in the statistics of the weather such as temperature, radiation, and wind and rainfall characteristics of a particular region. Sustainability in livestock production system is largely affected by climate change. An imbalance between metabolic heat production inside the animal body and its dissipation to the surroundings results to heat stress under high air temperature and humid climates. The foremost reaction of animals under thermal weather is increase in respiration rate, rectal temperature and heart rate. The anticipated rise in temperature due to climate change is likely to aggravate the heat stress in livestock, adversely affecting their productive and reproductive performance and even death in extreme cases. The predicted negative impact of climate change on agriculture would also adversely affect livestock production by aggravating the feed and fodder shortages. The paper mainly reviews the impacts of climate change on livestock productive and reproductive performance.
Keywords: environment, greenhouse gas, heat stress, population, temperature
The world‘s population has reached seven billion people (Tollefson 2011). Currently, we emit over 29 billion metric tonnes of CO2 in our atmosphere each year (Boden et al 2009). Most climatologists agree that the increase in green-house gases in our atmosphere is causing an increase in air temperature (Ta) and that future increases in temperature pose a clear and present danger to the distribution and abundance of animal and plant populations worldwide (Thompson 2010). In the decades to come, if they are to survive, species will need to alter their distribution patterns, change their behavior patterns, and/or make adjustments in their physiology, either by short-term acclimation through phenotypic flexibility or by longer-term evolutionary shifts in physiological phenotype by means of natural selection (Angilletta 2009; Chown et al 2010). If scientists are to predict the consequences of global warming for animals, we will need to understand how individual animals will respond to higher air temperatures through phenotypic flexibility (Portner and Farrell 2008; Somero 2011). Direct effects from air temperature, humidity, wind speed and other climate factors influence animal performance: growth, milk production, wool production and reproduction (Houghton et al 2001).
Livestock systems occupy about 30% of the planet’s ice-free terrestrial surface area and this sector is increasingly organized in long market chains employing approximately 1.3 billion people globally and directly supporting the livelihoods of 600 million smallholding farmers in the developing countries (Thornton 2010). Livestock production is therefore a key component of world agriculture. In fact, throughout the world, human populations largely depend on domestic animals for a multitude of purposes, essentially the production of meat, fat, milk, and other dairy products, eggs and fibers like wool or cashmere as well as other purposes such as transport, draft, and provision of fertilizers, especially in developing countries. Livestock production is adversely affected by detrimental effects of extreme climatic conditions. Consequently, adaptation and mitigation of detrimental effects of extreme climates have played a major role in combating the climatic impact in livestock production (Khalifa 2003). Housing and management technologies which can reduce climatic impacts on livestock are available, but the rational use of such technologies is crucial for the survival and profitability of the livestock enterprise (Hahn 1981; Gaughan et al 2002). Therefore, this paper focused on the effect of Climate Change on Livestock Productive and Reproductive Performance.
Climate change has many elements, affecting biological and human systems in different ways. The considerable spatial heterogeneity of climate change impacts has been widely studied; global average temperature increases mask considerable differences in temperature rise between land and sea and between high latitudes and low; precipitation increases are very likely in high latitudes, while decreases are likely in most of the tropics and subtropical land regions (IPCC 2007). It is widely projected that as the planet warms, climate and weather variability will increase. Changes in the frequency and severity of extreme climate events and in the variability of weather patterns will have significant consequences for human and natural systems. Increasing frequencies of heat stress, drought and flooding events are projected for the rest of this century, and these are expected to have many adverse effects over and above the impacts due to changes in mean variables alone (IPCC 2012).
Some of the greatest impacts of global warming will be visible in grazing systems in arid and semi-arid areas (Hoffman & Vogel 2008). Increasing temperatures and decreasing rainfall reduce yields of rangelands and contribute to their degradation. Higher temperatures tend to reduce animal feed intake and lower feed conversion rates (Rowlinson 2008). There is also evidence that growing seasons may become shorter in many grazing lands, particularly in sub-Saharan Africa. The probability of extreme weather events (droughts, floods) is likely to increase. In the non-grazing systems, which are characterized by the confinement of animals (often in climate-controlled buildings), the direct impacts of climate change can be expected to be limited and mostly indirect resulting from reduction of yields and increased prices of the main feed used in animal production (OECD–FAO 2008). The development of energy-saving programs (biocarburants) may also result in increased energy prices. A warmer climate may also increase the costs of keeping animals cool by the building of adapted housing and the use of cooling devices. With higher temperatures, all countries are likely to be subject to increased animal-disease incidence but poor countries are more vulnerable to emerging diseases because of inappropriate veterinary services. Despite all the expected negative impacts of global warming on livestock, some positive effects can be addressed. For example, higher winter temperature can reduce the cold stress experienced by livestock raised outside. Furthermore, warmer winter weather may reduce the maintenance energy requirements of animals and reduce the need for heating in animal housing (FAO 2009a).
Of all the factors influencing livestock production and reproduction, climate and location are undoubtedly the most significant. In fact, climatology characteristics such as ambient temperature and rainfall patterns have great influence on pasture and food resources availability cycle throughout the year, and types of disease and parasite outbreaks among animal populations (Elsa Lamy et al 2012). Livestock generally expend more energy and increase their voluntary feed intake in order to maintain their core temperature, resulting in lower feed efficiency (NRC 1981). Maintaining an adequate temperature can be an important factor influencing design of housing and in husbandry decisions for cold susceptible animals such as poultry, swine, and young animals. Low temperatures resulting from particularly cold weather or loss of power to buildings housing confined animals, can cause economic losses from increased animal morbidity or death (Mader 2003).
The effects of climate change can be direct or indirect. The direct effects of climate change include higher temperatures and changing rainfall patterns, which could translate into the increased spread of existing vector-borne diseases and macro-parasites, accompanied by the emergence and circulation of new diseases. The indirect effects are attributable to changes in feed resources associated with the carrying capacity of rangelands, the buffering abilities of ecosystems, intensified desertification processes, increased scarcity of water resources and decreased grain production. Other indirect effects are linked to the expected shortage of feed arising from the increasingly competitive demands of food, feed and fuel production, and land use systems (Calvosa et al 2009). Smit et al (1996) attributed the indirect effects of climate driven changes in animal performance to mainly alterations in the nutritional environment.
Climatic factors or seasonal changes greatly influence the behavior of animals due to neuron endocrine response to climatic elements, consequently affecting production and health of animals (Shelton, 2000; Sejian et al 2010a; Baumgard et al 2012). Climate change is a major threat to the viability and sustainability of livestock production systems in many regions of the world (Gaughan et al 2009). High production animals are subjected to greater influence by climatic factors, particularly those rose under tropical conditions, due to high air temperatures and relative humidity (Gaughan et al 2008; Martello et al 2010).
Heat stress adversely affects milk production and its composition in dairy animals; especially animals of high genetic merit (Wheelock et al 2010). Berman, A.J. (2005) estimated that effective environmental heat loads above 35°C activate the stress response systems in lactating dairy cows. In response dairy cows reduce feed intake which is directly associated with negative energy balance, which largely responsible for the decline in milk synthesis (Wheelock et al 2010). Moreover, maintenance requirements of energy also increased by 30% in heat stress dairy animal NRC. (2007). Therefore, energy intake would not be enough to cover the daily requirements for milk production. West, J.W. (2003) reported a reduction in dry matter intake by 0.85 kg with every 1°C rise in air temperature above a cow’s the thermo neutral zone, this decrease in intake accounts approximately 36% of the decrease in milk production (Rhoads et al 2009). Drop in milk production up to 50% in dairy animals might be due to reduced feed intake , whereas, rest could be reasons of metabolic adaptations to heat stress as heat stress response markedly alters post-absorptive carbohydrate, lipid, and protein metabolism a part of reduced feed intake (Baumgard, L.H. and Rhoads, R.P. 2013). Increased in basal insulin levels with improved insulin response in heat-stressed cows (Wheelock et al 2010) and in ewes (Sejian et al 2010c) were observed that explains the shift in glucose utilization in non-mammary gland tissue affecting milk synthesis (Rhoads et al 2013). Heat stress during the dry period (i.e., last 2 months of gestation) reduced mammary cell proliferation and so, decreases milk yield in the following lactation. Moreover, stress during the dry period negatively affects the function of the immune cell in dairy cows facing calving and also extended to the following lactation (Tao, S. and Dahl G.E., 2013). Singh et al (2013) also reported negative impacts of stress on lactation length, dry period, calving interval, milk constituents and milk yield in Murrah buffaloes. Hot and humid environment not only affects milk yield but also effects milk quality. Kadzere et al 2002) reported that milk fat, solids-not-fat (SNF) and milk protein percentage decreased by 39.7, 18.9 and 16.9%, respectively. Bouraoui et al (2002) observed lower milk fat and milk protein in the summer season. Zheng et al (2009) observed that hat stress significantly reduces the production of milk, the percentage of milk fat and percentage of proteins, but that it has no effect on the content of lactose in milk.
Birth weight and survival of neonatal lambs was improved when shade was provided during late pregnancy (Hopkins et al 1980). This suggests that heat stress has an effect on the uterine environment, substantially reduces the total embryo cell number and placentome size resulting in smaller size of lambs. They would also be more susceptible to dehydration during the early stages of life. Temperatures ranging between 15°C and 29°C do not seem to have any effect on growth performance. The effects of high ambient temperature on growth performance are induced by the decrease of the anabolic activity and the increase in tissue catabolism (Marai et al 2007). This decrease in anabolism is essentially caused by a decrease in voluntary feed intake of main nutrients. The increase in tissue catabolism occurs mainly in fat depots and/or lean body mass. Lamb production is deleteriously affected by exposure to heat stress and this causes an economic loss.
High air temperature and humidity affects cellular functions by direct alteration and impairment of various tissues or organs of the reproductive system in both the sexes of the animal. Reproductive functions of livestock are vulnerable to climate changes and both female and males are affected adversely. Heat stress also negatively affects reproductive function (Amundson et al 2006; Sprott et al 2001). The climate change scenario due to rise in temperature and higher intensity of radiant heat load will affect reproductive rhythm via hypothalamo- hypophyseal–ovarian axis. The main factor regulating ovarian activity is GnRH from hypothalamus and the gonadotropins i.e. FSH and LH from anterior pituitary gland (Madan and Prakash 2007). The effects are more pronounced in buffaloes than 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; Shashikant et al 2010). Therefore, heat mitigation measures and strategies need to be adopted not only to reduce thermal stress but also to curtail fertility losses and other health consequences on animals. The expression of estrus and conception rate was recorded low during summer in crossbred cattle and buffaloes. Low estradiol level on the day of estrus during summer period in buffaloes may be the likely factor for poor expression of estrus in this species (Upadhyay et al 2009).
Heat stress reduces the length and intensity of estrus besides increases incidence of anestrous and silent heat in farm animals (Kadokawaet al 2012). It increases Adrenocorticotropic hormone and cortisol secretion Singh et al (2013), and blocks estradiol-induced sexual behavior Hein, K.G. and Allrich, R.D. (1992). Roth et al (2000) reported that developed follicles suffer damage and become non-viable when the body temperature exceeds 40°C. When female goats exposed to 36.8°C and 70% relative humidity for 48 h follicular growth to ovulation suppresses, accompanied by decreased LH receptor level and follicular estradiol synthesis activity. Reduced granulosa cells aromatase activity and viability also contributed to poor estradiol secretion (Ozawa et al 2005). Low estradiol secretion suppresses signs of estrus, gonadotropin surge, ovulation, transport of gametes and ultimately reduced fertilization (Wolfenson, D., Roth, Z. and Meidan, R. 2000). A temperature rise of more than 2°C in unabated buffaloes may cause negative impacts due to low or desynchronized endocrine activities particularly pineal-hypothalamo- hypophyseal-gonadal axis altering respective hormone functions. They also reported that low estradiol level on the day of estrus during summer period may be the likely factor for poor expression of heat in Indian buffaloes (Upadhyay et al 2009).
Multi-factorial mechanisms involved in reducing fertility of dairy animals depending on the magnitude of HS. HS reduces oocyte development by affecting its growth and maturation. It increases circulating prolactin level in animal’s results to acyclicity and infertility (Singh et al 2013). Moreover, 80% of estrus may be unnoticeable during summer Rutledge, J.J. (2001) which further reduces fertility. A period of high-temperature results to increase secretion of endometrial PGF-2α, thereby threatening pregnancy maintenance leads to infertility (Bilby et al 2008). Plasma follicle-stimulating hormone (FSH) surge increases and inhibit concentrations decrease during HS leading to variation in follicular dynamics and depression of follicular dominance that could be associated with low fertility of cattle during the summer and autumn (Roth et al 2000). However, FSH secretion is elevated under heat stress condition probably due to reduced inhibition of negative feedback from smaller follicles which ultimately affect the reproductive efficiency of dairy animals (Khodaei et al 2011). Conception rates were drop from about 40% to 60% in cooler months to 10-20% or lower in summer, depending on the severity of the thermal stress (Cavestany et al 1985). About 20-27% drop in conception rates Chebel et al (2004) or decrease in 90-day non-return rate to the first service in lactating dairy cows were recorded in summer (Al-Katananiet al 1999). Moreover, severe heat stress, only 10-20% of inseminations were resulted, in normal pregnancies, were also reported (Roth et al 2000). Oocytes of cows exposed to thermal stress lose their competence for fertilization Gendelman, M., and Roth, Z. (2012a) and development to the blastocyst stage (Gendelman, M. and Roth, Z. 2012b). Recently, Lacerda and Loureiro (2015) also reported heat stress decreases fertility by diminishing quality of oocytes and embryos through direct and indirect effects.
Embryonic growth and survival also affected during thermal stress in dairy animals. Heat stress causes embryonic death by interfering with protein synthesis Edwards, J.L. and Hansen, P.J. (1996), oxidative cell damage Wolfenson, D., Roth, Z. and Meidan, R. (2000), reducing interferon- tau production for signaling pregnancy recognition Bilby et al (2008) and expression of stress-related genes associated with apoptosis (Fear, J.M. and Hansen, P.J. 2011). Low progesterone secretion limits endometrial function and embryo development (Khodaei et al 2011). Exposure of lactating cows to HS on the 1st day after estrus reduced the proportion of embryos that developed to the blastocyst stage on the day 8th after estrus (Ealy, A.D., Drost, M. and Hansen, P.J 1993). Further, exposure of post-implantation embryos (early organogenesis) and fetus to HS also leads to various teratologies (Wolfenson, D., Roth, Z. and Meidan, R. 2000). The deleterious effects of heat stress in the embryo are most evident in early stages of its development. However, embryos subjected to high temperatures in vitro or in vivo until day 7 of development (blastocyst) showed lower pregnancy rates at day 30 and higher rates of embryonic loss on day 42 of gestation Cardozo et al (2006) and lactation yield as well as postpartum ovarian activity. Fetal malnutrition and eventually fetal growth retardation under thermal stress were also reported (Tao, S. and Dahl, G.E. 2013).
Bull is recognizing as more than half of the herd and hence, bull’s fertility is equally or more important for fertilization of oocyte to produce a good, viable and genetically potential concepts. It is well known that bull testes must be 2-6°C cooler than core body temperature for fertile sperm to be produced. Therefore, increased testicular temperature results from thermal stress could changes in seminal and biochemical parameters leads to infertility problems in bulls. The significant seasonal difference in semen characteristics was reported by several studies (Bhakat et al 2014). Cardozo et al (2006) reported seasonal effects on changes in testicular volume, hormonal profiles, sexual behavior and semen quality that affect the reproductive performance of males. Balic et al (2012) studied seasonal influence on 19 Bos taurus (simmental) bulls and found summer heat stress declined semen quality parameters. They also reported that younger bulls are more sensitive to elevated air temperatures during the summer seasons. Observed optimal semen qualities during winter, poor during summer and intermediate during rainy season and conclude that hot-dry or summer season adversely affect the various bio-physical characteristics of semen in Karan Fries bulls. Hence, heat stress significantly lowers conception as well as fertility rates per insemination of male and subsequently reduces male’s fitness (Bhakat et al 2014).
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Figure 1: Schematic view of the expected outcome of climate change as a consequence of global warming on farm animal productivity and food security (Elsa et al 2012). |
Advances in environmental modifications and nutritional management in part alleviate the impact of thermal stress on animal performance during the hotter seasons. However, long-term strategies have to be evolved for adaptation to climate change. Differences in thermal tolerance exist between livestock species provide clues or tools to select thermo tolerant animals using genetic tools. The identification of heat-tolerant animals within high-producing breeds will be useful only if these animals are able to maintain high productivity and survivability when exposed to heat stress conditions. Cattle with shorter hair, hair of greater diameter and lighter coat color are more adapted to hot environments than those with longer hair coats and darker colors (Bernabucci et al 2010). This phenotype has been characterized in B. taurus tropical cattle (senepol and carona), and this dominant gene is associated with an increased sweating rate, lower rectal temperature and lower respiratory rate in homozygous cattle under hot conditions (Mariasegaram, et al 2007). There is heat shock gene related to thermo tolerance that was identified and being used as marker in marker assisted selection and genome-wide selection to developed thermo tolerant bull that are used in breeding program. Several reports showed associations of SNP in the Hsp genes with thermal stress response and tolerance in farm animals. Association of polymorphisms in Hsp90AB1 with heat tolerance has also been reported in Thai native cattle (Charoensook et al 2012), Sahiwal and Frieswal cattle (Deb et al 2014), HSF1 gene (Li et al 2011a), HSP70A1A gene (Li et al 2011b), HSBP1 (Wang et al 2013) in Chinese Holstein cattle. There are non-Hsps genes also revealed to undergo changes in expression in response to heat stress. For example ATP1B2 gene in Chinese Holstein cows (Wang et al 2011) and ATP1A1 gene in jersey crossbred cows (Das et al 2015) was observed to have associated with thermo tolerance. These SNPs could be used as markers in marker assisted selection to developed thermo tolerant animal in early ages. Further, thermo tolerant bull can be used in breeding policy to have thermal adapted offspring.
The growing human population and its increasing affluence would increase the global demand for livestock products. But the expected big changes in the climate globally will affect directly or indirectly the animal productivity and health and the sustainability of livestock-based production systems. Extended periods of high air temperature compromise the ability of livestock to dissipate excess body heat which affects feed intake, milk production, and reproductive efficiency. However, by minimizing body temperature, greater feed intake could be encouraged. Moreover, the gross efficiency with which dietary nutrients are used by the livestock for performance could also be improved. The loss of electrolytes via skin secretions has to be minimized by improvement of housing and cooling of the animals. Increase pregnancy rate of heat stress livestock could be achieved by improving various manage-mental conditions. Identification of genes associated with thermo tolerance and using these genes as markers in the breeding program or marker assisted selection should be applied to identify animals adapted to thermal stress considering genotype-environment interactions (G × E) in addition to higher productivity. Further research on climate resilient animal agriculture is the need of the hour for sustainability in livestock farming system, especially in hot humid climatic regions.
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Received 25 July 2016; Accepted 19 October 2016; Published 1 December 2016