Effect of Climate Change on Animal Reproduction
Climate change is a global phenomenon that affects ecosystems and biodiversity, influencing various aspects of environmental conditions. Among the many repercussions, the impact on animal reproduction is of particular concern. Changes in temperature, precipitation patterns, and the frequency of extreme weather events can disrupt reproductive processes, posing challenges for both wild and domesticated animal populations. This article explores the multifaceted effects of climate change on animal reproduction and the potential consequences for species survival and biodiversity.
India’s human population (about 70%) is dependent on agriculture for their livelihood. Livestock sector is the integral part of Indian agriculture. This sector provides sustainability and stability to the national economy by contributing to farm energy and food security. It also provides economic stability to farmers due to uncertainties in the crop production and yield. Livestock sector is affected by climate change both directly and indirectly. Many environmental parameters like air temperature, humidity, wind speed and other climatic factors influence animal performance viz. growth, milk production, wool production and reproduction. The effect of climate change on animal production has been identified from(a) feed grain availability, (b) pasture and forage crop production and quality, (c) health, growth and reproduction and, (d) disease and their spread. Studies have revealed that milk yield of crossbred cows in India are negatively correlated with temperature humidity index. The influence of climatic conditions on milk production has been also observed for local cows which are more adapted to the tropical climate of India. Heat stress has detrimental effects on the reproduction of buffaloes, although buffaloes are well adapted morphologically and anatomically to hot and humid climate. Thermal stress on Indian livestock particularly cattle and buffaloes has been reported to decrease oestrus expression and conception rate. The length of service period and dry period of all dairy animals was increased from normal during drought. Heat stress affects the reproductivefunctions of dairy animals mainly by two general mechanisms (i) Increase in body temperature which can compromise reproductive function mainly due toredistribution of blood flow from the bodycore to the periphery and therebyincreasing sensible heat loss. (ii) Reduced feed intake which reduces metabolic heatproduction, affects energy balance andavailability of nutrients for productive functions such as cyclicity, establishment of pregnancy and foetal development, functions of germ cells, the earlydeveloping embryo and other cellsinvolved in reproduction.
Climate Change Scenario
One of the environmental threats that our earth faces today is the potential changes in earth’s climate and temperature patterns. An estimate indicated that the earth’s average temperature has increased between 0.3°C-0.6°C, the sea level between 10-25 cm, atmospheric carbon dioxide concentration by more than 20 percent and methane by 145 percent over pre-industrial levels. TheIntergovernmental Panel on Climate Change (IPCC) indicated that many of the developing countries tend to be especially vulnerable to extreme climatic events as they largely depend on climate sensitive sectors like agriculture and forestry. Therefore, climate change is one of the most serious long-term challenges facing farmers and livestock owners around the world. Rise in temperature due to climate change is likely to have impact on livestock production and health. The temperate cattle breeds and their crossbred will be affected more compared to zebu cattle because Indian breeds have more capacity to withstand the stress of thermal stress, feed and water scarcity, diseases and parasite load.
Heat stress assessment
A simple and most practical method to measure the heat stress in cattle and buffaloes is temperature–humidity index (THI).It plays an important role in the reproductive functions of cattle and buffaloes and it is suggested that THI has negative effect on reproductive performances of buffaloes.The test is based on atmospheric temperature and relative humidity (RH %). Equations for calculation of THI and their interpretation based on ambient temperature is measured in °F (LPHSI, 1990), When temperature is expressed in °C and Body temperature and respiratory frequency can also be used to determine heat stress in cattle and buffaloes.
Adaptation of buffaloes and crossbred cattle
Effect of temperature and humidity on cattle and buffaloes has been investigated with emphasis on their thermal stability and adaptability.Metabolism of animals has been affected by increased environmental temperature and magnitude of the response depended upon species, breed and physiological stage of the animal. Heat production study on adult cattle and buffaloes indicated that the heat produced by Zebu cattle was 62.0 Kcal/hr/100 Kg body weight against 96.3 Kcal/hr/ 100Kg for buffaloes during summer season. The heat production was more during hothumid and winter season than summer season in both cattle (80 Kcal/hr/ 100Kg) and buffaloes (107 Kcal/hr/100 Kg). This study clearly indicates higher energy needs during winter and rainy season than summer due to extra energy expenditure during rainy season and winter season. In maintaining body temperature heat dissipation by radiation, conduction, convection and evaporation plays significant role. The distribution of sweat gland, the capacity of skin vascular blood dispersion and the effective adrenergic governing the sweating rate are the mechanism responsible for efficient distribution of heat from animal’s surface. As the environmental temperature increases heat loss by conduction, convection and radiation decreases and heat loss by evaporation increases. The Zebu cattle have higher number of sweat glands and produce more sweat than Taurus cattle and the crossbred. This mechanism helps the Zebu cattle to maintain low body temperature compared to Taurus cattle. The necessity of heat dissipation to maintain thermal balance particularly during hot humid conditions force animals to employ open mouth panting mechanism with protruding tongue to complement heat elimination process.
Effect of Climate on Reproductive functions
The livestock species which are more vulnerable to climatic changes are cattle and buffaloesand both female and males are adverselyaffected. During hot dry (March- June) and hot humid (JulySeptember) season, the THI values exceeds 80 in most parts of India. The pattern of estrus varies among cattle and buffaloes. Most of the buffaloes exhibit sexual activity during cooler parts of the year (October- Feb), when the THI generally remains < 72. The thermal stress depressed estrus activity from April to June in temperate cattle. The heat stress (>32 °C) was aggravated by high humidity (vapour pressure >24 mmHg) from July to September and it had harmful effects on the ovarian activity, resulting in depressed estrus frequency during rainy season.The dairy cows that become pregnant during the warm months are less than the cool month of the year. The pattern of estrus in buffalo is different from that of cattle since majority of buffaloes exhibits estrus from October to March when ambient temperature is low and THI value is less than 70. In addition to ambient temperature, humidity and solar radiation profoundly affect expression of reproductive rhythm in buffaloes and cattle. The incidence of calving is also predominant from October to March, facilitating upbringing of offsprings due to availability of good quality fodders during this period. 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. There is decrease inLH pulse amplitude and frequency in heat stressed cattle. Plasma inhibin content was lower in heat stress cows and cyclic buffaloes. 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 gland. The higher thermal loads, if persisted for longer periods due to either non dissipation of heat or uncomfortable environment conditions, will affect production, reproduction and health on long term basis. Therefore, heat mitigation measures and strategies need to be adopted to reduce thermal stress, fertility losses and health consequences on animals.
Reproductive functions and Seasonal trends
There is adverse effect of heat stress on many reproductive functions like gamete formation, embryonic development, foetal growth and development. The potential impact of heat stress on a mammalian population can be seen by examining seasonal trends in reproductive functions of livestock species. The effects of summer in lowering fertility are much more in high yielding cows. Domestic animals with high yielding genetic potential have direct impact of global warming on reproductive performance. In addition, the existence of allelic variation in genes regulating body temperature and cellular resistance to heat shock will be responsible and may be tool to manipulate genetic adaptation to increasing global temperature in various species of domestic animals. The maximum occurrence of estrus was seen during winter months and the lowest during summer months. Due to high incidence of silent heat, large numbers of buffaloes are left un-bred during summer. Season of calving had a profound influence on the service period in this species. The longer service period of buffaloes in summer may be due to the high incidence of silent estrus. Severe heat stress days with temperature humidity index > 85 were from May to August. After onset of monsoon in June /July difference between morning and evening THI is reduced and buffaloes got some opportunity for relief from thermal stress. From May to June, THI with a value of > 80 increased by approximately 450% than March. Low temperature and THI during nights in summer provide an opportunity to buffaloes to dissipate heat during night hours compared to day hours. This may be the reason that buffaloes experienced less stress during hot dry season compared with hot humid season. The peak of reproductive activity in Zebu and crossbred cows was observed in March which coincided with the start of increase in sun shine days and subsequently through in reproductive behaviour was observed during peak solar radiation and hot days. Reproductive activity in buffaloes started increasing from July and reached at the peak during October. The expression of estrus and conception rate was recorded low during summer in crossbred cattle and buffaloes.The levels of estradiol 17ß on the day of estrus were significantly low during this period in both species. 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. During heat stress, motor activity and other manifestations of estrus reduced and the incidence of anestrus and silent ovulation are increased. Due to these effects a reduction in the number of mounts during heat stress compared to cold weather, leading to poor detection of estrus. The effects of heat stress can be directly related to the increase in rectal temperature of heat-stressed cows/ buffaloes during summer/ hot humid season. A small increase in maternal rectal temperature would cause decreased pregnancy rates in cattle. The increase in body temperature affects the reproductive tract and the early embryonic development.
Reproductive disorders and Season/Climate
The incidences of reproductive disorders were higher from April-September, when ambient temperature and humidity were higher.The prevalence of retained placenta was highest during JulySeptember. The overall reproductive disorders were maximum in September and minimum in November. Seasonal effects on reproductive disorder associated with calving in cattle have been observed by Verma et al. (1986). The author observed that the reproductive problems were highest during rainy season (14.87%) and lowest during winter-season (7.44%). Occurrence of retained placenta, dystocia and urethra prolapse was 11.27, 2.38 and 1.88%, respectively in unfavourable summer/rainy season. The increased intervention of man in regulating behaviour and environment of livestock so as to exploit the best of their genetic potentials has led to an increase in the incidence of the reproductive disorders. Underfeeding coupled with high environmental temperature stress was also incriminated for long anestrous and anovulatory periods. Inadequate nutrient intake has been found to deplete body energy reserves resulting in extended interval from calving to first estrus. Season of calving had influence on the reproductive performance.
Climate change impact on reproductive functions
A rise in temperature by >4°C due to global warming is likely to impact cattle and buffaloes negatively. The increase in thermal stress days by 260% will negatively impact estrus expression/ ovarian activity and conception rate in cattle and buffaloes. The effect may be much more pronounced in buffaloes, temperate and crossbred breeds compared to indigenous breed of cattle due to poor adaptability of these species to tropical climatic conditions. Changes in climate would lead to decrease in milk yield and conception rate in dairy cows. Hahn (1995) further reported that conception rates in dairy cows were reduced 4.6% for each unit change in THI, when the THI reaches above 70. Increase in temperature and/or humidity have the potential to affect the conception rates of domestic animals which were not adapted to these conditions. The number of changes in reproductive performance due to further global warming will include: · Decreased duration and intensity of the estrus period. · Decreased conception (fertility) rate. · Decreased size and development of ovarian follicles. · Decreased fetal growth and calf weight at calving. · Increased risk of early embryonic losses. · Increased number of artificial insemination per conception. · Increased incidence of silent heat in buffaloes.
Temperature Extremes and Reproductive Physiology
- Heat Stress
Rising temperatures, especially in regions prone to heatwaves, can lead to heat stress in animals. Heat stress adversely affects reproductive physiology by disrupting hormonal regulation, reducing fertility, and increasing the likelihood of embryonic mortality.
- Altered Breeding Seasons
Shifts in temperature patterns can alter the timing of breeding seasons for many species. This mismatch between optimal reproductive timing and resource availability, such as food and shelter, can result in reduced reproductive success.
- Impact on Sperm Quality and Viability
Heat stress can impair sperm production and quality in male animals. Elevated temperatures may lead to decreased sperm motility and increased DNA damage, affecting fertility and reproductive success.
Changes in Food Availability and Quality
- Altered Foraging Patterns
Climate change influences the distribution and abundance of vegetation, impacting the availability of food resources for herbivores. Changes in foraging patterns and the quality of available food can affect reproductive energy reserves and overall reproductive health.
- Cascade Effects on Predators and Prey
Disruptions in the reproductive patterns of prey species can have cascading effects on predator populations. Changes in the abundance and availability of prey can challenge the reproductive success of predators, leading to potential imbalances in ecosystems.
Water Scarcity and Reproductive Challenges
- Dehydration and Stress
Water scarcity, a consequence of changing precipitation patterns and prolonged droughts, can lead to dehydration and increased stress in animals. Elevated stress levels have been linked to reproductive abnormalities and reduced reproductive success.
- Disruption of Aquatic Reproduction
Aquatic species, including fish, amphibians, and aquatic mammals, rely on specific water conditions for successful reproduction. Changes in water temperature, flow patterns, and oxygen levels can disrupt the breeding behavior and reproductive success of aquatic species.
Extreme Weather Events
- Storms and Flooding
Extreme weather events, such as storms and flooding, can directly impact reproductive habitats and nesting sites. Destruction of nests, loss of offspring, and changes in the availability of suitable breeding environments can occur.
- Migration Challenges
Many species undertake seasonal migrations for breeding purposes. Extreme weather events can disrupt migration routes, leading to delays or detours that may affect the synchronization of reproductive activities.
Adaptation Strategies
- Behavioral Adaptations
Some species exhibit behavioral adaptations in response to climate change. Changes in nesting behavior, alteration of breeding territories, and adjustments in the timing of reproductive activities may help mitigate the impact of environmental changes.
- Physiological Responses
Certain species may exhibit physiological adaptations to cope with changing environmental conditions. For example, alterations in metabolic rates or hormone production may occur to enhance reproductive success under stressful conditions.
- Human Intervention and Conservation Efforts
In the face of climate change, conservationists and wildlife managers may implement interventions to support endangered or vulnerable species. This may involve habitat restoration, controlled breeding programs, or the creation of protected zones.
Conclusion
The impact of climate change on animal reproduction is a complex and interconnected issue that extends across diverse ecosystems. From disruptions in reproductive physiology due to temperature extremes to changes in food availability and the increased frequency of extreme weather events, the challenges are manifold. Conservation efforts and adaptive strategies are crucial to mitigate the adverse effects on animal reproduction, safeguard biodiversity, and ensure the resilience of ecosystems in the face of ongoing climate change. As we strive to address the root causes of climate change, it is equally important to implement strategies that support the adaptive capacity of animal species, fostering their ability to cope with a changing environment.
The high temperature adversely affected production and reproduction in buffaloes and cattle. The reproductive efficiency in these species decreased considerably. The frequency, intensity and duration of estrus decreased due to adverse climatic conditions in the summer season. Conception rate falls between 20-30% in summer compared to winter. Reproductive disorders viz. Dystocia, retained placenta and uterine prolapsed were higher in crossbreds compared to native breeds of cattle. Incidences of anestrus, silent estrus were more in buffaloes during summer period. Increase in temperature due to global warming is likely to further reduce the reproductive efficiency and milk production of livestock species. Therefore, it will be important to modify the managemental practices of cattle and buffaloes as per the climatic conditions. It requires development of suitable breeds by selection of cattle and buffaloes species which are more tolerant to heat stress and can sustain the productivity in the changing climatic scenario. Climatic conditions will ultimately be the limiting factors for livestock production system. Therefore, changing of micro environmental conditions in the tropics is very important particularly for exotic and crossbred breeds of cattle and buffaloes compared to heat tolerant breeds (Zebu).
Compiled & Shared by- This paper is a compilation of groupwork provided by the
Team, LITD (Livestock Institute of Training & Development)
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Reference-On Request.
