Environmental Physiology | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Introduction

Right after birth, animals react to their surroundings, like temperature, light, and humidity, by adjusting their body functions. External factors affect animals through direct contact with skin or sensory organs like the eyes.

Physiological Responses

• Skin and sensory receptors relay information to the brain, triggering compensatory actions.
• Key concepts include homeostasis, hibernation, aestivation, biological rhythms, and stress responses.

Homeostasis

• Body's ability to maintain stable conditions despite external influences.
• Involves temperature regulation, chemical balance, and cardiovascular activity.
• Blood composition is tightly regulated, and deviations are corrected by homeostatic mechanisms.

Adaptations in Different Climates

• Animals in hot or cold climates adjust metabolism, respiration, blood circulation, and fluid balance.
• Cardiovascular changes and electrolyte transport adapt to specific needs.

Water Balance

• Animals need to maintain water balance by offsetting losses through evaporation, urine, and feces with equal intake from drinking and food.
• Despite variations in size and structure, water balance is crucial for long-term survival.

Variations in Thermal Tolerance

• Different animals tolerate diverse temperatures; for example, humans tolerate 27-28°C, while arctic species can endure -40°C.

Central Nervous System and Endocrine Regulation

• The brain and spinal cord (central nervous system) control internal conditions.
• Somatic/Cerebrospinal part manages voluntary and involuntary muscle control through nerves.

Hypothalamus and Neurosecretory Tract

The hypothalamus, located within the central nervous system (CNS), serves as the control center for various physiological functions such as thermoregulation, feed and water intake, amegulation, and cardiovascular activity. Additionally, it plays a crucial role in connecting the nervous and endocrine systems through the neurosecretory tract leading to the pituitary gland.

Physiological Actions Regulated by Homeostatic Mechanisms

• Several homeostatic mechanisms work in tandem to regulate key physiological actions, including heat production, heat loss, defense against cold, and body fluid regulation. These mechanisms address heat production during metabolic processes, heat loss through convection, radiation, and evaporation, as well as fluid intake, exchange between plasma and interstitial fluid, kidney function, and fluid loss.

Heat Production in Life Processes

• The continuous production of heat accompanies life processes in the body. Animals generate heat through the transformation of chemical energy from food into work. Heat absorption from solar radiation further contributes to the animal's heat gain. This heat gain must be balanced by heat loss through convection, radiation, and evaporation. The latent heat of evaporation, involving water evaporated from the skin and respiratory tracts, represents a significant component of heat loss.

Proportion of Heat Loss in Different Environments

• At 20°C environmental temperature, the proportion of heat loss varies through convection, radiation, and evaporation. Additionally, the heating of consumed food, heating of air inhaled into the lungs, and heat loss through urine and feces contribute to the overall heat balance.

Maintaining Body Temperature and Sensitivity to Changes

• The balance between heat production and heat loss determines the constancy of body temperature. Any imbalance over time results in variations in body temperature. Animals, especially those with a constant body temperature, operate within narrow limits (0°C to 45-50°C). Human sensitivity to temperature changes, particularly affecting nerve cells, emphasizes the need for precise thermoregulation.

Thermoregulation in Animals

• Animals without mechanisms for heat regulation are termed "poikilothermal," while those with such mechanisms are termed "homeothermal" or "homoiothermal." These classifications highlight the adaptation of organisms to either tolerate or regulate temperature variations in their internal environment.

Temperature Dynamics in Organisms

Heterothermal Adaptation

• Animals with the ability to transition from homeothermic to poikilothermic states for adaptation to unfavorable conditions.

Diurnal Variations in Body Temperature

• Regular fluctuations in human body temperature throughout the day, with the highest levels observed in the afternoon and the lowest in the early morning.

Factors Affecting Body Temperature

• Various conditions influencing normal variations in the body temperature of homeothermic organisms, including age, sex, season, time of day, environmental temperature, exercise, eating, digestion, and water consumption.

Heat Balance and Thermoregulation

• Discussion on thermal steady state, thermo-neutral zones, and the mechanisms involved in maintaining heat balance, including circulatory adjustments, insulation, and metabolic changes.

Heat Loss Mechanisms

• Explanation of the ways heat is transferred from the body to the environment, encompassing radiation, convection, conduction, and evaporation of water.

Defense Against Cold

• Strategies employed by animals to defend against cold, such as conserving heat through insulation, increasing metabolism, and muscular activity like shivering in response to falling environmental temperatures.

Body Fluid Regulation

• Discussion on the alteration of volume and composition of body fluids due to diseases, high altitudes, heat, and stressful conditions. Emphasis on hormonal mechanisms involving adrenal and posterior pituitary glands in normal fluid regulation.

Fluid Intake

• Our body constantly loses water and salts.
• Thirst is the body's signal for water intake, triggered by dryness in the mouth and pharynx.
• The hypothalamus in the brain regulates water intake; warmer temperatures increase thirst, while cooler temperatures reduce it.
• Active transport mechanisms in the gut control the absorption of ions, influenced by hormones like cortisone.

Fluid Exchange between Blood and Tissues

• Capillary permeability affects fluid exchange between blood and tissues.
• Histamine increases capillary permeability.
• Temperature changes affect capillary wall permeability; higher temperatures facilitate filtration.
• This is crucial in tissues like skin, especially in varying conditions.

Fluid Exchange in the Kidneys

• Sympathetic nerves can cause kidney vasoconstriction, reducing blood flow and glomerular filtration rate.
• Renal-vasoconstriction occurs reflexively in response to low arterial pressure.
• Increased blood volume inhibits sympathetic nerve impulses to renal arterioles.
• Aldosterone and ADH levels adjust blood volume by acting on the kidneys.

Fluid Loss

• Excessive water loss (e.g., in a hot environment) or reduced water intake (due to illness or withholding) can lead to dehydration.
• Animals conserve water by producing concentrated urine and increasing ADH levels.
• Metabolic rate decreases to minimize water loss through respiration and skin.

Consequences of Reduced Water Intake

• Reduced water intake leads to concentrated plasma and reduced volume.
• Increased colloid osmotic pressure draws fluid from interstitial spaces.
• Adequate blood volume is maintained by minimizing water loss through various means.

Hypothalamus and Homeostasis

• The hypothalamus regulates feed intake based on carbohydrate and fat needs.
• It influences various behaviors and physiological patterns in animals.

Endocrine System and Homeostasis

• Environmental temperature inversely relates to the basal metabolic rate.
• Nervous and endocrine systems work together to regulate metabolic rate in response to temperature changes.

Survival Strategies in the Animal Kingdom

Hibernation and Aestivation

• Some mammals, like marmots, groundhogs, hamsters, and hedgehogs, maintain a high body temperature in favorable temperatures but switch to hibernation in the cold.
• Hibernation involves a pause in activity, reduced body temperature, metabolism, heart rate, and respiration during winter.
• The animal can naturally return to normal temperature without external heat.
• Aestivation is a summer sleeping state, conserving energy and water through reduced metabolic rates.

Biological Rhythms:

• Biological rhythms are repeated physiological processes influenced by a biological clock.
• Circadian rhythms follow 24-hour day-and-night cycles.
• Some are habitual, like cows assembling for milking, while others, such as heartbeat, temperature, and metabolism, have their own biological clock.

Stress Syndrome

• Animals may face various stress types: climate stress, nutritional stress, social stress, or internal stress.
• Stress responses include acute changes (fight or flight), specific actions based on conditions, and non-specific reactions causing general adaptation syndrome.
• Stress affects blood characteristics, respiratory function, metabolism, and more.

Adjustments to Stress:

• Stress triggers changes in physiological systems controlled by the nervous and endocrine systems.
• Extreme stress can lead to injury or death.
• Adaptations involve alterations in hormone concentrations, enzyme levels, and metabolite turnover at the cellular level.

Habituation:

• Habituation occurs when an animal, after repeated exposure to a stimulus, decreases its natural response.
• For example, animals may become less responsive to a repeated, moderate stimulus over time.

Adaptations in Animal Survival

Mechanism of Adaptations

• Adaptations involve morphological, anatomical, physiological, biochemical, and behavioral characteristics that support animal welfare and survival in specific environments.
• Mammals use hair as a defense against ambient heat and radiation, influencing skin receptors and behavioral responses.
• Sheep and cattle adjust to hot-wet and hot-dry climates through anatomical and physiological changes.
• Coat length, thickness, and color in animals are adapted to regulate heat passing to or from the animal.

Adaptation to Hot Environments

• Loose wool coats in sheep act as insulators but can trap heat, preventing penetration to the skin.
• Animals in specific regions develop coats suitable for their environment.
• Ultraviolet light intensity in dry subtropics leads to black pigment in tropical animals, preventing skin penetration.

Metabolic Rate and Summer Adaptation

• Sheep and cattle have lower metabolic rates in summer.
• Exposure to heat reduces pituitary hormone output, resulting in lower metabolic rate, thyroid, adrenaline, and gonadotrophin activity.
• Some animals adapt well to these lower rates in hot-dry or hot-wet areas.

Adaptation to Cold

• Higher metabolic rates and non-shivering thermogenesis defend animals against cold.
• Sympathetic nervous system stimulation releases epinephrine and activates pituitary, thyroid, and adrenal cortex for non-shivering thermogenesis.
• Low melting points of pads on feet of certain animals contribute to tissue flexibility in cold climates.

Environmental Factors and Animal Behavior

• Animal behavior is a response to internal and external conditions.
• Sensory capacities, like sound localization and odor detection, play a role in behavioral patterns.
• Selective breeding in domestic animals has produced specific behaviors, such as fighting bulls, racing horses, and guide dogs.

Cyclic Locomotor Activity

• Many animals exhibit regular patterns of locomotor activity controlled by biological clocks.
• Environmental factors, called zeitgebers, cyclically govern these endogenous rhythms.
• Examples include sound localization and odor detection, which play significant roles in various behaviors.

Living Spaces and Behaviors of Domestic Animals

Living Space Classification

• Domestic animals are categorized based on living space availability:
• Free-ranging animals like cattle and sheep.
• Confined animals like rabbits and house pets.

Home Range

• Free-ranging mammals establish a home range where they live and wander.
• Home range size varies; for instance, sheep may extend their range within 120 acres.
• Artificial limitations, like fences, confine domestic animals, recognized by visual or olfactory cues.

Behavioral Systems and Animal Husbandry

• Grazing, feeding, and sexual behavior impact animal husbandry economics.
• These systems are studied more extensively due to their economic significance.

Thermoregulation in Mammals and Birds

• Animals exhibit specific behaviors in response to surrounding temperatures.
• High temperatures prompt activities like wallowing, rooting, or extending wings.
• Low temperatures lead to behaviors such as fluffing feathers, covering heads, and huddling.
• In cold environments, animals may increase feed intake to maintain heat balance.

Thermoregulatory Behavior

• Thermoregulation involves physical and physiological adjustments.
• Physical adjustments include posture changes, altered water consumption, and shifts in nocturnal habits.
• Physiological adjustments involve involuntary somatic responses and voluntary behavioral changes.
• The central nervous system (CNS) and hypothalamic centers control thermoregulatory behaviors.
• The anterior hypothalamus is the sensory receptor for thermoregulation, with cutaneous temperature being crucial for responding to surrounding temperatures.
• Skin, respiratory surfaces, and endocrine glands influence both behavioral and physiological adjustments.