Due to the super-imposing influence of the environment on the survival, behavior, character (expressed as performance, productivity and responses) of farm animals, great consideration is often given to modifying the environment by livestock owner to ensure its suitability.
Equally of primary importance is the need for adaptation and acclimatisation of the hereditary and physical features of the animal itself to the predominating environment if stock must survive under favourable and harsh environment conditions.
Adaptation and acclimatisation of the animal to the environmental conditions form the basis for any modification or adjustment required on the part of farmer to apply into the management system for survival and improved productivity of the stock.
In other words, an animal must first and foremost undergo natural selection for survivals in an environed before improve growth, reproduction, and other productive traits can be contemplated. By natural selection therefore, the genes favourable for survival in that environment interact, interrelate, associate and coordinate with the environment to ensure the survival of the animal.
This condition is known as adaptive norm which is an array of related genotype capable of adjusting to the demands of the environment. It embodies heterosis, adaptive polymorphism and homeostasis. From the genetic point in view, fitness is the ability to produce offspring which will survive and produce their likes.
Thus, a biologically fit population is one that is capable of adapting to its environment in such a way that it can survive and reproduce. The fitness of animals includes more than their ability to survive but also to withstand the demands of future environment.
These criteria of fitness or ability will depend on adaptation variability, stability and rate of environmental change. It is important to note that while domestication improves on all criteria of
fitness, diseases negate and reduce fitness to almost nil.
It may be deduced from the foregoing that living system not only respond to the environment but also control and regulate their reactions towards environmental effects. This is the concept of homeostasis.
Concept of Homeostasis
Homeostasis is the constancy of the internal environment of an animal and the mechanism by which such constancy is maintained. It involves regulation of many internal body variables as temperature, PH, salt, water content, nutrient and chemical composition etc. mammals and birds that occupy the highest evolutionary scale, possess the greatest regulatory capacity and regulate the greatest number of internal factors with the best precision through a deployment of appropriate physiological adaptation and compensation.
Physiological Adaptation
Any change in the internal condition of an organism which favours its survival during changes in the environment is known as physiological adaptation.
Physiological adaptation involves the possession of mechanisms and capacity that allow organism to adjust itself to other living organisms and to external physical environment.
Physiological adaptation may manifest as acclimatisation, acclimation, habituation, learning and conditioning.
Acclimatisation: Acclimatisation refers to a long term adaptive physiological adjustment which results in an increased tolerance to continuous or repeated exposure to complex climatic conditions occurring under natural condition.
Acclimation: Acclimation refers to adaptive changes to a single climatic variable normally produces in an artificial environment e.g. increasing temperature in a climatic chamber.
Habituation: habituation is a gradual change which may lead to a loss of response as a result of repeated stimulation.
Learning: Learning is the acquisition of a new response or a qualitative change of an existing response which may be inform of inhibition or increase of an existing response by a new stimulation.
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Conditioning: Conditioning is the transfer of an existing response of new stimulus. Besides physiological adaptation, other forms of adaptations in organisms include biological and genetic adaptation.
Biological Adaptation
Biological adaptation involves the morphological, anatomical, physiological, biochemical and behavioural characteristic of the animal which promote welfare and favours survival in a specific environment.
Genetic Adaptation
Genetic adaptation refers to the heritable animal characteristics, which favour the survival of a population in a particular environment; such favourable characters are derived from evolutionary changes over many generations.
It is important to note that individual animal has limit to its ability to regulate its reaction according to genetic make-up.
Animal has a defined range of environmental variation within it can live. This is referred to as Zone or Range of Tolerance, beyond which the animal will exhibit some resistance, suffer some damage, and eventually succeed.
The Zone or Range of tolerance has upper and lower limits at either ends also known as Upper and Lower Incident Lethal levels at which death occurs.
The micro-climatic environment has the most profound influence on animal production, physiology and behavior. It is determined by such meteorological factors as: air temperature, air pressure, relative humidity of air, wind density and air density as well as radiation (defined as the
heating and cooling of the atmospheric air).
Man can modify his micro-climate by building houses, offices, travelling in cars, planes, ships, wearing clothes etc. animals on the other hand modify the micro-climate by burrowing or moving into or from these meteorological factors in search of warmth, cold or calm.
The behavioural entrance or escape from inclement meteorological conditions is, however, limited in providing the required optimum body conditions at all times. The primary means by which animal control, or respond to variations in the meteorological factors, and thereby maintain its body conditions, is through the flow of energy or total energy exchange between the animal and environment.
Energy is the ability to do work. It is regarded biologically as the source of life and movement. All life process involves in one way or other the expenditure of energy through work. An animal cannot continuously gain or lose energy to the environment, otherwise it will die. Thus animal tolerates energy gains or losses from their immediate environment only within certain limits in the Zone or Range of Tolerance.
An animal exchanges its energy with its environment (micro-climate) through radiation, convention, condition, evaporation and metabolism. The pathways of energy flow are many and characterised by direct interaction between animal and its environment. In order to survive in a given environment over a long period of time, the energy gain of an animal must be equal to energy loss.
Modes of Energy Transfer
1. Radiation: Radiation is a form of energy transfer in wavelength by electromagnetic waves. Radiant energy is ubiquitous (i.e. found everywhere) and is emitted from all objects whenever the
surface temperature of the object exceeds absolute zero. Energy loss by radiation is one of the primary sources of heat loss by animals. Objects at ambient temperature (23 – 250C) radiate
mostly infrared rays at long wavelength and beyond. Objects at very high temperature e.g. the sun radiate shorter wavelength in the ultraviolet and blue region. The amount of energy radiated is proportional to the 4th power of the surface temperature in absolute degree i.e.
Where δ = Stetan – Boltzman Constant
E = Total energy radiated/M2/S
T0 = Temperature (Absolute) of surface radiation
Also,
E = e δ T4
Where e = Emissivity
Radiation in the natural environment is derived from 2 – main sources: high temperature of the sun (direct source) and the extended source which is the thermal radiation from the ground, trees clouds or atmosphere.
An animal exposed to direct solar radiation, absorbs certain quantity of incident energy depending on the surface exposed, angle of surface and absorbance of the surface. The absorbance of the surface determines the greatest percentage of the incident radiation absorbed.
An animal with a black body surface absorbs all the incident energy and its body temperature is much more affected by the quantity of radiation falling on its surface.
2. Conduction: When an object is in contact with another, molecular motion can be transferred from one object to another by a process of bombardment similar to diffusion activity. Such transfer of molecular motion is known as thermal conduction.
Air for example, is a poor thermal conductor while water is a good one. Conduction however occurs only from regions of higher to region of lower temperature. It is only the heat that is transferred and not the material.
3. Convection: this is a special form of heat transfer by conduction. It occurs where the surrounding medium is fluid e.g. air or water.
Upon increase in temperature air or water rises due to its decreasing density (becoming less dense) and the layer of fluid next to the warm object is replaced by another mass of cooler (more dense) fluid. The exchange of energy by convection is proportional to:
a. Surface area
b. Temperature differential between animal surface and freeair beyond the boundary layer
c. Convection coefficient
C α A (Ts – Tc)
C = hcA (Ts – Tc)
Where hc = Coefficient of convection which depends on thermal conductivity and thickness of the boundary.
A = Surface area
Ts – Tc = Temperature differential between animal surface and free air beyond the boundary layer.
The Boundary Layer plays an important role in maintaining body temperature. The concept of Boundary Layer is given as: Just immediately to the surface of the animal is a bound layer of air which is more or less stationary and it is the transfer zone between the integument temperature (skin temperature) and temperature of the free air beyond the boundary layer.
As it is already known heat is always transferred along the temperature gradient occur between the surface temperature of animal and air temperature of short distance away from the surface. The rate of heat conduction across the boundary layer is dependent on:
(1) The thickness of the layer
(2) The temperature differential between the skin and fluid
(3) The thermal conductivity of the fluid
(4) Movement or stillness of air.
Transfer of energy across the boundary involves two methods: by molecular conduction across the boundary layer and into the free air and by mass movement of air. Natural convection occurs when there is no wind or free air while forced convection occurs when there is wind to
transfer energy.
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