With regards to Animal Energy Balance, since mammals and avian that form bulk of farm animals are homeotherms and hence maintain a constant body temperature, they possess means for producing and losing heat during extreme cold or heat muscular activities form the animal heat gain.
Hear Production: Animal produce heat when transforming chemical energy of food into work. Under normal circumstances a grazing animal while in the sun may gain heat directly or indirectly from solar radiation. The added solar heat and metabolic heat generated from food and muscular activities form the animal heat gain.
The heat gains in one animal vary from another as aresult of:
- Theintensity of heat production by different organs varies depending of the weightof the organ. On net weight basis, the brain generates heat faster than themuscular tissue due to higher density of the former
- Thebody size also affects heat requirement, for instance, smaller sized animalrequire a greater heat production per unit weight than larger sized animal ifthe same temperature is to be maintained. This is because the smaller theanimal, the greater the surface area and the more heat loss
- Specificsurface area which is the ratio of surface to volume determines heat loss. Thisis because with increasing body size, the surface to volume of the animalincreases, and therefore the relative surface from which is dissipatedincreased. When heat production is better expressed per unit surface area, theeffect of body size is largely eliminated. Heat production is better expressedin term of body surface area.
Evaporation: Evaporative water loss occurs from the skin after it has been secreted by the sweat glands. Other areas of evaporative of water losses include respiration water loss and sweating. The two forms of water are two major processes used in temperature regulation in animal.
The process of evaporation of water requires a large amount of energy and is therefore used to cool the body of animal. Evaporation occurs only when the air is not saturated already with water.
Metabolic and Chemical Heat Transfer in Animal Energy
With increasing environmental temperature body in animal energy for homeotherm is constant while that for poikilotherm increases the metabolic rate and decreases with decreasing ambient temperature similar normal chemical reaction.
However, with homeotherms , the metabolic rate decreases with increasing temperature and increase with decreasing temperature. Other chemical reaction like muscular activities, shivering and metabolic reaction of the liver are also involved e.g. liver apart from producing heat also releases glucose into circulation which is a basic requirement for chemical temperature regulation.
Factors Affecting Heat Production in Animal Energy
Ingestion of food leads into in heat production whichvaries greatly with the type of nutrients ingestion. Also in ruminants therumen micro-organism constitutes an auxiliary source of heat (about 10 percent) in addition to the animal’s moral heat production. The fetuses as well aslactation add up to the amount of heat production by the dam.
During severe cold or active physical exercise, the heat generation by muscular activities increases while the heat from abdominal organ decreases. In cattle and sheep, heat production is about 1o per cent greater in standing position than in the lying position.
In pregnant animal, foetus metabolism together with the acceleration of body processes of the dam result in an increment in the total heat production.
The presence of brown fat is another source of heatproduction. Brown fat is found in rodent but has been found in other animalsincluding man. It is especially useful in homeotherms exposed to cold andhibernators.
The brown adipose tissue is distributed around vital organs of the thorax, along sympathetic ganglia of the central nervous system around the cervical and thoracic segment of the spinal cord to prevent loss of heat and excessive cold from inactivating the function of the vital organs.
Both the metabolic and thermogenic action of the brown fat re by stimulation from sympathetic nervous system under cold condition.
Heatloss: Heat loss from animal body is by two means:
- Sensibleheat loss i.e. through radiation,convection and conduction
- Insensiblethat loss which is through evaporation of water.
Heat loss by means of sensible of sensible heat loss offers little or no control for the animal to regulate unlike insensible heat loss in which animal exerts market control.
Heat transfer by sensible heat can be in either direction of loss or gain, while insensible heat transfer is only along one direction i.e. through loss from animal to the environment.
Heat transfer involves two forms of gradient:
. Inner gradient and out gradient: Inner gradient concerns with heat flows from the core of the body to the surface of the body.
. Outer gradient on the other hand refers to the heat that goes from the surface of the body to the environment.
Heat transfer along the inner gradient is affected by conduction across the tissues and by convection by the blood. Along the outer gradient, heat transport is by the following:
- Convectionacross the hair coat and boundary layer of still air surrounding the body
- Convectionfrom the boundary layer of air to the full moving air
- Byradiation from the tips of the air across the boundary
- Evaporationacross the hair coat and boundary layer.