APM 210 Ecology Lecture Notes - February 2024 PDF
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Uploaded by EnoughRealism2529
University of Ibadan
2024
O. A. Sokunbi
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Summary
These lecture notes cover the ecology of animal production, examining the influence of various environmental factors on livestock performance. The document discusses climate elements like temperature, humidity, and solar radiation, and how they affect animal physiology and production parameters.
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APM 210 Lecture notes: February 2024 O. A. Sokunbi (Animal Physiology) ECOLOGY OF ANIMAL PRODUCTION Ecology is the study of organisms in relation to their environment. An organism’s structure, physiology, behaviour, adaptation processes and evolution are influ...
APM 210 Lecture notes: February 2024 O. A. Sokunbi (Animal Physiology) ECOLOGY OF ANIMAL PRODUCTION Ecology is the study of organisms in relation to their environment. An organism’s structure, physiology, behaviour, adaptation processes and evolution are influenced by its environment. Influence of Environment on Animal Production Modern livestock producers are concerned over producing environment conditions for their animals that will lead to high performance. To obtain a near optimal input-output ratio for various classes of livestock, the required range of temperature and relative humidity are 10 to 20 °C and 55 to 65 % respectively. A medium level of sunshine is also required. Because these conditions seldom prevails, it becomes necessary for livestock producers to continually improve their animals’ environment in order to obtain the desired level of performance as determined by production parameters such as gain in weight, yield of milk, feed conversion efficiency, eggs, wool/hair, and other outputs such as work (from work animals). Effect of Climate on Livestock Production The elements of climate; temperature, sunshine, wind, light, precipitation, and humidity are generally thought of as the prevailing environmental conditions but are actually only a portion of the animal’s environment. Still, the elements are important because they have influence on most of the other elements of the animal’s environment in some ways. The conditions created by the climatic elements, not only directly affect the animal but also influence the growth and quality of feedstuffs, the incidence of diseases and parasites, the efficiency of labour and other conditions. Direct Effect of Climatic Elements Temperature This is the major climatic element that affects the physiological functions of an animal. For most domestic animals there is a range of environmental temperatures within which no extra body heat production is needed to keep the animal warm or cool. This is referred to as the ‘comfort zone’. Outside this comfort (or thermoneutrality) zone, other elements of the climate assume greater significance in the comfort of animals. Humidity 1 APM 210 Lecture notes: February 2024 O. A. Sokunbi (Animal Physiology) This is the water vapour content of the air. For most domestic animals, relative humidity is apparently not an important factor in animal performance except when above 75 % at higher temperatures. Humidity becomes increasingly important as an interacting factor when air temperature rises or falls. Solar radiation At low temperatures, solar radiation tends to raise the temperature of the animal’s surrounding, which helps it maintain thermal balance, but at high temperatures, solar radiation imposes an excess heat load on the animal. Precipitation (rainfall) Comfort is improved for animals exposed to rain on a hot day, since heat is removed from the body more rapidly than normal through evaporation. At low temperatures, exposure to rain may cause considerable discomfort because of a rapid rise in heat loss from the body as the precipitation evaporates. Photoperiod This refers to the period of light for a given day. Photoperiod varies with latitude and season. Near the equator, there is little change with season but variations could be up to ± 2 hours at 30° latitude. The length of photoperiod has an influence on the breeding season for sheep and goats and affects the onset of sexual activity in many species of poultry. Wind velocity A high wind velocity increases the rate of movement of air around the animal’s body, thereby accelerating the rate at which heat from the body is dissipated into the atmosphere. However, when the ambient air temperature exceeds the temperature of the animal’s surface, a significant amount of heat may be accumulated in the animal’s body. Altitude Altitude influences the prevailing air temperature pattern. Air temperature tends to diminish at a rate of about 0.65°C per 100 metres increase in elevation. Above 2500 metres, livestock begin to feel the stresses imposed by insufficient oxygen. In addition to low oxygen pressure, the dry atmosphere of high altitude affects the body’s water balance, temperature regulation, respiration, and vulnerability to diseases. In spite of these disadvantages, reasonably productive livestock enterprises, using local breeds are carried on at 2000-3000 metres elevation. 2 APM 210 Lecture notes: February 2024 O. A. Sokunbi (Animal Physiology) Indirect Effect of Climate When we consider the animal’s total environment, the amount and quality of feed available is the most important factor. The amount and quality of feed consumed directly determines the productivity of the animal. This also determines an animal’s resistance to other conditions, such as diseases. Feed supply is markedly affected by temperature, humidity, rainfall, solar radiation, light, wind, altitude, and soil fertility. High temperatures for instance cause crops to mature rapidly, with a corresponding decline in nutritive value. On the other hand, low temperatures cause a decline in crops growth thereby reducing feed supplies. Rainfall distribution and humidity level also play important roles in the amount and quality of feed available for animals. Low quality or inadequate feeding brings the animal under nutritional stress, causing greater susceptibility to health problems. Maintaining Homeostasis When homeotherms leave the intrauterine environment (which is ideal for temperature) they struggle to maintain homeostasis (constant body temperature). The animal tries to achieve a heat balance by evolving sensitive and quickly acting mechanisms that balance any change in heat production or heat loss. The body temperature of most mammals is kept at a relatively high level (usually 38°C or higher) that is considerably above the environment temperature to which the body is exposed most of the time. Control of the body temperature is achieved by varying both the rate of heat production and heat loss. Food energy is required for this maintenance. Most mammals will utilize more than 30 % of the energy they consume throughout life to provide heat or promote cooling to maintain a stable equilibrium. Heat balance in the animal body may be expressed as S = (M – W) – (R + C + E) Where: S = rate of change in heat content of the body, M = rate of energy liberation in metabolism, W = rate of energy usage for productive processes, R = rate of heat loss by radiation, C = rate of heat loss by conduction-convection, and E = rate of heat loss by evaporation-convection. The objective of heat regulation is to keep S as close as possible to zero, or (M – W) = (R + C + E). 3 APM 210 Lecture notes: February 2024 O. A. Sokunbi (Animal Physiology) When an animal is in an environment outside its comfort zone, it must respond by: Shifting the rate of metabolic heat production upward in a low temperature condition or downward as temperature rises. Increasing or decreasing the rate of heat loss. A combination of the two if S continues near zero. Changes in Heat Production Animals have three means of changing heat production: Changes in basal metabolic rate Changes in behaviour Changes in performance Lowering basal metabolic rate has advantage to the animal in a hot environment, but such action usually results in lowered performance. Heat production may also be changed by modification of behaviour; an animal on a hot day is more interested in lying in the shade than looking for food. Under hot condition, lowered rate of performance accounts for the greatest change in heat production. An animal can be helped to minimize its performance changes for instance by reducing the distance the animal must travel for shade, food and water. In the cold, the animal achieves homeostasis by reducing overall heat loss to a minimum and making up the deficit by increased heat production. The increased in heat production to maintain thermal balance comes from two sources: Dietary sources Radiant heat from the environment Initially, the extra heat may come from muscular activity, such as shivering and non- shivering thermogenesis (the expenditure of energy directly from the body reserves). Unless the animal can seek protection to prevent excessive heat loss, the increased heat production to maintain body temperature will bring about lowered performance corresponding to that for hot conditions. Changes in heat loss Heat is removed from the animal’s body through the physical processes of conduction, convection, evaporation, and radiation. 4 APM 210 Lecture notes: February 2024 O. A. Sokunbi (Animal Physiology) Each of these has a climatic element counterpart, temperature, air movement, humidity, and radiant energy respectively. Conduction Conduction serves two roles in heat loss: In the movement of heat from the core of the body to the external surface In the flow of heat from the skin surface to the surrounding. Convection This is the transfer of heat energy by circulatory motion that occurs at a non-uniform temperature. Heat is lost from the body through the convection process internally by the circulating blood and externally by air flow about the body. In still warm air, convection plays a minor role, but in a cold wind the animal is subject to loss of great amount of body heat. Evaporation Heat loss by evaporation occurs from the skin and respiratory tract. It is the most efficient means of removing heat. The water evaporated from the skin becomes available from the sweat glands for most animals except for swine and fowl, or by external application of water. Radiation An animal consistently exchanges heat with its surrounding by radiation. The amount depends on the nature of the surrounding and the amount of body surface exposed. An animal in the natural environment is exposed to: Direct solar radiation from the sun, part of which is reflected, and the remainder absorbed as heat. Solar radiation reflected from the clouds. Radiation reflected from the grounds and other surroundings. The portion of the radiant energy that is absorbed by the animal’s body is changed into heat, thus adding to discomfort under hot conditions, but aiding the animal in maintaining comfort in a cold environment. The radiant heat load is greatest in the afternoon because the ground radiation and air temperatures are higher. 5