Effect of Environment on Nutrient Requirements of Domestic Animals (1981) / Chapter Skim
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ANIMAL-ENVIRONMENT INTERACTIONS
ANIMAL-ENVIRONMENT INTERACTIONS
Pages 5-12
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From page 5... ...
THERMAL BALANCE Homeothermic animals maintain a relatively constant core temperature by balancing the heat gained from metabolism against that gained from or given up to the environment. This heat balance is achieved through the concerted effects of physiological, morphological, and behavioral thermoregulatory mechanisms (Monteith, 1974; Robertshaw, 19744.
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From page 6... ...
EFFECTIVE AMBIENT TEMPERATURE Because animals are always exposed to and affected by several components of the climatic environment, there are advantages to evaluating responses of the animals to an index value representing the collective thermal impact of the animal's total environment. EAT iS one such index described in terms of environmental heat demand: the temperature of an isothermal environment without appreciable air movement or radiation gain that results in the same heat demand as the environment in question.
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From page 7... ...
The increase in rate of heat loss or gain per unit increase in air velocity is greatest at low air velocities because disruption of the boundary layer of still air surrounding the body requires relatively little air movement. Above 6 km/in, increased air velocity results in little additional increase in convective heat transfer.
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From page 8... ...
THERMAL ZONES salt 2. The range of EAT over which the body temperature remains normal, sweating and panting do not occur, and heat production remains at a minimum.
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From page 9... ...
where the animal must increase its rate of metabolic heat production to maintain homeothermy. Increases in metabolic heat production parallel increased envi Lower Critical Temperature Cold Stress Cool 1 TH E RMON EUTRA ZON E i ' Optimum for Performance and I Warm Health (Jpper Critical Temperature Heat Stress _ .1 1 ' '- - -'' 1 1 Low E FF ECTI VE AM Bl ENT TEMPERATU R E High FIGURE 1.
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From page 10... ...
In general, initial responses of animals to cold stress rely more on increasing metabolic heat production, but long-term exposure to cold gradually results in adaptive responses through physiological and morphological change. Increased insulation, for example, is an added barrier to heat flow in animals and influences the rate at which sensible heat is exchanged with the environment.
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From page 11... ...
25 5 mm fleece, fasting 31 5 mm fleece, full feed 18 1 mm fleece, maintenance 28 10 m.m fleece, maintenance 22 50 mm fleece, maintenance 100 mm fleece, maintenance -3 Ames, 1969 Brink and Ames, 1975 Blaxter, lg67^ Blaster, 1967 Blaxter, 1967.',' Blaxter, 19~' BIaxter, 1967'' Blaxter, 1967 Blaster, 1967 Ca'tt~:-. 8 mm hair, -fasting 18 .
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From page 12... ...
The extremely low values for the feedlot animal and dairy cow result from the large amounts of heat produced as an inevitable consequence of digestion and metabolism at high levels of production, from the small surface area to mass ratio of these relatively large animals, and from their large amount of insulative tissue. In contrast, the pig has a poorly developed hair coat and utilizes dietary energy more efficiently, thus producing less metabolic heat; hence it has a higher LCT.
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