Thesis - Open Access
Master of Science (MS)
When a warm-blooded animal, homeotherm, is subjected to an environment colder than body temperature, according to the physical laws of heat and mass transfer, heat dissipation from the animal will be increased. Left unchecked the body temperature will drop, homeothermia, possibly resulting in death. The animal compensates for this heat loss by increasing heat production and/or reducing heat loss by a number of chemical or physical adjustments. One such adjustment is vasoconstriction, which reduces blood flow to the surface, thereby, reducing the temperature of the skin and extremities, with peripheral temperatures of some homeotherms dropping to slightly above freezing without injury or apparent discomfort, Scholander. The blood flow to the surface is further reduced by a decreased pulse rate, resulting in less heat transfer from within the body to the surface. With the skin temperature reduced, heat loss to the environment by convection, radiation, and conduction is reduced, because the surface and ambient temperature difference is lessened. Respiration rates of animals subjected to cold environments are reduced to minimize evaporative and sensible heat loss from the respiratory system. Many types of animals will acclimate to the environment by increasing the thickness of the insulating hair coat and the subcutaneous fat layer. Pilomotor reflexes provide another adjustment to falling temperature by erecting hair or feathers. Ambient temperature, relative humidity, wind velocity, and solar radiation are factors affecting comfort and production of livestock. A knowledge of the significance of each of these factors on skin temperature, rectal temperature, pulse rate, and respiration rate of cattle would be useful in determining stress causing conditions. Activities of the chemical and physical mechanisms to maintain constant body temperature are minimum at critical temperature, which varies with type and age of livestock. Increased activity of these homeothermic mechanisms indicate animal discomfort and reflect energy uses not available for production. Relationships between climatic conditions and animal comfort are essential in the design of improved shelters and housing systems. Therefore, a study was initiated with the following objectives: 1. To relate the winter climatic factors of ambient temperature, wind velocity, relative humidity, and solar radiation to dairy calf rectal and skin temperatures, pulse rate, and respiration rate. 2. To develop a cold weather effective temperature index for dairy calves from the skin and rectal temperatures, pulse rate, and respiration rate responses to natural winter climatic factors.
Library of Congress Subject Headings
Weather -- Physiological aspects
Number of Pages
South Dakota State University
Runestad, Jay A., "Physiological Responses of Holstein Steer Calves to Winter Climatic Conditions" (1974). Electronic Theses and Dissertations. 4756.