Heat Stress in Dairy Cattle

Heat Stress in Dairy Cattle Dr.Ir. Idat G. Permana, MSc. Departemen Ilmu Nutrisi dan Teknologi Pakan Fakultas Peternakan IPB permana@ipb.ac.id Introduction   All animals have a zone of thermo neutral temperatures conducive to normal function The upper critical temperature is where the effects of heat stress start to appear Heat Stress  The point at which a dairy cow (or other animal) cannot dissipate an adequate quantity of heat to maintain body thermal balance or normal body temperature Thermoneutral Zone A B C D Cold Stress Heat Stress Deep-Body Temperature Evaporation Heat Loss Environmental Temperature Thermoneutral Zone A : temperature of summit metabolism B : lower critical temperature C : temperature associated with marked increase of evaporative loss D : upper critical temperature BC : zone of less thermoregulatory effort (thermoneutral zone) Thermoneutral Zone Critical Temperature   UCT (Upper Critical Temperature): above this temperature, evaporation become the dominant method of heat loss. LCT (Lower Critical Temperature): Below this temperature, metabolism must increase to offset losses to the environment. Heat Stress  Physiological state induced by ambient temperatures above the Upper Critical Temperature (LCT) of the thermoneutral zone Cold Stress  Physiological state induced by ambient temperatures below the Lower Critical Temperature (LCT) of the thermoneutral zone Thermoneutrality   The range of ambient temperature in which normal metabolism provides sufficient by- product heat to maintain an essentially constant body temperature. The limits of the thermoneutral zone (TNZ) are dependent on acclimatization, age, sex, breed and species, body conformation, feed and even the time of day. Range of Rectal Temperature Temperature Humidity Index (THI)  Includes both temperature and humidity in determining the point sat which heat stress may occur  A THI > 72 is considered to indicate heat stress in dairy cattle 0 72 Relative Humidity, % Relative Humidity, % 80 60 40 20 NO 80 STRESS 90 MILD STRESS HEAT STRESS 100 110 120 SEVERE STRESS DEAD COWS 100 Heat Weather Stress     STABILITY OF BODY TEMPERATURE is a prerequisite for high productivity in dairy cattle. Bos Taurus (in temperate or cold regions): higher production potential Bos Indicus (tropical regions): relative heat tolerance Crossing of two types: improve productivity and heat tolerance Body Heat Gained and Lost Radiation Conduction Metabolic Heat Environmental Heat HEAT GAIN Convection Evaporation HEAT LOSS Modes of Heat Tranfers     Conduction - direct molecular contact Convection - motion of gas or liquid heated surface Radiation - infared rays Evaporation - as fluid evaporates, heat lost How Do Cows Respond to Heat Stress?       Higher body temperatures Increased respiration rates Less activity Increased water intake Seek shade Look for cool areas in the barn Evaporative heat loss What Happens Metabolically?  Energy requirements for maintenance increase     Increased respiration rate More blood flow to the skin Less blood flow to body core May increase by 20-30% What About Dry Matter Intake?  Dry matter intake decreases in cows subjected to heat stress    May drop 10-20% in commercial herds Becomes variable May be short or long-term Feed Intake & Digestibility Feed Intake & Digestibility How About Milk Production?  Decreases due to:      More energy for maintenance Less energy for productive functions Lower dry matter intake Alterations in nutrient use Can drop 10 to > 25% Effect on Milk Production What Happens to Reproduction?       Usually decreases in heat stress situations Estrus intensity and length decrease Fertility rate decreases Ovarian follicle growth decreases Increase early embryonic death May affect fetal growth Effect on Reproduction Effect on Neonatal Survival and Growth What Determines the Severity of Heat Stress?        Actual temperature and humidity Length of the heat stress period Degree of cooling that occurs at night Ventilation and air flow Cow factors (size, milk production) Water availability Hair coat depth Feeding Strategy       Unlimited quantities of clean water Low fiber feeding, but adequate dietary fiber to maintenance rumen function Adding fat Increase CP supply Increase mineral (K, Na & Mg) supply Feed additives Cold Weather Stress    In general, cattle are tolerant of cold Wide genetic differences among cattel breed Some unique aspects:      Maturity of newborn External insulator (haircoat) Heat production Large body size Consume large quantities of feed COLD EXPOSURE HEAT LOSS AND METABOLIC RATE COLOSTRUM CONSUMPTION RESISTANCE TO DISEASE Energy Energy and Milk Energy Disappearance Immunoglobulin Intake Hypoglycemia Pasive Antibody Hypoglycemia Protection Hypothermia Infection Disease MORBIDITY OR DEATH Incidence of Disease References   World Meteorological Organization. 1989. Animal Health and Production at Extremes of Weather. World Meteorological Organization, Geneva. Switzeland. Ect.