ENVIRONMENT & ANIMAL HEALTH

by

David R. Hawkins

Michigan State University

An animal’s ability to express its genetic potential is impacted by the environment in which it exists.

HOMEOTHERMS

• Farm animals and humans are classified as homeotherms since they maintain a constant core body temperature across a wide range of environments.

• Poikilotherms (cold blooded animals such as fish and snakes) do not maintain a constant body temperature, but rather are influenced by the environment.

NORMAL RECTAL BODY TEMPERATURE (o F)

• Cattle (100.4 – 102.8) av. 101.5

• Sheep (100.9 – 103.8) av. 102.3

• Swine (101.6 – 103.6) av. 102.5

• Horse (99.1 – 100.8) av. 100.0

• Chicken (105.0 – 109.4) av. 107.1

SEASONAL CHANGES IN ENVIRONMENT

• In temperate climates, as seasons change, ambient temperature and photoperiod (length of daylight) also change.

• In spring, both temperature and day length increase.

• In fall, both temperature and day length decrease.

• Hormonal changes help the animals adapt.

Basal Metabolic Rate

• The thyroid gland near the trachea controls basal metabolic rate (BMR). As cool air is inspired, thyroxine secretion increases and BMR increases heat production.

• Hair growth and shedding are also influenced by hormones.

THERMONEUTRAL ZONE

• The thermoneutral zone (TNZ) or comfort zone is a range of environmental temperatures where heat production and heat loss from the body are about the same.

• When ambient temperatures drop below the TNZ, animals increase feed intake and reduce blood flow to body extremities. Mammals generate heat by shivering. Birds fluff their feathers to increase insulation space around their bodies.

THERMONEUTRAL ZONE

• When ambient temperature rises above the TNZ, water consumption increases, respiration rate increases and if the animal can sweat, perspiration increases. Evaporation of sweat results in cooling.

Effect of Temperature on Feed Intake, Maintenance & Gain

BASIC MECHANISMS OF HEAT LOSS OR GAIN

• Conduction is a flow of heat between objects that are touching.– A pig laying on a cold concrete floor loses heat

by conduction.

• Radiation is an exchange of heat between objects not touching.– Animals absorb heat from the sun and lose heat

in cool shade.

BASIC MECHANISMS OF HEAT LOSS OR GAIN

• Convection is influenced by body surface area, air movement, body temperature and air temperature.

• Evaporation – Animals that can sweat, lose heat from the surface of their skin.

• All animals vaporize moisture and heat via respiration.

COLD STRESS

• Wind chill is a function of ambient temperature and wind speed.

• Heat increment can help offset cold.

• Warm food such as milk to newborn increases body temperature.

• Animals crowd together to keep warm.

HEAT STRESS

• High ambient temperatures cause decreases in feed intake, growth rate, milk production and reproduction (higher embryonic mortality and reduced sperm production).

• With severe heat stress, central nervous system is affected and animal may die.

VENTILATION

• In confinement facilities for livestock, it is important to remove dust, ammonia and other odors as well as to provide fresh air.

• If humidity builds up in a confinement building, respiratory problems increase and production declines.

HEALTH DEFINITIONS

• Mortality = Death Loss• Morbidity = Sickness• Disease = Any deviation from normal

health that results in physiological, anatomical or chemical changes in the animal’s body.

• Diseases may be either infectious or noninfectious.

HEALTH DEFINITIONS

• Infectious diseases are caused by microoganisms such as bacteria, viruses and protozoa.

• A contagious disease is an infectious disease that spreads rapidly from one animal to another.

• Noninfectious diseases include nutritional deficiencies, toxicities, etc.

DISEASE PREVENTION

• Biosecurity will be a major issue in the future.

• Isolation and testing of new animals before they enter the herd or flock.

• Restricting visitors and vehicles to farms.• Sanitation is the first line of defense.• A herd health program planned with your

veterinarian is critical.

DISEASE PREVENTION & TREATMENT

• Biologicals are used to prevent diseases.– Vaccines

• Pharmaceuticals are used to treat diseases.

• Selection of injection sites are critical.

• Employees must be trained regarding early disease detection and treatment protocol.

DISEASE DETECTION

• Know normal vital signs– Body Temperature– Respiration Rate– Heart Rate

• Recognize abnormal behavior– Loss of appetite– Abnormal respiration– Listlessness and depression