Environmental Physiology – SS2 Agricultural Science Lesson Note (First Term)

Environmental physiology is the study of how farm animals respond to their environment and how the environment affects their growth and performance.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define environmental physiology and climate;
2. list the climatic factors that affect farm animals;
3. state the effects of rainfall, wind, temperature, relative humidity and light on farm animals;
4. describe ways of controlling these factors in animal houses;
5. explain the effects of changes in climate on growth, milk production and egg production.

What is environmental physiology?

Environmental physiology is the study of how farm animals respond to the conditions around them.

• Effects: the environment can affect animals in a high or a low way, and both can harm performance.
• Target: moderate conditions give the best growth and performance.
• Farmer’s task: the farmer keeps conditions in the animal house close to what the animals need.

What is climate?

Climate is the average condition of the atmosphere of a place over a long period.

There are five climatic factors that affect farm animals: rainfall, wind, temperature, relative humidity and light.

• Rainfall: the amount of water that falls from the sky as rain.
• Wind: moving air.
• Temperature: how hot or cold the air is.
• Relative humidity: the amount of water vapour in the air compared with the most the air can hold.
• Light: the brightness and the length of daylight.

What instruments measure the climatic factors?

Each climatic factor is measured with its own instrument.

How do the climatic factors affect farm animals?

Each of the five climatic factors has its own effects on farm animals and its own ways of control.

How does rainfall affect farm animals?

Too much or too little rain harms animals, pests and the grass they feed on.

Effects of rainfall

• Pests and diseases: high rainfall increases pests such as tsetse flies, and also diseases.
• Chilling: high rainfall chills young animals.
• Pasture: extremes of rainfall do not favour the growth of grasses for food.

Control of rainfall

• Shelter: a roofed house keeps rain off the animals.
• Rain break: a barrier that stops rain from beating into the house.
• Drainage channels: they carry water away from the pens.
• Building orientation: the house is sited so that rain does not blow into it.

How does wind affect farm animals?

Wind is moving air, and its effect depends on its speed.

The picture shows the instrument used to measure wind.

Effects of wind

• Disease spread: wind carries air-borne diseases such as tuberculosis, which may lead to death.
• Ventilation: moderate wind speed gives good ventilation.
• Stress: strong wind scares animals and upsets their growth.

Control of wind

• Shelter: a house protects animals from strong wind.
• Windbreak: a row of trees or a wall slows the wind.
• Openings: windows and vents let in enough air.
• Building orientation: the house is placed to suit the direction of the wind.

How does temperature affect farm animals?

Temperature is the degree of hotness or coldness of the air, and it strongly affects feeding, health and output.

Effects of temperature

• Feed intake: high temperature reduces feed intake, while low temperature increases it.
• Water intake: animals drink more in hot weather and less in cold weather.
• Breeding: high temperature reduces sperm production (spermatogenesis) and libido in males.
• Heat stress: high temperature causes stress and reduced activity.
• Death: extreme heat may kill adult animals, young animals such as chicks, and layers.
• Yield: high temperature lowers output, for example fewer eggs.
• Hatching: high temperature reduces the hatching of eggs.
• Storage: animal products do not store for long in high temperature.
• Incubation: a suitable temperature is needed to incubate eggs.

A thermometer that registers temperature in Celsius and Fahrenheit. It is an instrument for measuring temperature.

Control of heat and temperature

• Fans and air conditioners: install them in animal houses to cool the air.
• Windows and openings: provide enough of them for ventilation.
• Roof vents: provide vents at the rooftop to let hot air out.
• Roofing: use poor conductors of heat or sun-reflecting sheets.
• Roof colour: paint the roof a reflecting colour such as white.
• Ceiling boards: fix them under the roof of the pen.
• Cloth on windows: cover windows with cloth to conserve heat in cold weather.
• Heaters and lanterns: use them to warm the building when it is cold.

How does relative humidity affect farm animals?

Relative humidity is the amount of water vapour in the air compared with the most the air can hold at that temperature.

A hygrometer is the instrument for measuring humidity.

Effects of relative humidity

• Physiological processes: humidity is important in processes such as incubation.
• Stress: high humidity adds to heat stress.
• Water loss: low humidity makes animals lose water quickly, so they drink more.
• Disease: high humidity encourages the spread of diseases.
• Mould: high humidity makes feed go mouldy.
• Chilling: high humidity chills young animals.

Control of humidity

• Humidifiers or open trays of water: fix them to raise humidity when it is low.
• Free ventilation: allow it when humidity is high.
• Avoid spilling water: this reduces dampness, for example in a poultry house.

How does light affect farm animals?

Light affects animals through its brightness (intensity) and the number of hours it shines (duration).

Effects of light

• Egg laying: light controls egg laying in hens.
• Feeding time: the length of lighting controls the time spent feeding, which regulates growth and the rate of feathering and furring.
• Eye stress: direct light of high intensity stresses the eyes.
• Activity: bright light makes animals such as birds more active.
• Sight: light makes objects visible to the animals’ eyes.

Control of light

• Extra lighting: provide extra illumination when daylight is short.
• Openings: use wire mesh and glass as parts of the building so that light enters.
• Dark cloth: cover windows to reduce light intensity.

How do changes in climate affect growth?

Extreme climate lowers growth, because animals may eat too little or eat more and still not grow well.

• Wind: it aids the spread of disease.
• Rainfall: high rainfall increases tsetse flies and other pests.
• Humidity: high humidity favours mould in pens and feed, which can cause diseases.

How can a farmer keep the climate favourable for growth?

1. Install fans and air conditioners.
2. Plan for good ventilation when building an animal house.
3. Use building materials that are poor conductors of heat.
4. Paint the walls of animal houses white to reflect sun rays.
5. Build the house in an east-west direction.
6. Use mesh in place of brick walls at some heights.
7. Install humidifiers or open trays of water to raise humidity.

How do changes in climate affect milk production?

Extreme climate reduces milk yield in dairy animals.

• Sunlight: too much sunlight causes heat stress.
• Humidity: high humidity favours the growth of disease-causing organisms (pathogens).
• Heat: milk spoils quickly in hot conditions.

How do changes in climate affect egg production?

High temperature lowers egg production and egg quality.

• Shelf life: high temperature reduces the shelf life of eggs.
• Hatchability: high temperature reduces the hatching of eggs.
• Feed intake: high temperature reduces feed intake, so fewer eggs are laid.
• Light duration: longer light increases feeding time, but this may not give extra eggs.

Evaluation

1. Define environmental physiology.
2. List the five climatic factors that affect farm animals.
3. State three effects of high temperature on farm animals.
4. State three ways of controlling heat in an animal house.
5. Name the instrument used to measure relative humidity.

Assignment

1. Choose any two climatic factors. For each one, state two effects on farm animals and two ways of controlling it in an animal house.