Ventilation, Air Quality and Environmental Management

Chapter 13 of McGlone and Pond, 2002

Components of the microenvironment

• Thermal environment
• Physical environment
• Social environment
• Microbial environment

Thermal Environment

Heating, Ventilation and Air Conditioning (HVAC) Objectives

General Objectives

• To provide fresh air
• To remove pollutants
• To provide thermal modulation (heating or cooling)

Seasonal Objectives

• In winter, to remove air pollutants and moisture and to conserve heat

• In summer, to remove heat and consequently pollutants and moisture

Specific Ventilation Standards

· Keep air changes between 6 and 60 air changes/hour

· Keep drafts to a minimum (a draft is cold air blowing on the pigs)

· If condensation is observed, the air is too humid

Modes of heat flux – heat moves from warm to cold, down its gradient

• Convection – heat moving in streams of air
• Conduction – heat moving from one mass to another
• Radiation – heat moving through space from one ‘body’ to another
• Evaporation – heat absorbed as water evaporates
• Condensation – heat released when water condenses

The Effective Environmental Temperature (EET) is the temperature that the pig feels or experiences. The EET takes into account not just air temperature, but all modes of heat flux.

Heat is lost more quickly when it is windy (conversely, when air temperature exceeds body temperature; heat is gained more quickly when it is windy).

The Wind-Chill index estimates the added impact of cold temperature in windy conditions. For example, if it is 10 F outside with a 10 mph wind, it feels like it is -4 F. It is assumed that the pig feels the wind-chill temperatures about the same as humans. However, because humans wear clothes and pigs do not; it is likely that the pig is more chilled when exposed to the same cold temperature and wind. During cold periods, the wind-chill index gives the best estimate of the EET the pig experiences.

Cold air does not hold much moisture (the water condenses out of the air). Thus, humidity has little impact on how cold the air feels to pigs.

During warm weather, the humidity has a large impact on how warm an environment is to an animal. When animals experience warm air temperatures (above body temperature) the only way they can lose heat is by evaporation. Because pigs do not actively sweat, they can lose heat by evaporation over their respiratory tract and by applying water to their skin (wallowing, for example). Pigs keep cool, not by sweating, but by behavioral thermoregulation.

As the humidity increases, the animal has less opportunities to evaporate water from their skin or respiratory tract. If the air temperature is above body temperature and it is 100 % relative humidity (and evaporation is not possible), then the pig is in danger of dying of heat stroke. The Heat Index Chart gives the approximate EET when it is warm and humid. Note that at 90 F air temperature and 90% RH, the air temperature feels like 119 F.

Building components flux heat by each mode

In this picture:

• Outside is cold (10 F) and inside is warm (80 F)
• Arrows represent heat flux from the warm building through building components to the colder outside.
• Ventilation includes the primary air current (moving from inlet to exhaust fans) and secondary air currents (thinner, round arrows) that provide warmer, fresh air to ventilation animals)
• Building components include:
• Ceiling
• Ventilation air flow
• Walls above the foundation
• Walls at the level of the foundation
• Floor and perimeter (the wall at the level of the floor)

Pigs in outdoor environments have exchanges in heat through the same modes

Management of the thermal environment

Pig behavior changes as the thermal environment becomes warmer or colder

• Warm pigs spread out
• Cold pigs pile on each other

The requirement for an adequate thermal environment are given in this table.

Physical environment

Pigs take up a certain amount of space. Standing requires less space than lying down. The amount of space pigs need to accommodate their body is expressed by the formula:

Area (m²) = k X weight (kg)^0.667

k is the Space constant

The pigs body while lying down is represented by k=0.024.

The space required for maximum weight gain is a higher number, with a k between 0.030 and 0.033.

Individual pigs have three potential space allowances. The static space allowance is the space that a pig’s body occupies. This space represents the size of pigs based on its length, width and height. The dynamic space allowance represents the space pigs need to make normal postural adjustments (standing, lying, turning, moving) without bumping into objects or structures. The dynamic space requirement is more than double the static space requirement. The social space allowance is the space required for pigs to engage in normal social interactions. Note that the floor area needed for social interactions is about the same space per pig as the dynamic space allowance.

The amount of space pigs in pens need varies with time of day. Pigs are more active during the day and spend more time standing up than at night when they spend more time lying down.

The Free Space is the space that pigs do not use in a pen. The space pigs use is called Occupied Space. Free Space is greater during the middle of the day because more pigs are standing up and active. Shown in this figure are the mean Free Space (solid line) and the lower 95% confidence limit (dashed line) which represents the Free Space available for the least 95% of pens of pigs. Note that in a group size of 20 pigs per pen, at midnight (0000 hours or 2400 hours), and at 8 ft² per pen (160 ft² of total pen space), there are 5 m² (about 50 ft²) of Free Space.

The recommended space allowances for pigs housed individually or in groups is given in the table below. These space allowances are based, primarily, on the space needed for maximum weight gain for growing pigs and to meet the static space requirements for individually-housed pigs.

Pen components also are influenced by numbers of pigs. Feeder space has to be adequate to allow all pigs to eat if the intention is to feed pigs ad libitum. With 20 pigs per pen, the number of feeder holes needed for all pigs to eat freely is 2 feeder holes per 20 pigs (10 pigs per feeding space). Note in the figure below that when there is only one feeder hole per 20 pigs that the feeder is occupied nearly 100% of the day (meaning some pigs are not getting enough to eat and feed intake and weight gain will be negatively impacted).

Social Environment

· The social environment includes other pigs and human care givers

· The social environment can influence food and water consumption

· Pigs who do not know each other fight, which causes

o Reduced feed intake (especially a concern in older pigs)

o Scratches and wounds

o Physiological signs of stress including the potential for

§ Reduced levels of immune protection and poor health

§ Poor meat quality

§ Lower reproductive rates

Microbial Environment

The Microbial environment includes all bacteria and viruses in the environment. Some of the microbes are pathogenic under any conditions. Some of the microbes are opportunistic pathogens (causing disease when pigs are stressed.

Proper sanitation can improve animal health, growth and mortality.

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