A Presentation that was made by David Speller (Managing Director of Applied & OPTIfarm) at the Avi Carne Forum, Madrid – 26th April, 2018
Levels of Foot Pad Dermatitis (FPD) are not only used as key welfare indicators during inspections by animal health authorities but can also lead to reduced financial returns from a flock. The resultant ulceration on the underside of the broiler foot means that moving around can become uncomfortable and as such movement to feeders and drinkers maybe impaired which can result in lower weight gains, poorer quality carcases and for processors the inability to trade lesion free feet into markets such as China. Principally FPD is caused by wet and sticky litter, although causes have been noted on our own farms due to sticky droppings.
The FPD lesion starts from an erosion of the skin caused by the litter conditions, once the surface of the skin has been eroded the lesion progresses to become an ulcer. As wells as being painful the break in the skin surface can offer an entry point for bacteria causing infections.
The aim of this paper will be to discuss the specifically the management of the ventilation to ensure the litter in the broiler house is kept dry and friable and thus the occurrence of FPD should be reduced. Other matters such as litter type, drinker management, nutrition, stocking density, genetics, light management, etc are not discussed.
Ventilation Control to Reduce FPD
Given that the major cause of FPD on farm is wet or more importantly sticky litter, keeping litter dry and friable must be a key goal. It is worth suggesting that when broilers are younger the skin cells on the feet are softer and more prone to damage and hence leading to increased resultant FPD.
What should be classed as cold damp weather is dependent on the difference between the external climate and the internal conditions of the broiler house. What we are concerned with is the difference between the internal and the external and not necessarily the specific temperature or relative humidity outside.
Basic Principles of Air & Moisture Together
- Warm air can hold more moisture by way of water vapour than cold air
- Warm air rises and cold air sinks
- Simply put, warm air is light and cool air is heavy
- Relative humidity is the amount of water vapour present given as a percentage of the total potential of that air given its temperature stated as a percentage.
- As air temperature changes by 1-degree Celsius the ability to hold moisture changes by 5%.
- Warm the air by 1 degree and the RH% falls by 5% as the warmer air could have held more moisture so relatively it is not as full of water any more, drop the temperature by 1 degree and the RH increase by 5% as the air is becoming saturated.
- As air cools it is unable to hold as much water vapour and the vapour is released (Dew Point) which can settle on cool surfaces, cold windows, cold walls, cold litter.
- Air has a mass and should be thought of like water in the way it is moved, to get air or water moving takes a force, once moving to keep it moving requires less force.
- Like water air in small jet streams does not travel very far, but large columns of air move further but require more force, like a large water jet will go long distances but needs lots of force to propel it.
Problem with Venting in Cold Damp Weather
Firstly, lets understand how much air we need to bring into a broiler house at any one time. We all appreciate that the amount of air needed is dependent on the total amount of body weight in the shed. Lots of small birds need less air than lots of big birds. We also know that in hot weather we need more air than in cold weather.
Aside from replenishing oxygen in the broiler house a considerable amount of the air volume vented through a broiler house is done so to keep birds cool, remove moisture, remove dust and remove waste gases. The actual requirement of the bird to replenish the available oxygen required is quite low (approximately 0.5 M3/Kg/Hr).
If we remember that we have stated young birds, with softer skin on the feet, are susceptible to FPD as their skin cells can be eroded easily and a lesion can form and if we link this to the fact that younger, smaller birds need less ventilation we can start to see the problems we may encounter. We want dry friable litter to minimise the FPD, which is best achieved with lots of warm dry ventilation, but what we have is young birds with low ventilation requirements and what we are bringing into the broiler house is low volume, cool damp air as it is cold and wet outside.
Our only hope is to bring the cold damp air into the house and let it mix with the warmer air away from the broilers in the broiler house with the aim of reaching the birds with a mixture of the airs with some fresh oxygen having allowed some of the old air to be expelled through the extraction fans or naturally aspirated vents.
However, this low volume cold damp air wants to do everything we don’t want it to do, it is cold so it wants to sink down on to the birds, it is damp and so full of moisture that wants to condense somewhere and it is in low volumes so it doesn’t want to be thrown very far.
Shed Design Assisting Cold Damp Weather Ventilation
We have many designs of broiler houses around the world with shed structure and ventilation methods designed dependant on the most common local conditions. Often the main focus is how to keep the birds cool in the summer as heat stress can kill the broilers, whilst poor venting in cooler weather, whilst impacting on performance, rarely kills the birds. In countries that are relatively cool all year we see buildings with high roofs to allow cool air to remain away from birds whilst in hooter climates the roofs are kept low to minimise the create better wind tunnels during hot weather venting. It is generally these lower ceiling sheds that create the greatest challenge to vent in cold damp weather.
So How Can We Manage to Ventilate in Cold Damp Weather and Minimise FPD
We must accept the parameters we cannot change, or at least not easily within the budget of a broiler farm, namely the external temperature and humidity.
Now consider what we can manage which is the number of inlets we can utilise, the size of the column of air we want to bring in and at what speed.
We know that cold damp air is heavy and takes a lot of force to get it moving, and we know that like water, once it is moving it takes less energy to keep it moving, therefore we might want to consider ensuring sufficient air pressure to get the air moving from no movement such as with modulating fans controls, but where we have constant fans running we may want to reduce that pressure slightly so as not to over speed the air causing excessive turbulence above the birds.
Remembering how water comes out of a hose, and that air moves like water, we know that a larger column of air moves distance better than a small fine jet of air, so in cold damp conditions aim for fewer larger air streams than lots of tiny little air streams. Some inlet manufacturers have tried to make this happen automatically.
How Does Cold Air Sinking Cause Wet Sticky Litter?
The first thing that happens when cold ventilation air sinks to the floor is that it drops down on to the litter surface leading to the litter surface cooling down. This cooler surface to the litter then allows either warmer moisture rising from within the litter or the moisture in any of the warm air above the litter to condense on the litters surface, creating moist sticky conditions.
This is especially noticeable if it occurs during dark periods when the birds are resting and the air movement in the broiler house become less turbulent without the thermal currents created by the broilers body heat warming the air in the house. In addition, the birds sit on the litter bringing the warm moist air immediately surrounding their bodies down to cold litter where the moisture can condense.
The key to successful ventilation which will reduce the occurrence of FPD is to ensure you keep the cool damp air up above the birds for sufficient time to mix with existing warm air and you must ensure the air reaches across the desired distance to replenish all areas in the broiler house.
It is possible to ventilate most facilities for cold damp weather however each location can be unique and each shed requires initial setup and monitoring. Ultimately air flow should be tested with a smoke machine as it is only then that the human eye can really appreciate where this air is going and try to predict its impact on the birds and their litter.