Page 9 - National Poultry Newspaper

Temperature and air flow critical to year-round broiler performance
ONE of the most com- mon subjects among broiler producers con- cerns the determining of how much cooler birds feel with various amounts of air movement.
ing it – and the cooler it will feel.
of feed it consumes and the greater the amount of heat it will produce.
Bird density
than an older bird, which further increases the rate at which heat is lost from a chick compared to a mar- ket-age bird.
how a bird ‘feels’ with any given combination of envi- ronmental or management factors would literally re- quire thousands of studies. Deciding the right course of action
specific situation.
Then, most importantly,
Though there are charts that provide rough es- timates, we really don’t know exact degrees of cooling and probably nev- er will.
As much as 60 percent of a bird’s heat loss is through the evaporation of mois- ture from its respiratory system.
A fast-growing bird be- ing fed a high-energy diet may not be losing enough of the heat it’s produc- ing, which could possibly cause heat stress.
Studies have shown that the higher the density, the lower the rate of heat loss and the warmer it will feel, regardless of house tem- perature.
So, what is the most ac- curate way to determine if a bird is comfortable?
Don’t be in too much of a hurry to pick up mor- talities or adjust feed and drinker lines – simply en- ter the house, take a 20-li- tre bucket, turn it upside down and spend 10 min- utes or so watching your birds.
This is because the way a bird perceives its en- vironment thermally is extremely difficult to de- termine.
This is true whether it is a day-old chick or a 50-week-old broiler breed- er.
Conversely, a bird not consuming as much feed as a broiler breeder pul- let may feel cool at 24C, because it may be losing too much of the relatively small amount of heat it produces.
Then take time to study the general relationship between the previously mentioned factors and heat loss.
Are they spread out? Are they bunching? How many are lightly
The concept of ‘hot’ or ‘cold’ is determined by a bird’s perception of its environment.
A bird’s respiratory sys- tem is essentially a min- iature evaporative cooling pad.
The amount of air mov- ing over a bird also con- tributes to the rate at which heat is lost.
Unfortunately, these aren’t the only factors that affect rates of heat loss.
Realise that as humid- ity increases, a bird feels hotter.
panting?
Are they too noisy?
How many are eating? How many are sleeping? It may be a cliche, but if
In reality, hot and cold relate to the rate at which heat is being lost by a bird.
The lower the relative humidity, the greater the amount of moisture that will evaporate from a bird’s respiratory system.
This holds true for young chicks too.
Radiant heat gain or loss from poorly insulated ceil- ings or curtains, level of bird activity, night versus day, bedding type and depth can all have an im- pact too.
Higher growth rates will generally require lower house temperatures.
you take the time to listen to your birds, they will tell you all you need to know.
A bird is always losing heat to the environment around it because its deep body temperature of about 41C is greater than house air temperature.
The greater the amount of heat removed from a bird, the cooler it will feel.
If a chick is consuming a lot of feed and grow- ing quickly, the house temperature will generally need to be decreased more rapidly over the first week than for a bird that is grow- ing slowly.
In general, higher wind speeds result in greater heat removal.
As air speed increases, a bird will feel cooler.
Michael Czarick Engineering specialist
at University of Georgia Department of Poultry Science
First appeared in Poultry Health Today
The greater the amount of heat a bird is losing, the colder it will feel.
This is because the fast- growing chick produces more heat and therefore requires a lower house temperature to help it feel comfortable.
As a result, determining
Make small adjustments to the recommended house temperature based on your
Relative humidity is an- other major factor that af- fects heat loss.
So, whether 24C for in- stance is perceived as hot to a 1.8kg bird will depend to an extent on its growth rate.
Density can have a major influence on a bird’s per- ception of its thermal en- vironment, especially to- wards the end of the flock.
A young chick’s rapid heat loss is the primary reason we typically start off a flock at around 32C and decrease it to 18C, then to 21C as the birds reach processing age.
take the time to sit in your houses and observe your birds.
Every time a bird breathes it is removing heat from its body.
For instance, a tempera- ture of 21C would be more appropriate for a five- week-old bird that is soon to be processed, than for one that is being grown to a weight of about 4kg to be processed at eight weeks of age.
We want to help reduce the rate of heat loss of a poorly insulated chick and increase it as it gets older and has difficulty losing the heat it needs to feel comfortable.
First, start off with your primary breeder’s recom- mended house-tempera- ture guidelines.
So, even though you may be maintaining the recom- mended house tempera- ture, you could be chill- ing a day-old chick if the humidity is too low – 20 percent.
However, to complicate matters, the amount of heat removed depends on the difference between the bird’s body temperature and the air temperature.
To make matters more complicated, all of these factors interact.
Feather coverage as well as density will affect heat loss.
If a bird is not losing enough of the heat it is producing, its body tem- perature will start to rise and it will feel hot.
Conversely, a house tem- perature of 18C could be perceived by a market-age broiler as hot if the humid- ityistoohigh–80percent.
Breed is another factor that can affect a bird’s perception of hot and cold.
The closer the air tem- perature gets to the bird’s body temperature, the less effective the movement is at removing heat from a bird.
If a bird loses just enough heat to maintain its body temperature with little to no effort on its part, it would be consid- ered comfortable.
Feathercoverage
Obviously, temperature has a major impact on the rate of bird heat loss.
Growth rate and breed
The lower the level of feather coverage at a giv- en age, the greater the heat loss will be from a bird and the colder it will tend to feel.
A young bird’s feather coverage has a relatively low ‘R-value’ and there- fore it will lose heat quicker than an older fully feathered bird.
The lower the air tem- perature, the greater the amount of heat a bird will lose to the air surround-
One consideration is growth rate.
Furthermore, a young bird has a higher surface area per gram of weight
These might be the most obvious issues that affect a bird’s perception of hot and cold, but there are other equally important factors.
For instance, certain breeds become fully feathered at a younger age than others.
Bird age will also affect how easily heat is lost.
The faster a bird is grow- ing, the greater the amount
As air speed increases, a bird will feel cooler.
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National Poultry Newspaper, August 2021 – Page 9