Agriculture Reference
In-Depth Information
use no more than a 20% increase in main-
tenance requirements.
Health status adjustment is calculated as:
Maintenance_Adjust: 1 / Health status
SHL slope 64  - 0.5 × ( FP/BW 0.67 )
(kJ/day)
Where FP is feather protein weight.
Where Maintenance_Adj ≤1.20 and ≥1.0.
This adjustment is applied only for energy
maintenance requirements.
Estimating EHL min and EHL max
Evaporative heat loss is minimal ( EHL min )
and constant for a particular body weight at
low temperatures and may represent up to
20% of the thermoneutral heat production
( TerHP ).
Effect of Environmental Temperature
on Heat Production
EHL min = 0.20 × TerHP (kJ/day)
TerHP is estimated by the following equation:
Environmental temperature influences heat
production ( HP ), and consequently affects
growth rate and feed intake. Estimating
total heat production ( THP ) of a bird, con-
sidering both dietary and environmental
factors, assists in determining its feed intake.
When THP is between maximum ( THL max )
and minimum ( THL min ) heat loss, feed intake
is not affected. However, THP outside that
range affects feed intake, which is used as a
regulatory mechanism for body heat homeo-
stasis. In addition to environmental tem-
perature, body heat production may be in-
fluenced by the relative humidity and air
velocity.
Total heat loss ( THL ) is the sum of sens-
ible ( SHL ) and evaporative ( EHL ) heat
losses. Therefore, in order to estimate THL max
and THL min , both the minimum and max-
imum SHL and EHL , respectively, need to
be determined.
The concept of Emmans (1989) was
adopted to estimate THL max and THL min . In
order to calculate THL , HP can be parti-
tioned into SHL and EHL :
THL max = SHL + EHL max (kJ/day)
TerHP =  ( aFI × ME ) - [( 50  × PD )
+ ( 56  × LD )](kJ/day)
Maximum EHL is usually constant and sev-
eral times greater than EHL min . In the study
of Simmons et  al . (1997) an equation was
derived to calculate the external effects of
temperature and ventilation on body heat
production. That study was carried out to
determine latent HP in 35- and 42- day-old
broilers subjected to different air velocities
and temperatures under conditions similar
to those found in commercial settings. The
authors estimated 12 polynomial equations
to predict latent HP as a function of air
speed and temperature. Those equations
were re-parameterized in a single equation
to predict latent HP (kJ/day) as a function of
air velocity, temperature ( T , ºC) and body
weight.
EHL max = BW × [9.4434 × ( Vel - 0.0215) 
× T ] (kJ/day)
Where Vel = air velocity (m/s).
In order to determine thermal environ-
ment effects on growth rate and feed intake,
THP is compared with THL max and THL min .
THP is calculated as the difference between
energy intake and energy retention for pro-
tein and fat deposition:
THL min = SHL + EHL min (kJ/day)
SHL is obtained by the equation:
SHL = SHL slope × ( 41 × T ) × ( EBWFF 0.67 )
(kJ/day)
THP =  ( aFI × ME ) - [(23.8 × PD
+ (39.6 × LD )] (kJ/day)
Where EBWFF is feather-free empty body
weight. The SHL slope equation was obtained
from Emmans (1989), and allows the effect
of feathering on sensible heat loss to be
considered.
Comparing maximum or minimum THL with
THP indicates whether the birds are too
hot, too cold or comfortable, and enables
 
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