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