Agriculture Reference
In-Depth Information
sufficient to meet their amino acid require-
ment, leading to an overconsumption of en-
ergy. As the requirement for protein as a pro-
portion of the feed decreases, birds make use
of body lipid as an energy source thereby util-
izing the feed very efficiently. When these
body lipid reserves are depleted, energy in-
take increases again. Nevertheless, it must be
noted that external effects, such as environ-
mental temperature, may also limit feed in-
take. These findings are consistent with the
hypothesis that there is a desired body lipid
content that the bird attempts to maintain.
requirements (Latshaw, 1991). In addition,
changes in daily feed intake and daily aver-
age weight gain (Marcq
et al
., 2011; Quintei-
ro-Filho
et al
., 2012) and feed efficiency
(Marcq
et al
., 2011) depend on the type of
health challenge imposed. There are still
many gaps when considering the quantita-
tive determination of the effects of immune
challenges on maintenance, growth rate and
efficiency. Therefore, a meta-analysis on the
performance responses of chickens sub-
jected to immune challenge by different en-
teric bacteria was performed. The database
included
60
papers published between
1997 and 2012 (mode: 2006) with a total of
86,300
birds. The meta-analysis showed
that birds challenged with
Clostridium
spp.,
Escherichia coli
and
Salmonella
spp. re-
duced their feed intake by 15%, 7% and
9%, and growth rate by 40%, 10% and 29%,
respectively
(Table 14.3
).
In an attempt to explain the mechan-
isms responsible for these reductions,
daily average weight gain (
ADG
) was re-
gressed against average daily feed intake
(
ADFI
). Feed intake and weight gain data
of the challenged birds were transformed
into percentages relative to the control
treatment (not challenged) in order to re-
duce variation between studies. In the re-
gression equation the intercept (
a
) shows
that
ADG
reduction is not related to
ADFI
Actual Feed Intake
The desired feed intake (
dFI
) of a bird in a
thermal-neutral environment would be the
greater of
dFI
e
and
dFI
AA
, while the actual
daily feed intake (
aFI
) would be the lower
of
dFI
and
cFI
. For a perfectly balanced diet,
dFI
e
would equal
dFI
AA
.
External Effects on Bird Response
Health challenges
Immune challenges affect body homeostasis,
and consequently, maintenance nutritional
Table 14.3.
Effect of different health challenges on feed intake and growth of broilers.
Clostridium
spp.
Escherichia coli
Salmonella
spp.
Description
n
a
Mean ±
sd
n
Mean ±
sd
n
Mean ±
sd
Birds/treatment
198
775 ± 872
309
445 ± 463
213
1576 ± 2903
Initial age
b
212
11
±
9
320
10
±
8
242
11
±
11
Initial BW
85
311 ± 353
200
249
±
227
144
230
± 352
Duration experiment
(days)
148
17
± 0
320
11
±
8
187
14
±
11
Response
Feed intake
reduction
c
(%)
-15.83
R
² = 86.6
-7.09
R² = 95.8
-9.29
R² = 99.8
Growth rate
reduction
c
(%)
-40.09
R
² = 79.8
-10.55
R
² = 77.1
-29.19
R
² = 98.8
a
Number of treatments used to calculate the mean.
b
At the beginning of the experimental challenge.
c
Results are the slope differences between challenged and control birds (not challenged), expressed as a percentage of the
slope obtained with control birds.
