Description of the Growth of Body Components of Broilers and Laying Pullets - Nutritional Modelling for Pigs and Poultry - page 255

The allometric regression coefficient b
for water, ash and lipid contents of RM, CM,
RF and CF reveal similarities between the
strains and sexes ( Table 18.3 ) . The overall
means for each chemical component were
0.921, 0.907 and 1.220 for water, ash and
lipid, respectively. Despite the similarities,
major differences were found in lipid
contents for RF and CM, being 0.04 and
0.05, respectively.
For the laying strains, WPRm, LPRm and
APRm showed average values of 2.694, 0.985
and 0.198, respectively. The Hy-Line birds
showed a lower proportion of water per unit
of protein weight compared to the Hisex line.
For lipid, the brown strains showed the high-
est lipid retention per unit of protein weight.
Based on these relationships, the HLW line
showed the greatest deviation from the mean
values, including APRm ( Table 18.3 ).
These results suggest that the growth pat-
terns of the chemical components are similar
in the laying strains; mean b values were
0.858, 1.278 and 1.023 for water, lipid and
ash, respectively (Table 18.3 ). The biggest dif-
ference in this parameter was recorded for the
ash content of HLW, with a growth rate that
was 0.042 higher than the overall mean.

weight of the broiler and laying strains are in
Table 18.4 .
In broilers, the proportion of feathers
at maturity (FWm) in EBWm was 0.07 and
0.08 for males and females and 0.08 and
0.07 for Ross and Cobb, respectively, and
in the laying strains, 0.08 and 0.1 for the
white and brown strains and 0.09 and 0.1
for the Hisex and Hy-Line strains, respect-
ively. The protein content of feathers at
maturity in both broilers and laying pullets
was 840 g/kg.
The values of parameter B fitted to BW
( Table 18.1 ) and BP ( Table 18.2) indicate that
FW and FP grow approximately 1.22 and
1.13 times faster than BW and BP, respectively.
The results obtained for the feathering
factor (FFc) indicate similarities between the
broiler genotypes and sexes, with an average
value of 0.343. For laying pullets the diffe-
rence in FFc was less than 0.05 when grouped
by colour, with an overall mean of 0.303.

Discussion

According to the theory of Emmans (1997)
animals will attempt to consume enough of
a given food to meet their growth potential.
This concept suggests that a description of
the growth potential is essential to initiate
nutritional studies of growing birds (Gous
et al ., 1999).

Feather growth

The parameters of the Gompertz function
fitted for feather growth and feather protein

Table 18.4. Estimates of three parameters of the Gompertz equation for feather weight of commercial broiler
chickens and laying type pullets.

Broiler chickens Pullets

Variables RM CM RF CF HLB HSB HLW HSW

Feather weight, FW

FWm 0.482 0.420 0.383 0.298 0.172 0.167 0.164 0.147

B 0.035 0.035 0.036 0.044 0.032 0.032 0.026 0.028

t* 49 44 45 37 55 55 57 55

Feather protein, FP

FPm 0.405 0.0353 0.321 0.250 0.144 0.140 0.138 0.124

B 0.035 0.0350 0.036 0.044 0.032 0.033 0.026 0.028

t* 49 44 45 37 55 56 58 55

Feathering
factor, FFc

0.337 0.347 0.354 0.332 0.284 0.295 0.320 0.314

RM = Ross 308 males; RF = Ross 308 females; CM = Cobb 500 males; CF = Cobb 500 females; HLB = Hy-Line Brown;
HSB = Hisex Brown; HLW = Hy-Line White W- 36; HSW = Hisex White.