Growth Description Of The Poultry Body Components

Published Date: 02 Nov 2017

Abstract: This review presents the description of the growth in the broiler and laying strains studied at the Laboratory of Poultry Science FCAV/UNESP. Two commercial broiler strains were assessed, Ross 308® and Cobb 500® of both sexes, from 1 to 56 days of age. In this study 1,920 broiler chicks were divided into four groups with four replicates of 120 birds, resulting in 16 experimental units. The groups consisted of Ross 308 male, Ross 308 female, Cobb 500 male and Cobb 500 female. Four laying strains were studied, Hy-Line Brown and Hisex Brown and Hy-Line White W-36 and Hisex White of 1 to 126 days of age. Three hundred chicks of each strain were separated into groups with four replicates of 75 birds, resulting in 16 experimental units. Every week, the birds were weighed and selected based on the average weight of the experimental unit for slaughter. It was evaluated growth of the body and feathers and their chemical components (water, protein, lipid and ash) through the Gompertz function. Allometric coefficients were determined for the chemical components of the body in relation to the body protein weight. Differences were observed in some parameters of the Gompertz function between the broiler and laying strains. Among the broiler strains differences were found in body protein and feather weight. The differences between laying strains were in protein weight and maturity rate. The allometric coefficients revealed little difference between genotypes, both to broiler and laying strains, indicating that it is possible to use generalized parameters to describe the growth by allometry. The description of the growth of genotypes indicates that they have different rates of feed intake, energy and amino acids requirements to reach the genetic potential.

INTRODUCTION

The body composition was suggested as a reference to estimate the amino acid requirements of poultry since the 50s (Williams et al., 1954)V, and after twenty years it was used in a factorial model to predict protein and amino acids requirements for poultry (Hurwitz and Bornstein, 1973). The factorial model described by these authors fractionates the requirements for maintenance and weight gain, that make evident the need to foresee the growth, since from birth to maturity many modifications occurs in the physical and chemical composition in the poultry body (Emmans, 1981a .) Thus, the mathematical description of these changes helps to determine body composition with advancing age (Gous et al., 1999), and allows estimating the nutritional requirements with greater precision.

Accurate estimation of the amino acid requirements in growing animals is of fundamental importance for diet formulation. Physiological-based models for simulating growth have been partly used to predict these requirements (Smith, 1978; Hurwitz et al., 1983; Alleman et al., 1999). Although there is already a mathematical description of growth (Winsor, 1932), only in the 80s was shown a method (Emmans, 1981a) that integrates the growth with factorial models to calculate the requirements of the bird. Protein is used to define the genetic potential for growth and in the growth model of Emmans (1981a) it is the guide-variable used in the factorial model to predict maintenance requirements and growth of protein weight, since there is a close relationship between these components with the growth potential of the bird. Therefore, the first step to estimate the nutritional requirements is the description of the genotype, which has traditionally been determinate by the Gompertz function. (Gous et al. 1999).

Gompertz function parameters allow differentiating the genotypes based on the weight at maturity, maturation rate and the ratio of fat and protein in the mature bird (Hancock et al. 1995). These parameters are altered by genetic selection, and influence the feed intake, energy and amino acids requirements to reach the genetic potential (Gous et al., 1999). The individual experimental period was divided into an adaptation period (5 d) and 2 consecutive collecting periods (each 5 d). At the beginning of the adaptation period, the feed was given ad libitum to estimate the proper level of individual feed intake under housing conditions in metabolic cages. The individual feed supply was kept constant beginning at the d 3 of the adaptation period, slightly adapted during the first 2 d of the collecting period, and kept constant again up to the end of the collecting period.

Considering the proposal of Emmans (1981a) for the application of factorial models, it is necessary to know the potential of growth and nutrient deposition in the body. Based on this, the Laboratory of Poultry Science of UNESP - Jaboticabal (Lavinesp) has developed models to predict energy requirements (Sakomura et al., 2010) and amino acids (Siqueira et al., 2010). With this approach, Lavinesp studies have been performed to determine the growth parameters of two broiler and four laying lines used in Brazil, which are presented in this paper.

MATERIAL AND METHODS

The studies were conducted in the Laboratory of Poultry Science, Faculty of Agriculture and Veterinary Sciences, UNESP-FCAV (Lavinesp), Jaboticabal - SP, Brazil. It was determined the genetic parameters of two broiler strains and four laying strains. The broiler strains studied were Ross308® and Cobb500®, of both sexes. In this study 1,920 broiler chicks were separated into four groups with four replicates of 120 birds, resulting in 16 experimental units. The birds were housed in boxes using density of 10 birds/m² and wood shavings litter. Groups consisted of Ross 308 male (RM), Ross 308 female (RF), Cobb 500 male (CM) and Cobb 500 female (CF). The experimental period was 56 days.

The laying strains used were Hy Line Brown (HLB) and Hisex Brown (HSB) and Hy Line White W-36 (HLW) and Hisex White (HSW). Three hundred chicks of each strain were housed in breeding (1st to 6th week) and rearing cages (7th to 18th week).

The birds were divided into four groups with four replicates of 75 birds, resulting in 16 experimental units. The experimental period was 126 days.

The broiler strains were fed diets based on corn and soybean meal to meet their nutritional requirements, according with the recommendation of the strains in each phase. Levels of metabolizable energy (AMEn) and crude protein (CP) were: 3,010 kcal AMEn /kg and 22% CP (1-7 days); 3,150 kcal AMEn /kg and 21.50% CP (8-28 days ); 3,200 kcal AMEn /kg and 20% CP (29-49 days) and 3,245 kcal AMEn/kg and 18% CP (50-56 days).

The laying strains fed diets based on corn, soybean meal and wheat bran, to meet their nutritional requirements, according to the recommendation of Rostagno et al. (2000) in each phase. The lightweight strains levels of metabolizable energy (AMEn) and crude protein (CP) were: 2,950 kcal AMEn/kg and 21% CP, from 1st to 6th week, 2,850 kcal AMEn/kg and 18% CP of 7th to 12th week; 2,800 kcal AMEn/kg and 16% CP from 13th to 18th weeks. For semi heavy weight strains were used 2,950 kcal AMEn/kg and 21% CP from 1st to 6th week; 2,850 kcal AMEn/kg and 17% CP of 7th to 12th week; 2,750 kcal AMEn/kg and 16% CP from 13th to 18th week.

Every week, the birds were weighed and a sample was selected for slaughter based on the average weight of the experimental units. After a fasting period of 24 hours the birds were individually weighed and euthanized using CO2 and then feather samples were collected. The weight of feathers was determined by difference between the weight of the fasted bird and weight of defeathered carcass.

Defeathered carcasses were ground to obtain homogeneous samples. A aliquot of the samples was retired for subsequent pre-drying. Then, the samples were ground in micro-mill and analyzed for nitrogen (Kjeldahl method, crude protein = nitrogen x 6.25), ether extract (petroleum ether in Soxlet equipament), dry matter (oven at 105 º C) and ash (muffle at 550 ° C). The feather samples were chopped with scissors and subjected to the same chemical analysis.

To describe the growth of the major body components it was used the Gompertz function (Gompertz, 1825).

Wt = Wm × e{–e [–B × (t – t*)]}

where t is the age in days; Wt is the weight at time t, in kg, Wm is the weight at maturity in kg; B is the maturity rate, per day, t* is the age at which growth rate is maximum, expressed in days, and e is the numerical base of Euler.

The absolute growth rate (dW/dt), weight gain or deposition of the chemical components in g/day can be calculated using the following equation:

dW/dt = B·× Wt × ln(Wm/Wt)

The absolute growth rate increases until reach the maximum rate when the Wt is 36.8% of Wm, at this point t coincides t*. After this age, the rate decreases as Wt approaches of Wm.

Considering B, Wm and the numerical base e, the maximum deposition is calculate (dW/dtmax) dW/dtmax = B × Wm/e, in kg/day. The maximum weight (Wmax) Wmax = Wm/e.

The allometric coefficients were obtained from the relationship between the natural logarithm of the chemical component weight (LnCq): protein, water, fat and ash as a function of the natural logarithm of the protein weight (LnBP) according to the equation:

lnCq = a + b×lnBP

The feathering factor (FFc) was calculated according to Gous et al. (1999), considering the relationship of weight at maturity (Wm) feather (FW) and body protein (BP).

FFc = 0,84× FWWm / BPWm2/3

RESULTS

Growth of the Body

The results presented here describe the growth potential of broiler and laying lines in terms of body weight, feather weight and chemical composition. The parameters of the Gompertz function fitted for each genotype have biological significance and therefore allow comparisons between the growth parameters of the strains and sexes. Table 1 shows values ​​of empty body weight (EBW) and empty feather free weight (EFFW).

Table 1 Estimates of the three parameters of the Gompertz equation for body weight and empty feather free weight from of strains of commercial broiler chickens and laying type pullets

Variables

Broiler chickens

Pullets

RM

CM

RF

CF

HLB

HSB

HLW

HSW

Body weight, BW

Wm, kg

6.560

6.544

4.658

4.283

2.060

2.064

1.533

1.598

B, /d

0.042

0.042

0.047

0.051

0.023

0.023

0.026

0.023

t*, dias

39

39

34

32

59

59

52

55

Empty feather free weight, EFFW

Wm, kg

6.239

6.374

4.319

3.977

1.769

1.764

1.261

1.345

B, /d

0.042

0.041

0.047

0.051

0.024

0.024

0.026

0.024

t*, days

39

39

34

32

60

60

51

55

RM, Ross 308 Males; RF, Ross 308 Female; CM, Cobb 500 Males; CF, Cobb 500 Female; HLB, Hy Line Brown; HSB, Hisex Brown; HLW, Hy Line White W-36; HSW, Hisex White

The parameter Wm for EBW of males and females differ by about 2.08 kg. Females are smaller, however, the parameters B and t* indicate that are more precocius than males. The broiler lines can be ranked by precocity in the following order: CF, RF, CM and RM, with maximum weight gain (WGmax) at 28, 35, 35 and 42 days of age, respectively. The only difference observed with the removal of the feathers in the parameters (Wm, B and t*) fitted for EFFW with a delay of one week in the WGmax for CF strain (35 days of age).

For laying strains, the brown (HLB and HSB) and white (HLW and HSW) showed distinct patterns of growth. Based on Wm the white birds were lighter about 0.5 kg or approximately 75% than Wm of brown birds. The parameter B is related to the early growth and consequently, less time to reach the sexual maturity and starting to laying eggs. The HLW strain showed higher B and t* values compared to other strains for EBW and EFFW. Among the brown lines no differences regarding the parameters for early growth (B and t*) of the EBW and EFFW.

Growth of the Chemical Body

The parameters which describe the growth of the four chemical components are shown in Table 2.

For broiler strains, the parameters Wm, B and t* fitted for protein weight reveal clear differences in growth pattern between strains and sex.

Table 2 Estimates of Gompertz parameters for protein, water, lipid, and ash weight of commercial and laying type pullets strains

Variables

Broiler chickens

Pullets

RM

CM

RF

CF

HLB

HSB

HLW

HSW

Body protein, BP

Wm, kg

1.313

1.023

0.866

0.657

0.365

0.329

0.284

0.248

B, /d

0.036

0.047

0.044

0.056

0.025

0.026

0.028

0.026

t*, days

44

37

38

31

77

57

58

63

Body water, BWA

Wm, kg

3.216

3.653

2.269

2.342

0.931

0.983

0.606

0.771

B, /d

0.052

0.045

0.057

0.054

0.026

0.025

0.0316

0.025

t*, days

32

36

29

29

52

55

40

50

Body lipid, BL

Wm, kg

0.892

0.931

0.810

0.781

0.368

0.389

0.226

0.237

B, /d

0.039

0.041

0.041

0.043

0.022

0.022

0.028

0.022

t*, days

47

46

44

43

79

79

60

75

Body ash, BA

Wm, kg

0.360

0.174

0.115

0.087

0.073

0.068

0.050

0.052

B, /d

0.038

0.051

0.061

0.081

0.024

0.026

0.028

0.025

t*, days

52

34

29

24

63

58

55

56

RM, Ross 308 Males; RF, Ross 308 Female; CM, Cobb 500 Males; CF, Cobb 500 Female; HLB, Hy Line Brown; HSB, Hisex Brown; HLW, Hy Line White W-36; HSW, Hisex White

The results constitute Ross as the largest bird with protein deposition rate more distributed during the rearing period of 42 days. The Cobb despite being smaller, about 0.250 kg, presents higher maturity rate, indicating higher precocity.

The parameters obtained for lipid growth reveals similarity (Wm, B and t*) for broilers, strains and sex. The difference in Wm between the two strains was less than 0.6%, and between the sexes CM showed higher lipid weight, about 4.4%, compared to RM. For females, Ross showed a difference of 3.7% compared to Cobb.

The parameter Wm fitted for the component, body water, indicates that Cobb broilers have higher water content (6%). This difference in composition provided the greater water weight to males. To body ashes, the greatest differences were observed for RM and CF in relation to the parameters Wm and B, respectively. The RM showed higher Wm and lower B, while CF showed lower Wm and higher B value.

The parameters Wm, B and t* fitted for the chemical components of laying strains (Table 2) showed that Wm of brown birds differ from white. The values ​​obtained for rate, B, reveal similarity between strains, except HLW that had the highest rates for all body components.

The B rates obtained for water, protein and ash deposition suggest that occur at similar speeds, while the body lipid deposition occurs at lower rates and other components are relative delayed.

The Wm values ​​for protein weight of laying hens indicate differences in growth between white and brown strains. The B and t* values ​suggest that maximum protein deposition (PDmax) for HLB, HSB, HLW and HSW strains were 3.36, 3.15, 2.93 and 2.37 g/day at 77 , 57, 58, 63 days of age, respectively.

Allometric relationship non isometric

The ratio of water weight at maturity: protein (WPRm), lipid:protein (LPRm) and ash:protein (APRm), which are shown in Table 3. The average value for WPRm strain RM and RF was 2.63 while for CM and CF was 3.47. Considering all broiler strains, the average value for WPRm was 3.05, the Ross and Cobb were situated at -13.74 and +13.74% around the overall mean value, respectively.

In Table 2 were shown the differences in Wm for protein and lipid between sexes in the broiler strains, however, when LPRm were calculated it was observed that females have greater fat retention in carcass compared to males per unit of protein weight .

To APRm the average values ​​were similar between strains and sexes of broilers except to RF (Table 3) where the greatest differences of the overall mean of 0.198 were observed.

Table 3 Water to protein (WPRm), lipid to protein (LPRm) ash to protein (APRm) and ratios at maturity broiler chickens and laying type pullets and slope of Allometric relationship ¹

Itens

Broiler chickens

Pullets

RM

CM

RF

CF

HLB

HSB

HLW

HSW

Ratio

WPRm

2.753

3.571

2.511

3.370

2.553

2.983

2.133

3.105

LPRm

0.845

0.868

0.978

0.977

1.011

1.182

0.795

0.953

APRm

0.248

0.169

0.127

0.248

0.200

0.206

0.175

0.211

Slope

water vs protein, bW

0.921

0.925

0.910

0.929

0.850

0.862

0.835

0.885

Lipid vs protein, bL

1.210

1.164

1.263

1.243

1.275

1.281

1.277

1.277

Ash vs protein, bA

0.923

0.916

0.923

0.865

1.001

1.008

1.066

1.017

¹calculated using the estimates of mature component weights from Table 2

RM, Ross 308 Males; RF, Ross 308 Female; CM, Cobb 500 Males; CF, Cobb 500 Female; HLB, Hy Line Brown; HSB, Hisex Brown; HLW, Hy Line White W-36; HSW, Hisex White

The parameters b for water, ash and fat of RM, CM, RF and CF reveals similarity between strains and sexes (Table 3). The overall mean was calculated for each chemical component, being 0.921, 0.907 and 1.220 for water, ash and fat, respectively. Despite the similarity, the major differences were found in lipids of 4.0 and 5.0% for RF and CM, respectively.

To the laying strains the WPRm, LPRm and APRm showed average values ​​of 2.694; 0.985 and 0.198, respectively. The Hy line birds showed less proportion of water per unit of protein weight in relation to Hisex line. For lipids brown birds showed greater lipid retention per unit protein weight. Based on these relationships HLW line showed the greatest difference from the mean values​​, including the APRm (Table 3).

The parameters b of the chemical components in the studied genotypes suggest that the growth patterns of the components are similar, the mean values ​​were 0.858, 1.278 and 1.023 for water, lipid and ash, respectively (Table 3). The biggest difference in this parameter was recorded for the ashes of HLW, with a growth rate 4.2% higher than the overall mean.

Growth of the Feathers

The parameters of the Gompertz function fitted for the feather growth and feather protein weight of broiler and laying lines are shown in Table 4.

For broiler chicks, the relationship between the parameters Wm adjusted for FW (Table 1) and BW shows that the proportion of feathers is 6.9 to 7.6% for males and females, 7.8 and 6.7% for Ross and Cobb, respectively. The relationship between Wm fitted for FP and FW of broilers suggests a content of 84% protein in the feathers at maturity.

For pullets, the feathers protein at maturity was 84%. The percentage of feather at maturity was 8 and 10% for white and brown birds; 9 and 10 for Hisex and Hy line strains, respectively. In general, at maturity of these birds, FP corresponded approximately to 31% of total protein (FP + BP). Based on the values ​​of the parameter B fitted to BW (Table 1) and BP (Table 2) showed that FP and FW grow in greater velocity than BW and BP approximately 1.22 and 1.13 times, respectively.

The results obtained for feathering factor (FFc) indicate similarity between the broiler genotypes and sexes with average value of 0.343. For laying hens differences in FFc were less than 5% when grouped by color, the overall mean was 0.303.

Table 4 Estimates of three parameters of the Gompertz equation for feather weight of commercial broiler chickens and laying hens type pullets

Variables

Broiler chickens

Pullets

RM

CM

RF

CF

HLB

HSB

HLW

HSW

Feather weight, FW

Wm

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

Wm

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 Female; CM, Cobb 500 Males; CF, Cobb 500 Female

HLB, Hy Line Brown; HSB, Hisex Brown; HLW, Hy Line White W-36; HSW, Hisex White

DISCUSSION

According to the theory of Emmans (1997), the animal will feed to meet their growth potential. This concept suggests that the description of the growth potential is essential to initiate nutritional studies with growing birds (Gous et al., 1999).

The description of the BW growth (Table 1) showed that the major differences are found between sexes. But, when comparing BP and BL, the differences are clear between sexes and strains. These differences indicate that strains with higher protein and lipid increased at higher rates and achieved a greater weight. Despite the differences in lipid weight at maturity, the growth rates of BP were greater than the BL rate. From a nutritional perspective, the greater protein deposition directly affects the amino acid requirement and when related to a lower rate of lipid deposition, protein requirements tends to increase at a greater speed than energy requirement. Likewise it is expected that strains with higher lipid weight at maturity have a greater energy requirement to regulate body lipid deposition.

However, the lipid content of the bird reflects not only the bird genotype as well as the environmental conditions and diet in which were created (Hancock et al. 1995). Therefore, the growth parameters determinated can be interpreted to a certain desired pattern for lipid growth, since there is clear evidences (Emmans and Kyriazakis, 1997) that the deposition of lipids can be changed according to adverse environmental conditions and diet. Moreover, the animal will attempt to correct the deviation of deposited lipid compared to desirable, as soon as the limiting condition is removed (for details see Ferguson 2006).

The fitted parameters for BWA and BA (Table 2) showed that water and ash are the chemical components of the highest growth rate, and thus reach the maturity earlier than the other components. Despite the differences in Wm of these chemical components, the values ​​obtained for broilers and laying hens of 2.9 (WPRm) and 0.2 (APRm ) were close to the coefficients for all species suggested (Emmans and Kyriazakis, 1995; Ferguson, 2006) and because this similarity it can be considered almost constant (Kyriazakis and Emmans, 1995).

The existent reasons to accurately estimate the EFFW, are the same that justifying the prediction of water, fat and ash weight (Emmans and Kyriazakis, 1995), and a practical way has been the use of allometric equations combined with the Gompertz .

The growth rate of the component (dC/dt) can be estimated from the protein growth rate (dBP/dt) using dC/dt = dC/dP×dBP/dt (Martin et al. 1994). The dC/dP represents the relationship between the water component (WPRm and bW), lipid (LPRm and bL) and ash (APRm and bA) with the protein weight, thereby, the EFFW weight gain can be obtained by summing the protein, lipid, water and ash deposition.

The slopes of the logarithmic relationship between the components water (bW), lipid (bL) and ash (bA) with the protein weight showed similar values ​​for broilers and laying hens. The maximum difference found was 10.4% for the ash slope, while water and lipid showed 6.1 and 6.8%, respectively. It was expected that the values ​obtained ​for bL variate between the genotypes (Emmans and Fisher, 1986), but the variation observed was similar to the other components. These results are supported by other findings in the literature (Martin et al. 1994).

In general, the allometric coefficients indicate that as the protein weight increases, there is an increases in the proportion of fat and a decrease in the proportion of water and ashes of the body. This explains the sequence of nutrient depositions in the bird body, the deposition of ash and water occurs at greater extent in the post-hatching phase (Marcato et al. 2008).

The feathers have a peculiarity in their composition and therefore should be studied separately from the body. The differences found in the feather weight within genetic groups of the broilers and laying birds may be related to natural loss of feathers that occurs during the growth period, which seems to be specific to the genotype, and damage inflicted on the feathers (Hancock et al., 1995). These factors affect the feathers weight and consequently reflected in the adjustment of the growth parameters.

The FFc describes the feather growth with different rate value of the Gompertz function (Gous et al. 1999). The average value of 0.343 and 0.303 for broilers and laying hens, respectively, indicates that broilers have an earlier feathering than laying hens. For broilers, the FFc rates were higher in relation to other findings in the literature (Gous et al., 1999; Hruby et al., 1994), indicating a precocity in the feathering observed in this study.

The presented differences for the growth pattern of body protein and feathers imply variation in the proportion of protein deposited in the body of the bird during growth, especially in the post-hatching, where the feathering rate is strictly positive (Emmans, 1989). The feathers have a different amino acid composition of the body protein, and these differences affect the total amino acid required by the bird. Therefore, it is necessary to consider the calculation of the requirement of feathers separately of the body (Emmans and Fisher, 1986; Emmans, 1989, 1997). Furthermore, a coherent model should include the maintenance and growth of the body and feathers separately (Emmans, 1989). The growth information described in this work can be combined with other nutritional constants to calculate the requirements and feed intake (Emmans and Fisher, 1986; Emmans, 1989, 1997).