- Email: [email protected]
Prediction of whole-body composition from the whole-body dry matter percentage of three-week-old broiler chicks
Prediction of Whole-Body Composition from the Whole-Body Dry Matter Percentage of Three-Week-Old Broiler Chicks1 K. Bregendahl,2,3 J. L. Sell, and D. R. Zimmerman Department of Animal Science, Iowa State University, Ames, Iowa 50011 CP (P = 0.29; r2 = 0.010). The percentage of whole-body ash was moderately correlated with the percentage of whole-body DM (P = 0.04; r2 = 0.036). In conclusion, the percentage of whole-body ether extract of 3-wk-old broiler chicks can be predicted from the percentage of whole-body DM by using the prediction equation Y = 0.961x − 17.855. Neither the percentages of whole-body CP nor ash could be accurately predicted from the wholebody DM percentage.
(Key words: broiler chick, whole-body composition, regression equations, dry matter, ether extract) 2002 Poultry Science 81:1168–1171
INTRODUCTION Abdominal fat of broiler chicks contains approximately 85% DM by weight, whereas muscle (skinless, boneless breast, and thigh) contains approximately 30% DM (Moran, 1995). Thus, carcasses with a relatively high percentage of DM contain a relatively large proportion of fat compared with carcasses with a low percentage of DM. The opposite holds true in regard to percentage muscle, in which a low DM percentage would indicate a leaner carcass. In investigations of whole-body composition of 3-wk-old broiler chicks fed diets containing varying concentrations of CP—but adequate concentrations of essential amino acids—we found a large variation in percentage whole-body DM, ether extract (EE), and CP (Bregendahl, 2001; Bregendahl et al., 2002). In those experiments, the whole-body compositions of DM, EE, and CP were analyzed, although predicting the composition from the whole-body percentage of DM could potentially have saved time without forfeiting accuracy (Velu et al., 1972; Wolynetz and Sibbald, 1986, 1990). The correlations be-
2002 Poultry Science Association, Inc. Received for publication October 9, 2001. Accepted for publication January 22, 2002. 1 Journal Paper Number J-19504 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, Project Number 3812, and supported by Hatch Act and State of Iowa funds. 2 To whom correspondence should be addressed: kbregend@ uoguelph.ca. 3 Current address: Department of Animal and Poultry Science, Room 255 Animal Science and Nutrition Building, University of Guelph, Guelph, Ontario N1G 2W1, Canada. 4 Welp Inc., Bancroft, IA.
tween percentage whole-body DM and percentage whole-body EE, CP, and ash of 3-wk-old broiler chicks are characterized below.
MATERIALS AND METHODS In four independent experiments with similar experimental designs and management (Bregendahl, 2001; Bregendahl et al., 2002), 1-d-old male broiler chicks (Petersen × Hubbard or Hubbard × Hubbard) were purchased from a commercial hatchery4 and fed a common corn-soybean meal diet (23% CP) for 7 d. Subsequently, 1,140 chicks were allotted on the basis of BW to floor pens (1.3 × 1.3 m) containing pine shavings. Within each experiment, six replicates of pens, each containing 10 chicks, were randomly assigned a dietary treatment, consisting of corn-soybean meal diets of varying CP concentrations, fortified with crystalline amino acids. All diets were formulated to be isoenergetic (3,200 kcal MEn/kg) and to meet or exceed NRC (1994) recommended levels of minerals and vitamins. At the end of the experiments (Day 21 posthatching), feed was withdrawn from chicks (with free access to water) for 24 h, after which two chicks per pen with BW close to the pen mean were selected, euthanized by cervical dislocation, and stored in airtight plastic bags at −20 C for later determination of the whole-body composition. All procedures relating to the use of live animals were approved by the Laboratory Animal Resources Committee of Iowa State University.
1168
Abbreviation Key: EE = ether extract.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
ABSTRACT Whole carcasses of 3-wk-old broiler chicks from four independent experiments were analyzed for percentage of whole-body DM, ether extract, and CP. The percentage of whole-body ash was calculated by the difference among DM, ether extract, and CP. A linear relationship between percentage whole-body DM and percentage whole-body ether extract (P < 0.001; r2 = 0.798) was found, but no relationships were detected between percentage whole-body DM and percentage whole-body
1169
PREDICTION OF WHOLE-BODY COMPOSITION
TABLE 1. Means and ranges of whole-body DM, CP, and ether extract of 3-wk-old broiler chicks in the four experiments Experiments2
DM
CP
29.5 (27.4–33.6) 29.6 (24.0–31.8) 30.3 (26.4–32.1) 29.3 (26.0–32.2) 29.7 (24.0–33.6) 0.026
15.5 (14.5–16.4) 16.1 (14.7–16.9) 16.1 (15.2–17.1) 16.1 (15.0–17.1) 16.0 (14.5–17.1) 0.001
Ether extract
(%) Experiment Experiment Experiment Experiment Overall P-value3
1 2 3 4
10.3 (8.1–13.6) 11.0 (7.2–13.6) 11.0 (6.6–12.8) 10.4 (7.3–13.4) 10.7 (6.6–13.6) 0.168
1
Mean (range). n = 24, 24, 30, and 36 for Experiments 1, 2, 3 and 4, respectively. 3 Main effect among experiments. 2
Statistical Analysis Data were subjected to linear regression procedures (Neter et al., 1990) using JMP (JMP, 2000) with the percentage whole-body DM serving as the independent value and percentage whole-body CP, EE, or ash serving as dependent values. The pooled whole-body composition data of two chicks per pen served as the experimental units (n = 114) and P ≤ 0.05 was considered significant.
FIGURE 1. Linear regression of percentage whole-body ether extract (Y) on percentage whole-body DM (x) of 3-wk-old broiler chicks (n = 114).
RESULTS AND DISCUSSION Means of whole-body EE did not differ (P > 0.10) among the four experiments (Table 1), as did means of DM and CP (P < 0.05), yet there was a large variation and overlap in the ranges of all observations of whole-body composition. Percentages of whole-body DM of all chicks were within the range reported by Velu et al. (1972) for 3-wkold chicks. Percentage DM, rather than percentage water, was used in the regressions in agreement with Wolynetz and Sibbald (1986), because percentage DM was determined directly in the analyses of whole-body composition. As shown in Figure 1, a linear relationship (P < 0.001; r2 = 0.798) was observed between percentage whole-body
5
Waring Products Division, New Hartford, CT. U.S. Tecator Inc., Herndon, VA. Laboratory Construction Co., Kansas City, MO.
6 7
DM and percentage whole-body EE, which is in agreement with broiler chick data from other experiments (Velu et al., 1972; Wolynetz and Sibbald, 1986, 1990; Kranen et al., 1998). The relationship between whole-body DM and EE differed moderately from that of Velu et al. (1972) and Kranen et al. (1998), potentially because we used a different strain of broiler chicks. Furthermore, differences in the length of feed withdrawal and methods of analyses between our experiments and those by Velu et al. (1972) and Kranen et al. (1998) might have contributed to the differences. Wolynetz and Sibbald (1986, 1990) included BW in addition to DM in their prediction equation of whole-body EE. However, use of BW and DM as independent variables in the analysis did not (P < 0.001; R2 = 0.800) further improve the relationship compared with that of DM alone (P < 0.001; r2 = 0.798). We expected to find a negative relationship between the percentages of whole-body DM and CP, but no rela-
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
The whole bodies of the euthanized chicks were thawed overnight at room temperature and subsequently homogenized and sampled according to procedures described by Barker and Sell (1994) modified from Sibbald and Wolynetz (1984). The whole body of individual chicks was combined with distilled water (1 × BW) in glass beakers, autoclaved for 8 h, and allowed to cool overnight in the autoclave. Weight loss during this process was assumed to be water, which was replaced, and the birds were subsequently blended in a Waring blender5 for 2 min after addition of distilled water (2 × BW). Duplicate aliquots of 90 to 100 g were dried in plastic weigh boats at 50 C for 3 d, ground with a mortar and pestle, and stored in airtight plastic bags at room temperature before Kjeldahl N and EE analyses. Whole-body DM was calculated from the dry weights of the ground chicks and the records of additions and losses of water (Barker and Sell, 1994). Kjeldahl N and EE were analyzed on pooled samples of the two chicks per pen. The whole-body N content was analyzed in triplicate by a micro-Kjeldahl procedure (Association of Official Analytical Chemists, 1984) on a Kjeltech 1028 distilling unit,6 and whole-body CP was calculated as Kjeldahl N × 6.25. The whole-body fat content was determined in triplicate as EE according to the Association of Official Analytical Chemists (1984) by using a Goldfisch extraction apparatus.7 Percentage whole-body ash was calculated as the difference between percentages of whole-body DM, EE, and CP.
1
1170
BREGENDAHL ET AL. TABLE 2. Body weight and whole-body composition of 3-wk-old broiler chicks fed diets containing varying amounts of CP but adequate concentrations of amino acids Item
Mean1
Standard error
Coefficient of variation
Body weight (g/chick) DM (%) CP (%) Ether extract (%) Ash2 (%)
743.77 29.67 15.97 10.65 3.05
8.06 0.14 0.05 0.15 0.06
11.58 4.87 3.62 4.87 19.76
n = 114. Calculated as the difference between the percentages of DM, CP, and ether extract. 1 2
tionship (P = 0.29; r2 = 0.010) was found (Figure 2). This result differs from the findings by Velu et al. (1972), who found a linear (P < 0.01) relationship between percentage body water and percentage body protein of 3-wk-old chicks, and from results by Wolynetz and Sibbald (1986, 1990), who found a linear relationship among percentage whole-body DM, BW, and percentage whole-body CP in 1- to 3-wk-old chicks. In our experiment, multiple regression with percentage whole-body DM and BW as independent values, rather than percentage whole-body DM alone, decreased the root mean square error slightly from 0.578 to 0.533 and increased the coefficient of determination from 0.010 (r2) to 0.168 (R2). This improvement stemmed mainly from the correlation between BW and percentage whole-body CP (P < 0.001; r2 = 0.150). However, the relatively small coefficients of determination indicate only weak correlations between the percentages of whole-body DM and CP. Hunt (1965) showed that the dietary CP concentration influenced the whole-body nitrogen-to-water ratio of 3-wk-old broiler chicks, potentially explaining the lack of correlation between percentages of whole-body DM and CP in our data. When only the positive control diets (approximately 23% dietary CP) were used in the regression analysis (n = 24), the r2 increased to a still-very-low value, 0.047, whereas the Pvalue was virtually unchanged (P = 0.31) compared to the regression analysis with observations from all diets (P = 0.29; r2 = 0.010; n = 114). This small improvement indicated that the influence of dietary CP concentration on the relationship between percentages of whole-body DM and CP was minimal. Ascites is characterized by accumulation of fluid in body cavities and is common in fast-growing broiler chicks (Julian, 1998). Although ascites would affect the whole-body DM contents, potentially
FIGURE 3. Linear regression of percentage whole-body ash (Y) on percentage whole-body DM (x) of 3-wk-old broiler chicks (n = 114).
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
FIGURE 2. Linear regression of percentage whole-body CP (Y) on percentage whole-body DM (x) of 3-wk-old broiler chicks (n = 114).
explaining the lack of relationship between percentages of whole-body DM and CP, we did not observe edemas in the chicks. The majority of the chick DM consisted of CP and EE (Table 2), with the remainder DM contributed by minerals (ash) and carbohydrates (nitrogen-free extract). Nitrogenfree extract constitutes approximately one percentage point of the DM (calculated from Barker and Sell, 1994), and the difference among percentage whole-body DM, CP, and EE, may therefore be viewed as ash. The percentage of whole-body ash increased linearly (P = 0.04) with increasing whole-body DM (Figure 3). Experimental errors in the determinations of DM, CP, and EE affect the calculation of ash, partly explaining the high CV (Table 2) and the weak correlation (r = 0.190) between percentage whole-body DM and percentage ash (Figure 3). In conclusion, the whole-body percentage of EE of 3wk-old broiler chicks was directly correlated (P < 0.001; r2 = 0.798) with the whole-body percentage of DM. Hence, the percentage of whole-body EE can be predicted from
PREDICTION OF WHOLE-BODY COMPOSITION
the percentage whole-body DM using the equation Y = 0.961x − 17.855, where Y = percentage whole-body EE and x = percentage whole-body DM. Standard errors associated with the slope and intercept were 0.046 and 1.358, respectively. On the contrary, the percentage of wholebody CP and ash could not be predicted accurately (r2 = 0.010 and 0.036, respectively) from the percentage of whole-body DM.
ACKNOWLEDGMENTS The assistance of the staff of the Poultry Science Center for care of the chicks, the expertise of A. Weisberg in the chemical analyses, and R. Wei for statistical advice are gratefully acknowledged.
Association of Official Analytical Chemists. 1984. Official Methods of Analysis of the Association of Analytical Chemists. 14th ed. Association of Analytical Chemists, Washington, DC. Barker, D. L., and J. L. Sell. 1994. Dietary carnitine did not influence performance and carcass composition of broiler chickens and young turkeys fed low- or high-fat diets. Poult. Sci. 73:281–287. Bregendahl, K. 2001. Effects of low crude-protein diets fortified with crystalline amino acids on growth performance and nitrogen retention of broiler chicks. Ph.D. Dissertation. Iowa State University, Ames, IA.
Bregendahl, K., J. L. Sell, and D. R. Zimmerman. 2002. Effect of low-protein diets on growth performance and body composition of broiler chicks. Poult. Sci. 81:1156–1167. Hunt, J. R. 1965. Factors influencing body N:H2O ratio of growing chicks. Poult. Sci. 44:236–240. JMP. 2000. JMP User’s Guide. Version 4.0.3. SAS Institute Inc., Cary, NC. Julian, R. J. 1998. Rapid growth problems: Ascites and skeletal deformities in broilers. Poult. Sci. 77:1773–1780. Kranen, R. W., C. W. Scheele, C. H. Veerkamp, E. Lambooy, T. H. van Kuppevelt, and J. H. Veerkamp. 1998. Susceptibility of broiler chickens to hemorrhages in muscles: The effect of stock and rearing temperature regimen. Poult. Sci. 77:334– 341. Moran, E. T., Jr. 1995. Body composition. Pages 139-156 in Poultry Production. P. Huntington, ed. Elsevier Science B. V., Amsterdam, The Netherlands. Neter, J., W. Wasserman, and M. H. Kutner. 1990. Applied Linear Statistical Models. Regression, Analysis of Variance, and Experimental Designs. 3rd ed. Irwin, Burr Ridge, IL. NRC. 1994. Nutrient Requirements of Poultry. 9th ed. National Academy Press, Washington, DC. Sibbald, I. R., and M. S. Wolynetz. 1984. Variation among aliquots of entire chicken homogenates. Poult. Sci. 63:1446– 1448. Velu, J. G., D. H. Baker, and H. M. Scott. 1972. Regression equations for determining body composition of young chicks. Poult. Sci. 51:698–699. Wolynetz, M. S., and I. R. Sibbald. 1986. Prediction of major body components of broiler chicks. Poult. Sci. 65:2173–2185. Wolynetz, M. S., and I. R. Sibbald. 1990. Estimates of body components in broiler chickens from body weight and dry matter. Poult. Sci. 69:1318–1324.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
REFERENCES
1171
(Key words: broiler chick, whole-body composition, regression equations, dry matter, ether extract) 2002 Poultry Science 81:1168–1171
INTRODUCTION Abdominal fat of broiler chicks contains approximately 85% DM by weight, whereas muscle (skinless, boneless breast, and thigh) contains approximately 30% DM (Moran, 1995). Thus, carcasses with a relatively high percentage of DM contain a relatively large proportion of fat compared with carcasses with a low percentage of DM. The opposite holds true in regard to percentage muscle, in which a low DM percentage would indicate a leaner carcass. In investigations of whole-body composition of 3-wk-old broiler chicks fed diets containing varying concentrations of CP—but adequate concentrations of essential amino acids—we found a large variation in percentage whole-body DM, ether extract (EE), and CP (Bregendahl, 2001; Bregendahl et al., 2002). In those experiments, the whole-body compositions of DM, EE, and CP were analyzed, although predicting the composition from the whole-body percentage of DM could potentially have saved time without forfeiting accuracy (Velu et al., 1972; Wolynetz and Sibbald, 1986, 1990). The correlations be-
2002 Poultry Science Association, Inc. Received for publication October 9, 2001. Accepted for publication January 22, 2002. 1 Journal Paper Number J-19504 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, Project Number 3812, and supported by Hatch Act and State of Iowa funds. 2 To whom correspondence should be addressed: kbregend@ uoguelph.ca. 3 Current address: Department of Animal and Poultry Science, Room 255 Animal Science and Nutrition Building, University of Guelph, Guelph, Ontario N1G 2W1, Canada. 4 Welp Inc., Bancroft, IA.
tween percentage whole-body DM and percentage whole-body EE, CP, and ash of 3-wk-old broiler chicks are characterized below.
MATERIALS AND METHODS In four independent experiments with similar experimental designs and management (Bregendahl, 2001; Bregendahl et al., 2002), 1-d-old male broiler chicks (Petersen × Hubbard or Hubbard × Hubbard) were purchased from a commercial hatchery4 and fed a common corn-soybean meal diet (23% CP) for 7 d. Subsequently, 1,140 chicks were allotted on the basis of BW to floor pens (1.3 × 1.3 m) containing pine shavings. Within each experiment, six replicates of pens, each containing 10 chicks, were randomly assigned a dietary treatment, consisting of corn-soybean meal diets of varying CP concentrations, fortified with crystalline amino acids. All diets were formulated to be isoenergetic (3,200 kcal MEn/kg) and to meet or exceed NRC (1994) recommended levels of minerals and vitamins. At the end of the experiments (Day 21 posthatching), feed was withdrawn from chicks (with free access to water) for 24 h, after which two chicks per pen with BW close to the pen mean were selected, euthanized by cervical dislocation, and stored in airtight plastic bags at −20 C for later determination of the whole-body composition. All procedures relating to the use of live animals were approved by the Laboratory Animal Resources Committee of Iowa State University.
1168
Abbreviation Key: EE = ether extract.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
ABSTRACT Whole carcasses of 3-wk-old broiler chicks from four independent experiments were analyzed for percentage of whole-body DM, ether extract, and CP. The percentage of whole-body ash was calculated by the difference among DM, ether extract, and CP. A linear relationship between percentage whole-body DM and percentage whole-body ether extract (P < 0.001; r2 = 0.798) was found, but no relationships were detected between percentage whole-body DM and percentage whole-body
1169
PREDICTION OF WHOLE-BODY COMPOSITION
TABLE 1. Means and ranges of whole-body DM, CP, and ether extract of 3-wk-old broiler chicks in the four experiments Experiments2
DM
CP
29.5 (27.4–33.6) 29.6 (24.0–31.8) 30.3 (26.4–32.1) 29.3 (26.0–32.2) 29.7 (24.0–33.6) 0.026
15.5 (14.5–16.4) 16.1 (14.7–16.9) 16.1 (15.2–17.1) 16.1 (15.0–17.1) 16.0 (14.5–17.1) 0.001
Ether extract
(%) Experiment Experiment Experiment Experiment Overall P-value3
1 2 3 4
10.3 (8.1–13.6) 11.0 (7.2–13.6) 11.0 (6.6–12.8) 10.4 (7.3–13.4) 10.7 (6.6–13.6) 0.168
1
Mean (range). n = 24, 24, 30, and 36 for Experiments 1, 2, 3 and 4, respectively. 3 Main effect among experiments. 2
Statistical Analysis Data were subjected to linear regression procedures (Neter et al., 1990) using JMP (JMP, 2000) with the percentage whole-body DM serving as the independent value and percentage whole-body CP, EE, or ash serving as dependent values. The pooled whole-body composition data of two chicks per pen served as the experimental units (n = 114) and P ≤ 0.05 was considered significant.
FIGURE 1. Linear regression of percentage whole-body ether extract (Y) on percentage whole-body DM (x) of 3-wk-old broiler chicks (n = 114).
RESULTS AND DISCUSSION Means of whole-body EE did not differ (P > 0.10) among the four experiments (Table 1), as did means of DM and CP (P < 0.05), yet there was a large variation and overlap in the ranges of all observations of whole-body composition. Percentages of whole-body DM of all chicks were within the range reported by Velu et al. (1972) for 3-wkold chicks. Percentage DM, rather than percentage water, was used in the regressions in agreement with Wolynetz and Sibbald (1986), because percentage DM was determined directly in the analyses of whole-body composition. As shown in Figure 1, a linear relationship (P < 0.001; r2 = 0.798) was observed between percentage whole-body
5
Waring Products Division, New Hartford, CT. U.S. Tecator Inc., Herndon, VA. Laboratory Construction Co., Kansas City, MO.
6 7
DM and percentage whole-body EE, which is in agreement with broiler chick data from other experiments (Velu et al., 1972; Wolynetz and Sibbald, 1986, 1990; Kranen et al., 1998). The relationship between whole-body DM and EE differed moderately from that of Velu et al. (1972) and Kranen et al. (1998), potentially because we used a different strain of broiler chicks. Furthermore, differences in the length of feed withdrawal and methods of analyses between our experiments and those by Velu et al. (1972) and Kranen et al. (1998) might have contributed to the differences. Wolynetz and Sibbald (1986, 1990) included BW in addition to DM in their prediction equation of whole-body EE. However, use of BW and DM as independent variables in the analysis did not (P < 0.001; R2 = 0.800) further improve the relationship compared with that of DM alone (P < 0.001; r2 = 0.798). We expected to find a negative relationship between the percentages of whole-body DM and CP, but no rela-
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
The whole bodies of the euthanized chicks were thawed overnight at room temperature and subsequently homogenized and sampled according to procedures described by Barker and Sell (1994) modified from Sibbald and Wolynetz (1984). The whole body of individual chicks was combined with distilled water (1 × BW) in glass beakers, autoclaved for 8 h, and allowed to cool overnight in the autoclave. Weight loss during this process was assumed to be water, which was replaced, and the birds were subsequently blended in a Waring blender5 for 2 min after addition of distilled water (2 × BW). Duplicate aliquots of 90 to 100 g were dried in plastic weigh boats at 50 C for 3 d, ground with a mortar and pestle, and stored in airtight plastic bags at room temperature before Kjeldahl N and EE analyses. Whole-body DM was calculated from the dry weights of the ground chicks and the records of additions and losses of water (Barker and Sell, 1994). Kjeldahl N and EE were analyzed on pooled samples of the two chicks per pen. The whole-body N content was analyzed in triplicate by a micro-Kjeldahl procedure (Association of Official Analytical Chemists, 1984) on a Kjeltech 1028 distilling unit,6 and whole-body CP was calculated as Kjeldahl N × 6.25. The whole-body fat content was determined in triplicate as EE according to the Association of Official Analytical Chemists (1984) by using a Goldfisch extraction apparatus.7 Percentage whole-body ash was calculated as the difference between percentages of whole-body DM, EE, and CP.
1
1170
BREGENDAHL ET AL. TABLE 2. Body weight and whole-body composition of 3-wk-old broiler chicks fed diets containing varying amounts of CP but adequate concentrations of amino acids Item
Mean1
Standard error
Coefficient of variation
Body weight (g/chick) DM (%) CP (%) Ether extract (%) Ash2 (%)
743.77 29.67 15.97 10.65 3.05
8.06 0.14 0.05 0.15 0.06
11.58 4.87 3.62 4.87 19.76
n = 114. Calculated as the difference between the percentages of DM, CP, and ether extract. 1 2
tionship (P = 0.29; r2 = 0.010) was found (Figure 2). This result differs from the findings by Velu et al. (1972), who found a linear (P < 0.01) relationship between percentage body water and percentage body protein of 3-wk-old chicks, and from results by Wolynetz and Sibbald (1986, 1990), who found a linear relationship among percentage whole-body DM, BW, and percentage whole-body CP in 1- to 3-wk-old chicks. In our experiment, multiple regression with percentage whole-body DM and BW as independent values, rather than percentage whole-body DM alone, decreased the root mean square error slightly from 0.578 to 0.533 and increased the coefficient of determination from 0.010 (r2) to 0.168 (R2). This improvement stemmed mainly from the correlation between BW and percentage whole-body CP (P < 0.001; r2 = 0.150). However, the relatively small coefficients of determination indicate only weak correlations between the percentages of whole-body DM and CP. Hunt (1965) showed that the dietary CP concentration influenced the whole-body nitrogen-to-water ratio of 3-wk-old broiler chicks, potentially explaining the lack of correlation between percentages of whole-body DM and CP in our data. When only the positive control diets (approximately 23% dietary CP) were used in the regression analysis (n = 24), the r2 increased to a still-very-low value, 0.047, whereas the Pvalue was virtually unchanged (P = 0.31) compared to the regression analysis with observations from all diets (P = 0.29; r2 = 0.010; n = 114). This small improvement indicated that the influence of dietary CP concentration on the relationship between percentages of whole-body DM and CP was minimal. Ascites is characterized by accumulation of fluid in body cavities and is common in fast-growing broiler chicks (Julian, 1998). Although ascites would affect the whole-body DM contents, potentially
FIGURE 3. Linear regression of percentage whole-body ash (Y) on percentage whole-body DM (x) of 3-wk-old broiler chicks (n = 114).
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
FIGURE 2. Linear regression of percentage whole-body CP (Y) on percentage whole-body DM (x) of 3-wk-old broiler chicks (n = 114).
explaining the lack of relationship between percentages of whole-body DM and CP, we did not observe edemas in the chicks. The majority of the chick DM consisted of CP and EE (Table 2), with the remainder DM contributed by minerals (ash) and carbohydrates (nitrogen-free extract). Nitrogenfree extract constitutes approximately one percentage point of the DM (calculated from Barker and Sell, 1994), and the difference among percentage whole-body DM, CP, and EE, may therefore be viewed as ash. The percentage of whole-body ash increased linearly (P = 0.04) with increasing whole-body DM (Figure 3). Experimental errors in the determinations of DM, CP, and EE affect the calculation of ash, partly explaining the high CV (Table 2) and the weak correlation (r = 0.190) between percentage whole-body DM and percentage ash (Figure 3). In conclusion, the whole-body percentage of EE of 3wk-old broiler chicks was directly correlated (P < 0.001; r2 = 0.798) with the whole-body percentage of DM. Hence, the percentage of whole-body EE can be predicted from
PREDICTION OF WHOLE-BODY COMPOSITION
the percentage whole-body DM using the equation Y = 0.961x − 17.855, where Y = percentage whole-body EE and x = percentage whole-body DM. Standard errors associated with the slope and intercept were 0.046 and 1.358, respectively. On the contrary, the percentage of wholebody CP and ash could not be predicted accurately (r2 = 0.010 and 0.036, respectively) from the percentage of whole-body DM.
ACKNOWLEDGMENTS The assistance of the staff of the Poultry Science Center for care of the chicks, the expertise of A. Weisberg in the chemical analyses, and R. Wei for statistical advice are gratefully acknowledged.
Association of Official Analytical Chemists. 1984. Official Methods of Analysis of the Association of Analytical Chemists. 14th ed. Association of Analytical Chemists, Washington, DC. Barker, D. L., and J. L. Sell. 1994. Dietary carnitine did not influence performance and carcass composition of broiler chickens and young turkeys fed low- or high-fat diets. Poult. Sci. 73:281–287. Bregendahl, K. 2001. Effects of low crude-protein diets fortified with crystalline amino acids on growth performance and nitrogen retention of broiler chicks. Ph.D. Dissertation. Iowa State University, Ames, IA.
Bregendahl, K., J. L. Sell, and D. R. Zimmerman. 2002. Effect of low-protein diets on growth performance and body composition of broiler chicks. Poult. Sci. 81:1156–1167. Hunt, J. R. 1965. Factors influencing body N:H2O ratio of growing chicks. Poult. Sci. 44:236–240. JMP. 2000. JMP User’s Guide. Version 4.0.3. SAS Institute Inc., Cary, NC. Julian, R. J. 1998. Rapid growth problems: Ascites and skeletal deformities in broilers. Poult. Sci. 77:1773–1780. Kranen, R. W., C. W. Scheele, C. H. Veerkamp, E. Lambooy, T. H. van Kuppevelt, and J. H. Veerkamp. 1998. Susceptibility of broiler chickens to hemorrhages in muscles: The effect of stock and rearing temperature regimen. Poult. Sci. 77:334– 341. Moran, E. T., Jr. 1995. Body composition. Pages 139-156 in Poultry Production. P. Huntington, ed. Elsevier Science B. V., Amsterdam, The Netherlands. Neter, J., W. Wasserman, and M. H. Kutner. 1990. Applied Linear Statistical Models. Regression, Analysis of Variance, and Experimental Designs. 3rd ed. Irwin, Burr Ridge, IL. NRC. 1994. Nutrient Requirements of Poultry. 9th ed. National Academy Press, Washington, DC. Sibbald, I. R., and M. S. Wolynetz. 1984. Variation among aliquots of entire chicken homogenates. Poult. Sci. 63:1446– 1448. Velu, J. G., D. H. Baker, and H. M. Scott. 1972. Regression equations for determining body composition of young chicks. Poult. Sci. 51:698–699. Wolynetz, M. S., and I. R. Sibbald. 1986. Prediction of major body components of broiler chicks. Poult. Sci. 65:2173–2185. Wolynetz, M. S., and I. R. Sibbald. 1990. Estimates of body components in broiler chickens from body weight and dry matter. Poult. Sci. 69:1318–1324.
Downloaded from http://ps.oxfordjournals.org/ at East Tennessee State University on June 20, 2015
REFERENCES
1171