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Live Body and Carcass Measurements as Predictors of Chemical Composition of Carcasses of Male Broiler Chickens1
Live Body and Carcass Measurements as Predictors of Chemical Composition of Carcasses of Male Broiler Chickens1 J. R. CHAMBERS and A. FORTIN Animal Research Centre, Agriculture Canada, Ottawa, Canada K1A 0C6 (Received for publication November 15, 1982)
1984 Poultry Science 63:2187-2196
INTRODUCTION An important goal of the poultry meat industry is to improve meat quality to increase consumer acceptability. One improvement is reduction of excessive fat found in some broiler carcasses. Before genetic procedures can be applied to make such changes, breeders of meat strains of poultry must be able to assess meat properties. Taste panel evaluation best predicts eating properties; however, this method is destructive and too laborious and costly for rapid, routine analysis of numerous meat samples. Chemical composition of the carcass determines meat properties, but like taste panel evaluation it is destructive and requires extensive technical labor and time. Ideally, the broiler breeder would prefer simple, nondestructive measurements of the live chicken or broiler carcass suitable for predicting chemical composition of the carcass. There are few references in the literature that relate either live broiler or carcass mea-
1
Animal Research Centre Contribution No. 1123.
surements to chemical components of the carcass. Furthermore, the available material involves only carcass fat. Abdominal fat weight is a better predictor of percent carcass fat than percent backskin fat (Becker et al, 1979) and carcass specific gravity (Spencer et al, 1978). Correlations between percent abdominal fat and percent carcass fat, .51 and .77 for males and females, respectively, are higher than those between percent abdominal fat and fat-free carcass weight, .26 and .07 for males and females, respectively (Becker et al, 1981). Live broiler and carcass measurements, including chemical composition, were available from two small experiments. The live broiler measurements included body weight and indicators of: body conformation—breast angle, body depth, body width and keel length; skeletal development—shank length and circumference; and muscle development—leg circumference. The carcass traits tested were carcass weight (eviscerated), carcass specific gravity, and proportions of the carcass cuts: wings, legs, breast, and back and weight and percentage of abdominal fat. Chemical components of the carcass determined by proximate analysis were
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ABSTRACT Live body, carcass, and abdominal fat data from 67 male broilers of two strains reared in cages and in pens in two separate experiments were evaluated for use in predicting carcass fat, protein, ash, and water. Chemical component weights were predicted more accurately than percentages, R2 = .75 to .98 vs. .54 to .67. Best predictions were for weights of carcass protein and water and for carcass percentages of fat, protein, and water. In this study, traits predicting chemical component weights included either live broiler or carcass weight, either weight or percentage abdominal fat, and either shank length or carcass specific gravity. Traits predicting chemical component percentages included either weight or percentage of abdominal fat plus carcass specific gravity and percentage back of the carcass. Carcass and abdominal fat measurements predicted weights of chemical components other than ash better than live measurements in this study; however, the differences may not justify the slaughter of the broiler to obtain carcass measurements. Except for ash, abdominal fat measurements predicted component percentages better than other carcass or live broiler measurements; however, additional predictor traits appear to be required before chemical component percentages of the carcass could be predicted accurately. Prediction of percentages was improved, R' = .35 to .66 vs. .13 to .45 for protein and .29 to .54 vs. .16 to .42 for ash, by expressing these components as percentages of carcass dry matter. (Key words: broiler measurements, carcass composition, prediction)
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CHAMBERS AND FORTIN
water, fat, protein, and ash. The available information provided an opportunity to evaluate various measurements of the live broiler and the carcass for predicting chemical composition of the carcasses, especially fatness, of these chickens as well as correlations among chemical components and other traits. MATERIALS AND METHODS
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Thirty-six male chicks of a cross of two commercial broiler breeder male lines were hatched and brooded for 18 days in a Petersime battery in Experiment 1. An additional 36 male chicks of experimental Strain A (Chambers et al, 1981) were hatched and similarly brooded for 14 days in Experiment 2. Strain A was synthesized by combining three lines derived from an experimental population of meat-type chickens in 1958 and selected for 14 generations for high 63-day body weight. In each experiment, broilers were removed from the battery, 18 were placed in a small pen, and 18 were assigned to individual wire cages, 25.4 cm wide and 40.6 cm long and high with level floors and individual water cups. Supplementary heat was provided to maintain appropriate brooding and rearing temperatures. A starter ration (23.5% crude protein and 3155 kcal metabolizable energy (ME)/kg) was fed to the chicks in the battery. After leaving the battery, they were fed an additional .55 and .85 kg of starter in Experiments 1 and 2, respectively, after which they received a finisher ration (20.8% crude protein, 3210 kcal ME/kg). Broilers were slaughtered at 47 days in Experiment 1 and 61 days in Experiment 2 to ensure comparable slaughter weights. This was necessary because Strain A broilers grow more slowly than modern broilers (Chambers et al, 1981). Prior to slaughter broilers were weighed and breast angle, body width, body depth, keel length, shank length, shank circumference, and leg circumference were measured. With the exception of body width, live broiler measures were taken according to the procedures of Ricard and Rouvier (1965). Breast angle was measured to the nearest degree using a breast angle meter placed 2 cm behind the anterior tip of the keel. Body depth was measured from the point on the keel of measurement of breast angle to the back using a combination square. jxcel lengtn, trie distance between tuc anterior and posterior tips of the keel, and shank length, the distance from the back of the hock joint to the surface of the foot pad, were measured
using a calibrated caliper. Shank circumference, the shortest distance around the shank, and leg circumference, the maximum distance around the drumstick, were measured using a measuring tape. Body width, the distance between the external protrusions around the wing sockets of the bird at peak inspiration, was measured using a caliper. After the broilers were killed, bled, scalded, and plucked, carcasses were eviscerated by hand. Abdominal fat and the eviscerated carcass without leaf fat were weighed separately. Specific gravity was determined by weighing the chilled carcass in air and in water (4 C) as described by Fortin and Chambers (1981). The chilled carcass was then wiped dry with a cloth towel and divided into wings, legs, breast and back. The legs were removed from the carcass at the femur-ilium junction and the wings at the humerus-scapula junction. The back was separated from the breast by cutting along a line parallel to the thoracic vertebrae extending from the caudal tip of the floating ribs through the junctions of the vertebral (dorsal segment) and sternal (ventral segment) ribs. After weighing, the carcass parts were frozen (—20 C) and stored prior to grinding in preparation for proximate analysis. A Hobart grinder (Model 185-1, Toronto, Ontario) was used to grind each carcass to a homogeneous mass by four successive grindings. A 10-mm aperture plate was used for the first two and a 5-mm aperture plate was used for the last two grindings. Tissue samples were then packaged in plastic containers and frozen (—20 C) until they could be sampled in triplicate for chemical composition determination. Dry matter was determined by drying (75 C) to a constant weight under reduced pressure (<100 mm Hg) for 16 hr. Protein (N X 6.25), ether extract, and ash (Association of Official Analytical Chemists, 1970) were also determined. Live broiler and carcass measurements were evaluated by examining correlations among these measurements and the chemical components of the carcass and by using the stepwise multiple regression procedure to determine which measurement combinations best predicted the chemical components of the carcass. Factorial analyses of variance were applied to all traits to test for interactions among experiments (strains) and housing types (cages vs. pens). Due to interactions (P<.05) for body width, leg circumference, and back percentage,
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PREDICTION OF CARCASS COMPOSITION
RESULTS For each experiment, means and their standard errors for measurements of the live broiler,
the broiler carcass, and percentages of fat, protein and ash (wet and dry matter basis), and moisture of the eviscerated carcass (without leaf fat) are presented in Table 1. Similarities between corresponding means and standard errors of the two broiler groups indicate that the additional 2 weeks of growth allowed the slower growing strain used in the second experiment to attain weights and compositions comparable to those of broilers in the first experiment. Examination of correlation coefficients between traits (Tables 2 and 3) led to the following observations. Live broiler and eviscerated carcass weights were highly positively correlated (.98). Live broiler weight was positively correlated with: live broiler measurements (.18 to .81); abdominal fat weight and percentage (.63 and .49, respectively); chemical component weights; and percentage fat (Table 2). Live broiler weight was negatively correlated with carcass specific
TABLE 1. Means f± standard errors) for live broiler and carcass measurements and for chemical composition of the carcasses of two strains of meat-type male chickens1 Trait
Experiment 1
Experiment 2
Live measurements Broiler weight, g Breast angle, ° Body depth, cm Body width, cm Keel length, cm Shank length, cm Shank circumference, cm Leg circumference, cm
2060. 96.6 11.2 8.1 10.3 11.6 5.2 10.9
± 36 ± .9 + .1 ± .1 ± .1 ± .1 ± .1 + .3
2064. 87.4 11.7 7.8 10.5 12.0 5.1 12.2
± 51
Carcass measurements Weight, g (eviscerated) Abdominal fat weight, g Specific gravity % Wings % Legs % Breast % Back
1299. 34.0 1.062 13.4 34.3 30.6 22.4
24 ± 2.6 ± .001 + .2 + .3 ± .4 ± .4
1269. 38.7 1.063 13.9 33.9 28.6 24.3
± 33 ± 3.3 ± .001 ± .1 ± .3 + .3 ± .3
Chemical composition 2 Fat, % Protein, % Ash, % Water, % Fat, %3 Protein, %3 Ash, %3
14.5 17.5 2.59 65.2 41.4 50.4 7.44
+
± ± ± ± +
± ±
.3 .1 .05 .3 .7 .7 .16
14.8 17.4 2.78 64.7 41.6 49.4 7.91
+
.8
± ± ± ± +
±
± ± ± ± ± ± +
.2
.5 .5 .04 .4 .9 .7 .18
1
Numbers per mean were: 35 in Experiment 1 except for specific gravity which had 34; 32 in Experiment 2.
2
Percentages of the eviscerated carcass weight (without leaf fat).
3
Dry matter basis.
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correlations among traits were calculated after the data of each subclass had been adjusted for the effects of experiment, housing type, and their interaction. A forward stepwise multiple regression procedure was applied to determine the value of live broiler and carcass traits for predicting chemical composition of the carcass. This method adds the variable with the highest R 2 to the model provided the effect of its entry has a significant (P«.50) F value. Variables stay in the model as long as their effect remains significant (P< .10). Trait combinations with the highest multiple correlation coefficient (R 2 ) were considered to be best. Procedures of SAS (Barr et ah, 1976) were used to perform statistical analyses of the data.
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CHAMBERS AND FORTIN TABLE 2. Correlations between chemical carcass component weights and percentages of the wet carcass (Wet) and carcass dry matter (DM) and live broiler measurements of meat-type male chickens*
components Weight of Fat Protein Ash Water
1
Live weight
Breast angle
Depth
Width
.82 .93 .79 .96
.21 .38 .28 .28
.48 .53 .47 .56
.69 .75 .63 .76
.56 .53
.08 .02
.35 .35
-.18 -.47
.28 .04
-.25 -.46 -.59
Circumference of Leg
Shank
Shank
.50 .64 .60 .68
.50 .80 .75 .83
.28 .55 .56 .60
.23 .16 .06 .17
.48 .45
.31 .29
.23 .22
.05 .05
.23 .25
-.15 -.31
-.14 -.41
-.15 -.32
-.03 -.21
.02 -.01
-.10 -.18
-.03 -.07
-.12 -.26
-.20 -.39
-.10 -.25
-.05 -.17
.07 .04
-.20 -.25
-.16
-.36
-.53
-.36
-.28
-.04
-.20
Keel
Required size of coefficient to be significantly different from zero P<.05 = .25, P<.01 = .33.
TABLE 3. Correlations between chemical carcass component weights and percentages of the wet carcass (Wet) and carcass dry matter (DM) and carcass measurements of meat-type male chickens1 Abdominal fat
Carcass components Weight of Fat Protein Ash Water Percentage of Fat Wet DM Protein Wet DM Ash Wet DM Water Wet 1
Percentage Weight
Percentage
.25 .07 .03 .15
.81 .44 .36 .46
.71 .28 .24 .30
-.01 -.05
.27 .30
.79 .77
.77 .75
.03 .10
.27 .07
-.34 -.27
-.50 -.76
-.54 -.76
.32 .36
.16 .17
-.04 -.07
-.21 -.23
-.32 -.62
-.28 -.58
.28
.14
-.08
-.17
-.81
-.78
Specific gravity
Wing
Leg
Breast
.82 .95 .80 .98
-.60 -.28 -.24 -.30
-.38 -.47 -.28 -.46
-.23 -.24 -.15 -.25
.12 .32 .23 .25
.54 .51
-.61 -.60
-.24 -.22
-.15 -.14
-.16 -.45
.42 .60
.00 .18
-.26 -.46
.24 .48
-.58
.61
Weight
Back
Required size of coefficient to be significantly different from zero P<.05 = .25, P<.01 = .33.
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Percentage of Fat Wet DM Protein Wet DM Ash Wet DM Water Wet
Length of
Body
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PREDICTION OF CARCASS COMPOSITION
weights were positive. Percentage fat was negatively correlated with the other chemical component percentages whereas the remaining chemical component percentages were positively correlated (Table 4). Correlations involving protein and ash percentages were larger when expressed on the basis of carcass dry matter instead of wet carcass. Expressing fat percentage on a dry matter basis reduced negative correlations with water percentage from —.96 to —.92; however, little change was noted among other correlations. Prediction of Chemical Components. Multiple regression analyses were used to determine those trait combinations best predicting either weights or percentages of the chemical components of the carcass. Predictive values, R 2 , trait combinations, and partial regression coefficients in the best regression models are presented in Tables 5 and 6. Generally, component weights were predicted more accurately than percentages (.61 to .98 vs. .29 to .67). Weights of carcass protein and water were predicted better than weights of carcass fat and ash (.89 to .98 vs. .61 to .87). Percentages of protein and ash based on carcass dry matter were predicted better than percentages based on the wet carcass. No improvement in prediction was observed when percentage fat was expressed on a dry matter basis. Percentages of components other than ash tended to be predicted more accurately (.35 to .67 vs. .29 to .54). With the exception of ash weight, groups of traits did not differ markedly in their value for predicting specific component weights. The .61 R 2 value for ash weight prediction by abdomi-
TABLE 4. Correlation coefficients for pairs of chemical of the carcass1
components
Correlations
Correlated components
Weights
Percentages (wet basis)
Fat and protein Fat and ash Fat and water Protein and ash Protein and water Ash and water
.65 .49 .69 .84 .97 .82
-.70 -.46 -.96 .42 .58 .34
1
n=64.
2
Carcass dry matter basis for protein and ash.
Percentages 2 -.95 -.80 .74 .92 .72
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gravity, protein and ash percentages of carcass dry matter, and percentage water. Corresponding values for eviscerated carcass instead of live broiler weight were quite similar. Correlations among broiler measurements were either positive or did not differ from zero (P>.05). Live broiler measurements were positively correlated with chemical component weights (Table 2). Correlations of these measurements with chemical component percentages that differed from zero (P«.05) tended to be similar in size to correlations of live broiler weight with chemical component percentages. Among carcass traits, abdominal fat weight and carcass specific gravity were negatively correlated (—.54). Correlations among carcass cut percentages were either negative or not different from zero (P>.05). Weight of abdominal fat was positively correlated with chemical component weights and percentage fat, but was negatively correlated with percentage of protein, ash, and water (Table 3). Abdominal fat percentage of the eviscerated carcass was positively correlated with abdominal fat weight (.98) and carcass fat weight and percentage (Table 3). Correlations were negative between percentages of abdominal fat and water, protein, and ash. Larger negative correlations were obtained when protein and ash were expressed as percentages of carcass dry matter. However, carcass specific gravity was negatively correlated with chemical component weights and with percentage fat. Specific gravity was positively correlated with percentages of protein, ash and water. Other correlations rarely differed from zero (P> .05). Correlations between chemical component
1
.181
5 2
2.60 .904
1 2
3
1 2
2
1 3
6 3 1 4
.87
.78
.76
.74
Rank
1775 -.824 -25.6 .211 -1482
-38.2 .142 1.25
3.79
-2878
2927
-43.8
.216 -1.09
360
Fat
.086 .736
.172
.179
-3.47
1.53
393
-459
-4.02
2.56 .181
1.42
693
-775
10.9
-149
.95
.93
.93
.89
Protein
These results were obtained after variation due to strain differences had been removed.
All traits R2 Intercept Breast angle Shank length Carcass weight Specific gravity Wing percentage Breast percentage Back percentage Abdominal fat weight Abdominal fat percentage
Live broiler traits R2 Intercept Broiler weight Breast angle Keel length Shank length Carcass traits R2 Intercept: Carcass weight Specific gravity Wing percentage Breast percentage Back percentage Abdominal fat traits R2 Intercept Carcass weight Abdominal fat weight Abdominal fat percentage
bi
2
3
1 4
2
1
3
1 2
3
1 2
Rank
-.4
1.2
49.8 .1 3.3 .0
2.2 .0
-.6
1.3
-5.5 .0
-61.3 .0 .2 2.1 3.5
bi
Component weights
TABLE 5. Multiple correlation coefficients (R7), partial regression coefficients (b;) and importanc and abdominal fat traits for predicting chemical component weights of male chick
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2
1
-133
-147
.262 .077
.67
3 1
2
1
-1.96
-.388
249
-200
-2.55
56.9
3
.293
.54
-.463
2 1
.004
4.34
11.6 -.015 .196
bi
-354 -.005 397
-11.0 .100
-215
.51
2
-3.09
231
1 3
.45
39.8 .010 -.101
Rank
.66
.54
.46
.35
Protein
Protein and ash as percentage of carcass dry matter.
These results were obtained after variation due to strain differences had been removed.
All traits R2 Intercept Breast angle Specific gravity Wing percentage Back percentage Abdominal fat weight Abdominal fat percentage
Abdominal fat traits R2 Intercept Abdominal fat weight Abdominal fat percentage
Carcass traits R2 Intercept Carcass weight Specific gravity Wing percentage Back percentage
Live broiler traits R2 Intercept Broiler weight Breast angle Keel length Shank length
bi
Fat
1
3
2
1
2
3 1
2
1 3
Rank
•42.3 .03 43.0 .31 -.12 -.01
8.64 -.02
.36 -.17
67.4
-64.9
-5.97 -.00 .05 .33 1.09
bi
Component percentages
TABLE 6. Multiple correlation coefficients (R2), partial regression coefficients (bj), and imp predicting chemical component percentages of male chicken carcasses
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CHAMBERS AND FORTIN
DISCUSSION
Relationships Among Chemical Carcass Components. All chemical components of the carcass of the growing broiler increase if the supply of nutrients is adequate. Consequently, chemical component weights are positively and, in some cases, highly correlated with one another. The chemical component weights measured account for almost all of the carcass weight and a major portion of broiler weight; hence, they are positively correlated with carcass and broiler weights. Conversely, expressing components as a percentage of the carcass consisting of these components gives rise to negative correlations among component proportions. As the proportion of one component increases, the sum of proportions of the remaining components must decrease. Broilers become fatter as they grow (Leeson and Summers, 1980); hence, fat percentage must be negatively correlated with one or more of the remaining chemical component percentages. In this study, fat was negatively related to all of the other chemical components (Table 4). This relationship gave rise to positive correlations among the remaining chemical components. In addition, negative correlations arise between percentages of live broiler weight and chemical components other than fat. The high negative correlation observed between fat and water, —.96, was in good agreement with other
reports: —.98 for carcasses of 60-day-old cockerels (Taylor and Shaffner, 1975); - . 8 7 to - . 9 0 for 300 carcasses of male and female broilers at either 55 or 59 days of age (Verstrate et al., 1980); and —.94 and —.97 for carcasses of 9-week-old broilers (Pym and Solvyns, 1979). Negative relationships among proportions can be reduced by deducting from the denominator (carcass weight) the other component involved in the correlation. In instances involving carcass water, this is achieved by expressing other chemical components on a carcass dry matter basis. In the current study, positive correlations between water and either protein or ash increased when the latter were expressed on carcass dry matter bases (Table 4). Similarly, the negative correlation between proportions of water and fat was slightly reduced when fat was expressed in terms of carcass dry matter. The latter values are better indicators of the "true" component relationships due to partial correction for the negative relationship imposed by the mode of expressing proportions. True component relationships are probably slightly higher than the observed correlations. Measurement errors of correlated traits are expected to be independent giving rise to a zero correlation; hence, measurement error will tend to reduce the magnitude of correlations. Prediction of Chemical Carcass Components. The high positive correlations between live broiler and carcass weights and the similar correlations between either live broiler or carcass weight and other traits indicate these weights have similar predictive value and little benefit is gained by using both live broiler and carcass weights. Live broiler weight is preferred because measurement does not require slaughter of the bird. Trait combinations predicting chemical component weights or percentages usually include either live broiler or carcass weight (Tables 5 and 6). Exceptions included chemical component percentage prediction by either abdominal fat measurement or combinations of traits from all groups. For chemical component weight prediction, live broiler or carcass weight were the most important traits in the combinations. Live broiler measurements and chemical carcass component weights increase with body weight; hence, positive correlations were observed among live measurements and chemical component weights (Table 2). Relationships between live broiler measurements and chemical component percentages were weaker. The dif-
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nal fat traits was solely due to carcass weight. For component percentages other than ash, abdominal fat traits predicted components better using fewer traits. Percentage ash was predicted more accurately by live broiler and by carcass traits. Carcass traits in turn, were superior to live broiler traits as predictors of component percentages. Combinations of live broiler, carcass, and abdominal fat traits predicted component weights and percentages best (Tables 5 and 6). The more important predictor traits included either live broiler or carcass weight, shank length, breast angle, either weight or percentage of abdominal fat, carcass specific gravity, and back percentage. Live broiler and carcass traits were tested for their ability to predict either weight or percentage of abdominal fat. The best predictions (R 2 ) by live broiler traits were .45 and .30 for weight and percentage abdominal fat, respectively; corresponding values using carcass traits were .45 and .32.
PREDICTION OF CARCASS COMPOSITION
cerated carcass and percentage carcass fat for male broilers of the current study, .77, agrees with these values. Abdominal fat weight or percentage was the most predictive trait for chemical components other than ash (Tables 5 and 6). Abdominal fat trait combinations not only had the highest multiple correlation coefficients (R 2 ) but also used the fewest traits. In fact, abdominal fat weight or percentage was the sole predictor trait for percentages of fat, water, and protein. In all group trait combinations, abdominal fat was second only to carcass weight for chemical component weight prediction and was first followed by specific gravity for prediction of chemical component percentages. With the exception of ash measurements, correlations of chemical carcass component weights and percentages with abdominal fat weight were larger than those with carcass specific gravity. These results comply with the conclusion of Spencer et al. (1978) that abdominal fat weight was superior to specific gravity for determining percentage carcass fat. The current results suggest this situation holds for percentages of carcass moisture and protein as well. Abdominal fat weight can be measured more readily than carcass specific gravity. Moreover, Fortin and Chambers (1981) recommended restricting use of specific gravity for estimation of compositional differences to those among groups of broiler carcasses. It is debatable whether the added benefit of specific gravity values warrants the labor required for measurement. The values of live and carcass measurements for predicting abdominal fat weight and percentage (of eviscerated carcass weight) were tested using multiple regression analysis. Multiple regression correlations for abdominal fat weight were at best, .45 for both live measures and carcass measures. Corresponding values for abdominal fat percentage were .30 for live measures and .32 for carcass measures. These results agree with those of Mirosh et al. (1980) who recommended direct measurement of abdominal fat as opposed to prediction using skin pinch thickness, feather tract weight, percentage moisture of feather tract, and total serum lipid measurements. The use of broilers from two stocks that differ in growth rate enhances the generality of these results. In addition, the general concordance of these correlations with others in the literature adds to their credibility. Of the live and carcass traits examined, few of them alone
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ference in sign between correlations of live broiler and carcass measurements with carcass fat versus carcass water traits is consistent with the high negative correlation between fat and water. Live broiler trait combinations predicted chemical component weights and percentages almost as well as combinations of carcass or abdominal fat traits. Of the live measurements, live broiler weight and shank length were the most predictive traits followed by breast angle and keel length. Body depth and width and shank and leg circumferences were of little value. The most predictive carcass traits included carcass weight and specific gravity (Tables 5 and 6). Specific gravity declines as carcass fatness increases (Fortin and Chambers, 1981). This accounts for the negative correlation of specific gravity with fat percentage and its positive correlation with the other chemical component proportions. The specific gravity and fat percentage correlation for male broilers in this study was —.61. This is larger than the —.36 for males and similar to the —.69 for females at 59 days of age reported by Spencer et al. (1978). The positive relationship between live broiler weight and carcass fatness appears responsible for the negative correlations between specific gravity and all chemical component weights. Specific gravity was the most predictive carcass trait in terms of R 2 for chemical component percentages and was second only to carcass weight for chemical component weight prediction. Specific gravity precluded shank length in all group trait combinations predicting chemical component percentages. With the exception of wing percentage, carcass cut percentages were of limited value for predicting chemical component weights and percentages. Negative correlations existed among the carcass cut percentages. Factors contributing to these relationships include the mode of expression of the part-to-whole relationship discussed earlier for chemical component percentages and any deviations in cutting procedure. Cutting errors, believed to be small, would favor one of the adjacent cuts at the expense of the other. Correlations between abdominal fat percentage of live body weight and percentage carcass fat were .76 and .74 for male and female, 59-day-old broilers, respectively (Becker et al., 1979). In spite of differences in expressing abdominal fat proportion, the correlation between percentage abdominal fat of the evis-
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CHAMBERS AND FORTIN
2196
ACKNOWLEDGMENTS The authors are grateful to M. Baker and M. Sauermann for technical assistance and to R. Cloutier and staff of the Chemistry and Biology Research Institute, Agriculture Canada for chemical determinations of each carcass.
REFERENCES Association of Official Analytical Chemists, 1970. Official Methods of Analysis. 11th ed. Assoc. Offic. Anal. Chem., Washington, DC. Barr, A. J., J. H. Goodnight, J. P. Sail, and J. T. Helwig, 1976. A User's Guide to SAS-76. SAS Inst., Inc., Raleigh, NC. Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate, 1979. Prediction of fat and fat free live weight in broiler chickens using backskin fat, abdominal fat and live body weight. Poultry Sci. 58:835-842. Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate, 1981. Specific gravity, carcass fat, abdominal fat, and yield data in broiler chickens. Poultry Sci. 60:2045-2052. Chambers, J. R., J. S. Gavora, and A. Fortin, 1981. Genetic changes in meat-type chickens in the last twenty years. Can. J. Anim. Sci. 61:555—563. Fortin, A., and J. R. Chambers, 1981. Specific gravity of the carcass and its parts as predictors of carcass composition in broiler chickens. Poultry Sci. 60:2454-2462. Leeson, S., and J. D. Summers, 1980. Production and carcass characteristics of the broiler chicken. Poultry Sci. 59:786-798. Mirosh, L. W., W. A. Becker, J. V. Spencer, and J. A. Verstrate, 1980. Prediction of abdominal fat in live broiler chickens. Poultry Sci. 59:945—950. Pym, R.A.E., and A. J. Solvyns, 1979. Selection for food conversion in broilers: body composition of birds selected for increased body-weight gain, food consumption and food conversion ratio. Br. Poult. Sci. 2 0 : 8 7 - 9 7 . Ricard, F. H., and R. Rouvier, 1965. Etude des mesures de conformation du poulet I. Analyse statistique preliminaire concernant le poids et 13 mensurations corporelles du poulet vivant. Ann. Zootech. 14:191-212. Spencer, J. V., W. A. Becker, J. A. Verstrate, and L. W. Mirosh, 1978. Relationship of carcass fat to abdominal fat and specific gravity in broiler chickens. Poultry Sci. 57:1164. (Abstr.) Taylor, M. H., and C. S. Shaffner, 1975. The relationship of ether extract and moisture in eviscerated broilers. Poultry Sci. 54:663-666. Verstrate, J. A., J. V. Spencer, L. W. Mirosh, and W. A. Becker, 1980. A comparison of methods for determining the fat content of broiler carcasses. Poultry Sci. 59:298-302.
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were useful for accurate prediction of chemical component percentages. Either live body weight or carcass weight in conjunction with abdominal fat weight appear suitable for efficient prediction of weights of carcass fat, moisture, and, on a dry matter basis, protein. Either weight or percentage abdominal fat was an important predictor of corresponding component percentages; however, multiple correlation coefficients were .60 or less. If greater precision is required, additional traits must be tested to find effective component predictors. Failing this, one or more of the chemical components must be measured directly. Carcass moisture has been used to predict carcass fatness (Taylor and Shaffner, 1975; Verstrate et al., 1980). Multiple correlation coefficients of .76 and .78 were obtained by Verstrate et al. (1980) for carcass fat prediction models containing carcass moisture. In the current study, as mentioned earlier, correlations between carcass moisture and ether extract were high and negative. In addition, the correlation between percentage moisture and percentage protein in carcass dry matter was large, .92. Hence, percentage carcass moisture may be an effective means of accurately predicting percentages of carcass fat and protein provided: 1) the bird and the carcass can be sacrificed, 2) the rate of grinding carcasses in preparation for sampling is not too slow, and 3) the cost of an appropriate vacuum oven or freeze drier and the energy to operate it are not prohibitive.
1984 Poultry Science 63:2187-2196
INTRODUCTION An important goal of the poultry meat industry is to improve meat quality to increase consumer acceptability. One improvement is reduction of excessive fat found in some broiler carcasses. Before genetic procedures can be applied to make such changes, breeders of meat strains of poultry must be able to assess meat properties. Taste panel evaluation best predicts eating properties; however, this method is destructive and too laborious and costly for rapid, routine analysis of numerous meat samples. Chemical composition of the carcass determines meat properties, but like taste panel evaluation it is destructive and requires extensive technical labor and time. Ideally, the broiler breeder would prefer simple, nondestructive measurements of the live chicken or broiler carcass suitable for predicting chemical composition of the carcass. There are few references in the literature that relate either live broiler or carcass mea-
1
Animal Research Centre Contribution No. 1123.
surements to chemical components of the carcass. Furthermore, the available material involves only carcass fat. Abdominal fat weight is a better predictor of percent carcass fat than percent backskin fat (Becker et al, 1979) and carcass specific gravity (Spencer et al, 1978). Correlations between percent abdominal fat and percent carcass fat, .51 and .77 for males and females, respectively, are higher than those between percent abdominal fat and fat-free carcass weight, .26 and .07 for males and females, respectively (Becker et al, 1981). Live broiler and carcass measurements, including chemical composition, were available from two small experiments. The live broiler measurements included body weight and indicators of: body conformation—breast angle, body depth, body width and keel length; skeletal development—shank length and circumference; and muscle development—leg circumference. The carcass traits tested were carcass weight (eviscerated), carcass specific gravity, and proportions of the carcass cuts: wings, legs, breast, and back and weight and percentage of abdominal fat. Chemical components of the carcass determined by proximate analysis were
2187
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ABSTRACT Live body, carcass, and abdominal fat data from 67 male broilers of two strains reared in cages and in pens in two separate experiments were evaluated for use in predicting carcass fat, protein, ash, and water. Chemical component weights were predicted more accurately than percentages, R2 = .75 to .98 vs. .54 to .67. Best predictions were for weights of carcass protein and water and for carcass percentages of fat, protein, and water. In this study, traits predicting chemical component weights included either live broiler or carcass weight, either weight or percentage abdominal fat, and either shank length or carcass specific gravity. Traits predicting chemical component percentages included either weight or percentage of abdominal fat plus carcass specific gravity and percentage back of the carcass. Carcass and abdominal fat measurements predicted weights of chemical components other than ash better than live measurements in this study; however, the differences may not justify the slaughter of the broiler to obtain carcass measurements. Except for ash, abdominal fat measurements predicted component percentages better than other carcass or live broiler measurements; however, additional predictor traits appear to be required before chemical component percentages of the carcass could be predicted accurately. Prediction of percentages was improved, R' = .35 to .66 vs. .13 to .45 for protein and .29 to .54 vs. .16 to .42 for ash, by expressing these components as percentages of carcass dry matter. (Key words: broiler measurements, carcass composition, prediction)
2188
CHAMBERS AND FORTIN
water, fat, protein, and ash. The available information provided an opportunity to evaluate various measurements of the live broiler and the carcass for predicting chemical composition of the carcasses, especially fatness, of these chickens as well as correlations among chemical components and other traits. MATERIALS AND METHODS
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Thirty-six male chicks of a cross of two commercial broiler breeder male lines were hatched and brooded for 18 days in a Petersime battery in Experiment 1. An additional 36 male chicks of experimental Strain A (Chambers et al, 1981) were hatched and similarly brooded for 14 days in Experiment 2. Strain A was synthesized by combining three lines derived from an experimental population of meat-type chickens in 1958 and selected for 14 generations for high 63-day body weight. In each experiment, broilers were removed from the battery, 18 were placed in a small pen, and 18 were assigned to individual wire cages, 25.4 cm wide and 40.6 cm long and high with level floors and individual water cups. Supplementary heat was provided to maintain appropriate brooding and rearing temperatures. A starter ration (23.5% crude protein and 3155 kcal metabolizable energy (ME)/kg) was fed to the chicks in the battery. After leaving the battery, they were fed an additional .55 and .85 kg of starter in Experiments 1 and 2, respectively, after which they received a finisher ration (20.8% crude protein, 3210 kcal ME/kg). Broilers were slaughtered at 47 days in Experiment 1 and 61 days in Experiment 2 to ensure comparable slaughter weights. This was necessary because Strain A broilers grow more slowly than modern broilers (Chambers et al, 1981). Prior to slaughter broilers were weighed and breast angle, body width, body depth, keel length, shank length, shank circumference, and leg circumference were measured. With the exception of body width, live broiler measures were taken according to the procedures of Ricard and Rouvier (1965). Breast angle was measured to the nearest degree using a breast angle meter placed 2 cm behind the anterior tip of the keel. Body depth was measured from the point on the keel of measurement of breast angle to the back using a combination square. jxcel lengtn, trie distance between tuc anterior and posterior tips of the keel, and shank length, the distance from the back of the hock joint to the surface of the foot pad, were measured
using a calibrated caliper. Shank circumference, the shortest distance around the shank, and leg circumference, the maximum distance around the drumstick, were measured using a measuring tape. Body width, the distance between the external protrusions around the wing sockets of the bird at peak inspiration, was measured using a caliper. After the broilers were killed, bled, scalded, and plucked, carcasses were eviscerated by hand. Abdominal fat and the eviscerated carcass without leaf fat were weighed separately. Specific gravity was determined by weighing the chilled carcass in air and in water (4 C) as described by Fortin and Chambers (1981). The chilled carcass was then wiped dry with a cloth towel and divided into wings, legs, breast and back. The legs were removed from the carcass at the femur-ilium junction and the wings at the humerus-scapula junction. The back was separated from the breast by cutting along a line parallel to the thoracic vertebrae extending from the caudal tip of the floating ribs through the junctions of the vertebral (dorsal segment) and sternal (ventral segment) ribs. After weighing, the carcass parts were frozen (—20 C) and stored prior to grinding in preparation for proximate analysis. A Hobart grinder (Model 185-1, Toronto, Ontario) was used to grind each carcass to a homogeneous mass by four successive grindings. A 10-mm aperture plate was used for the first two and a 5-mm aperture plate was used for the last two grindings. Tissue samples were then packaged in plastic containers and frozen (—20 C) until they could be sampled in triplicate for chemical composition determination. Dry matter was determined by drying (75 C) to a constant weight under reduced pressure (<100 mm Hg) for 16 hr. Protein (N X 6.25), ether extract, and ash (Association of Official Analytical Chemists, 1970) were also determined. Live broiler and carcass measurements were evaluated by examining correlations among these measurements and the chemical components of the carcass and by using the stepwise multiple regression procedure to determine which measurement combinations best predicted the chemical components of the carcass. Factorial analyses of variance were applied to all traits to test for interactions among experiments (strains) and housing types (cages vs. pens). Due to interactions (P<.05) for body width, leg circumference, and back percentage,
2189
PREDICTION OF CARCASS COMPOSITION
RESULTS For each experiment, means and their standard errors for measurements of the live broiler,
the broiler carcass, and percentages of fat, protein and ash (wet and dry matter basis), and moisture of the eviscerated carcass (without leaf fat) are presented in Table 1. Similarities between corresponding means and standard errors of the two broiler groups indicate that the additional 2 weeks of growth allowed the slower growing strain used in the second experiment to attain weights and compositions comparable to those of broilers in the first experiment. Examination of correlation coefficients between traits (Tables 2 and 3) led to the following observations. Live broiler and eviscerated carcass weights were highly positively correlated (.98). Live broiler weight was positively correlated with: live broiler measurements (.18 to .81); abdominal fat weight and percentage (.63 and .49, respectively); chemical component weights; and percentage fat (Table 2). Live broiler weight was negatively correlated with carcass specific
TABLE 1. Means f± standard errors) for live broiler and carcass measurements and for chemical composition of the carcasses of two strains of meat-type male chickens1 Trait
Experiment 1
Experiment 2
Live measurements Broiler weight, g Breast angle, ° Body depth, cm Body width, cm Keel length, cm Shank length, cm Shank circumference, cm Leg circumference, cm
2060. 96.6 11.2 8.1 10.3 11.6 5.2 10.9
± 36 ± .9 + .1 ± .1 ± .1 ± .1 ± .1 + .3
2064. 87.4 11.7 7.8 10.5 12.0 5.1 12.2
± 51
Carcass measurements Weight, g (eviscerated) Abdominal fat weight, g Specific gravity % Wings % Legs % Breast % Back
1299. 34.0 1.062 13.4 34.3 30.6 22.4
24 ± 2.6 ± .001 + .2 + .3 ± .4 ± .4
1269. 38.7 1.063 13.9 33.9 28.6 24.3
± 33 ± 3.3 ± .001 ± .1 ± .3 + .3 ± .3
Chemical composition 2 Fat, % Protein, % Ash, % Water, % Fat, %3 Protein, %3 Ash, %3
14.5 17.5 2.59 65.2 41.4 50.4 7.44
+
± ± ± ± +
± ±
.3 .1 .05 .3 .7 .7 .16
14.8 17.4 2.78 64.7 41.6 49.4 7.91
+
.8
± ± ± ± +
±
± ± ± ± ± ± +
.2
.5 .5 .04 .4 .9 .7 .18
1
Numbers per mean were: 35 in Experiment 1 except for specific gravity which had 34; 32 in Experiment 2.
2
Percentages of the eviscerated carcass weight (without leaf fat).
3
Dry matter basis.
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correlations among traits were calculated after the data of each subclass had been adjusted for the effects of experiment, housing type, and their interaction. A forward stepwise multiple regression procedure was applied to determine the value of live broiler and carcass traits for predicting chemical composition of the carcass. This method adds the variable with the highest R 2 to the model provided the effect of its entry has a significant (P«.50) F value. Variables stay in the model as long as their effect remains significant (P< .10). Trait combinations with the highest multiple correlation coefficient (R 2 ) were considered to be best. Procedures of SAS (Barr et ah, 1976) were used to perform statistical analyses of the data.
2190
CHAMBERS AND FORTIN TABLE 2. Correlations between chemical carcass component weights and percentages of the wet carcass (Wet) and carcass dry matter (DM) and live broiler measurements of meat-type male chickens*
components Weight of Fat Protein Ash Water
1
Live weight
Breast angle
Depth
Width
.82 .93 .79 .96
.21 .38 .28 .28
.48 .53 .47 .56
.69 .75 .63 .76
.56 .53
.08 .02
.35 .35
-.18 -.47
.28 .04
-.25 -.46 -.59
Circumference of Leg
Shank
Shank
.50 .64 .60 .68
.50 .80 .75 .83
.28 .55 .56 .60
.23 .16 .06 .17
.48 .45
.31 .29
.23 .22
.05 .05
.23 .25
-.15 -.31
-.14 -.41
-.15 -.32
-.03 -.21
.02 -.01
-.10 -.18
-.03 -.07
-.12 -.26
-.20 -.39
-.10 -.25
-.05 -.17
.07 .04
-.20 -.25
-.16
-.36
-.53
-.36
-.28
-.04
-.20
Keel
Required size of coefficient to be significantly different from zero P<.05 = .25, P<.01 = .33.
TABLE 3. Correlations between chemical carcass component weights and percentages of the wet carcass (Wet) and carcass dry matter (DM) and carcass measurements of meat-type male chickens1 Abdominal fat
Carcass components Weight of Fat Protein Ash Water Percentage of Fat Wet DM Protein Wet DM Ash Wet DM Water Wet 1
Percentage Weight
Percentage
.25 .07 .03 .15
.81 .44 .36 .46
.71 .28 .24 .30
-.01 -.05
.27 .30
.79 .77
.77 .75
.03 .10
.27 .07
-.34 -.27
-.50 -.76
-.54 -.76
.32 .36
.16 .17
-.04 -.07
-.21 -.23
-.32 -.62
-.28 -.58
.28
.14
-.08
-.17
-.81
-.78
Specific gravity
Wing
Leg
Breast
.82 .95 .80 .98
-.60 -.28 -.24 -.30
-.38 -.47 -.28 -.46
-.23 -.24 -.15 -.25
.12 .32 .23 .25
.54 .51
-.61 -.60
-.24 -.22
-.15 -.14
-.16 -.45
.42 .60
.00 .18
-.26 -.46
.24 .48
-.58
.61
Weight
Back
Required size of coefficient to be significantly different from zero P<.05 = .25, P<.01 = .33.
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Percentage of Fat Wet DM Protein Wet DM Ash Wet DM Water Wet
Length of
Body
2191
PREDICTION OF CARCASS COMPOSITION
weights were positive. Percentage fat was negatively correlated with the other chemical component percentages whereas the remaining chemical component percentages were positively correlated (Table 4). Correlations involving protein and ash percentages were larger when expressed on the basis of carcass dry matter instead of wet carcass. Expressing fat percentage on a dry matter basis reduced negative correlations with water percentage from —.96 to —.92; however, little change was noted among other correlations. Prediction of Chemical Components. Multiple regression analyses were used to determine those trait combinations best predicting either weights or percentages of the chemical components of the carcass. Predictive values, R 2 , trait combinations, and partial regression coefficients in the best regression models are presented in Tables 5 and 6. Generally, component weights were predicted more accurately than percentages (.61 to .98 vs. .29 to .67). Weights of carcass protein and water were predicted better than weights of carcass fat and ash (.89 to .98 vs. .61 to .87). Percentages of protein and ash based on carcass dry matter were predicted better than percentages based on the wet carcass. No improvement in prediction was observed when percentage fat was expressed on a dry matter basis. Percentages of components other than ash tended to be predicted more accurately (.35 to .67 vs. .29 to .54). With the exception of ash weight, groups of traits did not differ markedly in their value for predicting specific component weights. The .61 R 2 value for ash weight prediction by abdomi-
TABLE 4. Correlation coefficients for pairs of chemical of the carcass1
components
Correlations
Correlated components
Weights
Percentages (wet basis)
Fat and protein Fat and ash Fat and water Protein and ash Protein and water Ash and water
.65 .49 .69 .84 .97 .82
-.70 -.46 -.96 .42 .58 .34
1
n=64.
2
Carcass dry matter basis for protein and ash.
Percentages 2 -.95 -.80 .74 .92 .72
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gravity, protein and ash percentages of carcass dry matter, and percentage water. Corresponding values for eviscerated carcass instead of live broiler weight were quite similar. Correlations among broiler measurements were either positive or did not differ from zero (P>.05). Live broiler measurements were positively correlated with chemical component weights (Table 2). Correlations of these measurements with chemical component percentages that differed from zero (P«.05) tended to be similar in size to correlations of live broiler weight with chemical component percentages. Among carcass traits, abdominal fat weight and carcass specific gravity were negatively correlated (—.54). Correlations among carcass cut percentages were either negative or not different from zero (P>.05). Weight of abdominal fat was positively correlated with chemical component weights and percentage fat, but was negatively correlated with percentage of protein, ash, and water (Table 3). Abdominal fat percentage of the eviscerated carcass was positively correlated with abdominal fat weight (.98) and carcass fat weight and percentage (Table 3). Correlations were negative between percentages of abdominal fat and water, protein, and ash. Larger negative correlations were obtained when protein and ash were expressed as percentages of carcass dry matter. However, carcass specific gravity was negatively correlated with chemical component weights and with percentage fat. Specific gravity was positively correlated with percentages of protein, ash and water. Other correlations rarely differed from zero (P> .05). Correlations between chemical component
1
.181
5 2
2.60 .904
1 2
3
1 2
2
1 3
6 3 1 4
.87
.78
.76
.74
Rank
1775 -.824 -25.6 .211 -1482
-38.2 .142 1.25
3.79
-2878
2927
-43.8
.216 -1.09
360
Fat
.086 .736
.172
.179
-3.47
1.53
393
-459
-4.02
2.56 .181
1.42
693
-775
10.9
-149
.95
.93
.93
.89
Protein
These results were obtained after variation due to strain differences had been removed.
All traits R2 Intercept Breast angle Shank length Carcass weight Specific gravity Wing percentage Breast percentage Back percentage Abdominal fat weight Abdominal fat percentage
Live broiler traits R2 Intercept Broiler weight Breast angle Keel length Shank length Carcass traits R2 Intercept: Carcass weight Specific gravity Wing percentage Breast percentage Back percentage Abdominal fat traits R2 Intercept Carcass weight Abdominal fat weight Abdominal fat percentage
bi
2
3
1 4
2
1
3
1 2
3
1 2
Rank
-.4
1.2
49.8 .1 3.3 .0
2.2 .0
-.6
1.3
-5.5 .0
-61.3 .0 .2 2.1 3.5
bi
Component weights
TABLE 5. Multiple correlation coefficients (R7), partial regression coefficients (b;) and importanc and abdominal fat traits for predicting chemical component weights of male chick
om http://ps.oxfordjournals.org/ at Michigan State University on February 22, 2015
2
1
-133
-147
.262 .077
.67
3 1
2
1
-1.96
-.388
249
-200
-2.55
56.9
3
.293
.54
-.463
2 1
.004
4.34
11.6 -.015 .196
bi
-354 -.005 397
-11.0 .100
-215
.51
2
-3.09
231
1 3
.45
39.8 .010 -.101
Rank
.66
.54
.46
.35
Protein
Protein and ash as percentage of carcass dry matter.
These results were obtained after variation due to strain differences had been removed.
All traits R2 Intercept Breast angle Specific gravity Wing percentage Back percentage Abdominal fat weight Abdominal fat percentage
Abdominal fat traits R2 Intercept Abdominal fat weight Abdominal fat percentage
Carcass traits R2 Intercept Carcass weight Specific gravity Wing percentage Back percentage
Live broiler traits R2 Intercept Broiler weight Breast angle Keel length Shank length
bi
Fat
1
3
2
1
2
3 1
2
1 3
Rank
•42.3 .03 43.0 .31 -.12 -.01
8.64 -.02
.36 -.17
67.4
-64.9
-5.97 -.00 .05 .33 1.09
bi
Component percentages
TABLE 6. Multiple correlation coefficients (R2), partial regression coefficients (bj), and imp predicting chemical component percentages of male chicken carcasses
rom http://ps.oxfordjournals.org/ at Michigan State University on February 22, 2015
2194
CHAMBERS AND FORTIN
DISCUSSION
Relationships Among Chemical Carcass Components. All chemical components of the carcass of the growing broiler increase if the supply of nutrients is adequate. Consequently, chemical component weights are positively and, in some cases, highly correlated with one another. The chemical component weights measured account for almost all of the carcass weight and a major portion of broiler weight; hence, they are positively correlated with carcass and broiler weights. Conversely, expressing components as a percentage of the carcass consisting of these components gives rise to negative correlations among component proportions. As the proportion of one component increases, the sum of proportions of the remaining components must decrease. Broilers become fatter as they grow (Leeson and Summers, 1980); hence, fat percentage must be negatively correlated with one or more of the remaining chemical component percentages. In this study, fat was negatively related to all of the other chemical components (Table 4). This relationship gave rise to positive correlations among the remaining chemical components. In addition, negative correlations arise between percentages of live broiler weight and chemical components other than fat. The high negative correlation observed between fat and water, —.96, was in good agreement with other
reports: —.98 for carcasses of 60-day-old cockerels (Taylor and Shaffner, 1975); - . 8 7 to - . 9 0 for 300 carcasses of male and female broilers at either 55 or 59 days of age (Verstrate et al., 1980); and —.94 and —.97 for carcasses of 9-week-old broilers (Pym and Solvyns, 1979). Negative relationships among proportions can be reduced by deducting from the denominator (carcass weight) the other component involved in the correlation. In instances involving carcass water, this is achieved by expressing other chemical components on a carcass dry matter basis. In the current study, positive correlations between water and either protein or ash increased when the latter were expressed on carcass dry matter bases (Table 4). Similarly, the negative correlation between proportions of water and fat was slightly reduced when fat was expressed in terms of carcass dry matter. The latter values are better indicators of the "true" component relationships due to partial correction for the negative relationship imposed by the mode of expressing proportions. True component relationships are probably slightly higher than the observed correlations. Measurement errors of correlated traits are expected to be independent giving rise to a zero correlation; hence, measurement error will tend to reduce the magnitude of correlations. Prediction of Chemical Carcass Components. The high positive correlations between live broiler and carcass weights and the similar correlations between either live broiler or carcass weight and other traits indicate these weights have similar predictive value and little benefit is gained by using both live broiler and carcass weights. Live broiler weight is preferred because measurement does not require slaughter of the bird. Trait combinations predicting chemical component weights or percentages usually include either live broiler or carcass weight (Tables 5 and 6). Exceptions included chemical component percentage prediction by either abdominal fat measurement or combinations of traits from all groups. For chemical component weight prediction, live broiler or carcass weight were the most important traits in the combinations. Live broiler measurements and chemical carcass component weights increase with body weight; hence, positive correlations were observed among live measurements and chemical component weights (Table 2). Relationships between live broiler measurements and chemical component percentages were weaker. The dif-
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nal fat traits was solely due to carcass weight. For component percentages other than ash, abdominal fat traits predicted components better using fewer traits. Percentage ash was predicted more accurately by live broiler and by carcass traits. Carcass traits in turn, were superior to live broiler traits as predictors of component percentages. Combinations of live broiler, carcass, and abdominal fat traits predicted component weights and percentages best (Tables 5 and 6). The more important predictor traits included either live broiler or carcass weight, shank length, breast angle, either weight or percentage of abdominal fat, carcass specific gravity, and back percentage. Live broiler and carcass traits were tested for their ability to predict either weight or percentage of abdominal fat. The best predictions (R 2 ) by live broiler traits were .45 and .30 for weight and percentage abdominal fat, respectively; corresponding values using carcass traits were .45 and .32.
PREDICTION OF CARCASS COMPOSITION
cerated carcass and percentage carcass fat for male broilers of the current study, .77, agrees with these values. Abdominal fat weight or percentage was the most predictive trait for chemical components other than ash (Tables 5 and 6). Abdominal fat trait combinations not only had the highest multiple correlation coefficients (R 2 ) but also used the fewest traits. In fact, abdominal fat weight or percentage was the sole predictor trait for percentages of fat, water, and protein. In all group trait combinations, abdominal fat was second only to carcass weight for chemical component weight prediction and was first followed by specific gravity for prediction of chemical component percentages. With the exception of ash measurements, correlations of chemical carcass component weights and percentages with abdominal fat weight were larger than those with carcass specific gravity. These results comply with the conclusion of Spencer et al. (1978) that abdominal fat weight was superior to specific gravity for determining percentage carcass fat. The current results suggest this situation holds for percentages of carcass moisture and protein as well. Abdominal fat weight can be measured more readily than carcass specific gravity. Moreover, Fortin and Chambers (1981) recommended restricting use of specific gravity for estimation of compositional differences to those among groups of broiler carcasses. It is debatable whether the added benefit of specific gravity values warrants the labor required for measurement. The values of live and carcass measurements for predicting abdominal fat weight and percentage (of eviscerated carcass weight) were tested using multiple regression analysis. Multiple regression correlations for abdominal fat weight were at best, .45 for both live measures and carcass measures. Corresponding values for abdominal fat percentage were .30 for live measures and .32 for carcass measures. These results agree with those of Mirosh et al. (1980) who recommended direct measurement of abdominal fat as opposed to prediction using skin pinch thickness, feather tract weight, percentage moisture of feather tract, and total serum lipid measurements. The use of broilers from two stocks that differ in growth rate enhances the generality of these results. In addition, the general concordance of these correlations with others in the literature adds to their credibility. Of the live and carcass traits examined, few of them alone
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ference in sign between correlations of live broiler and carcass measurements with carcass fat versus carcass water traits is consistent with the high negative correlation between fat and water. Live broiler trait combinations predicted chemical component weights and percentages almost as well as combinations of carcass or abdominal fat traits. Of the live measurements, live broiler weight and shank length were the most predictive traits followed by breast angle and keel length. Body depth and width and shank and leg circumferences were of little value. The most predictive carcass traits included carcass weight and specific gravity (Tables 5 and 6). Specific gravity declines as carcass fatness increases (Fortin and Chambers, 1981). This accounts for the negative correlation of specific gravity with fat percentage and its positive correlation with the other chemical component proportions. The specific gravity and fat percentage correlation for male broilers in this study was —.61. This is larger than the —.36 for males and similar to the —.69 for females at 59 days of age reported by Spencer et al. (1978). The positive relationship between live broiler weight and carcass fatness appears responsible for the negative correlations between specific gravity and all chemical component weights. Specific gravity was the most predictive carcass trait in terms of R 2 for chemical component percentages and was second only to carcass weight for chemical component weight prediction. Specific gravity precluded shank length in all group trait combinations predicting chemical component percentages. With the exception of wing percentage, carcass cut percentages were of limited value for predicting chemical component weights and percentages. Negative correlations existed among the carcass cut percentages. Factors contributing to these relationships include the mode of expression of the part-to-whole relationship discussed earlier for chemical component percentages and any deviations in cutting procedure. Cutting errors, believed to be small, would favor one of the adjacent cuts at the expense of the other. Correlations between abdominal fat percentage of live body weight and percentage carcass fat were .76 and .74 for male and female, 59-day-old broilers, respectively (Becker et al., 1979). In spite of differences in expressing abdominal fat proportion, the correlation between percentage abdominal fat of the evis-
2195
CHAMBERS AND FORTIN
2196
ACKNOWLEDGMENTS The authors are grateful to M. Baker and M. Sauermann for technical assistance and to R. Cloutier and staff of the Chemistry and Biology Research Institute, Agriculture Canada for chemical determinations of each carcass.
REFERENCES Association of Official Analytical Chemists, 1970. Official Methods of Analysis. 11th ed. Assoc. Offic. Anal. Chem., Washington, DC. Barr, A. J., J. H. Goodnight, J. P. Sail, and J. T. Helwig, 1976. A User's Guide to SAS-76. SAS Inst., Inc., Raleigh, NC. Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate, 1979. Prediction of fat and fat free live weight in broiler chickens using backskin fat, abdominal fat and live body weight. Poultry Sci. 58:835-842. Becker, W. A., J. V. Spencer, L. W. Mirosh, and J. A. Verstrate, 1981. Specific gravity, carcass fat, abdominal fat, and yield data in broiler chickens. Poultry Sci. 60:2045-2052. Chambers, J. R., J. S. Gavora, and A. Fortin, 1981. Genetic changes in meat-type chickens in the last twenty years. Can. J. Anim. Sci. 61:555—563. Fortin, A., and J. R. Chambers, 1981. Specific gravity of the carcass and its parts as predictors of carcass composition in broiler chickens. Poultry Sci. 60:2454-2462. Leeson, S., and J. D. Summers, 1980. Production and carcass characteristics of the broiler chicken. Poultry Sci. 59:786-798. Mirosh, L. W., W. A. Becker, J. V. Spencer, and J. A. Verstrate, 1980. Prediction of abdominal fat in live broiler chickens. Poultry Sci. 59:945—950. Pym, R.A.E., and A. J. Solvyns, 1979. Selection for food conversion in broilers: body composition of birds selected for increased body-weight gain, food consumption and food conversion ratio. Br. Poult. Sci. 2 0 : 8 7 - 9 7 . Ricard, F. H., and R. Rouvier, 1965. Etude des mesures de conformation du poulet I. Analyse statistique preliminaire concernant le poids et 13 mensurations corporelles du poulet vivant. Ann. Zootech. 14:191-212. Spencer, J. V., W. A. Becker, J. A. Verstrate, and L. W. Mirosh, 1978. Relationship of carcass fat to abdominal fat and specific gravity in broiler chickens. Poultry Sci. 57:1164. (Abstr.) Taylor, M. H., and C. S. Shaffner, 1975. The relationship of ether extract and moisture in eviscerated broilers. Poultry Sci. 54:663-666. Verstrate, J. A., J. V. Spencer, L. W. Mirosh, and W. A. Becker, 1980. A comparison of methods for determining the fat content of broiler carcasses. Poultry Sci. 59:298-302.
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were useful for accurate prediction of chemical component percentages. Either live body weight or carcass weight in conjunction with abdominal fat weight appear suitable for efficient prediction of weights of carcass fat, moisture, and, on a dry matter basis, protein. Either weight or percentage abdominal fat was an important predictor of corresponding component percentages; however, multiple correlation coefficients were .60 or less. If greater precision is required, additional traits must be tested to find effective component predictors. Failing this, one or more of the chemical components must be measured directly. Carcass moisture has been used to predict carcass fatness (Taylor and Shaffner, 1975; Verstrate et al., 1980). Multiple correlation coefficients of .76 and .78 were obtained by Verstrate et al. (1980) for carcass fat prediction models containing carcass moisture. In the current study, as mentioned earlier, correlations between carcass moisture and ether extract were high and negative. In addition, the correlation between percentage moisture and percentage protein in carcass dry matter was large, .92. Hence, percentage carcass moisture may be an effective means of accurately predicting percentages of carcass fat and protein provided: 1) the bird and the carcass can be sacrificed, 2) the rate of grinding carcasses in preparation for sampling is not too slow, and 3) the cost of an appropriate vacuum oven or freeze drier and the energy to operate it are not prohibitive.