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Body Weight and Carcass Development in Different Lines of Turkeys1
Body Weight and Carcass Development in Different Lines of Turkeys M. S. LILBURN and K. E. NESTOR Department of Poultry Science, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 (Received for publication April 7, 1991)
1991 Poultry Science 70:2223-2231 INTRODUCTION
Within the past decade, there has been a large increase in the per capita consumption of poultry products. A driving force behind this change in consumer trends is the perception that poultry meat is lower in saturated fat and cholesterol. Increased demand for poultry meat increased pressures on the breeding and production sectors of the poultry industry to develop management and nutrition practices that will result in maximal rates of BW gain and lean carcass development, particularly the breast muscle portion of the carcass. In the older literature, there are a number of reports dealing with the relationships between BW and carcass part development (Marsden, 1940; Johnson and Asmundson, 1957a,b; Fry et al, 1962; MacNeil and Buss, 1968; MacNeil, 1969). These studies utilized lines of turkeys that had rates of BW gain and breast muscle development very different from contemporary, rapidly growing turkeys. Nestor et al. (1987) reported on selected bone and muscle comparisons between a line selected
'Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Manuscript Number 23-91.
for increased BW (F line) and its unselected, randombred control population (RBC2). There was a decrease in the relative weight of the thigh and drumstick in the F line compared with the RBC2, but the differences were evident only at later ages. The ubiotarsus and femur (percentage of BW) were also heavier in the RBC2 line at 20 wk but not at 16 wk At the latter age, leg problems are usually apparent in rapidly growing turkeys. Food products derived from turkey breast meat have gained considerable consumer acceptance, and, therefore, modern commercial turkeys have been developed for both rapid BW gain and maximal breast muscle yield. Nestor et al. (1988) compared carcass traits of turkeys from F and RBC2 lines with those of a commercial sire line (C line). There was no difference in BW between the F and C lines, but total breast muscle percentage was significantly greater in the C line. Selection for BW alone (F versus RBC2) did not influence percentage breast yield. The relative leg muscle weight was greater in the F and RBC2 lines than the C line. This was also reflected in increased weights of total leg bones (shank, femur, tibiotarsus) in the experimental (or selected and randombred) lines. Selection for BW alone (F versus RBC2) reduced the relative weight of total leg bones.
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ABSTRACT Body weight and carcass component weights of turkeys from a growth-selected line (F), a randombred control population (RBC2), and a commercial sire line (C) were compared at hatch, 4,8,12, and 16 wk of age. At natch there were no significant differences in BW between the F and RBC2 lines, but the C line poults weighed significantly less than the F line poults. Total Pectoralis muscle weight of the F line was larger than for Lines C and RBC2 at hatch, but there were no line differences in drum weight or length. The F line was still heavier than the other lines at 4, 8, and 12 wk, but the absolute and relative weights of the Pectoralis major (P. major) muscle were larger in the C line than the other lines at all ages. Selection for BW increased the weight of the P. major in the F line compared with the RBC2, but differences in the relative weight of the muscle were not consistent. The large line differences for the absolute and relative weight of the P. major were not observed for the Pectoralis minor. At all ages, the lengths of the tibia and femur were greater in the F line than the other lines. At 4 and 8 wk, bone length in the C line was greater than the RBC2,but at 12 and 16 wk there were no significant differences between these lines. The fast-growing F and C lines had more abdominal fat than the RBC2 at 16 wk of age. (Key words: turkeys, selection, body weight, bone length, muscle growth)
2224
LILBURN AND NESTOR
The aforementioned comparisons of selected, randombred, and commercial turkeys were made at an age (16 wk) when line differences would be assumed to be maximal. It is important, however, to know at approximately what ages these carcass changes are occurring, particularly when trying to understand the relative effects that selection for BW alone (F line) or in combination with breast muscle yield (C line) have on overall growth and development of turkeys. The objective of the present study was to compare carcass traits of F, RBC2, and C line turkeys at different ages from hatch through 16 wk of age.
Male and female poults from the F, RBC2, and C lines were hatched at 2-wk intervals. The ages of the parental breeders were the same. The details of the selection protocol used to develop and maintain the F line and RBC2 lines were described by Nestor et al. (1985). Each poult was wing-banded at hatch and poults within a hatch were reared with sexes intermingled. At young ages, the RBC2 poults grew noticeably slower than the faster growing lines, so each line was reared in separate but adjoining pens. There was approximately .3 m 2 (3 ft2) per bird at the start of the study, and for the duration of the experiment the birds were fed a turkey starter diet (Table 1). The birds were fed the starter diet to maximize genetic differences in growth and muscle protein accretion. Fifteen poults from each line were selected at 0 (hatch), 4, 8, 12, and 16 wk of age for carcass comparisons. Within an age, all line and carcass comparisons were made on poults that were randomly chosen from the same hatch. Birds were weighed, killed by cervical dislocation, and sexed by gonadal examination. For the 0 wk (hatch) comparisons, the entire Pectoralis major (P. major) breast muscle, the weight of the tibia plus associated muscles (total tibia), and the length of the tibia were recorded. At subsequent sample ages the right half of Pectoralis minor (P. minor) as well as the P. major was individually dissected out and weighed. The weight of the two halfmuscles was doubled for calculation of total muscle weights. The length of the femur and tibia, the weight of these parts plus associated muscles (total femur, total tibia), the weight of the Gastrocnemius muscle, and abdominal fat content were all recorded at older ages.
Ingredients
Composition
Corn Soybean meal (44% CP) Fish meal (60% CP) Meat meal (50% CP) Animal-vegetable fat Salt Ground limestone Dicalcium phosphate (18.5%) Premix1'2'3
(kg/100 kg) 40.00 42.50 6.50 5.00 2.15 .40 .80 .65 2.00
'The premix contributed the following per 100 kg of feed: ground corn, 422 g; choline chloride (60%), 100 g; amprolium (25%), 22.7 g; selenium premix (200 mg/kg Se), 45.4 g; DL-methionine (99%), 45.4 g; trace mineral premix, 45.4 g; vitamin premix, 227 g. 2 The vitamin premix contributed the following per kilogram of diet: vitamin A, 8,745 IU; vitamin D, 3,745 IU; vitamin E, 60 U; vitamin K (menadione sodium bisulfite), 2.91 mg; thiamine HC1, 2.2 mg; riboflavin, 6.6 mg; niacin, 99 mg; pantothenic acid, 15.4 mg; folic acid, 1.2 mg; pyridoxine, 2.2 mg; biotin, 165 mg; vitamin Bj2, 15 mg; ethoxyquin, 113.5 mg. The trace mineral premix contributed the following per kilogram of diet zinc oxide (72% Zn), 147 mg; manganous oxide (55% Mn), 152 mg; copper sulfate (25.2% Cu), 35 mg; ferrous sulfate monohydrate (31% Fe), 72 mg; potassium iodide, 1.5 mg.
Statistical Analysis All data were analyzed by analysis of variance using the General Linear Model (GLM) program of SAS® (SAS Institute, 1985). Data were analyzed within an age period with line, sex, and the line by sex interaction as main effects tested. Data are reported as the least squares means estimates for each parameter within an age. Where significant main effects occurred, the means were separated by Duncan's new multiple range test (Steel and Torrie, 1960). RESULTS
At hatch, there were no differences in BW between the F line and RBC2 poults but C line poults were lighter than poults of the F line (Table 2). The weight of the P. major was greater in the F line compared with the other two lines. There were no line differences in total tibia weight or tibia length. The F line was still heavier than the C line at 4 wk of age (Table 3). The BW and the absolute weight of all carcass parts were smaller for the RBC2 poults than the F or C line poults (Tables 3 to
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MATERIALS AND METHODS
TABLE 1. Composition of starter diet (selection diet)
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CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS TABLE 2. Line differences in carcass components of turkeys at hatch
Line
Body weight
Pectoralis major weight
Tibia weight
Tibia length
C F RBC2
47.7b 56.3 a 52. Vab
(g) .610b .882a .652b
1.98 2.08 1.95
(cm) 4.02 4.04 3.88
a,b
Least squares means within a column with no common superscripts are significantly different (P<05). ' c = commercial sire line; F = line selected for increased 16-wk BW; RBC2 = randombred control line. ^ e weight of the total muscle from both sides of the keel.
relative weight of this muscle. Males had greater BW and individual breast muscle weight, but the relative size of both breast muscles was similar in males and females. The absolute weights of the total femur, total tibia, and Gastrocnemius muscle were lower in the RBC2 poults (Table 5). The weight of these parts in the F line was greater than the C line. The same line differences (F > C > RBC2) occurred for the relative weight of the total femur but were slightly different for the total tibia, for which the RBC2 was intermediate to the two selected lines. Line differences in the length of the femur and tibia followed the same pattern as absolute weight of the femur (Table 6). Males had significantly longer and heavier leg parts, but the relative weights of the total femur and total tibia were similar in
TABLE 3. Line differences in total body weight and body weight less the weight of the Pectoralis major
Body weight1 Variable Line3 C F RBC2 Sex Male Female
4 wk
8 wk 2
12 wk
16 wk 2
8 wk
Body weight - Pectoralis major weight 12 wk 16 wk
y&>
l,082 b (10/5) U16a (9/6) 676° (9/6)
3,837 (10/6) 4,090 (12/3) 2,463 (6/9)
6,472b (7/8) 7,067a (13/3) 4,209° (6/10)
9,448 (6/10) 9,194 (10/6) 5,714 (10/6)
l,032 a 950 b
3,865 3,061
6,620* 5,212b
9,271 6,967
3,187b
5,252b
7,441 b
3,533a
6,029"
7,647a
2,122°
3,629°
4,866°
3,292a 2,603b
5,58 l a 4,358b
7,626a 5,677b
a_ °Least squares means within a column and variable with no common superscripts are significantly different (P<05). (no. of males/no. of females). There was a significant line by sex interaction (P<05). 3
C = commercial sire line; F = line selected for increased 16-wk BW; RBC2 = randombred control line.
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5). The absolute weights of the P. major and P. minor muscles were similar in the F and C lines, but relative to BW, they were larger in the C line (Table 4). The weight of the total tibia, the length of the tibia, and the weight of the Gastrocnemius muscle were all greater in the F line (Tables 5 and 6). Males were significantly heavier than the females. At 8 wk, both the absolute and relative weights of the P. major muscle were greater in the C line than for Lines F and RBC2 (Table 4). There was no difference in the relative weight of the P. major of the F and RBC2, but these lines differed in the absolute weight of the muscle. The absolute weight of the P. minor muscle was similar in the C and F lines and heavier than in the RBC2 poults. There were no line differences, however, in the
18.87* 14.64b 13.87b
15.43 16.16
14.74 14.82
10.73 11.06
1,038* 854 b
16.97* 13.57b 13.81°
573.6* 458.6b
113.1 106.3
1,221* l,038 b 580°
12 wk
Pectoralis major
12.15* 10.66b 9.87°
649.8* 557.4b 341.0°
8 wk
131.9* 129.9* 67.3 b
4 wk
17.29 17.99
21.37* 16.80b 14.74°
1,644* U90b
2,007* l,546 b 848°
16 wk
2.91 2.98
3.18* 2.88b 2.78b
30.6 28.3
34.6* 34.9* 18.8b
4 wk
4.502 3.84 4.18 4.26 4.14
3.81 3.97
284 211
73.5* 61.1 b (% BW) 4.05 3.75 3.88
296 274 176
12 wk1
Pectoralis minor
77.5* 76.5* 47.9 b
— (g)
8 wk
*~°Least squares means within a column and variable with no common superscripts are significantly different (P<05). 'There was a significant line by sex interaction (P<05). 2 C = commercial sire line; F = line selected for increased 16-wk BW; RBC2 = randombred control line.
Line C F RBC2 Sex Male Female
Line2 C F RBC2 Sex Male Female
Variable
TABLE 4. Line differences in breast muscle and abdominal fat
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16 wk
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS
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LELBTJRN AND NESTOR TABLE 6. Line differences in the length of the femur and tibia Tibia length
Femur length Variable
wk
12 wk
16 wk
4 wk
8 wk
12 wk
16 wk
(cm) Line
c
F RBC2 Sex Male Female
10.8" 11.5a 9.9°
n.9° 13.1a 11.8b
12.6" 13.5a 12.3b
10.1" 10.6a 8.8C
16.0° 16.9a 15. l c
18.2" 19.5a 18.1 b
19.6° 20.1 a 19.5b
11.2a 10.2b
13.1a 11.5b
13.9a 11.7b
9.9 9.7
16.6a 15.3b
19.9a 17.3 b
21.5a 17.9b
Least squares means within a column and variable with no common superscripts are significantly different (<.05). C = commercial sire line; F = line selected for increased 16-wk BW; RBC2 randombred control line.
resulting in a significant line by sex interaction (Table 7). The lengths of the femur and tibia were similar in C line and RBC2 birds, but both bones were longer in the F line (Table 6). Line differences in both the absolute and relative weight of the Gastrocnemius muscle were the same as those observed for the absolute and relative total tibia weight, respectively (Table 5). At 16 wk of age, the C line was significantly heavier and both the absolute and relative weights of the P. major muscles were greater than those of the F line (Tables 3 and 4). When BW was compared without the P. major weight, however, the F line was heavier than the C line. The F line had larger BW and absolute and relative weights of the P. major muscle than the RBC2 birds. The absolute weight of the P. minor was similar in the F and C lines, both of which were greater than that of the RBC2 line, but there were no differences between lines in the relative weight of this muscle (Table 4). The two faster growing lines also had more abdominal fat than the RBC2 line. Across lines, the weight of the P. major and P. minor breast muscles, males were heavier than females, but the relative weights were similar between sexes. The absolute weight of the femur was greater in the F line compared with the C and RBC2 lines but the relative weight of the femur was greatest for the RBC2 line (Table 5). There was also a line by sex interaction in femur weight because of the greater sex difference in the C line compared with the other lines (Table 7). The length of the femur and tibia was similar in the RBC2 and C lines but these bones were shorter in both lines than in the F line (Table 6). Line differences in the absolute
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males and females. There was a significant sex by line interaction for BW and femur weight, which was due to the greater sex difference for these traits in the F and RBC2 lines uian for the C line (Table 7). The relative weight of the Gastrocnemius muscles was greater in C line males compared with females but this was reversed in the F and RBC2 lines (Table 5). Relative tibia weight was similar in males and females of the RBC2 line but males had larger tibia weights in the C line and females had larger tibia weights in the F line. Line differences in BW and the weights of the P. major and P. minor muscles were similar, with one exception, at 12 wk as they were at 8 wk (Tables 3 and 4). The only line difference not evident at 8 wk was the relative weight of the P. minor, which was smaller in the F line than the other two lines, whereas at 8 wk it was similar across all three lines. There were line by sex interactions for both the absolute and relative weights of the P. minor muscle (Table 7). This was due to the disproportionately larger weight of this muscle in the F line males compared with the smaller differences between sexes in the C and RBC2 lines. The F and C lines had more abdominal fat both on an absolute and relative basis than the slower growing RBC2 line (Table 4). The absolute weights of the total femur and total tibia were smaller in the RBC2 line (Table 5). The relative weight of these parts, however, was similar to (femur) or greater than (tibia) the F line and both weights were greater than for the C line. The absolute and relative weights of both the femur and tibia were greater in the F line compared with the C line. The sex difference in thigh weight of the F line was considerably less than in the other lines
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS
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2229
weight of the total tibia were similar to those observed for the femur (Table 5). The relative tibia weight was significantly less in the C line than in the other two lines. The weight of the Gastrocnemius muscle followed the same pattern as observed for the total tibia.
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Although there were few line differences at hatch, many of the line differences observed at later ages were already apparent by 4 wk of age. The divergence observed in development from 0 to 4 wk, particularly in the RBC2 and C lines, which had similar BW and pectoral muscle weights at hatch, emphasizes the overall effects that selection for growth and carcass measures at later ages can have on early growth and differentiation. Body weight of the C line was smaller than the F line until 16 wk, but by 4 wk of age the absolute weights of the P. major and P. minor were similar in both lines but the relative weights of these muscles were greater in the C line. Compared with the RBC2 line, the F line showed an increase in the relative weight of the P. major muscle at 4 and 16 wk (selection age). This supports suggestions in the literature (Johnson and Asmundson, 1957a) that because of the high positive correlation between pectoral weight and BW, genetic gains in the former can be made through simple emphasis on BW selection. This is supported by one report (Nestor et ah, 1987) in which the F line had increased percentage breast muscle weight at 16 wk compared with the RBC2 line, but is contrary to a later study in which there were no line differences (Nestor et ah, 1988). In the latter study, the comparisons were made over two generations and the percentage breast muscle weights were considerably lower than those reported by Nestor et al. (1987). They were also low compared with die sum of the P. major and P. minor percentages reported here. This suggests that environmental influences on growth and development should be considered when comparisons are made across experiments or generations of selection. The large difference between the relative weight of the P. major muscle in the C line and the F line supports the results of Nestor et al. (1988) and suggests that dual selection for BW and some indices of breast development would result in maximal breast yield. Selection for breast muscle development would also appear to have a singular effect on P. major weight, as the F
2230
IILBURN AND NESTOR
associated with increased length of long bones (Asmundson, 1948; Lasley, 1949). At 12 and 16 wk, however, the lengths of the femur and tibia were similar in the RBC2 and C lines, and at the latter age there were only marginal overall line differences (P<.088) in the length of the tibia. Nestor et al. (1988) reported that the length of the shank (tarsometatarsus) was significantly greater in the F line compared with the RBC2, but the approximately 4% difference (14.8 versus 14.2 cm) at 16 wk was considerably less than the 15 to 17% difference in bone density and 23% difference in defatted bone weight. The combined data from Nestor et al. (1988) and the current study demonstrate that in response to genetic increases in BW and carcass development, there has been some skeletal compensation (i.e., increased bone density and bone weight) without great changes in bone length. These responses have been far less, however, than the 30 to 40% changes observed in the absolute weights of the muscles associated with the breast and leg. The increased incidence of leg problems observed in commercial, fast-growing turkeys probably results, therefore, from a combination of developmental stresses associated with rapid growth and changes in the architectural relationships between muscle and bone. ACKNOWLEDGMENTS
The authors wish to thank Laurel Newman and Wanda Acord for their help in the preparation and handling of the manuscript. REFERENCES Asmundson, V. S., 1948. Inherited differences in weight and conformation of Bronze turkeys. Poultry Sci. 27: 695-708. El-Ibiary, H. M., 1948. Body conformation in turkeys. Poultry Sci. 27:825-826. Fry, J. L„ O. S. Rao, and L. D. Rasplicka, 1962. Factors affecting the yield of turkey parts. Poultry Sci. 41: 1299-1303. Jaap, R. G., 1938. Body conformation of the live market turkey. Poultry Sci. 17:120-125. Johnson, A. S., and V. S. Asmundson, 1957a. Genetic and environmental factors affecting size of body weight and body parts of turkeys. 2. The relation of body weight and certain body measurements to pectoral and tibial muscle weights. Poultry Sci. 36:959-966. Johnson, A. S., and V. S. Asmundson, 1957b. Genetic and environmental factors affecting size of body and body parts of turkeys. 1. The heritability and interrelationships of body size and live body measurements. Poultry Sci. 36:296-301. Lasley, E. L., 1949. A comparison of skeletal and fleshing
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line was still heavier when BW are compared independent of this muscle weight. The large differences in the relative weight of the P. major muscle were not associated with similar differences in the P. minor muscle. There were no line differences at 16 wk and even at the younger ages there were no consistent differences between lines. Johnson and Asmundson (1957a) reported that the heritability for each muscle was similar and that the correlation between each pectoral muscle and BW was high. The correlation between individual muscle weights at 24 wk, however, was not as great as expected. The data from the present experiment suggest that genetic gains in breast yield associated with selection for increased BW or selection for breast conformation or both have primarily influenced the development of the P. major muscle. The P. minor muscle lies along the keel and has little room to expand. The disproportionate development of the P. major compared with the P. minor muscle may also contribute to the increased prevalence of deep pectoral myopathy (green muscle disease), a result of focalized ischemia and subsequent necrosis within the P. minor (Siller, 1985). The consistent negative association between the relative weights of total femur and total tibia and breast yield supports previous studies in which body conformational patterns in turkeys have been reported. Jaap (1938) reported that better fleshing was associated with shorter shanks and thighs. El-Ibiary (1948) reported that in turkeys of similar BW, narrower breasted birds had longer shanks than those with wider breasts. MacNeil (1969) compared males from numerous broadbreasted Bronze and White strains and found that although eviscerated carcass weights were similar, there was a negative relationship between thigh and skinless breast portions. Nestor et al. (1988) reported line differences in the relative weight of drumstick muscles and the Gastrocnemius data from the current experiment are in support of those observations. The differences in the absolute weight of the femur and tibia were not always associated with significant differences in the length of the femur and tibia. Selection for BW in Line F resulted in a significant increase in the length of the long bones at early ages compared with the RBC2 population. This agrees with observations in the literature, in which heavier BW has been
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS development in three types of domestic turkeys. North Dakota Agriculture Experiment Station Bulletin 335:1-50. MacNeil, J. H., 1969. Yield characteristics and relationships to body measurements of commercial strains of turkeys. Poultry Sci. 48:1598-1603. MacNeil, J. H., and E. G. Buss, 1968. Skin and meat yields of turkeys as influenced by strain. Poultry Sci. 47:1566-1570. Marsden, S. J., 1940. Weights and measurements of parts and organs of turkeys. Poultry Sci. 19:23-28. Nestor, K. E., W. L. Bacon, G. B. Havenstein, Y. M. Saif, and P. A. Renner, 1988. Carcass traits of turkeys from lines selected for increased growth rate or increased shank width. Poultry Sci. 67:1660-1667. Nestor, K. E., W. L. Bacon, P. D. Moorhead, Y. M. Saif,
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G. B. Havenstein, and P. A. Renner, 1987. Comparison of bone and muscle growth in turkey lines selected for increased body weight and increased shank width. Poultry Sci. 66:1421-1428. Nestor, K. E„ W. L. Bacon, Y. M. Saif, and P. A. Renner, 1985. The influence of genetic increases in shank width on body weight, walking ability, and reproduction of turkeys. Poultry Sci. 64:2248-2255. SAS Institute, 1985. SAS® User's Guide: Statistics, Version 5 Edition. SAS Institute Inc., Cary, NC. Siller, W. G., 1985. Deep pectoral myopathy: A penalty of successful selection for muscle growth. Poultry Sci. 64:1591-1595. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw Hill Book Co., New York, NY.
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1991 Poultry Science 70:2223-2231 INTRODUCTION
Within the past decade, there has been a large increase in the per capita consumption of poultry products. A driving force behind this change in consumer trends is the perception that poultry meat is lower in saturated fat and cholesterol. Increased demand for poultry meat increased pressures on the breeding and production sectors of the poultry industry to develop management and nutrition practices that will result in maximal rates of BW gain and lean carcass development, particularly the breast muscle portion of the carcass. In the older literature, there are a number of reports dealing with the relationships between BW and carcass part development (Marsden, 1940; Johnson and Asmundson, 1957a,b; Fry et al, 1962; MacNeil and Buss, 1968; MacNeil, 1969). These studies utilized lines of turkeys that had rates of BW gain and breast muscle development very different from contemporary, rapidly growing turkeys. Nestor et al. (1987) reported on selected bone and muscle comparisons between a line selected
'Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Manuscript Number 23-91.
for increased BW (F line) and its unselected, randombred control population (RBC2). There was a decrease in the relative weight of the thigh and drumstick in the F line compared with the RBC2, but the differences were evident only at later ages. The ubiotarsus and femur (percentage of BW) were also heavier in the RBC2 line at 20 wk but not at 16 wk At the latter age, leg problems are usually apparent in rapidly growing turkeys. Food products derived from turkey breast meat have gained considerable consumer acceptance, and, therefore, modern commercial turkeys have been developed for both rapid BW gain and maximal breast muscle yield. Nestor et al. (1988) compared carcass traits of turkeys from F and RBC2 lines with those of a commercial sire line (C line). There was no difference in BW between the F and C lines, but total breast muscle percentage was significantly greater in the C line. Selection for BW alone (F versus RBC2) did not influence percentage breast yield. The relative leg muscle weight was greater in the F and RBC2 lines than the C line. This was also reflected in increased weights of total leg bones (shank, femur, tibiotarsus) in the experimental (or selected and randombred) lines. Selection for BW alone (F versus RBC2) reduced the relative weight of total leg bones.
2223
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ABSTRACT Body weight and carcass component weights of turkeys from a growth-selected line (F), a randombred control population (RBC2), and a commercial sire line (C) were compared at hatch, 4,8,12, and 16 wk of age. At natch there were no significant differences in BW between the F and RBC2 lines, but the C line poults weighed significantly less than the F line poults. Total Pectoralis muscle weight of the F line was larger than for Lines C and RBC2 at hatch, but there were no line differences in drum weight or length. The F line was still heavier than the other lines at 4, 8, and 12 wk, but the absolute and relative weights of the Pectoralis major (P. major) muscle were larger in the C line than the other lines at all ages. Selection for BW increased the weight of the P. major in the F line compared with the RBC2, but differences in the relative weight of the muscle were not consistent. The large line differences for the absolute and relative weight of the P. major were not observed for the Pectoralis minor. At all ages, the lengths of the tibia and femur were greater in the F line than the other lines. At 4 and 8 wk, bone length in the C line was greater than the RBC2,but at 12 and 16 wk there were no significant differences between these lines. The fast-growing F and C lines had more abdominal fat than the RBC2 at 16 wk of age. (Key words: turkeys, selection, body weight, bone length, muscle growth)
2224
LILBURN AND NESTOR
The aforementioned comparisons of selected, randombred, and commercial turkeys were made at an age (16 wk) when line differences would be assumed to be maximal. It is important, however, to know at approximately what ages these carcass changes are occurring, particularly when trying to understand the relative effects that selection for BW alone (F line) or in combination with breast muscle yield (C line) have on overall growth and development of turkeys. The objective of the present study was to compare carcass traits of F, RBC2, and C line turkeys at different ages from hatch through 16 wk of age.
Male and female poults from the F, RBC2, and C lines were hatched at 2-wk intervals. The ages of the parental breeders were the same. The details of the selection protocol used to develop and maintain the F line and RBC2 lines were described by Nestor et al. (1985). Each poult was wing-banded at hatch and poults within a hatch were reared with sexes intermingled. At young ages, the RBC2 poults grew noticeably slower than the faster growing lines, so each line was reared in separate but adjoining pens. There was approximately .3 m 2 (3 ft2) per bird at the start of the study, and for the duration of the experiment the birds were fed a turkey starter diet (Table 1). The birds were fed the starter diet to maximize genetic differences in growth and muscle protein accretion. Fifteen poults from each line were selected at 0 (hatch), 4, 8, 12, and 16 wk of age for carcass comparisons. Within an age, all line and carcass comparisons were made on poults that were randomly chosen from the same hatch. Birds were weighed, killed by cervical dislocation, and sexed by gonadal examination. For the 0 wk (hatch) comparisons, the entire Pectoralis major (P. major) breast muscle, the weight of the tibia plus associated muscles (total tibia), and the length of the tibia were recorded. At subsequent sample ages the right half of Pectoralis minor (P. minor) as well as the P. major was individually dissected out and weighed. The weight of the two halfmuscles was doubled for calculation of total muscle weights. The length of the femur and tibia, the weight of these parts plus associated muscles (total femur, total tibia), the weight of the Gastrocnemius muscle, and abdominal fat content were all recorded at older ages.
Ingredients
Composition
Corn Soybean meal (44% CP) Fish meal (60% CP) Meat meal (50% CP) Animal-vegetable fat Salt Ground limestone Dicalcium phosphate (18.5%) Premix1'2'3
(kg/100 kg) 40.00 42.50 6.50 5.00 2.15 .40 .80 .65 2.00
'The premix contributed the following per 100 kg of feed: ground corn, 422 g; choline chloride (60%), 100 g; amprolium (25%), 22.7 g; selenium premix (200 mg/kg Se), 45.4 g; DL-methionine (99%), 45.4 g; trace mineral premix, 45.4 g; vitamin premix, 227 g. 2 The vitamin premix contributed the following per kilogram of diet: vitamin A, 8,745 IU; vitamin D, 3,745 IU; vitamin E, 60 U; vitamin K (menadione sodium bisulfite), 2.91 mg; thiamine HC1, 2.2 mg; riboflavin, 6.6 mg; niacin, 99 mg; pantothenic acid, 15.4 mg; folic acid, 1.2 mg; pyridoxine, 2.2 mg; biotin, 165 mg; vitamin Bj2, 15 mg; ethoxyquin, 113.5 mg. The trace mineral premix contributed the following per kilogram of diet zinc oxide (72% Zn), 147 mg; manganous oxide (55% Mn), 152 mg; copper sulfate (25.2% Cu), 35 mg; ferrous sulfate monohydrate (31% Fe), 72 mg; potassium iodide, 1.5 mg.
Statistical Analysis All data were analyzed by analysis of variance using the General Linear Model (GLM) program of SAS® (SAS Institute, 1985). Data were analyzed within an age period with line, sex, and the line by sex interaction as main effects tested. Data are reported as the least squares means estimates for each parameter within an age. Where significant main effects occurred, the means were separated by Duncan's new multiple range test (Steel and Torrie, 1960). RESULTS
At hatch, there were no differences in BW between the F line and RBC2 poults but C line poults were lighter than poults of the F line (Table 2). The weight of the P. major was greater in the F line compared with the other two lines. There were no line differences in total tibia weight or tibia length. The F line was still heavier than the C line at 4 wk of age (Table 3). The BW and the absolute weight of all carcass parts were smaller for the RBC2 poults than the F or C line poults (Tables 3 to
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MATERIALS AND METHODS
TABLE 1. Composition of starter diet (selection diet)
2225
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS TABLE 2. Line differences in carcass components of turkeys at hatch
Line
Body weight
Pectoralis major weight
Tibia weight
Tibia length
C F RBC2
47.7b 56.3 a 52. Vab
(g) .610b .882a .652b
1.98 2.08 1.95
(cm) 4.02 4.04 3.88
a,b
Least squares means within a column with no common superscripts are significantly different (P<05). ' c = commercial sire line; F = line selected for increased 16-wk BW; RBC2 = randombred control line. ^ e weight of the total muscle from both sides of the keel.
relative weight of this muscle. Males had greater BW and individual breast muscle weight, but the relative size of both breast muscles was similar in males and females. The absolute weights of the total femur, total tibia, and Gastrocnemius muscle were lower in the RBC2 poults (Table 5). The weight of these parts in the F line was greater than the C line. The same line differences (F > C > RBC2) occurred for the relative weight of the total femur but were slightly different for the total tibia, for which the RBC2 was intermediate to the two selected lines. Line differences in the length of the femur and tibia followed the same pattern as absolute weight of the femur (Table 6). Males had significantly longer and heavier leg parts, but the relative weights of the total femur and total tibia were similar in
TABLE 3. Line differences in total body weight and body weight less the weight of the Pectoralis major
Body weight1 Variable Line3 C F RBC2 Sex Male Female
4 wk
8 wk 2
12 wk
16 wk 2
8 wk
Body weight - Pectoralis major weight 12 wk 16 wk
y&>
l,082 b (10/5) U16a (9/6) 676° (9/6)
3,837 (10/6) 4,090 (12/3) 2,463 (6/9)
6,472b (7/8) 7,067a (13/3) 4,209° (6/10)
9,448 (6/10) 9,194 (10/6) 5,714 (10/6)
l,032 a 950 b
3,865 3,061
6,620* 5,212b
9,271 6,967
3,187b
5,252b
7,441 b
3,533a
6,029"
7,647a
2,122°
3,629°
4,866°
3,292a 2,603b
5,58 l a 4,358b
7,626a 5,677b
a_ °Least squares means within a column and variable with no common superscripts are significantly different (P<05). (no. of males/no. of females). There was a significant line by sex interaction (P<05). 3
C = commercial sire line; F = line selected for increased 16-wk BW; RBC2 = randombred control line.
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5). The absolute weights of the P. major and P. minor muscles were similar in the F and C lines, but relative to BW, they were larger in the C line (Table 4). The weight of the total tibia, the length of the tibia, and the weight of the Gastrocnemius muscle were all greater in the F line (Tables 5 and 6). Males were significantly heavier than the females. At 8 wk, both the absolute and relative weights of the P. major muscle were greater in the C line than for Lines F and RBC2 (Table 4). There was no difference in the relative weight of the P. major of the F and RBC2, but these lines differed in the absolute weight of the muscle. The absolute weight of the P. minor muscle was similar in the C and F lines and heavier than in the RBC2 poults. There were no line differences, however, in the
18.87* 14.64b 13.87b
15.43 16.16
14.74 14.82
10.73 11.06
1,038* 854 b
16.97* 13.57b 13.81°
573.6* 458.6b
113.1 106.3
1,221* l,038 b 580°
12 wk
Pectoralis major
12.15* 10.66b 9.87°
649.8* 557.4b 341.0°
8 wk
131.9* 129.9* 67.3 b
4 wk
17.29 17.99
21.37* 16.80b 14.74°
1,644* U90b
2,007* l,546 b 848°
16 wk
2.91 2.98
3.18* 2.88b 2.78b
30.6 28.3
34.6* 34.9* 18.8b
4 wk
4.502 3.84 4.18 4.26 4.14
3.81 3.97
284 211
73.5* 61.1 b (% BW) 4.05 3.75 3.88
296 274 176
12 wk1
Pectoralis minor
77.5* 76.5* 47.9 b
— (g)
8 wk
*~°Least squares means within a column and variable with no common superscripts are significantly different (P<05). 'There was a significant line by sex interaction (P<05). 2 C = commercial sire line; F = line selected for increased 16-wk BW; RBC2 = randombred control line.
Line C F RBC2 Sex Male Female
Line2 C F RBC2 Sex Male Female
Variable
TABLE 4. Line differences in breast muscle and abdominal fat
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16 wk
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS
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2228
LELBTJRN AND NESTOR TABLE 6. Line differences in the length of the femur and tibia Tibia length
Femur length Variable
wk
12 wk
16 wk
4 wk
8 wk
12 wk
16 wk
(cm) Line
c
F RBC2 Sex Male Female
10.8" 11.5a 9.9°
n.9° 13.1a 11.8b
12.6" 13.5a 12.3b
10.1" 10.6a 8.8C
16.0° 16.9a 15. l c
18.2" 19.5a 18.1 b
19.6° 20.1 a 19.5b
11.2a 10.2b
13.1a 11.5b
13.9a 11.7b
9.9 9.7
16.6a 15.3b
19.9a 17.3 b
21.5a 17.9b
Least squares means within a column and variable with no common superscripts are significantly different (<.05). C = commercial sire line; F = line selected for increased 16-wk BW; RBC2 randombred control line.
resulting in a significant line by sex interaction (Table 7). The lengths of the femur and tibia were similar in C line and RBC2 birds, but both bones were longer in the F line (Table 6). Line differences in both the absolute and relative weight of the Gastrocnemius muscle were the same as those observed for the absolute and relative total tibia weight, respectively (Table 5). At 16 wk of age, the C line was significantly heavier and both the absolute and relative weights of the P. major muscles were greater than those of the F line (Tables 3 and 4). When BW was compared without the P. major weight, however, the F line was heavier than the C line. The F line had larger BW and absolute and relative weights of the P. major muscle than the RBC2 birds. The absolute weight of the P. minor was similar in the F and C lines, both of which were greater than that of the RBC2 line, but there were no differences between lines in the relative weight of this muscle (Table 4). The two faster growing lines also had more abdominal fat than the RBC2 line. Across lines, the weight of the P. major and P. minor breast muscles, males were heavier than females, but the relative weights were similar between sexes. The absolute weight of the femur was greater in the F line compared with the C and RBC2 lines but the relative weight of the femur was greatest for the RBC2 line (Table 5). There was also a line by sex interaction in femur weight because of the greater sex difference in the C line compared with the other lines (Table 7). The length of the femur and tibia was similar in the RBC2 and C lines but these bones were shorter in both lines than in the F line (Table 6). Line differences in the absolute
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males and females. There was a significant sex by line interaction for BW and femur weight, which was due to the greater sex difference for these traits in the F and RBC2 lines uian for the C line (Table 7). The relative weight of the Gastrocnemius muscles was greater in C line males compared with females but this was reversed in the F and RBC2 lines (Table 5). Relative tibia weight was similar in males and females of the RBC2 line but males had larger tibia weights in the C line and females had larger tibia weights in the F line. Line differences in BW and the weights of the P. major and P. minor muscles were similar, with one exception, at 12 wk as they were at 8 wk (Tables 3 and 4). The only line difference not evident at 8 wk was the relative weight of the P. minor, which was smaller in the F line than the other two lines, whereas at 8 wk it was similar across all three lines. There were line by sex interactions for both the absolute and relative weights of the P. minor muscle (Table 7). This was due to the disproportionately larger weight of this muscle in the F line males compared with the smaller differences between sexes in the C and RBC2 lines. The F and C lines had more abdominal fat both on an absolute and relative basis than the slower growing RBC2 line (Table 4). The absolute weights of the total femur and total tibia were smaller in the RBC2 line (Table 5). The relative weight of these parts, however, was similar to (femur) or greater than (tibia) the F line and both weights were greater than for the C line. The absolute and relative weights of both the femur and tibia were greater in the F line compared with the C line. The sex difference in thigh weight of the F line was considerably less than in the other lines
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS
I "*
2229
weight of the total tibia were similar to those observed for the femur (Table 5). The relative tibia weight was significantly less in the C line than in the other two lines. The weight of the Gastrocnemius muscle followed the same pattern as observed for the total tibia.
-HI
DISCUSSION
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Although there were few line differences at hatch, many of the line differences observed at later ages were already apparent by 4 wk of age. The divergence observed in development from 0 to 4 wk, particularly in the RBC2 and C lines, which had similar BW and pectoral muscle weights at hatch, emphasizes the overall effects that selection for growth and carcass measures at later ages can have on early growth and differentiation. Body weight of the C line was smaller than the F line until 16 wk, but by 4 wk of age the absolute weights of the P. major and P. minor were similar in both lines but the relative weights of these muscles were greater in the C line. Compared with the RBC2 line, the F line showed an increase in the relative weight of the P. major muscle at 4 and 16 wk (selection age). This supports suggestions in the literature (Johnson and Asmundson, 1957a) that because of the high positive correlation between pectoral weight and BW, genetic gains in the former can be made through simple emphasis on BW selection. This is supported by one report (Nestor et ah, 1987) in which the F line had increased percentage breast muscle weight at 16 wk compared with the RBC2 line, but is contrary to a later study in which there were no line differences (Nestor et ah, 1988). In the latter study, the comparisons were made over two generations and the percentage breast muscle weights were considerably lower than those reported by Nestor et al. (1987). They were also low compared with die sum of the P. major and P. minor percentages reported here. This suggests that environmental influences on growth and development should be considered when comparisons are made across experiments or generations of selection. The large difference between the relative weight of the P. major muscle in the C line and the F line supports the results of Nestor et al. (1988) and suggests that dual selection for BW and some indices of breast development would result in maximal breast yield. Selection for breast muscle development would also appear to have a singular effect on P. major weight, as the F
2230
IILBURN AND NESTOR
associated with increased length of long bones (Asmundson, 1948; Lasley, 1949). At 12 and 16 wk, however, the lengths of the femur and tibia were similar in the RBC2 and C lines, and at the latter age there were only marginal overall line differences (P<.088) in the length of the tibia. Nestor et al. (1988) reported that the length of the shank (tarsometatarsus) was significantly greater in the F line compared with the RBC2, but the approximately 4% difference (14.8 versus 14.2 cm) at 16 wk was considerably less than the 15 to 17% difference in bone density and 23% difference in defatted bone weight. The combined data from Nestor et al. (1988) and the current study demonstrate that in response to genetic increases in BW and carcass development, there has been some skeletal compensation (i.e., increased bone density and bone weight) without great changes in bone length. These responses have been far less, however, than the 30 to 40% changes observed in the absolute weights of the muscles associated with the breast and leg. The increased incidence of leg problems observed in commercial, fast-growing turkeys probably results, therefore, from a combination of developmental stresses associated with rapid growth and changes in the architectural relationships between muscle and bone. ACKNOWLEDGMENTS
The authors wish to thank Laurel Newman and Wanda Acord for their help in the preparation and handling of the manuscript. REFERENCES Asmundson, V. S., 1948. Inherited differences in weight and conformation of Bronze turkeys. Poultry Sci. 27: 695-708. El-Ibiary, H. M., 1948. Body conformation in turkeys. Poultry Sci. 27:825-826. Fry, J. L„ O. S. Rao, and L. D. Rasplicka, 1962. Factors affecting the yield of turkey parts. Poultry Sci. 41: 1299-1303. Jaap, R. G., 1938. Body conformation of the live market turkey. Poultry Sci. 17:120-125. Johnson, A. S., and V. S. Asmundson, 1957a. Genetic and environmental factors affecting size of body weight and body parts of turkeys. 2. The relation of body weight and certain body measurements to pectoral and tibial muscle weights. Poultry Sci. 36:959-966. Johnson, A. S., and V. S. Asmundson, 1957b. Genetic and environmental factors affecting size of body and body parts of turkeys. 1. The heritability and interrelationships of body size and live body measurements. Poultry Sci. 36:296-301. Lasley, E. L., 1949. A comparison of skeletal and fleshing
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line was still heavier when BW are compared independent of this muscle weight. The large differences in the relative weight of the P. major muscle were not associated with similar differences in the P. minor muscle. There were no line differences at 16 wk and even at the younger ages there were no consistent differences between lines. Johnson and Asmundson (1957a) reported that the heritability for each muscle was similar and that the correlation between each pectoral muscle and BW was high. The correlation between individual muscle weights at 24 wk, however, was not as great as expected. The data from the present experiment suggest that genetic gains in breast yield associated with selection for increased BW or selection for breast conformation or both have primarily influenced the development of the P. major muscle. The P. minor muscle lies along the keel and has little room to expand. The disproportionate development of the P. major compared with the P. minor muscle may also contribute to the increased prevalence of deep pectoral myopathy (green muscle disease), a result of focalized ischemia and subsequent necrosis within the P. minor (Siller, 1985). The consistent negative association between the relative weights of total femur and total tibia and breast yield supports previous studies in which body conformational patterns in turkeys have been reported. Jaap (1938) reported that better fleshing was associated with shorter shanks and thighs. El-Ibiary (1948) reported that in turkeys of similar BW, narrower breasted birds had longer shanks than those with wider breasts. MacNeil (1969) compared males from numerous broadbreasted Bronze and White strains and found that although eviscerated carcass weights were similar, there was a negative relationship between thigh and skinless breast portions. Nestor et al. (1988) reported line differences in the relative weight of drumstick muscles and the Gastrocnemius data from the current experiment are in support of those observations. The differences in the absolute weight of the femur and tibia were not always associated with significant differences in the length of the femur and tibia. Selection for BW in Line F resulted in a significant increase in the length of the long bones at early ages compared with the RBC2 population. This agrees with observations in the literature, in which heavier BW has been
CARCASS GROWTH OF SELECTED AND RANDOMBRED TURKEYS development in three types of domestic turkeys. North Dakota Agriculture Experiment Station Bulletin 335:1-50. MacNeil, J. H., 1969. Yield characteristics and relationships to body measurements of commercial strains of turkeys. Poultry Sci. 48:1598-1603. MacNeil, J. H., and E. G. Buss, 1968. Skin and meat yields of turkeys as influenced by strain. Poultry Sci. 47:1566-1570. Marsden, S. J., 1940. Weights and measurements of parts and organs of turkeys. Poultry Sci. 19:23-28. Nestor, K. E., W. L. Bacon, G. B. Havenstein, Y. M. Saif, and P. A. Renner, 1988. Carcass traits of turkeys from lines selected for increased growth rate or increased shank width. Poultry Sci. 67:1660-1667. Nestor, K. E., W. L. Bacon, P. D. Moorhead, Y. M. Saif,
2231
G. B. Havenstein, and P. A. Renner, 1987. Comparison of bone and muscle growth in turkey lines selected for increased body weight and increased shank width. Poultry Sci. 66:1421-1428. Nestor, K. E„ W. L. Bacon, Y. M. Saif, and P. A. Renner, 1985. The influence of genetic increases in shank width on body weight, walking ability, and reproduction of turkeys. Poultry Sci. 64:2248-2255. SAS Institute, 1985. SAS® User's Guide: Statistics, Version 5 Edition. SAS Institute Inc., Cary, NC. Siller, W. G., 1985. Deep pectoral myopathy: A penalty of successful selection for muscle growth. Poultry Sci. 64:1591-1595. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw Hill Book Co., New York, NY.
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