- Email: [email protected]
Carcass Traits of Turkeys from Lines Selected for Increased Growth Rate or Increased Shank Width1
Carcass Traits of Turkeys from Lines Selected for Increased Growth Rate or Increased Shank Width 1 KARL E. NESTOR, WAYNE L. BACON, GERALD B. HAVENSTEIN, Y. MOHAMED SAIF, and PHILIP A. RENNER Department of Poultry Science, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 (Received for publication March 25, 1988)
1988 Poultry Science 67:1660-1667 INTRODUCTION
Direct selection for increased amount of breast muscles and total BW has increased both at a faster rate than the rate of increases in leg muscles (Marsden, 1940; Miller, 1968; Clayton etal., 1978; Nestor etal., 1987). Similarly, the relative amount of leg muscles declines with age as birds get heavier, particularly for males of large-bodied lines (Harshaw and Rector, 1940; Peng et al, 1985; Nestor et al, 1987). For females, Larsen etal. (1986) found that although the total weight (bone and muscle) of the drumstick increased with age, weight of the drumstick expressed as a percentage of BW decreased. Weight of thigh muscles increased greatly with age, but calculated as a percentage of BW, only a small increase occurred. Relative weight of the skeleton also declines with age (Clayton et al., 1978; Bacon et al., 1986; Nestor
'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 57-88.
etal., 1987). Nestor et al. (1985) hypothesized that selection in commercial turkeys for increased BW has been accompanied by a biologically incompatible reduction in relative leg support (leg muscles and leg bones), which is probably magnifying the severity of leg problems. To test this hypothesis, a subline (FL) of a long-term growth-selected line (F) was initiated by selecting only for increased width of the shank at the narrowest point (dewclaw). A previous report (Nestor, 1984) had shown that weight increases in Line F were associated with an increase in leg problems. Increases in shank width of Line FL resulted in significantly improved walking ability of males at 16 wk of age in comparison with ability of males in Line F, even though BW of males from the F and FL lines were similar through five generations (Nestor et al., 1985). Selection for shank width in the FL line was used in an attempt to increase the relative amount of leg bones. Nestor et al. (1987) compared the bone and muscle development in Lines F and FL and in a randombred control population (Line
1660
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
ABSTRACT Carcass composition of turkeys from a long-term growth-selected line (F), a subline (FL) of F selected only for increased shank width, and a randombred control population (RBC2) that served as the base population for F, were compared. Birds of both sexes were killed at 16 wk of age in the fifth and sixth generations in Line FL. A commercial sire line (C) was also included in the sixth generation. Body weight increased at comparable rates in F and FL males through the 5th generation of selection in Line FL, but the BW of FL males was significantly smaller than that observed in F males in the 6th generation. Body weights of FL females were significantly lower than BW of F females in both the 5th and 6th generations, resulting in a significant line x sex interaction. A similar interaction was also observed in both generations in the actual weight of most leg bones, leg muscles, and breast muscles. When expressed as a percentage of live BW, most of the latter line x sex interactions were not significant. Genetic increases in shank width of the FL line were associated with increases in the relative weight of all leg bones measured and drumstick muscles. This may have contributed to the improved walking ability consistently observed in FL males relative to that of F males. In general, genetic increases in BW in Line F were associated with a decreased amount of relative support (leg muscles and leg bones) in comparison with that observed in Line RBC2. These results support the hypothesis that a portion of the leg problems observed in large-bodied turkeys are attributable to an inherent weakness of body support structures resulting from the slower growth of these structures relative to that of total BW. (Key words: body weight, leg bones, leg muscles, leg weakness, turkeys)
1661
CARCASS TRAITS OF TURKEYS
RBC2, the base population of Line F) at 8, 16, and 20 wk of age. This comparison was made in the fourth generation of selection in Line FL. Weights of leg muscles were not significantly different in F and FL lines. Selection for increased shank width in Line FL did not increase the weights of tibiotarasal and femur bones relative to those of the F line. The tarsometatarsal bone was not measured. The purpose of the study reported herein was to make further comparisons of the F, FL, and RBC2 lines in two additional generations and to compare these lines with a commercial sire line (C). MATERIALS AND METHODS
RESULTS
Fifth Generation Comparisons. Sex differences were evident in most of the traits (Tables
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
Details of the origin and maintenance of the F, FL, and RBC2 lines were presented in Nestor et al. (1985). In the F line, individuals of both sexes were mass selected for increased 16-wk BW. The FL line was a subline of Line F started in Generation 13 and was formed by selecting both sexes on an individual basis only for increased shank width at 16 wk of age. Individuals of the RBC2 line were randomly selected to reproduce the line. All lines were maintained with a paired mating system (Nestor, 1977) involving 36 parental pairs. In the fifth generation of selection of Line FL, a comparison was made of the F, FL, and RBC2 lines at 16 wk of age. An additional line, (C), was included in the comparison during the sixth generation of Line FL, also at 16 wk of age. Offspring from a single hatch representing a 2-wk collection of eggs were used in both generations. Sexes and lines were grown intermingled in a windowless growing house. Continuous lighting was used for the first 4 wk after hatching; thereafter, 12 h light/day were provided. Both sexes were provided a four-ration feeding system with declining protein (Naber and Touchburn, 1970) based on requirements for males. Fifth Generation Comparisons. Line comparisons included the F (18th generation), the FL (5th generation), and RBC2 lines. Birds were weighed and the shank width measured in the afternoons prior to the day of killing. After an overnight fast, birds were killed by severing the jugular vein, scalded for about 30 s at 68 C, and picked. Carcasses were sawed in half longitudinally and one-half of the carcass was frozen for later dissection. After thawing, legs were removed from the carcass and separated into shanks, drumsticks, and thighs. The tarsometatarsal bone and associated tissues were separated from digits and
the remainder of the leg and weighed. The drumstick and thigh were separated by a cut through the knee joint (femuro-tibial and patellar joint). Drumstick and thigh muscles were carefully dissected from the bones and the weights of the muscles and bones were obtained. Breast muscles were removed from the breast bone and weighed. The shank was boiled for 15 min and the tarsometatarsal bone was cleaned of adhering tissue and weighed. Fat was then extracted with a methanol-chloroform mixture (1:2, vol/vol) and bones were oven dried for 24 h at 100 C, weighed, and the length measured. Density of the tarsometatarsus was measured at 40 and 60% of the length (proximal to distal end) using photoabsorption with an I125 source (Cantor et al, 1980). All birds were killed regardless of their walking ability. Two days were required to kill and process the birds. Half of the birds in each line was killed each day. Sixth Generation Comparisons. Birds were processed in a manner similar to that used for the previous generation except that 4 days were required to kill the birds, only the wet weights of the shank, tibiotarsal, and femur bones were obtained, and an additional line, C, was involved in the comparison. Thus, the line comparisons included F (19th generation), FL (6th generation), RBC2, and C lines. Ages of parents for Lines F, FL, and RBC2 were the same but the age of parents of Line C was unknown. A sample of hatching eggs for Line C was obtained from a primary breeder and the eggs were dipped and individually injected with an antibiotic solution (Saif and Nestor, 1983) to assure that the offspring would be free of Mycoplasma meleagridis infection. Mycoplasma meleagridis was previously eradicated from the F, FL, and RBC2 lines (Nestor, 1984). Statistical Analysis. The least squares and maximum likelihood computer program of Harvey (1977) was used for analysis of the data. Separate analyses were made for the fifth and sixth generation comparisons. Main effects were lines, sexes, and day of kill. The significance of two-way interaction among the main effects was estimated. Three-way interactions were included in the error term. Tukey's test was used to compare means where appropriate (Steel and Torrie, 1960).
NESTOR ET AL.
1662
from weights of muscles being equal to or slightly higher in FL than in F line males, whereas muscle weights were lower in FL than in F females. No significant differences were present between weights of breast and thigh muscles relative to BW for Lines F and FL (Table 1). Percentages of breast and thigh muscles were higher in Lines F and FL than in the RBC2 line. Percentages of drumstick muscles and total leg muscles were larger in Line FL than in Line F. The percentage of drumstick muscle of the RBC2 line was intermediate between those of Lines F and FL, whereas percentages of total leg muscles were similar in F and RBC2 lines. Most of the interactions between line and sex disappeared when muscle weights were adjusted for BW. Only one significant interaction (thigh muscles) between line and sex remained. In this case, there was a significant sex difference in the F line whereas no such difference existed in the FL or RBC2 lines. Shank width and shank weight were greater in Line FL than in Line F (Table 2). Lines F and FL were not significantly different in
TABLE 1. Influence (least squares means) of line, sex, and line X sex interaction on body weight and the weight of the breast and leg muscles expressed as actual weight and as a percentage of live body weight (fifth generation comparison)1
Variable
Line2 RBC2 F FL Sex 3 Male (M) Female (F) Line X Sex RBC2 X M RBC2 X F FXM FX F FLX M FLX F
Drumstick muscles
Birds
Live weight
(n)
(kg)
(g)
<%)
(g)
(%)
(g)
108 75 83
5.99 c 8.82 a 8.45 b
513c 775 a 734b
17.0 b 17.5 a 17.3 a
297 b 441a 433 a
9.9h 10.0 a b 10.2 a
233b 334 a 336 a
184 196
9.13 6.81
811 593
17.8 17.5
454 352
9.9 10.3
347 269
53 55 39 36 36 47
6.92 c 5.06 d 9.88 a 7.76 b 9.84 a 7.07 c
596 c 429 d 881a 668b 863 a 605 c
344 c 251d 475 a 407b 503 a 363 e
9 pab 9 pab 9.6 b 10.5 a 10.2 a b 10.3ab
262 c 203 d 371 a 298 b 384 a 288 b
Breast muscles
Thigh muscles
Total leg muscles
(%)
(g)
<%)
ab 7.58 b 7.98 a
530 b 775 a 770 a
17.7 b 17.6 b 18.2 a
7.62 7.94
801 621
17.5 18.2
782
606 c 45 5 d 846 a 704 b 888 a 651c
a—d Least squares means within line or line X sex subgroup for a trait with no common superscripts are significantly (P<.05) different. 'Weight of muscles was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control population; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width. 3 All differences between sexes, except for percentage breast muscles, were highly significant (P<.01). The difference in percentage breast muscles was significant (P<.05).
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
1, 2, and 3). Actual weights of the breast, leg muscles, and leg bones were larger in males than in females. As a percentage of live weight, the amount of breast muscles was larger in males but the amount of leg muscles was larger in females. Leg bone weights expressed as a percentage of BW were larger in males than in females. Birds in the F line were significantly heavier than those in the FL line at 16 wk of age, but the analyses showed a highly significant line x sex interaction (Table 1). When only males were compared, the difference between BW in Lines F and FL was not significant, but F females were heavier than FL females. Body weights of F and FL lines were much greater than those of the RBC2 line. Actual weights of breast and leg muscles were heavier in Lines F and FL than in the RBC2 line (Table 1). When sexes were combined, F and FL lines were not significantly different in leg muscle weights. Highly significant interactions between line and sex were found for weights of the breast, thigh, drumstick, and total leg muscles. Most of the interactions resulted
1663
CARCASS TRAITS OF TURKEYS
TABLE 2. Influence (least squares means) of line, sex, and line X sex interaction on shank width and the weights of the shank, tibiotarsal, and femur bones expressed as actual weights or as a percentage of live weight (fifth generation comparison)1
Variable
Shank width
(n)
(mm)
108 75 83
11.88 c 14.02 b 15.04 a
184 196 53 55 39 36 36 47
Tibiotarsal bone
Shank
Total leg bo nes
Femur
(%)
(g)
(%)
(g)
(%)
(g)
(%)
56.8 C 81.lb 86.0 a
1.90b 1.81 c 2.00 a
75.6 b 105.9 a 105.5 a
2.48 a 2.36 b 2.45 a
48.5 b 67.3 a 68.0 a
1.60a 1.50b 1.59 a
182 b 254 a 259 a
5.98 a 5.68 b 6.04 a
14.65 12.71
95.9 56.0
2.11 1.65
123.5 71.4
2.65 2.11
79.0 46.2
1.73 1.37
298 174
6.56 5.13
12.70 e 11.05 f 14.85 b 13.18 d 16.23 a 13.84 e
73.2 C 42.3 e 100.9 b 61.3 d 109.2 a 62.8 d
(g)
95.7 b 55.3 d 132.9 a 78.9 C 134.8 a 76.2 C
60.8 b 36.2 d 84.6 a 50.0 C 86.0 a 50.0 C
220 b 134 d 318 a 190 c 329 a 188 c
Least squares means within line or line X sex subgroup for a trait with no common superscripts are significantly (P<.05) different. 'Weight of muscles was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control population; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width. 3
A11 differences between sexes were highly significant (P<.01).
amounts of actual weight of tibiotarsal, femur, or total leg bones. Relative to BW, weights of the shank, tibiotarsal, femur, and total leg bones were greater in Line FL than in Line F. Actual weights of all leg bones were lighter in the RBC2 line than in the two heavy lines. On a relative basis, weights of the tibiotarsal, femur, and total leg bones were not significantly different in birds of the FL and RBC2 lines, but shank weights were larger in Line FL birds than in birds in the RBC2 line. Relative weight of the leg bones was greater in RBC2 line birds than in F line birds. Weight of the tarsometatarsal bone, after boiling and cleaning, was larger in Line FL birds than in Line F birds on an actual and on a percentage basis (Table 3). In actual weight, the tarsometatarsal bone was larger in Line F birds than in the RBC2 line birds, but the reverse was true on a percentage basis. The FL and RBC2 lines did not differ in relative weight of cleaned tarsometatarsal bones. Line differences in tarsometatarsal weight after defatting and drying were similar to those of the cleaned weights. Relative weight of the defatted tarsometatarsal
bone was greater in the RBC2 line than in Line FL, and the Line FL weight was larger than that in Line F. Lengths of the tarsometatarsal bone were similar in the F and FL lines, and both lines had longer bones than the RBC2 line. Densities of the defatted tarsometatarsal bone were similar in Lines F and FL when measured at 40 and 60% of its length. Both of the large-bodied lines had greater bone density than the RBC2 line. Highly significant line x sex interactions were present for cleaned, defatted, and dried weights of the tarsometatarsus. These interactions resulted from males of the FL line having greater weights than males of the F line, whereas none of the differences for females were significant. Interactions were not significant when cleaned, defatted, and dry weights of the tarsometatarsus were adjusted for BW differences. There was a significant line x sex interaction for density of the bone at 40% of its length, because density of bones from FL males was significantly higher than density of bones from F males. This difference did not exist in females. Line X sex interactions were not significant
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
Line 2 RBC2 F FL Sex 3 Male (M) Female (F) Line X Sex RBC2 X M RBC2 X F FX M F XF FL X M FLX F
Birds
NESTOR ET AL.
1664
TABLE 3. Influence (least squares means) of line and sex on weight, length, and density of the tarsometatarsal hones (fifth generation comparison)
Tarsomeitatarsal weight1 After cleaning
Variable
Line 3 RBC2 F FL Sex4 Male Female
After defatting
Tarsometatarsal length
Tarsometatarsal density 2 40%
60%
(g)
(%)
(g)
(%)
(cm)
21.8 C 29.0 b 31.5*
.718* .646 b .730*
11.4 C 14.8 b 15.2*
.376* .330 c .354 b
14.2 b 14.8* 14.8*
30.8 b 36.1* 36.9*
35.5 b 42.0* 41.4*
35.5 19.5
.782 .578
17.4 10.3
.384 .306
16.1 13.1
39.1 30.3
44.2 35.4
Line means with no common superscripts within traits are significantly (P<.05) different. Percentage was based on live body weight. Actual weights were measured on one-half of each carcass. These values were multiplied by two prior to calculating percentage. 2 Relative bone mineral mass (Cantor et al., 1980) measured at 40 and 60% of length when measured proximal to distal. 3 RBC2 = Randombred control; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width.
"All sex differences were highly (P<.01) significant. There was a highly significant (P<.01) interaction of line X sex for weight of the tarsometatarsal after cleaning and after defatting and drying. There was a significant (P<.05) line X sex interaction for density at 40% of the bone.
when density measurements were made at 60% of the bones' length. Sixth Generation Comparison. With the exception of percentage of breast muscles, differences between sexes were similar in comparisons for the two generations (Tables 4 and 5). In the fifth generation (Table 1), males had higher percentages of breast muscles than females, whereas in the sixth generation, the difference between the sexes was not significant (Table 4). Body weights of both males and females of the FL line were lower than those of the F line in the sixth generation (Table 5). This is in contrast to the comparison in the fifth generation of Line FL (Table 1), where males of the two lines had similar BW. However, the highly significant line X sex interaction was still evident in BW, which resulted in similar interactions of actual weights of the breast muscles and weights of the shank, tibiotarsal, and total leg bones. The interaction of line x sex remained significant (P< .01) only for shank weight when adjustment was made for BW by expressing the values as a percentage of live weight. The latter interaction resulted from the difference between sexes being smaller in Line C than in the other lines
(Table 5). Two major differences in results were obtained in the comparisons of the F and FL lines in the sixth generation of Line FL (Tables 4 and 5) vs. the results obtained in the fifth generation of Line FL (Tables 1 and 2). In the first case, breast muscles, expressed as a percentage of BW, were significantly lower in weight in Line FL than in Line F in the sixth generation, whereas the difference between breast muscle percentages of lines in the fifth generation was not significant. Secondly, actual weights of the muscles of the legs were significantly lower in Line FL than in Line F birds in the sixth generation, but no significant differences were observed in the fifth generation. Differences between the F and RBC2 lines were essentially the same in the fifth and sixth generation except for percentages of breast and drumstick muscles, wherein magnitudes of the line differences were similar, but significances of the differences varied among comparisons. The commercial C line and Line F had similar BW but the lines differed greatly in body conformation (muscling) and in amounts of leg bones (Tables 4 and 5). Leg muscle weights, both as actual weight or as a percentage of BW, were
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
1
1665
CARCASS TRAITS OF TURKEYS
TABLE 4. Influence (least squares means) of line and sex on the actual weight and weight expressed as a percentage of live weight for breast, drumstick, and thigh muscles (sixth generation comparison)1
Variable
Line2 RBC2 F FL C Sex 3 Male Female
Drumstick m uscles
Thigh muscles
Breast muscles
Birds
Total[leg muscles
(n)
(g)
<%)
(g)
(%)
(g)
(%)
(g)
(%)
133 104 118 111
523 d 808 b 704 c l,033a
17.0 b 17.4 b 16.2 C 22.3 a
318 c 486 a 45 3 b 473ab
10.3 a b 10.5 a 10.5 a 10.2 b
241d 35 6 a 341b 329 c
7.89 a 7.71 b 7.91 a 7.13 c
559 d 841a 794 c 802 b
18.2 a 18.2 a 18.4 a 17.4 b
273 312
878 654
18.0 18.2
496 388
10.2 10.5
361 282
7.46 7.90
857 660
17.7 18.5
a—d Line means within traits with no common superscripts are significantly (P<.05) different. Weight of muscles was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width; C = commercial sire line. 1
TABLE 5. Influence (least squares means) of line, sex, and line X sex interaction on bod and weight of the shank, tibiotarsal, and femur bones expressed as actual weight or as a percentage of live weight (sixth generation comparison)'
Variable
Birds
BW
(n)
(kg)
Line 2 RBC2 133 F 104 118 FL C 111 Sex 3 273 Male (M) Female (F) 312 Line X Sex RBC2 X M 63 RBC2 X F 70 F X M 54 F XF 50 FL X M 56 FL X F 62 CX M 48 C XF 63
Tibiotarsal bone
Shank (g)
Total leg bo nes
Femur bone
(%)
(g)
(%)
(g)
(%)
(g)
(%)
6.16 c 9.27 a 8.67 b 9.27 a
61.3 d 86.5 b 88.5 a 72.2 C
1.96a 1.83 b 2.01 a 1.54c
86.7 C 120.7 a 120.0 a 101.8 b
2.77 a 2.55 b 2.72 a 2.16 c
57.7 b 72.6 a 72.2 a 59.9 b
1.82a 1.54b 1.63 ab 1.27c
206 c 280 a 281a 234 b
6.55 a 5.92 b 6.37 a 4.97 c
9.71 7.15
99.1 57.0
2.06 1.61
138.7 78.7
2.88 2.23
86.1 48.5
1.81 1.37
324 184
6.75 5.21
7.26 d 5.05 e 10.61 a 7.93 c 10.05 b 7.29 d 10.58 a 7.95 c
78.9 d 43.8 h 110.8 b 62. l f 112.4 a 64.5 e 90. l c 54.4g
2.18 a 1.74c 2.10 b 1.57 d 2.24 a 1.77c 1.71 c 1.37e
111.5 C 61.9 f 155.2 a 86.1d 152.0 a 88.1d 129.7 b 73.8 e
268 c 144 f 360 a 200 d 357 a 204 d 297 b 171 e
Means within traits and lines and line X sex subgroups with no common superscripts are significantly (P<.05) different. 1
Weight of bones was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control population; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width; C = commercial sire line. 3
All differences between sexes were highly significant (P<.01).
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
3 All differences between sexes except for percentage breast muscles were highly significant (P<.01). The difference between sexes for percentage breast muscles was not statistically significant.
NESTOR ET AL.
1666
less in Line C than in Line F. Line C had a larger amount of breast muscles than Line F when calculations were based on actual weight or weight relative to live BW. Shank and leg bones were lighter in Line C than in Line F. DISCUSSION
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
Selecting only for increased shank width in Line FL resulted in increases in BW of males comparable to those obtained by males of the F line (selected only for increased BW) for five generations of selection. However, in the sixth generation of selection in Line FL, BW of FL males were significantly lower than BW of F males. In the FL line females' BW did not change relative to those of Line RBC2, resulting in a significant line X sex interaction. Similar results were reported by Nestor et al. (1985, 1987). Nestor et al. (1985) suggested that the most likely cause of the interaction was that some genes that increase both shank width and BW are expressed only in males, resulting in the line x sex interaction. Males of the F, FL, and RBC2 lines were rated for walking ability at 16 wk of age in other samples of the lines in the fifth (Nestor et al., 1985) and sixth (unpublished data) generations of selection in Line FL. This rating was from 1 (good legs, good walking ability) to 5 (poor legs, near inability to walk). Based on these comparisons, males of the FL line had walking ability superior to that of birds in Line F. The differences (FL-F) were .41 and .53, respectively, in the fifth and sixth generations of selection. Both differences were highly significant. There has been no significant change in walking ability of Line FL birds relative to those in Line RBC2 with generation of selection. Thus, males of the FL line have had major increases in BW without a loss in walking ability. Selection in the FL line aimed to increase genetically the relative amount of leg bones to test the hypothesis proposed by Nestor et al. (1985). This hypothesis is 1) there appears to be a biologically incompatible combination in large-bodied turkeys of increased BW with relatively less support, and 2) the resulting inherent weight stress probably magnifies the effect of various causes of leg weakness. It has been well established that as total B W is increased by genetic selection or with age, a decline occurs in relative amounts of leg muscles (Marsden, 1940; Harshaw and Rector, 1940; Miller, 1968; Clayton et al., 1978; Peng et al, 1985; Nestor
et al., 1987) and leg bones and skeleton (Clayton et al, 1978; Bacon et al., 1986; Nestor et al., 1987). Selection for shank width in Line FL was effective in increasing the width of the shank. For males in the fifth (Nestor et ah, 1985) and sixth (unpublished data) generations of selection in Line FL, the percentage increases in shank width relative to those in Line F were 6.8 and 8.5, respectively. For females, respective increases were 4.7 and 7.1. Average percentage increases for both sexes in Line FL were 5.8 and 7.8, respectively, in Generations 5 and 6. Average percentage increases in shank weight (bone and associated tissues) of Line FL relative to Line F were 6.0 in the fifth generation (based on data in Table 2) and 2.3 in the sixth generation (based on data in Table 5). Percentage increases in Line FL over Line F in the fifth generation were 8.6 for the weight of the tarsometatarsal bone after boiling and cleaning and 2.7 for the weight of the tarsometatarsal bone after defatting and drying. The latter value indicates that selection for increased shank width in Line FL has increased calcification, because there were no differences between lengths of the tarsometatarsal bones in the F and FL lines. The 2.7% increase in dried defatted weight of the tarsometatarsal bone was less than the increase in shank width (6.8%) observed in the same generation, suggesting that most of the increase in weight was attributable to an increase in diameter of the bone, without increased calcification. When bone density, a measure of calcification (Cantor et al., 1980) was measured at two points (40 and 60% of the length) on the tarsometatarsus, line differences were not significant. This indicates that the small increases in calcification, as measured by bone weight, were not evenly distributed over the length of the bone, so that measurements at two points on the bone did not detect the apparent increase in calcification implied from bone weight increases. Selection for shank width in Line FL did not result in a significant change, in comparison with results in Line F, in actual weights of tibiotarsal and femur bones in either the fourth (Nestor et al, 1987), fifth (Table 2), or sixth (Table 5) generations of selection. However, weights of these bones relative to BW were greater in the fifth and sixth generations (Tables 2 and 5), but were not different in the fourth generation (Nestor et al, 1987). Thus with respect to leg bones, selection for increased shank width in Line FL increased the relative amount
1667
CARCASS TRAITS OF TURKEYS REFERENCES
Bacon, W. L., K. E. Nestor, and P. A. Renner, 1986. The influence of genetic increases in body weight and shank width on the abdominal fat pad and carcass composition of turkeys. Poultry Sci. 65:391-397. Cantor, A. H., M. A. Musser, W. L. Bacon, and A. B. Hellewell, 1980. In use of bone mineral mass as an indicator of vitamin D status in turkeys. Poultry Sci. 59:563-568. Clayton, G. A., C. Nixey, and G. Monaghan, 1978. Meat yield in turkeys. Br. Poult. Sci. 19:755-763. Harshaw, H. M., and R. R. Rector, 1940. The composition of turkeys as affected by age and sex. Poultry Sci. 19:404-^111. Harvey, W. R., 1977. User's guide for LSML76 mixed model least-squares and maximum likelihood computer program. The Ohio State University, Columbus, OH. Larsen, J. E., R. L. Adams, I. C. Peng, and W. J. Stadelman, 1986. Growth, feed conversion, and yields of turkey parts of three strains of hen turkeys as influenced by age. Poultry Sci. 65:2076-2081. Marsden, S. J., 1940. Weights and measurements of parts and organs of turkeys. Poultry Sci. 19:23-28. Miller, B. F., 1968. Comparative yield of different size turkey carcasses. Poultry Sci. 47:1570-1574. Naber, E. C , and S. P. Touchbum, 1970. Ohio poultry rations. Ohio Coop. Ext. Serv. Bull. 343, The Ohio State University, Columbus, OH. Nestor, K. E., 1977. The use of a paired mating system for the maintenance of experimental populations of turkeys. Poultry Sci. 56:60-65. Nestor, K. E., 1984. Genetics of growth and reproduction in the turkey. 9. Long-term selection for increased 16-week body weight. Poultry Sci. 63:2114-2122. Nestor, K. E., W. L. Bacon, P. D. Moorhead, Y. M. Saif, G. B. Havenstein, and P. A. Renner, 1987. A 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. Peng, I. C , R. L. Adams, E. J. Furumoto, P. Y. Hester, J. E. Larsen, O. A. Pike, and W. J. Stadelman, 1985. Allometric growth patterns and meat yields of carcass parts of turkey toms as influenced by lighting programs and age. Poultry Sci. 64:871-876. Saif, Y. M., and K. E. Nestor, 1983. Eradication of a Mycoplasma meleagridis infection in an experimental flock of turkeys. Ohio Poultry Pointers 22 (3):2. Steel, R.G.D., and J. H. Torrte, 1960. Principals and Procedures of Statistics. McGraw Hill Book Co., New York, NY.
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
of tibiotarsal bone; the resulting increase was associated with better walking ability in the FL line. However, the increased relative amount of drumstick muscles observed in the FL lines relative to those in Line F in the fifth (Table 1) and sixth (Table 4) generations of selection may also be contributing to the improved walking ability. Similar differences were not observed in the fourth generation of selection (Nestor et al., 1987). From these results, it is apparent that continued selection for shank width in Line FL has increased the relative support (leg bones and leg muscles) of the total body. This increase may be occurring at the expense of breast muscles, because the percentage breast muscles of the FL line compared to that of Line F declined in the sixth generation (Table 4). Selection for increased shank width in Line FL has resulted in relative weights of leg bones and muscles that are similar to those of Line RBC2. The commercial C line used in the sixth generation comparisons had BW equivalent to those of the F line. However, the C and F lines differed greatly in body composition. The C line had less support (leg muscles and leg bones) than the F line. The F line was selected only for increased BW at 16 wk of age whereas the selection criteria in Line C were not known. It is evident from the comparison that a major selection emphasis must have been placed on amount of breast muscles in Line C. The walking ability of Line C males was much poorer than that of Line F based on measurements made on another sample of males at 16 wk of age. A part of the poorer walking ability of C line can probably be attributed to the extremely wide breast of Line C, which forces the legs laterally. However, the relatively lower amount of support in the form of leg bones and muscles in Line C relative to that of Line F would appear to be a contributing factor. The results of this study support the hypothesis proposed by Nestor et al. (1985). Improving the relative amount of support of large-bodied turkeys improves walking ability.
1988 Poultry Science 67:1660-1667 INTRODUCTION
Direct selection for increased amount of breast muscles and total BW has increased both at a faster rate than the rate of increases in leg muscles (Marsden, 1940; Miller, 1968; Clayton etal., 1978; Nestor etal., 1987). Similarly, the relative amount of leg muscles declines with age as birds get heavier, particularly for males of large-bodied lines (Harshaw and Rector, 1940; Peng et al, 1985; Nestor et al, 1987). For females, Larsen etal. (1986) found that although the total weight (bone and muscle) of the drumstick increased with age, weight of the drumstick expressed as a percentage of BW decreased. Weight of thigh muscles increased greatly with age, but calculated as a percentage of BW, only a small increase occurred. Relative weight of the skeleton also declines with age (Clayton et al., 1978; Bacon et al., 1986; Nestor
'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 57-88.
etal., 1987). Nestor et al. (1985) hypothesized that selection in commercial turkeys for increased BW has been accompanied by a biologically incompatible reduction in relative leg support (leg muscles and leg bones), which is probably magnifying the severity of leg problems. To test this hypothesis, a subline (FL) of a long-term growth-selected line (F) was initiated by selecting only for increased width of the shank at the narrowest point (dewclaw). A previous report (Nestor, 1984) had shown that weight increases in Line F were associated with an increase in leg problems. Increases in shank width of Line FL resulted in significantly improved walking ability of males at 16 wk of age in comparison with ability of males in Line F, even though BW of males from the F and FL lines were similar through five generations (Nestor et al., 1985). Selection for shank width in the FL line was used in an attempt to increase the relative amount of leg bones. Nestor et al. (1987) compared the bone and muscle development in Lines F and FL and in a randombred control population (Line
1660
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
ABSTRACT Carcass composition of turkeys from a long-term growth-selected line (F), a subline (FL) of F selected only for increased shank width, and a randombred control population (RBC2) that served as the base population for F, were compared. Birds of both sexes were killed at 16 wk of age in the fifth and sixth generations in Line FL. A commercial sire line (C) was also included in the sixth generation. Body weight increased at comparable rates in F and FL males through the 5th generation of selection in Line FL, but the BW of FL males was significantly smaller than that observed in F males in the 6th generation. Body weights of FL females were significantly lower than BW of F females in both the 5th and 6th generations, resulting in a significant line x sex interaction. A similar interaction was also observed in both generations in the actual weight of most leg bones, leg muscles, and breast muscles. When expressed as a percentage of live BW, most of the latter line x sex interactions were not significant. Genetic increases in shank width of the FL line were associated with increases in the relative weight of all leg bones measured and drumstick muscles. This may have contributed to the improved walking ability consistently observed in FL males relative to that of F males. In general, genetic increases in BW in Line F were associated with a decreased amount of relative support (leg muscles and leg bones) in comparison with that observed in Line RBC2. These results support the hypothesis that a portion of the leg problems observed in large-bodied turkeys are attributable to an inherent weakness of body support structures resulting from the slower growth of these structures relative to that of total BW. (Key words: body weight, leg bones, leg muscles, leg weakness, turkeys)
1661
CARCASS TRAITS OF TURKEYS
RBC2, the base population of Line F) at 8, 16, and 20 wk of age. This comparison was made in the fourth generation of selection in Line FL. Weights of leg muscles were not significantly different in F and FL lines. Selection for increased shank width in Line FL did not increase the weights of tibiotarasal and femur bones relative to those of the F line. The tarsometatarsal bone was not measured. The purpose of the study reported herein was to make further comparisons of the F, FL, and RBC2 lines in two additional generations and to compare these lines with a commercial sire line (C). MATERIALS AND METHODS
RESULTS
Fifth Generation Comparisons. Sex differences were evident in most of the traits (Tables
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
Details of the origin and maintenance of the F, FL, and RBC2 lines were presented in Nestor et al. (1985). In the F line, individuals of both sexes were mass selected for increased 16-wk BW. The FL line was a subline of Line F started in Generation 13 and was formed by selecting both sexes on an individual basis only for increased shank width at 16 wk of age. Individuals of the RBC2 line were randomly selected to reproduce the line. All lines were maintained with a paired mating system (Nestor, 1977) involving 36 parental pairs. In the fifth generation of selection of Line FL, a comparison was made of the F, FL, and RBC2 lines at 16 wk of age. An additional line, (C), was included in the comparison during the sixth generation of Line FL, also at 16 wk of age. Offspring from a single hatch representing a 2-wk collection of eggs were used in both generations. Sexes and lines were grown intermingled in a windowless growing house. Continuous lighting was used for the first 4 wk after hatching; thereafter, 12 h light/day were provided. Both sexes were provided a four-ration feeding system with declining protein (Naber and Touchburn, 1970) based on requirements for males. Fifth Generation Comparisons. Line comparisons included the F (18th generation), the FL (5th generation), and RBC2 lines. Birds were weighed and the shank width measured in the afternoons prior to the day of killing. After an overnight fast, birds were killed by severing the jugular vein, scalded for about 30 s at 68 C, and picked. Carcasses were sawed in half longitudinally and one-half of the carcass was frozen for later dissection. After thawing, legs were removed from the carcass and separated into shanks, drumsticks, and thighs. The tarsometatarsal bone and associated tissues were separated from digits and
the remainder of the leg and weighed. The drumstick and thigh were separated by a cut through the knee joint (femuro-tibial and patellar joint). Drumstick and thigh muscles were carefully dissected from the bones and the weights of the muscles and bones were obtained. Breast muscles were removed from the breast bone and weighed. The shank was boiled for 15 min and the tarsometatarsal bone was cleaned of adhering tissue and weighed. Fat was then extracted with a methanol-chloroform mixture (1:2, vol/vol) and bones were oven dried for 24 h at 100 C, weighed, and the length measured. Density of the tarsometatarsus was measured at 40 and 60% of the length (proximal to distal end) using photoabsorption with an I125 source (Cantor et al, 1980). All birds were killed regardless of their walking ability. Two days were required to kill and process the birds. Half of the birds in each line was killed each day. Sixth Generation Comparisons. Birds were processed in a manner similar to that used for the previous generation except that 4 days were required to kill the birds, only the wet weights of the shank, tibiotarsal, and femur bones were obtained, and an additional line, C, was involved in the comparison. Thus, the line comparisons included F (19th generation), FL (6th generation), RBC2, and C lines. Ages of parents for Lines F, FL, and RBC2 were the same but the age of parents of Line C was unknown. A sample of hatching eggs for Line C was obtained from a primary breeder and the eggs were dipped and individually injected with an antibiotic solution (Saif and Nestor, 1983) to assure that the offspring would be free of Mycoplasma meleagridis infection. Mycoplasma meleagridis was previously eradicated from the F, FL, and RBC2 lines (Nestor, 1984). Statistical Analysis. The least squares and maximum likelihood computer program of Harvey (1977) was used for analysis of the data. Separate analyses were made for the fifth and sixth generation comparisons. Main effects were lines, sexes, and day of kill. The significance of two-way interaction among the main effects was estimated. Three-way interactions were included in the error term. Tukey's test was used to compare means where appropriate (Steel and Torrie, 1960).
NESTOR ET AL.
1662
from weights of muscles being equal to or slightly higher in FL than in F line males, whereas muscle weights were lower in FL than in F females. No significant differences were present between weights of breast and thigh muscles relative to BW for Lines F and FL (Table 1). Percentages of breast and thigh muscles were higher in Lines F and FL than in the RBC2 line. Percentages of drumstick muscles and total leg muscles were larger in Line FL than in Line F. The percentage of drumstick muscle of the RBC2 line was intermediate between those of Lines F and FL, whereas percentages of total leg muscles were similar in F and RBC2 lines. Most of the interactions between line and sex disappeared when muscle weights were adjusted for BW. Only one significant interaction (thigh muscles) between line and sex remained. In this case, there was a significant sex difference in the F line whereas no such difference existed in the FL or RBC2 lines. Shank width and shank weight were greater in Line FL than in Line F (Table 2). Lines F and FL were not significantly different in
TABLE 1. Influence (least squares means) of line, sex, and line X sex interaction on body weight and the weight of the breast and leg muscles expressed as actual weight and as a percentage of live body weight (fifth generation comparison)1
Variable
Line2 RBC2 F FL Sex 3 Male (M) Female (F) Line X Sex RBC2 X M RBC2 X F FXM FX F FLX M FLX F
Drumstick muscles
Birds
Live weight
(n)
(kg)
(g)
<%)
(g)
(%)
(g)
108 75 83
5.99 c 8.82 a 8.45 b
513c 775 a 734b
17.0 b 17.5 a 17.3 a
297 b 441a 433 a
9.9h 10.0 a b 10.2 a
233b 334 a 336 a
184 196
9.13 6.81
811 593
17.8 17.5
454 352
9.9 10.3
347 269
53 55 39 36 36 47
6.92 c 5.06 d 9.88 a 7.76 b 9.84 a 7.07 c
596 c 429 d 881a 668b 863 a 605 c
344 c 251d 475 a 407b 503 a 363 e
9 pab 9 pab 9.6 b 10.5 a 10.2 a b 10.3ab
262 c 203 d 371 a 298 b 384 a 288 b
Breast muscles
Thigh muscles
Total leg muscles
(%)
(g)
<%)
ab 7.58 b 7.98 a
530 b 775 a 770 a
17.7 b 17.6 b 18.2 a
7.62 7.94
801 621
17.5 18.2
782
606 c 45 5 d 846 a 704 b 888 a 651c
a—d Least squares means within line or line X sex subgroup for a trait with no common superscripts are significantly (P<.05) different. 'Weight of muscles was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control population; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width. 3 All differences between sexes, except for percentage breast muscles, were highly significant (P<.01). The difference in percentage breast muscles was significant (P<.05).
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
1, 2, and 3). Actual weights of the breast, leg muscles, and leg bones were larger in males than in females. As a percentage of live weight, the amount of breast muscles was larger in males but the amount of leg muscles was larger in females. Leg bone weights expressed as a percentage of BW were larger in males than in females. Birds in the F line were significantly heavier than those in the FL line at 16 wk of age, but the analyses showed a highly significant line x sex interaction (Table 1). When only males were compared, the difference between BW in Lines F and FL was not significant, but F females were heavier than FL females. Body weights of F and FL lines were much greater than those of the RBC2 line. Actual weights of breast and leg muscles were heavier in Lines F and FL than in the RBC2 line (Table 1). When sexes were combined, F and FL lines were not significantly different in leg muscle weights. Highly significant interactions between line and sex were found for weights of the breast, thigh, drumstick, and total leg muscles. Most of the interactions resulted
1663
CARCASS TRAITS OF TURKEYS
TABLE 2. Influence (least squares means) of line, sex, and line X sex interaction on shank width and the weights of the shank, tibiotarsal, and femur bones expressed as actual weights or as a percentage of live weight (fifth generation comparison)1
Variable
Shank width
(n)
(mm)
108 75 83
11.88 c 14.02 b 15.04 a
184 196 53 55 39 36 36 47
Tibiotarsal bone
Shank
Total leg bo nes
Femur
(%)
(g)
(%)
(g)
(%)
(g)
(%)
56.8 C 81.lb 86.0 a
1.90b 1.81 c 2.00 a
75.6 b 105.9 a 105.5 a
2.48 a 2.36 b 2.45 a
48.5 b 67.3 a 68.0 a
1.60a 1.50b 1.59 a
182 b 254 a 259 a
5.98 a 5.68 b 6.04 a
14.65 12.71
95.9 56.0
2.11 1.65
123.5 71.4
2.65 2.11
79.0 46.2
1.73 1.37
298 174
6.56 5.13
12.70 e 11.05 f 14.85 b 13.18 d 16.23 a 13.84 e
73.2 C 42.3 e 100.9 b 61.3 d 109.2 a 62.8 d
(g)
95.7 b 55.3 d 132.9 a 78.9 C 134.8 a 76.2 C
60.8 b 36.2 d 84.6 a 50.0 C 86.0 a 50.0 C
220 b 134 d 318 a 190 c 329 a 188 c
Least squares means within line or line X sex subgroup for a trait with no common superscripts are significantly (P<.05) different. 'Weight of muscles was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control population; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width. 3
A11 differences between sexes were highly significant (P<.01).
amounts of actual weight of tibiotarsal, femur, or total leg bones. Relative to BW, weights of the shank, tibiotarsal, femur, and total leg bones were greater in Line FL than in Line F. Actual weights of all leg bones were lighter in the RBC2 line than in the two heavy lines. On a relative basis, weights of the tibiotarsal, femur, and total leg bones were not significantly different in birds of the FL and RBC2 lines, but shank weights were larger in Line FL birds than in birds in the RBC2 line. Relative weight of the leg bones was greater in RBC2 line birds than in F line birds. Weight of the tarsometatarsal bone, after boiling and cleaning, was larger in Line FL birds than in Line F birds on an actual and on a percentage basis (Table 3). In actual weight, the tarsometatarsal bone was larger in Line F birds than in the RBC2 line birds, but the reverse was true on a percentage basis. The FL and RBC2 lines did not differ in relative weight of cleaned tarsometatarsal bones. Line differences in tarsometatarsal weight after defatting and drying were similar to those of the cleaned weights. Relative weight of the defatted tarsometatarsal
bone was greater in the RBC2 line than in Line FL, and the Line FL weight was larger than that in Line F. Lengths of the tarsometatarsal bone were similar in the F and FL lines, and both lines had longer bones than the RBC2 line. Densities of the defatted tarsometatarsal bone were similar in Lines F and FL when measured at 40 and 60% of its length. Both of the large-bodied lines had greater bone density than the RBC2 line. Highly significant line x sex interactions were present for cleaned, defatted, and dried weights of the tarsometatarsus. These interactions resulted from males of the FL line having greater weights than males of the F line, whereas none of the differences for females were significant. Interactions were not significant when cleaned, defatted, and dry weights of the tarsometatarsus were adjusted for BW differences. There was a significant line x sex interaction for density of the bone at 40% of its length, because density of bones from FL males was significantly higher than density of bones from F males. This difference did not exist in females. Line X sex interactions were not significant
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
Line 2 RBC2 F FL Sex 3 Male (M) Female (F) Line X Sex RBC2 X M RBC2 X F FX M F XF FL X M FLX F
Birds
NESTOR ET AL.
1664
TABLE 3. Influence (least squares means) of line and sex on weight, length, and density of the tarsometatarsal hones (fifth generation comparison)
Tarsomeitatarsal weight1 After cleaning
Variable
Line 3 RBC2 F FL Sex4 Male Female
After defatting
Tarsometatarsal length
Tarsometatarsal density 2 40%
60%
(g)
(%)
(g)
(%)
(cm)
21.8 C 29.0 b 31.5*
.718* .646 b .730*
11.4 C 14.8 b 15.2*
.376* .330 c .354 b
14.2 b 14.8* 14.8*
30.8 b 36.1* 36.9*
35.5 b 42.0* 41.4*
35.5 19.5
.782 .578
17.4 10.3
.384 .306
16.1 13.1
39.1 30.3
44.2 35.4
Line means with no common superscripts within traits are significantly (P<.05) different. Percentage was based on live body weight. Actual weights were measured on one-half of each carcass. These values were multiplied by two prior to calculating percentage. 2 Relative bone mineral mass (Cantor et al., 1980) measured at 40 and 60% of length when measured proximal to distal. 3 RBC2 = Randombred control; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width.
"All sex differences were highly (P<.01) significant. There was a highly significant (P<.01) interaction of line X sex for weight of the tarsometatarsal after cleaning and after defatting and drying. There was a significant (P<.05) line X sex interaction for density at 40% of the bone.
when density measurements were made at 60% of the bones' length. Sixth Generation Comparison. With the exception of percentage of breast muscles, differences between sexes were similar in comparisons for the two generations (Tables 4 and 5). In the fifth generation (Table 1), males had higher percentages of breast muscles than females, whereas in the sixth generation, the difference between the sexes was not significant (Table 4). Body weights of both males and females of the FL line were lower than those of the F line in the sixth generation (Table 5). This is in contrast to the comparison in the fifth generation of Line FL (Table 1), where males of the two lines had similar BW. However, the highly significant line X sex interaction was still evident in BW, which resulted in similar interactions of actual weights of the breast muscles and weights of the shank, tibiotarsal, and total leg bones. The interaction of line x sex remained significant (P< .01) only for shank weight when adjustment was made for BW by expressing the values as a percentage of live weight. The latter interaction resulted from the difference between sexes being smaller in Line C than in the other lines
(Table 5). Two major differences in results were obtained in the comparisons of the F and FL lines in the sixth generation of Line FL (Tables 4 and 5) vs. the results obtained in the fifth generation of Line FL (Tables 1 and 2). In the first case, breast muscles, expressed as a percentage of BW, were significantly lower in weight in Line FL than in Line F in the sixth generation, whereas the difference between breast muscle percentages of lines in the fifth generation was not significant. Secondly, actual weights of the muscles of the legs were significantly lower in Line FL than in Line F birds in the sixth generation, but no significant differences were observed in the fifth generation. Differences between the F and RBC2 lines were essentially the same in the fifth and sixth generation except for percentages of breast and drumstick muscles, wherein magnitudes of the line differences were similar, but significances of the differences varied among comparisons. The commercial C line and Line F had similar BW but the lines differed greatly in body conformation (muscling) and in amounts of leg bones (Tables 4 and 5). Leg muscle weights, both as actual weight or as a percentage of BW, were
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
1
1665
CARCASS TRAITS OF TURKEYS
TABLE 4. Influence (least squares means) of line and sex on the actual weight and weight expressed as a percentage of live weight for breast, drumstick, and thigh muscles (sixth generation comparison)1
Variable
Line2 RBC2 F FL C Sex 3 Male Female
Drumstick m uscles
Thigh muscles
Breast muscles
Birds
Total[leg muscles
(n)
(g)
<%)
(g)
(%)
(g)
(%)
(g)
(%)
133 104 118 111
523 d 808 b 704 c l,033a
17.0 b 17.4 b 16.2 C 22.3 a
318 c 486 a 45 3 b 473ab
10.3 a b 10.5 a 10.5 a 10.2 b
241d 35 6 a 341b 329 c
7.89 a 7.71 b 7.91 a 7.13 c
559 d 841a 794 c 802 b
18.2 a 18.2 a 18.4 a 17.4 b
273 312
878 654
18.0 18.2
496 388
10.2 10.5
361 282
7.46 7.90
857 660
17.7 18.5
a—d Line means within traits with no common superscripts are significantly (P<.05) different. Weight of muscles was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width; C = commercial sire line. 1
TABLE 5. Influence (least squares means) of line, sex, and line X sex interaction on bod and weight of the shank, tibiotarsal, and femur bones expressed as actual weight or as a percentage of live weight (sixth generation comparison)'
Variable
Birds
BW
(n)
(kg)
Line 2 RBC2 133 F 104 118 FL C 111 Sex 3 273 Male (M) Female (F) 312 Line X Sex RBC2 X M 63 RBC2 X F 70 F X M 54 F XF 50 FL X M 56 FL X F 62 CX M 48 C XF 63
Tibiotarsal bone
Shank (g)
Total leg bo nes
Femur bone
(%)
(g)
(%)
(g)
(%)
(g)
(%)
6.16 c 9.27 a 8.67 b 9.27 a
61.3 d 86.5 b 88.5 a 72.2 C
1.96a 1.83 b 2.01 a 1.54c
86.7 C 120.7 a 120.0 a 101.8 b
2.77 a 2.55 b 2.72 a 2.16 c
57.7 b 72.6 a 72.2 a 59.9 b
1.82a 1.54b 1.63 ab 1.27c
206 c 280 a 281a 234 b
6.55 a 5.92 b 6.37 a 4.97 c
9.71 7.15
99.1 57.0
2.06 1.61
138.7 78.7
2.88 2.23
86.1 48.5
1.81 1.37
324 184
6.75 5.21
7.26 d 5.05 e 10.61 a 7.93 c 10.05 b 7.29 d 10.58 a 7.95 c
78.9 d 43.8 h 110.8 b 62. l f 112.4 a 64.5 e 90. l c 54.4g
2.18 a 1.74c 2.10 b 1.57 d 2.24 a 1.77c 1.71 c 1.37e
111.5 C 61.9 f 155.2 a 86.1d 152.0 a 88.1d 129.7 b 73.8 e
268 c 144 f 360 a 200 d 357 a 204 d 297 b 171 e
Means within traits and lines and line X sex subgroups with no common superscripts are significantly (P<.05) different. 1
Weight of bones was measured on one-half of each carcass. The actual weight was multiplied by 2 prior to obtaining the percentage of live weight. 2 RBC2 = Randombred control population; F = subline of RBC2 selected only for increased 16-wk body weight; FL = subline of F selected only for increased shank width; C = commercial sire line. 3
All differences between sexes were highly significant (P<.01).
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
3 All differences between sexes except for percentage breast muscles were highly significant (P<.01). The difference between sexes for percentage breast muscles was not statistically significant.
NESTOR ET AL.
1666
less in Line C than in Line F. Line C had a larger amount of breast muscles than Line F when calculations were based on actual weight or weight relative to live BW. Shank and leg bones were lighter in Line C than in Line F. DISCUSSION
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
Selecting only for increased shank width in Line FL resulted in increases in BW of males comparable to those obtained by males of the F line (selected only for increased BW) for five generations of selection. However, in the sixth generation of selection in Line FL, BW of FL males were significantly lower than BW of F males. In the FL line females' BW did not change relative to those of Line RBC2, resulting in a significant line X sex interaction. Similar results were reported by Nestor et al. (1985, 1987). Nestor et al. (1985) suggested that the most likely cause of the interaction was that some genes that increase both shank width and BW are expressed only in males, resulting in the line x sex interaction. Males of the F, FL, and RBC2 lines were rated for walking ability at 16 wk of age in other samples of the lines in the fifth (Nestor et al., 1985) and sixth (unpublished data) generations of selection in Line FL. This rating was from 1 (good legs, good walking ability) to 5 (poor legs, near inability to walk). Based on these comparisons, males of the FL line had walking ability superior to that of birds in Line F. The differences (FL-F) were .41 and .53, respectively, in the fifth and sixth generations of selection. Both differences were highly significant. There has been no significant change in walking ability of Line FL birds relative to those in Line RBC2 with generation of selection. Thus, males of the FL line have had major increases in BW without a loss in walking ability. Selection in the FL line aimed to increase genetically the relative amount of leg bones to test the hypothesis proposed by Nestor et al. (1985). This hypothesis is 1) there appears to be a biologically incompatible combination in large-bodied turkeys of increased BW with relatively less support, and 2) the resulting inherent weight stress probably magnifies the effect of various causes of leg weakness. It has been well established that as total B W is increased by genetic selection or with age, a decline occurs in relative amounts of leg muscles (Marsden, 1940; Harshaw and Rector, 1940; Miller, 1968; Clayton et al., 1978; Peng et al, 1985; Nestor
et al., 1987) and leg bones and skeleton (Clayton et al, 1978; Bacon et al., 1986; Nestor et al., 1987). Selection for shank width in Line FL was effective in increasing the width of the shank. For males in the fifth (Nestor et ah, 1985) and sixth (unpublished data) generations of selection in Line FL, the percentage increases in shank width relative to those in Line F were 6.8 and 8.5, respectively. For females, respective increases were 4.7 and 7.1. Average percentage increases for both sexes in Line FL were 5.8 and 7.8, respectively, in Generations 5 and 6. Average percentage increases in shank weight (bone and associated tissues) of Line FL relative to Line F were 6.0 in the fifth generation (based on data in Table 2) and 2.3 in the sixth generation (based on data in Table 5). Percentage increases in Line FL over Line F in the fifth generation were 8.6 for the weight of the tarsometatarsal bone after boiling and cleaning and 2.7 for the weight of the tarsometatarsal bone after defatting and drying. The latter value indicates that selection for increased shank width in Line FL has increased calcification, because there were no differences between lengths of the tarsometatarsal bones in the F and FL lines. The 2.7% increase in dried defatted weight of the tarsometatarsal bone was less than the increase in shank width (6.8%) observed in the same generation, suggesting that most of the increase in weight was attributable to an increase in diameter of the bone, without increased calcification. When bone density, a measure of calcification (Cantor et al., 1980) was measured at two points (40 and 60% of the length) on the tarsometatarsus, line differences were not significant. This indicates that the small increases in calcification, as measured by bone weight, were not evenly distributed over the length of the bone, so that measurements at two points on the bone did not detect the apparent increase in calcification implied from bone weight increases. Selection for shank width in Line FL did not result in a significant change, in comparison with results in Line F, in actual weights of tibiotarsal and femur bones in either the fourth (Nestor et al, 1987), fifth (Table 2), or sixth (Table 5) generations of selection. However, weights of these bones relative to BW were greater in the fifth and sixth generations (Tables 2 and 5), but were not different in the fourth generation (Nestor et al, 1987). Thus with respect to leg bones, selection for increased shank width in Line FL increased the relative amount
1667
CARCASS TRAITS OF TURKEYS REFERENCES
Bacon, W. L., K. E. Nestor, and P. A. Renner, 1986. The influence of genetic increases in body weight and shank width on the abdominal fat pad and carcass composition of turkeys. Poultry Sci. 65:391-397. Cantor, A. H., M. A. Musser, W. L. Bacon, and A. B. Hellewell, 1980. In use of bone mineral mass as an indicator of vitamin D status in turkeys. Poultry Sci. 59:563-568. Clayton, G. A., C. Nixey, and G. Monaghan, 1978. Meat yield in turkeys. Br. Poult. Sci. 19:755-763. Harshaw, H. M., and R. R. Rector, 1940. The composition of turkeys as affected by age and sex. Poultry Sci. 19:404-^111. Harvey, W. R., 1977. User's guide for LSML76 mixed model least-squares and maximum likelihood computer program. The Ohio State University, Columbus, OH. Larsen, J. E., R. L. Adams, I. C. Peng, and W. J. Stadelman, 1986. Growth, feed conversion, and yields of turkey parts of three strains of hen turkeys as influenced by age. Poultry Sci. 65:2076-2081. Marsden, S. J., 1940. Weights and measurements of parts and organs of turkeys. Poultry Sci. 19:23-28. Miller, B. F., 1968. Comparative yield of different size turkey carcasses. Poultry Sci. 47:1570-1574. Naber, E. C , and S. P. Touchbum, 1970. Ohio poultry rations. Ohio Coop. Ext. Serv. Bull. 343, The Ohio State University, Columbus, OH. Nestor, K. E., 1977. The use of a paired mating system for the maintenance of experimental populations of turkeys. Poultry Sci. 56:60-65. Nestor, K. E., 1984. Genetics of growth and reproduction in the turkey. 9. Long-term selection for increased 16-week body weight. Poultry Sci. 63:2114-2122. Nestor, K. E., W. L. Bacon, P. D. Moorhead, Y. M. Saif, G. B. Havenstein, and P. A. Renner, 1987. A 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. Peng, I. C , R. L. Adams, E. J. Furumoto, P. Y. Hester, J. E. Larsen, O. A. Pike, and W. J. Stadelman, 1985. Allometric growth patterns and meat yields of carcass parts of turkey toms as influenced by lighting programs and age. Poultry Sci. 64:871-876. Saif, Y. M., and K. E. Nestor, 1983. Eradication of a Mycoplasma meleagridis infection in an experimental flock of turkeys. Ohio Poultry Pointers 22 (3):2. Steel, R.G.D., and J. H. Torrte, 1960. Principals and Procedures of Statistics. McGraw Hill Book Co., New York, NY.
Downloaded from http://ps.oxfordjournals.org/ by guest on May 11, 2015
of tibiotarsal bone; the resulting increase was associated with better walking ability in the FL line. However, the increased relative amount of drumstick muscles observed in the FL lines relative to those in Line F in the fifth (Table 1) and sixth (Table 4) generations of selection may also be contributing to the improved walking ability. Similar differences were not observed in the fourth generation of selection (Nestor et al., 1987). From these results, it is apparent that continued selection for shank width in Line FL has increased the relative support (leg bones and leg muscles) of the total body. This increase may be occurring at the expense of breast muscles, because the percentage breast muscles of the FL line compared to that of Line F declined in the sixth generation (Table 4). Selection for increased shank width in Line FL has resulted in relative weights of leg bones and muscles that are similar to those of Line RBC2. The commercial C line used in the sixth generation comparisons had BW equivalent to those of the F line. However, the C and F lines differed greatly in body composition. The C line had less support (leg muscles and leg bones) than the F line. The F line was selected only for increased BW at 16 wk of age whereas the selection criteria in Line C were not known. It is evident from the comparison that a major selection emphasis must have been placed on amount of breast muscles in Line C. The walking ability of Line C males was much poorer than that of Line F based on measurements made on another sample of males at 16 wk of age. A part of the poorer walking ability of C line can probably be attributed to the extremely wide breast of Line C, which forces the legs laterally. However, the relatively lower amount of support in the form of leg bones and muscles in Line C relative to that of Line F would appear to be a contributing factor. The results of this study support the hypothesis proposed by Nestor et al. (1985). Improving the relative amount of support of large-bodied turkeys improves walking ability.