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The Influence of Genetic Increases in Shank Width on Body Weight, Walking Ability, and Reproduction of Turkeys1
The Influence of Genetic Increases in Shank Width on Body Weight, Walking Ability, and Reproduction of Turkeys1 K. E. NESTOR, W. L. BACON, Y. M. SAIF, and P. A. RENNER Department of Poultry Science, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 (Received for publication February 21, 1985)
1985 Poultry Science 64:2248-2255 INTRODUCTION Various leg abnormalities in broiler chickens have been s h o w n t o be highly heritable (Sheridan et al, 1974, 1 9 7 8 ; B u r t o n et al, 1 9 8 1 ) , exhibit strain differences (Haye and Simons, 1 9 7 8 ; V e l t m a n n and Jensen, 1 9 8 1 ) , respond rapidly t o selection (Serfontein and P a y n e , 1 9 3 4 ; Leach and Nesheim, 1 9 6 5 , 1 9 7 2 ; Riddell, 1 9 7 6 ) , and t o be u n d e r t h e influence of major genes (Somes, 1 9 6 9 ; Sheridan et al, 1 9 7 4 ) . Although t h e genetic influence o n leg weakness in turkeys has n o t been studied t o t h e same e x t e n t as in chickens, m a n y of t h e a b n o r m a l leg conditions that are found in broiler chickens also occur in t u r k e y s (Nairn and Watson, 1 9 7 2 ) .
1
Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University, and grant funds provided by USDA Grant No. 82-CRSR-2-1076. Journal Article No. 41-85.
Direct selection for increased a m o u n t of breast muscle as well as for greater b o d y weight has increased total b o d y weight and a m o u n t of breast muscle at a faster rate than t h e increase observed in t h e muscles of t h e legs (Marsden, 1 9 4 0 ; Miller, 1 9 6 8 ; Clayton et al, 1978). T h e relative a m o u n t of leg muscle also declines with age as t h e birds get heavier (Harshaw and Rector, 1 9 4 0 ) . T h e skeleton exhibits a similar relative decline w i t h age (Clayton et al, 1 9 7 8 ) . Thus, we h y p o t h e s i z e t h a t there appears to be a biologically i n c o m p a t i b l e c o m b i n a t i o n in t h e present commercial t u r k e y s of increased b o d y weight with relatively less s u p p o r t (leg muscles and bones), and this inherent stress p r o b a b l y magnifies t h e effect of t h e various causes of leg problems. T h e r e are several studies reported in t h e literature t h a t t e n d t o s u p p o r t t h e above hypothesis. Riddell ( 1 9 8 0 ) surveyed five commercial flocks of Nicholas t u r k e y s and found t h a t long b o n e distortion was t h e m o s t consistent and frequent cause of leg p r o b l e m s .
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ABSTRACT Body weight and breast width have been greatly increased in the modern turkey. However, the relative amounts of leg muscles and leg bones have declined. A similar decline also occurs with age. It was theorized that this is an inherent weakness that magnifies other causes of leg problems. In an attempt to increase the relative amount of leg bone, a subline (FL) was developed by mass selection for increased shank width at 16 weeks of age from a long-term growth-selected line of turkeys (F). Shank width of FL was increased greatly by selection. The realized heritability of shank width, based on the regression of accumulated selection response on accumulated selection differential, was .3 3 ± .05 over five generations of selection. Body weight of males from FL increased at a rate comparable to that of F at 16 weeks of age. However, there was no comparable improvement in body weight of FL females, resulting in a significant line X sex interaction. A similar interaction was observed for body weight at 8 and 20 weeks of age in these lines. The genetic increases in shank width in FL resulted in significantly improved walking ability of males at 16 weeks of age in comparison to F, even though body weight of males from the two lines was similar. The walking ability of FL did not change relative to the control line from which F originated. Thus, large genetic increases in body weight of males can be achieved without loss in walking ability by genetic increases in shank width. Genetic increases in shank width had no significant effect on egg production over a 180-day production period. Likewise, fertility, hatchability of fertile eggs and egg weight were not significantly influenced by genetic increases in shank width. (Key words: shank width, body weight, walking ability, reproduction, turkeys)
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SHANK WIDTH AND WALKING ABILITY OF TURKEYS
The objective of this study was to test a part of the proposed hypothesis. To do this, the influence of genetic increases of the diameter of the tarsometatarsal bone and associated tissues (i.e., shank width) on walking ability and some other traits of economical importance (body weight and reproduction) were measured. MATERIALS AND METHODS A subline (FL) was initiated by mass selecting for increased shank width from a largebodied strain (F) of turkeys which had undergone thirteen generations of selection for only increased 16-week body weight (Nestor, 1977a) and now exhibits a high frequency of leg weakness (Nestor, 1984). The selection criterion in the FL subline was shank width at the narrowest point (dew claw) at 16 weeks of age. A randombred control population (RBC2, Nestor et al, 1969), from which F was developed, was also maintained. All lines were maintained using a paired mating system with 36 parental pairs (Nestor, 1977b). In the base generation of FL, eggs from F females were hatched weekly for 4 consecutive weeks at the beginning of the laying period. Hatches 1 and 4 were assigned to F, while Hatches 2 and 3 were designated for FL.
After the initial selection for F in Hatches 1 and 4, any remaining individuals, if they qualified, were also used for starting FL. Similarly, individuals in Hatches 2 and 3 that were not selected for FL were used for F. In order to increase the selection pressure in both lines, 22 parental pairs that met the selection criteria in both lines were used to reproduce both lines. Six weekly hatches at the beginning of the egg production period were used in the second generation of selection in FL. For the common parental pairs, Hatches 1, 4, and 6 were assigned to F, while Hatches 2, 3, and 5 were assigned to FL. As in the previous generation, remaining individuals after the initial selection were available for selection in the other line. A program for eradication of Mycoplasma meleagridis in the second generation of FL (Saif and Nestor, 1983) adversely affected hatchability and resulted in a reduction in number of poults produced by females of the large-bodied lines. Therefore, 12 weekly hatches were required to reproduce F and FL. The number of offspring per line ranged from 145 to 257 in this generation. The number of offspring per line in subsequent generations ranged from 188 to 416 and 6 weekly hatches were used for F and FL. The selection differentials obtained in FL are presented in Table 1. A total of five generations of selection was accomplished in FL. All three strains were hatched in May and June and grown entirely in confinement in the first generation of selection in FL. In subsequent generations, the lines were hatched in April and May, grown in confinement until 8 weeks of age, and then range reared until 20 weeks of age. The large-bodied strains were reared intermingled in confinement, while the
TABLE 1. Selection differentials (mm) in the line selected for increased shank width (FL) Generation Males
Females
Average
.65 .77 .34 .76 1.01 .71
.65 .54 .44 1.13 .96 .74
.65 .66 .39 .94 .98 .72
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Walser et al. (1982) observed that the incidence of tibia dyschondroplasia was greatest in the heaviest toms. Nestor (1984) reported that genetic increases in a long-term growth-selected line were associated with increases in leg problems. On the other hand, there are some studies that tend to refute the hypothesis. Buffington et al. (1975) found that the lightest bird of each sex for a medium weight strain of turkeys was just as likely as the heaviest bird to have leg and foot abnormalities. It is possible that body weight does not have as large an influence on leg problems in the medium weight strain in their experiment as in larger strains. Adams and Stadelman (1978) reported that dietary reduction in body weight gains did not influence leg weakness. However, the relative amount of leg bones and muscle may not have changed with the observed reduction in body weight. Cook et al. (1984) observed that artificial weight loading of turkeys did not increase the frequency of leg abnormalities. However, the experiment was carried out only to 4 weeks of age, and body weight would not be expected to have a large influence at this age.
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NESTOR ET AL.
tions for body weight at 50% production, egg weight, and reproductive traits. A two-way ANOVA with lines and hatches as the main effects was used with the other traits. The sexes were analyzed separately. Turkey's test (Snedecor, 1959) was used to separate line means. Although hatch effects were usually significant, and occasionally, the interaction of hatch and line was significant, only line effects will be discussed for brevity. Linear regression coefficients were calculated for changes occurring over the five generations of selection. Realized heritability estimates for shank width were obtained for individual generations of selection and for the entire selection period. For the entire period, the accumulated selection response in shank width of FL was regressed on the accumulated selection differential. The standard error of this regression coefficient served as the standard error of the heritability.
RESULTS AND DISCUSSION
Shank width of F was significantly greater than that of the randombred control in the base generation of FL (Table 2). There was a slight increase in shank width of F during the selection experiment. The increase in shank width, based on the regression coefficient of response on generations, was significant only for male offspring. Shank width of FL males increased consistently, relative to RBC2 and F (Table 2). When the FL females were compared to the control, there was a slight decrease from the 2nd to the 3rd generation; values for FL, relative to F, increased consistently. The change in shank width of FL was .19 and .14 mm/ generation (P<.01) respectively, for males and females, when expressed as a difference from F. The realized heritability of shank width in individual generations of selection ranged from —.11 to .54 with an average of .29. This heritability, based on total gain over the five generations divided by the accumulated selection differential was .30. When the accumulated gain in shank width was regressed on the accumulated selection differential, the estimate of realized heritability was .33 ± .05. Body weight at 16 weeks of age of F increased with generations for both sexes (Table 3), which was expected as this was the selec-
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RBC2 control line was housed in separate, but similar, pens. All lines were reared intermingled on the ranges. Offspring from all lines were fed a declining protein six-ration system (Naber and Touchburn, 1970) during the growing period. Body weights were measured at 8, 16, and 20 weeks of age. Shank width and length were recorded at 16 weeks of age. At the 16-week weighing, males of the three lines were subjectively rated for their walking ability. Males were rated from 1 to 5, with 1 representing males whose legs did not have any defects and had no difficulty walking, and 5 indicating males whose legs exhibited extreme lateral deviation or had great difficulty in walking. Ratings of 2, 3 and 4 represented intermediate values. The same person did the rating in all generations. Selected males and females were housed after the 20-week weighing. The males were housed in a pole shelter, while the females were housed in floor pens in a windowless breeder house. The hens were exposed to 6 hr of light per day for 8 weeks prior to stimulatory lighting (14 hr light/day at 51 lx) at 39 weeks of age. Other details of the feeding and management of the breeder males and females were given by Nestor (1984). Egg production records were obtained for a 180-day production period beginning with the first egg of the flock, except when the production period was shortened to 120 days in the successful program for eradication of M. meleagridis. Fertility and hatchability of fertile eggs were obtained for a 12-week hatching period beginning when the hens first attained an egg production level of approximately 50%, except no reproduction data were collected during the second generation of FL when M. meleagridis was being eliminated. For collection of reproduction data, each hen was inseminated twice during the 1st week of egg production and biweekly thereafter. Volume of semen inseminated per hen varied but was almost always greater than the minimum amount generally recommended (.025 cc) for maximum fertility. Body weight of the selected females was recorded when the hens first attained approximately 50% egg production. Egg weight was obtained by group weighing the eggs laid by each hen every 2 weeks throughout the 12-week hatching period. A one-way analysis of variance (ANOVA) was used to compare line means within genera-
Generation of selection in FL
**P<.01.
b3
+ 1.77** + 2.08** + 2.15** + 2.59** + 2.94** .28**
FL1
+ 2.04* + 3.08** + 3.04** + 2.90** + 3.08** + .73 + .18
+ 2.35** + 2.22** + 2.99** + 3.04** + 3.08** + 3.13**
+ .78 + .18*
FL2
7.57 7.44 7.89 7.76 7.52 7.48
Males
F2
RBC2 1
RBC2 = Randombred control, F = increased 16-week body weight line.
-.01
Linear regression coefficient of mean or difference on generation.
**P<01.
+ + + + +
.20** .43** .47** .66** 1.04** .19**
FL-F
.02
11.71 11.75 12.16 12.14 11.77 11.84
RBC2 + + + + + +
F
.00
+ .18 + .05
0
+ .18 - .09
F-FL
+ +
+ + + + + +
5.40 5.44 5.58 5.62 5.40 5.66 .03
F
RBC2
TABLE 3. The effect of selection for increased shank width (FL) on body weight (kg) a
Expressed as a deviation from RBC2.
*P<.05.
3
2
1
Total gain
1 2 3 4 5
Base
1.65** 1.57** 1.65** 1.68** 1.72** 1.90** .05*
Males
Linear regression coefficient of shank: width on generation of selection.
Expressed as a deviation from RBC2.
*P<.05.
2
1
+ + + + + +
13.55 13.42 13.76 13.54 13.31 13.33 -.05
Base
1 2 3 4 5 b2
F1
RBC2
of selection in FL
TABLE 2. Shank width (mm) at 16 weeks of age of the mndombred control (RBC2) and lines selected for in and increased shank width (FL)
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NESTOR ET AL. The line differences (data not shown) in body weight at 20 weeks of age were quite similar to those at 16 weeks of age. Body weight of FL males was less than that of F males in the 5 th generation of selection of FL, but the line differences showed no significant trend. Body weight of FL females increased with generation, but the increase was not as great as that for F females, resulting in a significant increase in the difference between lines with generations. The F had significantly (P<.01) poorer walking ability (higher ratings) than the control line during the base generation, and the ratings exhibited a positive, but nonsignificant, increase with generations (Table 4). The ratings of FL, although significantly (P<.01) higher than the control, exhibited no change over generations. The FL males had better walking ability than the F males in the last 3 generations of selection, even though body weight gain at 16 weeks of age was identical for males of the two lines (Table 3). Based on these results, it is suggested that the genetic increase in shank width counteracted the decrease in walking ability normally expected from an increase in body weight. The interaction between line and sex for body weight at 8, 16, and 20 weeks of age could be due to: 1) difference in response to
TABLE 4. The influence of genetic increases in body weight (F) and shank width (FL) on walking ability of turkey males at 16 weeks of age Walking a b i l i t y ' of selection in F L Base 1 2 3 4 5 b4
RBC22 1.33, 1.48 1.77 1.90 2.22 1.54 + .10
F3
FL3
FL-F
+ .95** + .73** + .64** + 1.03** + 1.15** + 1.56** + .13
+ .67** + .67** + .73** + .72** + 1.15** + .03
-.06 + .03 -.30** -.43** — 41** -.12*
1 Walking ability was subjectively rated from 1 to 5 with 1 representing males with no lateral deviations of the legs and no difficulty walking and 5 representing males whose legs exhibited extreme lateral deviation or had great difficulty walking. Ratings of 2, 3, and 4 were for conditions intermediate to these extremes. 2
RBC2 = Randombred control.
3
Expressed as a deviation from RBC2.
4
Linear regression coefficient of mean or difference on generation.
*P<.05. **P<.01.
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tion criterion in F. Body weight of FL males increased at a rate similar (although the linear regression coefficient was not statistically significant) to that of F males. There was no trend with generations for the line differences in male body weight. Body weight of FL females did not exhibit a significant change over generations, which resulted in a positive trend for the line differences over generations. Thus, there was an apparent interaction between lines and sexes for 16-week body weights. Body weight at 8 weeks of age was significantly greater in F and FL than in the RBC2 in all generations of selection (data not shown). Body weight of F males did not significantly change over generations, as indicated by linear regression, but there was a significant increase with generation in females. Body weight of FL males was significantly less than that of the F in the 4th and 5th generations of selection of FL. Females of the FL . exhibited no significant change in body weight during selection, because the linear regression coefficient was zero. Differences in female body weight between F and FL were highly significant in the last two generations, and the difference between lines increased with generations. These results indicate that there was a significant interaction of line and sex.
SHANK WIDTH AND WALKING ABILITY OF TURKEYS
The possibility exists that some genes that increase both shank width and body weight are expressed only in males resulting in the line by sex interaction. Sexual dimorphism in body weight appears at about 6 weeks of age in fast-growing strains of turkeys (Proudman and Wentworth, 1980). There have been no studies on growth in the width of the shank for males and females. However, Jaap (1938) found in several varieties of turkeys that differences between sexes accounted for 91% of the total variation in mature shank length. Males obtained the maximum length of the shank
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selection for shank width between sexes resulting from a sex differential in growth of the shank (Jaap, 1938; Jaap and Penquite, 1938; Walser et al.y 1982); 2) the increased walking ability of FL allowed the heavier males to survive at a greater rate than heavier males of F; 3) the presence of genes that increased both shank width and body weight which were expressed only in males; and 4) the presence of sex-linked recessive genes in low frequency, which increased shank width with no effect on body weight. Selection for shank width was at 16 weeks of age, before mature shank length is normally obtained in either sex (Jaap, 1938; Jaap and Penquite, 1938; Walser et al, 1982). Although there was a slightly greater response to selection in males (Table 2), substantial progress was also made in females. Therefore, it is unlikely that sex differences in growth of the shank was responsible for the interaction. During the last 3 generations of selection in FL, when a line difference in walking ability existed, mortality of males and females combined was not significantly different between F and FL for the period from hatching to 8 weeks of age and from 8 weeks to 16 weeks of age. As the turkeys were not sexed until the 16-week weighing, it is unknown if the mortality was divided equally between sexes. Mortality from 16 to 20 weeks of age was 13.5 and 9.7%, respectively, for males of F and FL. This difference was not significant (P>.05) as indicated by chi-square and was primarily due to a large line difference in the last generation of selection. Although mortality was not significantly different between lines, it is still possible that the males of F, with the greater genetic potential for rapid growth rate, were lost due to bad legs, while mortality losses in FL males were random.
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NESTOR ET AL.
Egg' production for both F and FL was significantly lower than the randombred control over a 180-day production period, but there was no difference between F and FL. Egg weight increased in both lines, but there was no difference between lines. There were no consistent differences in fertility and hatchability of fertile eggs between F and FL. These results suggest that selection for increased shank width had no influence on egg production, egg weight, fertility, or hatch of fertile eggs. Data for the above parameters are not shown. Body weight of females at 50% production significantly increased over generations (b = .172, P<.05) in F, whereas there was no significant change in FL (b = .032, P>.05). The difference in body weight (F—FL) between lines increased with generations (b = .141, P<.05). The line differences observed in body weight at 50% production is similar to those observed during the growing period (Table 3).
REFERENCES Adams, R. L., and W. J. Stadelman, 1978. Effect of delay of growth on leg weakness of torn turkeys.
Proc. 16th World's Poult. Cong., Brazil, Vol. IV:559-565. Buffington, D. E., S. H. Kleven, and K. A. Jordan, 1975. The incidences of leg and foot abnormalities in Wrolstad white turkeys. Poultry Sci. 54:457-461. Burton, R. W., A. K. Sheridan, and C. R. Howlett, 1981. The incidence and importance of tibial dyschondroplasia to the commercial broiler industry in Australia. Br. Poult. Sci. 22:153— 160. Clayton, G. A., C. Nixey, and G. Monaghan, 1978. Meat yield in turkeys. Br. Poult. Sci. 19:755 — 763. Cook, M. E., P. H. Patterson, and M. L. Sunde, 1984. Leg deformities: inability to increase severity by increasing body weight of chicks and poults. Poultry Sci. 63:620-627. Harshaw, H. M., and R. R. Rector, 1940. The composition of turkeys as affected by age and sex. Poultry Sci. 19:404-411. Haye, U., and P.C.M. Simons, 1978. Twisted legs in broilers. Br. Poult. Sci. 19:549-557. Jaap, R. G., 1938. Body conformation of the live market turkey. Poultry Sci. 17:120-125. Jaap, R. G., and R. Penquite, 1938. Criteria of conformation in market poultry. Poultry Sci. 17: 425-430. Leach, R. M., Jr., and M. C. Nesheim, 1965. Nutritional, genetic and morphological studies of an abnormal cartilage formation in young chicks. J. Nutr. 86:236-244. Leach, R. M., Jr., and M. C. Nesheim, 1972. Further studies on tibial dyschondroplasia (cartilage abnormality) in young chicks. J. Nutr. 102: 1673-1680. 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. Touchburn, 1970. Ohio Poultry Rations. Ohio Coop. Ext. Serv. Bull. 343. Nairn, M. E., and A.R.A. Watson, 1972. Leg weakness of poultry — a clinical and pathological characterization. Aust. Vet. J. 48:645—656. Nestor, K. E., 1977a. Genetics of growth and reproduction in the turkey. 5. Selection for increased body weight alone and in combination with increased egg production. Poultry Sci. 56:337-347. Nestor, K. E., 1977b. 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., M. G. McCartney, and N. Bachev, 1969. Relative contributions of genetics and environment to turkey improvement. Poultry Sci. 48:1944-1949. Proudman, J. A., and B. C. Wentworth, 1980. Ontogenesis of plasma growth hormone in large and midget white strains of turkeys. Poultry Sci. 59:906-913. Riddell, C , 1976. Selection of broiler chickens for a
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later than females (Jaap, 1938; Jaap and Penquite, 1938; Walser et «/., 1982). If sex-linked recessive genes that increased shank width without influencing body weight were present in low frequency, their effect would be expressed to a greater extent in females. Increases in the frequency of these genes would increase shank width without any change in body weight. This possibility for explaining the line X sex interaction is not too likely because the realized heritability of shank width was moderately high (.33). Genetic increases in body weight at 16 weeks of age in F resulted in significant increases in shank length (Table 5). Although the length of the shank of FL was not consistently different from that of F, there was no significant change in shank length oTTTL over generations. The FL gained .52 and__133 cm in shank length, respectively, for males and females when the values of F j n the base generation were compared with FL values in the 5th generation of selection. This—gain in shank len^thJnJEX_^as-4irxLb.al^j.S5Qcia.ted with the increase in body_ weight observed (Table 3) and was no_^directly_associated with increases in shanR_width_—
SHANK WIDTH AND WALKING ABILITY OF TURKEYS
in Proc. XV World's Poult. Cong., New Orleans, LA. Sheridan, A. K., C. R. Howlett, and R. W. Burton, 1978. The inheritance of tibial dyschondroplasia in broilers. Br. Poult. Sci. 19:491-499. Snedecor, G. W., 1959. Statistical Methods. Iowa State College Press, Ames, IA. Somes, R. G., Jr., 1969. Genetic perosis in the domestic fowl. J. Hered. 60:163-166. Veltmann, J. R., Jr., and L. S. Jensen, 1981. Tibial dyschondroplasia in broilers: comparison of dietary additives and strains. Poultry Sci. 60: 1473-1478. Walser, M. M., F. L. Cherins, and H. E. Dziuk, 1982. Osseous development and tibial dyschondroplasia in five lines of turkeys. Avian Dis. 26:265—270.
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high and low incidence of tibial dyschondroplasia with observations on spondylolisthesis and twisted legs (Perosis). Poultry Sci. 55:145—151. Riddell, C., 1980. A survey of skeletal disorders in five turkey flocks in Saskatchewan. Can. J. Comp. Med. 44:275-279. Saif, Y. M., and K. E. Nestor, 1983. Eradication of a Mycoplasma meleagridis infection in an experimental flock of turkeys. Ohio Poultry Pointers 22:2. Serfontein, P. J., and L. F. Payne, 1934. Inheritance of abnormal anatomical condition in the tibial metatarsal joints. Poultry Sci. 13:61—63. Sheridan, A. K., C. R. Howlett, and J. A. Bruyn, 1974. Genetic factors influencing tibial dyschondroplasia in Australian meat chickens. Pages 34—35
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1985 Poultry Science 64:2248-2255 INTRODUCTION Various leg abnormalities in broiler chickens have been s h o w n t o be highly heritable (Sheridan et al, 1974, 1 9 7 8 ; B u r t o n et al, 1 9 8 1 ) , exhibit strain differences (Haye and Simons, 1 9 7 8 ; V e l t m a n n and Jensen, 1 9 8 1 ) , respond rapidly t o selection (Serfontein and P a y n e , 1 9 3 4 ; Leach and Nesheim, 1 9 6 5 , 1 9 7 2 ; Riddell, 1 9 7 6 ) , and t o be u n d e r t h e influence of major genes (Somes, 1 9 6 9 ; Sheridan et al, 1 9 7 4 ) . Although t h e genetic influence o n leg weakness in turkeys has n o t been studied t o t h e same e x t e n t as in chickens, m a n y of t h e a b n o r m a l leg conditions that are found in broiler chickens also occur in t u r k e y s (Nairn and Watson, 1 9 7 2 ) .
1
Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University, and grant funds provided by USDA Grant No. 82-CRSR-2-1076. Journal Article No. 41-85.
Direct selection for increased a m o u n t of breast muscle as well as for greater b o d y weight has increased total b o d y weight and a m o u n t of breast muscle at a faster rate than t h e increase observed in t h e muscles of t h e legs (Marsden, 1 9 4 0 ; Miller, 1 9 6 8 ; Clayton et al, 1978). T h e relative a m o u n t of leg muscle also declines with age as t h e birds get heavier (Harshaw and Rector, 1 9 4 0 ) . T h e skeleton exhibits a similar relative decline w i t h age (Clayton et al, 1 9 7 8 ) . Thus, we h y p o t h e s i z e t h a t there appears to be a biologically i n c o m p a t i b l e c o m b i n a t i o n in t h e present commercial t u r k e y s of increased b o d y weight with relatively less s u p p o r t (leg muscles and bones), and this inherent stress p r o b a b l y magnifies t h e effect of t h e various causes of leg problems. T h e r e are several studies reported in t h e literature t h a t t e n d t o s u p p o r t t h e above hypothesis. Riddell ( 1 9 8 0 ) surveyed five commercial flocks of Nicholas t u r k e y s and found t h a t long b o n e distortion was t h e m o s t consistent and frequent cause of leg p r o b l e m s .
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ABSTRACT Body weight and breast width have been greatly increased in the modern turkey. However, the relative amounts of leg muscles and leg bones have declined. A similar decline also occurs with age. It was theorized that this is an inherent weakness that magnifies other causes of leg problems. In an attempt to increase the relative amount of leg bone, a subline (FL) was developed by mass selection for increased shank width at 16 weeks of age from a long-term growth-selected line of turkeys (F). Shank width of FL was increased greatly by selection. The realized heritability of shank width, based on the regression of accumulated selection response on accumulated selection differential, was .3 3 ± .05 over five generations of selection. Body weight of males from FL increased at a rate comparable to that of F at 16 weeks of age. However, there was no comparable improvement in body weight of FL females, resulting in a significant line X sex interaction. A similar interaction was observed for body weight at 8 and 20 weeks of age in these lines. The genetic increases in shank width in FL resulted in significantly improved walking ability of males at 16 weeks of age in comparison to F, even though body weight of males from the two lines was similar. The walking ability of FL did not change relative to the control line from which F originated. Thus, large genetic increases in body weight of males can be achieved without loss in walking ability by genetic increases in shank width. Genetic increases in shank width had no significant effect on egg production over a 180-day production period. Likewise, fertility, hatchability of fertile eggs and egg weight were not significantly influenced by genetic increases in shank width. (Key words: shank width, body weight, walking ability, reproduction, turkeys)
2249
SHANK WIDTH AND WALKING ABILITY OF TURKEYS
The objective of this study was to test a part of the proposed hypothesis. To do this, the influence of genetic increases of the diameter of the tarsometatarsal bone and associated tissues (i.e., shank width) on walking ability and some other traits of economical importance (body weight and reproduction) were measured. MATERIALS AND METHODS A subline (FL) was initiated by mass selecting for increased shank width from a largebodied strain (F) of turkeys which had undergone thirteen generations of selection for only increased 16-week body weight (Nestor, 1977a) and now exhibits a high frequency of leg weakness (Nestor, 1984). The selection criterion in the FL subline was shank width at the narrowest point (dew claw) at 16 weeks of age. A randombred control population (RBC2, Nestor et al, 1969), from which F was developed, was also maintained. All lines were maintained using a paired mating system with 36 parental pairs (Nestor, 1977b). In the base generation of FL, eggs from F females were hatched weekly for 4 consecutive weeks at the beginning of the laying period. Hatches 1 and 4 were assigned to F, while Hatches 2 and 3 were designated for FL.
After the initial selection for F in Hatches 1 and 4, any remaining individuals, if they qualified, were also used for starting FL. Similarly, individuals in Hatches 2 and 3 that were not selected for FL were used for F. In order to increase the selection pressure in both lines, 22 parental pairs that met the selection criteria in both lines were used to reproduce both lines. Six weekly hatches at the beginning of the egg production period were used in the second generation of selection in FL. For the common parental pairs, Hatches 1, 4, and 6 were assigned to F, while Hatches 2, 3, and 5 were assigned to FL. As in the previous generation, remaining individuals after the initial selection were available for selection in the other line. A program for eradication of Mycoplasma meleagridis in the second generation of FL (Saif and Nestor, 1983) adversely affected hatchability and resulted in a reduction in number of poults produced by females of the large-bodied lines. Therefore, 12 weekly hatches were required to reproduce F and FL. The number of offspring per line ranged from 145 to 257 in this generation. The number of offspring per line in subsequent generations ranged from 188 to 416 and 6 weekly hatches were used for F and FL. The selection differentials obtained in FL are presented in Table 1. A total of five generations of selection was accomplished in FL. All three strains were hatched in May and June and grown entirely in confinement in the first generation of selection in FL. In subsequent generations, the lines were hatched in April and May, grown in confinement until 8 weeks of age, and then range reared until 20 weeks of age. The large-bodied strains were reared intermingled in confinement, while the
TABLE 1. Selection differentials (mm) in the line selected for increased shank width (FL) Generation Males
Females
Average
.65 .77 .34 .76 1.01 .71
.65 .54 .44 1.13 .96 .74
.65 .66 .39 .94 .98 .72
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Walser et al. (1982) observed that the incidence of tibia dyschondroplasia was greatest in the heaviest toms. Nestor (1984) reported that genetic increases in a long-term growth-selected line were associated with increases in leg problems. On the other hand, there are some studies that tend to refute the hypothesis. Buffington et al. (1975) found that the lightest bird of each sex for a medium weight strain of turkeys was just as likely as the heaviest bird to have leg and foot abnormalities. It is possible that body weight does not have as large an influence on leg problems in the medium weight strain in their experiment as in larger strains. Adams and Stadelman (1978) reported that dietary reduction in body weight gains did not influence leg weakness. However, the relative amount of leg bones and muscle may not have changed with the observed reduction in body weight. Cook et al. (1984) observed that artificial weight loading of turkeys did not increase the frequency of leg abnormalities. However, the experiment was carried out only to 4 weeks of age, and body weight would not be expected to have a large influence at this age.
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NESTOR ET AL.
tions for body weight at 50% production, egg weight, and reproductive traits. A two-way ANOVA with lines and hatches as the main effects was used with the other traits. The sexes were analyzed separately. Turkey's test (Snedecor, 1959) was used to separate line means. Although hatch effects were usually significant, and occasionally, the interaction of hatch and line was significant, only line effects will be discussed for brevity. Linear regression coefficients were calculated for changes occurring over the five generations of selection. Realized heritability estimates for shank width were obtained for individual generations of selection and for the entire selection period. For the entire period, the accumulated selection response in shank width of FL was regressed on the accumulated selection differential. The standard error of this regression coefficient served as the standard error of the heritability.
RESULTS AND DISCUSSION
Shank width of F was significantly greater than that of the randombred control in the base generation of FL (Table 2). There was a slight increase in shank width of F during the selection experiment. The increase in shank width, based on the regression coefficient of response on generations, was significant only for male offspring. Shank width of FL males increased consistently, relative to RBC2 and F (Table 2). When the FL females were compared to the control, there was a slight decrease from the 2nd to the 3rd generation; values for FL, relative to F, increased consistently. The change in shank width of FL was .19 and .14 mm/ generation (P<.01) respectively, for males and females, when expressed as a difference from F. The realized heritability of shank width in individual generations of selection ranged from —.11 to .54 with an average of .29. This heritability, based on total gain over the five generations divided by the accumulated selection differential was .30. When the accumulated gain in shank width was regressed on the accumulated selection differential, the estimate of realized heritability was .33 ± .05. Body weight at 16 weeks of age of F increased with generations for both sexes (Table 3), which was expected as this was the selec-
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RBC2 control line was housed in separate, but similar, pens. All lines were reared intermingled on the ranges. Offspring from all lines were fed a declining protein six-ration system (Naber and Touchburn, 1970) during the growing period. Body weights were measured at 8, 16, and 20 weeks of age. Shank width and length were recorded at 16 weeks of age. At the 16-week weighing, males of the three lines were subjectively rated for their walking ability. Males were rated from 1 to 5, with 1 representing males whose legs did not have any defects and had no difficulty walking, and 5 indicating males whose legs exhibited extreme lateral deviation or had great difficulty in walking. Ratings of 2, 3 and 4 represented intermediate values. The same person did the rating in all generations. Selected males and females were housed after the 20-week weighing. The males were housed in a pole shelter, while the females were housed in floor pens in a windowless breeder house. The hens were exposed to 6 hr of light per day for 8 weeks prior to stimulatory lighting (14 hr light/day at 51 lx) at 39 weeks of age. Other details of the feeding and management of the breeder males and females were given by Nestor (1984). Egg production records were obtained for a 180-day production period beginning with the first egg of the flock, except when the production period was shortened to 120 days in the successful program for eradication of M. meleagridis. Fertility and hatchability of fertile eggs were obtained for a 12-week hatching period beginning when the hens first attained an egg production level of approximately 50%, except no reproduction data were collected during the second generation of FL when M. meleagridis was being eliminated. For collection of reproduction data, each hen was inseminated twice during the 1st week of egg production and biweekly thereafter. Volume of semen inseminated per hen varied but was almost always greater than the minimum amount generally recommended (.025 cc) for maximum fertility. Body weight of the selected females was recorded when the hens first attained approximately 50% egg production. Egg weight was obtained by group weighing the eggs laid by each hen every 2 weeks throughout the 12-week hatching period. A one-way analysis of variance (ANOVA) was used to compare line means within genera-
Generation of selection in FL
**P<.01.
b3
+ 1.77** + 2.08** + 2.15** + 2.59** + 2.94** .28**
FL1
+ 2.04* + 3.08** + 3.04** + 2.90** + 3.08** + .73 + .18
+ 2.35** + 2.22** + 2.99** + 3.04** + 3.08** + 3.13**
+ .78 + .18*
FL2
7.57 7.44 7.89 7.76 7.52 7.48
Males
F2
RBC2 1
RBC2 = Randombred control, F = increased 16-week body weight line.
-.01
Linear regression coefficient of mean or difference on generation.
**P<01.
+ + + + +
.20** .43** .47** .66** 1.04** .19**
FL-F
.02
11.71 11.75 12.16 12.14 11.77 11.84
RBC2 + + + + + +
F
.00
+ .18 + .05
0
+ .18 - .09
F-FL
+ +
+ + + + + +
5.40 5.44 5.58 5.62 5.40 5.66 .03
F
RBC2
TABLE 3. The effect of selection for increased shank width (FL) on body weight (kg) a
Expressed as a deviation from RBC2.
*P<.05.
3
2
1
Total gain
1 2 3 4 5
Base
1.65** 1.57** 1.65** 1.68** 1.72** 1.90** .05*
Males
Linear regression coefficient of shank: width on generation of selection.
Expressed as a deviation from RBC2.
*P<.05.
2
1
+ + + + + +
13.55 13.42 13.76 13.54 13.31 13.33 -.05
Base
1 2 3 4 5 b2
F1
RBC2
of selection in FL
TABLE 2. Shank width (mm) at 16 weeks of age of the mndombred control (RBC2) and lines selected for in and increased shank width (FL)
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2252
NESTOR ET AL. The line differences (data not shown) in body weight at 20 weeks of age were quite similar to those at 16 weeks of age. Body weight of FL males was less than that of F males in the 5 th generation of selection of FL, but the line differences showed no significant trend. Body weight of FL females increased with generation, but the increase was not as great as that for F females, resulting in a significant increase in the difference between lines with generations. The F had significantly (P<.01) poorer walking ability (higher ratings) than the control line during the base generation, and the ratings exhibited a positive, but nonsignificant, increase with generations (Table 4). The ratings of FL, although significantly (P<.01) higher than the control, exhibited no change over generations. The FL males had better walking ability than the F males in the last 3 generations of selection, even though body weight gain at 16 weeks of age was identical for males of the two lines (Table 3). Based on these results, it is suggested that the genetic increase in shank width counteracted the decrease in walking ability normally expected from an increase in body weight. The interaction between line and sex for body weight at 8, 16, and 20 weeks of age could be due to: 1) difference in response to
TABLE 4. The influence of genetic increases in body weight (F) and shank width (FL) on walking ability of turkey males at 16 weeks of age Walking a b i l i t y ' of selection in F L Base 1 2 3 4 5 b4
RBC22 1.33, 1.48 1.77 1.90 2.22 1.54 + .10
F3
FL3
FL-F
+ .95** + .73** + .64** + 1.03** + 1.15** + 1.56** + .13
+ .67** + .67** + .73** + .72** + 1.15** + .03
-.06 + .03 -.30** -.43** — 41** -.12*
1 Walking ability was subjectively rated from 1 to 5 with 1 representing males with no lateral deviations of the legs and no difficulty walking and 5 representing males whose legs exhibited extreme lateral deviation or had great difficulty walking. Ratings of 2, 3, and 4 were for conditions intermediate to these extremes. 2
RBC2 = Randombred control.
3
Expressed as a deviation from RBC2.
4
Linear regression coefficient of mean or difference on generation.
*P<.05. **P<.01.
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tion criterion in F. Body weight of FL males increased at a rate similar (although the linear regression coefficient was not statistically significant) to that of F males. There was no trend with generations for the line differences in male body weight. Body weight of FL females did not exhibit a significant change over generations, which resulted in a positive trend for the line differences over generations. Thus, there was an apparent interaction between lines and sexes for 16-week body weights. Body weight at 8 weeks of age was significantly greater in F and FL than in the RBC2 in all generations of selection (data not shown). Body weight of F males did not significantly change over generations, as indicated by linear regression, but there was a significant increase with generation in females. Body weight of FL males was significantly less than that of the F in the 4th and 5th generations of selection of FL. Females of the FL . exhibited no significant change in body weight during selection, because the linear regression coefficient was zero. Differences in female body weight between F and FL were highly significant in the last two generations, and the difference between lines increased with generations. These results indicate that there was a significant interaction of line and sex.
SHANK WIDTH AND WALKING ABILITY OF TURKEYS
The possibility exists that some genes that increase both shank width and body weight are expressed only in males resulting in the line by sex interaction. Sexual dimorphism in body weight appears at about 6 weeks of age in fast-growing strains of turkeys (Proudman and Wentworth, 1980). There have been no studies on growth in the width of the shank for males and females. However, Jaap (1938) found in several varieties of turkeys that differences between sexes accounted for 91% of the total variation in mature shank length. Males obtained the maximum length of the shank
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selection for shank width between sexes resulting from a sex differential in growth of the shank (Jaap, 1938; Jaap and Penquite, 1938; Walser et al.y 1982); 2) the increased walking ability of FL allowed the heavier males to survive at a greater rate than heavier males of F; 3) the presence of genes that increased both shank width and body weight which were expressed only in males; and 4) the presence of sex-linked recessive genes in low frequency, which increased shank width with no effect on body weight. Selection for shank width was at 16 weeks of age, before mature shank length is normally obtained in either sex (Jaap, 1938; Jaap and Penquite, 1938; Walser et al, 1982). Although there was a slightly greater response to selection in males (Table 2), substantial progress was also made in females. Therefore, it is unlikely that sex differences in growth of the shank was responsible for the interaction. During the last 3 generations of selection in FL, when a line difference in walking ability existed, mortality of males and females combined was not significantly different between F and FL for the period from hatching to 8 weeks of age and from 8 weeks to 16 weeks of age. As the turkeys were not sexed until the 16-week weighing, it is unknown if the mortality was divided equally between sexes. Mortality from 16 to 20 weeks of age was 13.5 and 9.7%, respectively, for males of F and FL. This difference was not significant (P>.05) as indicated by chi-square and was primarily due to a large line difference in the last generation of selection. Although mortality was not significantly different between lines, it is still possible that the males of F, with the greater genetic potential for rapid growth rate, were lost due to bad legs, while mortality losses in FL males were random.
2253
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2254
NESTOR ET AL.
Egg' production for both F and FL was significantly lower than the randombred control over a 180-day production period, but there was no difference between F and FL. Egg weight increased in both lines, but there was no difference between lines. There were no consistent differences in fertility and hatchability of fertile eggs between F and FL. These results suggest that selection for increased shank width had no influence on egg production, egg weight, fertility, or hatch of fertile eggs. Data for the above parameters are not shown. Body weight of females at 50% production significantly increased over generations (b = .172, P<.05) in F, whereas there was no significant change in FL (b = .032, P>.05). The difference in body weight (F—FL) between lines increased with generations (b = .141, P<.05). The line differences observed in body weight at 50% production is similar to those observed during the growing period (Table 3).
REFERENCES Adams, R. L., and W. J. Stadelman, 1978. Effect of delay of growth on leg weakness of torn turkeys.
Proc. 16th World's Poult. Cong., Brazil, Vol. IV:559-565. Buffington, D. E., S. H. Kleven, and K. A. Jordan, 1975. The incidences of leg and foot abnormalities in Wrolstad white turkeys. Poultry Sci. 54:457-461. Burton, R. W., A. K. Sheridan, and C. R. Howlett, 1981. The incidence and importance of tibial dyschondroplasia to the commercial broiler industry in Australia. Br. Poult. Sci. 22:153— 160. Clayton, G. A., C. Nixey, and G. Monaghan, 1978. Meat yield in turkeys. Br. Poult. Sci. 19:755 — 763. Cook, M. E., P. H. Patterson, and M. L. Sunde, 1984. Leg deformities: inability to increase severity by increasing body weight of chicks and poults. Poultry Sci. 63:620-627. Harshaw, H. M., and R. R. Rector, 1940. The composition of turkeys as affected by age and sex. Poultry Sci. 19:404-411. Haye, U., and P.C.M. Simons, 1978. Twisted legs in broilers. Br. Poult. Sci. 19:549-557. Jaap, R. G., 1938. Body conformation of the live market turkey. Poultry Sci. 17:120-125. Jaap, R. G., and R. Penquite, 1938. Criteria of conformation in market poultry. Poultry Sci. 17: 425-430. Leach, R. M., Jr., and M. C. Nesheim, 1965. Nutritional, genetic and morphological studies of an abnormal cartilage formation in young chicks. J. Nutr. 86:236-244. Leach, R. M., Jr., and M. C. Nesheim, 1972. Further studies on tibial dyschondroplasia (cartilage abnormality) in young chicks. J. Nutr. 102: 1673-1680. 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. Touchburn, 1970. Ohio Poultry Rations. Ohio Coop. Ext. Serv. Bull. 343. Nairn, M. E., and A.R.A. Watson, 1972. Leg weakness of poultry — a clinical and pathological characterization. Aust. Vet. J. 48:645—656. Nestor, K. E., 1977a. Genetics of growth and reproduction in the turkey. 5. Selection for increased body weight alone and in combination with increased egg production. Poultry Sci. 56:337-347. Nestor, K. E., 1977b. 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., M. G. McCartney, and N. Bachev, 1969. Relative contributions of genetics and environment to turkey improvement. Poultry Sci. 48:1944-1949. Proudman, J. A., and B. C. Wentworth, 1980. Ontogenesis of plasma growth hormone in large and midget white strains of turkeys. Poultry Sci. 59:906-913. Riddell, C , 1976. Selection of broiler chickens for a
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later than females (Jaap, 1938; Jaap and Penquite, 1938; Walser et «/., 1982). If sex-linked recessive genes that increased shank width without influencing body weight were present in low frequency, their effect would be expressed to a greater extent in females. Increases in the frequency of these genes would increase shank width without any change in body weight. This possibility for explaining the line X sex interaction is not too likely because the realized heritability of shank width was moderately high (.33). Genetic increases in body weight at 16 weeks of age in F resulted in significant increases in shank length (Table 5). Although the length of the shank of FL was not consistently different from that of F, there was no significant change in shank length oTTTL over generations. The FL gained .52 and__133 cm in shank length, respectively, for males and females when the values of F j n the base generation were compared with FL values in the 5th generation of selection. This—gain in shank len^thJnJEX_^as-4irxLb.al^j.S5Qcia.ted with the increase in body_ weight observed (Table 3) and was no_^directly_associated with increases in shanR_width_—
SHANK WIDTH AND WALKING ABILITY OF TURKEYS
in Proc. XV World's Poult. Cong., New Orleans, LA. Sheridan, A. K., C. R. Howlett, and R. W. Burton, 1978. The inheritance of tibial dyschondroplasia in broilers. Br. Poult. Sci. 19:491-499. Snedecor, G. W., 1959. Statistical Methods. Iowa State College Press, Ames, IA. Somes, R. G., Jr., 1969. Genetic perosis in the domestic fowl. J. Hered. 60:163-166. Veltmann, J. R., Jr., and L. S. Jensen, 1981. Tibial dyschondroplasia in broilers: comparison of dietary additives and strains. Poultry Sci. 60: 1473-1478. Walser, M. M., F. L. Cherins, and H. E. Dziuk, 1982. Osseous development and tibial dyschondroplasia in five lines of turkeys. Avian Dis. 26:265—270.
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high and low incidence of tibial dyschondroplasia with observations on spondylolisthesis and twisted legs (Perosis). Poultry Sci. 55:145—151. Riddell, C., 1980. A survey of skeletal disorders in five turkey flocks in Saskatchewan. Can. J. Comp. Med. 44:275-279. Saif, Y. M., and K. E. Nestor, 1983. Eradication of a Mycoplasma meleagridis infection in an experimental flock of turkeys. Ohio Poultry Pointers 22:2. Serfontein, P. J., and L. F. Payne, 1934. Inheritance of abnormal anatomical condition in the tibial metatarsal joints. Poultry Sci. 13:61—63. Sheridan, A. K., C. R. Howlett, and J. A. Bruyn, 1974. Genetic factors influencing tibial dyschondroplasia in Australian meat chickens. Pages 34—35
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