Direct and Correlated Responses to Long-Term Selection for Increased Body Weight and Egg Production in Turkeys1

Direct and Correlated Responses to Long-Term Selection for Increased Body Weight and Egg Production in Turkeys1 KARL E. NESTOR, D. O. NOBLE, J. ZHU, and Y. MORITSU2 Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio 44691 correlation varied from near zero to strongly negative and fluctuated between these extremes in both lines even though they started from different base populations and selection criteria differed. Other correlated responses to selection for increased egg production were increased average clutch length (intensity of lay), and decreased broodiness (total days lost), egg weight, shell coloration, and rate of response to stimulatory lighting. Other correlated responses to selection for increased 16-wk BW in the F line included: increased egg weight (due to increased albumen), longer eating bouts, and decreased average clutch length, semen production, walking ability, and resistance to Pasteurella multocida and Newcastle disease virus. Selection within the E and F lines also changed the frequency of MHC haplotypes and the changes appeared to be in opposite directions in the two lines.

ABSTRACT Lines of turkeys were selected long-term for increased egg production (E line; 34 generations) or increased 16-wk BW (F line; 28 generations). The E and F lines were started from randombred control populations (RBC1 and RBC2, respectively) that were also maintained to remove environmental variation among generations. Realized heritabilities (h2) ± SE in the E line, based on regressions of response on cumulated actual selection differentials (selection differentials weighted for the number of offspring produced), for 180-d and 250-d egg production were 0.34 ± 0.02 (17 generations) and 0.26 ± 0.13 (8 generations), respectively. The realized h2 of 16-wk BW in the F line was 0.26 ± 0.01. There was no consistent evidence of selection response reaching a plateau in either line. The genetic association of BW and egg production changed with selection in the E and F lines. The genetic

(Key words: body weight, egg production, selection responses, correlated responses, turkey) 1996 Poultry Science 75:1180-1191

INTRODUCTION Published heritability (h2) estimates for BW of turkeys at various ages during the growing period are generally large. Nestor et al. (1967) reported the unweighted averages of published h 2 estimates of BW based on selected populations were 0.40, 0.42, 0.43, and 0.36, respectively, for birds in the age groups 0 to 8, 9 to 16, 17 to 24, and greater than 24 wk. Arthur and Abplanalp (1975) estimated the h 2 of 18-wk BW was 0.42 based on data from eight commercial flocks. Nestor et al. (1967) observed h 2 estimates in selected populations were lower than estimates in a randombred control (RBC) population when estimates were based on full-sib analysis but not when estimated from regression of

Received for publication August 16, 1995. Accepted for publication April 25, 1996. Claries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Manuscript Number 104-95. 2 Visiting Scholar. Permanent address: Laboratory of Animal Breeding, Department of Dairy Science, Rakuno Gakuen University, Hokkaido College of Arts and Sciences, Ebetsu, Hokkaido 069, Japan.

offspring on mid-parent. Estimates of h 2 of BW in RBC populations based on variance component analysis and parent-offspring regressions were high, ranging from 0.40 to 0.68 (McCartney, 1961; Nestor et al, 1967; Havenstein et al, 1988). Havenstein et al (1988) reported that the h 2 of 16-wk BW differed between the sexes when the estimate was based on the sire component of variance. Toelle et al. (1990) reported that scaling effects were not responsible for the sex difference in the h 2 estimates of 16-wk BW and that the genetic correlation between BW of the two sexes at 16 wk of age was close to unity. The h 2 of egg production of turkeys for various periods of measurement have been estimated by several workers. The individual estimates were quite variable, ranging from -0.51 to 1.51 (McCartney et al, 1968), with an unweighted average of all published estimates of 0.22 (Arthur and Abplanalp, 1975; Marks, 1990). The results of early selection experiments suggested the h 2 of both BW and egg production of turkeys is high. Asmundson and Lloyd (1935), Shaklee et al. (1952), and Knox and Marsden (1954) apparently increased egg production greatly in a few generations of selection.

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SYMPOSIUM: THE EFFECT OF LONG-TERM SELECTION ON GROWTH OF POULTRY Several growth and conformation traits were selected along with egg production by Knox and Marsden (1954). Egg production for 9 mo in Beltsville Small Whites was increased from 80 to 146 eggs per hen over an 8-yr period. However, no environmental control was used in these studies, and, as a result, a large part of the gains observed could have been the result of a positive environmental trend. Abplanalp et al. (1963) developed lines of turkeys by selecting for increased 8-wk or for increased 24-wk BW and compared them to a RBC developed from the same base population. The realized h 2 of 8- and 24-wk BW was 0.43 and 0.62, respectively. Little or no association between egg production and BW was observed in earlier selection studies during the first few generations of selection for either increased egg production (Kosin and Becker, 1959; Shoffner and Leighton, 1962) or increased BW (Ogasawara, et al, 1963; Mukherjee and Friars, 1970). Cook et al. (1962), Clayton (1971), and Arthur and Abplanalp (1975) estimated the genetic correlation between egg production and BW was approximately -0.1. The purpose of the present report was to analyze direct and correlated changes in two long-term selection studies in turkeys. Lines of turkeys were selected for increased egg production (E line; 34 generations) and increased 16-wk BW (F line; 28 generations).

DESIGN OF SELECTION EXPERIMENTS The selection studies described herein had basically the same design. Selected lines were initiated from a RBC line by single-trait selection. In the first generation of selection, methods were employed to insure the selected line included a large number of families in the base generation to reduce founder effect. Generally, this was done by assigning certain hatches to reproduction of the selected line and certain hatches to reproduction of the RBC line. Any individuals not used in the reproduction of the RBC line were available for use in the selected line. Gains in selected lines were expressed as a deviation from the corresponding RBC line in order to remove the influence of environmental variation among generations. Intended and actual selection differentials were calculated. The intended selection differential was the mean of the selected parents expressed as a difference from the population mean. For growth traits, the selection differentials were adjusted for hatch effects. The actual selection differentials were the intended selection differentials weighted for the number of offspring produced. Realized h 2 in the selected lines were estimated from the linear regression of accumulated responses on accumulated actual selection differentials. The standard error of the linear regression coefficient provided an approximate standard error for the h 2 estimate. In general, the RBC and selected lines were maintained with a paired-mating system (Nestor, 1977a)

1181

utilizing a minimum of 36 parental pairs. With this system, mating of parents was at random with the exception that full-sib matings were avoided. The increase in inbreeding in the selected and RBC lines was estimated from the variation in family size (Falconer, 1964). Little genetic drift is expected or was observed in RBC populations with the number of parental pairs used (Nestor, 1977b; Noble et al, 1995).

GENERAL MANAGEMENT OF BIRDS A general description of the husbandry methods, as well as details of data collection, has been published by McCartney et al. (1968) and Nestor (1971). Offspring were produced in multiple hatches in April and May. The same proportion of individuals from each hatch was selected in the selected lines to remove the influence of hatch from the selection response. Birds were reared in confinement until 8 wk of age and then transferred to ranges until 20 or 24 wk of age. Body weights were recorded during the growing period at 8, 16, and 20 or 24 wk of age. Females were given stimulatory lighting (14 h / d ) at approximately 39 wk of age. Males were given stimulatory lighting 2 to 4 wk earlier. For collection of reproduction data, each hen was artificially inseminated twice during the 1st wk of egg production and weekly or biweekly thereafter depending on the line. Volume of semen inseminated per hen varied but was usually greater than the minimum amount generally recommended (0.025 cc) for maximum fertility. Reproduction data were obtained for a 12-wk period beginning when an egg production level of 50% was first attained. Egg weight was obtained by periodically weighing eggs of each hen throughout the reproduction period.

LONG-TERM SELECTION FOR INCREASED EGG PRODUCTION A selection experiment was initiated in 1960 in which the E line was selected for increased egg production. The base population was a RBC line (RBC1; McCartney, 1964) developed from crossing four commercial strains of turkeys in all possible combinations. Selection in the E line was based on total number of eggs produced by dams for various periods of time (84 d for Generations 1 through 3,180 d for Generations 4 through 26, and 250 d for Generations 27 through 34). Unfortunately, egg production of the RBC1 line was recorded for only 84 d in Generations 4 and 5, so estimates of genetic gains in 180-d egg production of the E line were not possible during these generations. The number of E-line offspring grown per generation averaged 1,094 with a range of 1,007 to 1,310 from Generations 10 through 34. The RBC1 line was maintained with 48 parental pairs in Generations 1 and 2 and with 36 pairs thereafter. The E line was reproduced the first two generations with 48 sires and 96 dams (2 dams mated to each sire). In

1182

NESTOR ET AL.

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Generations 3 through 5, 36 parental pairs were used to maintain the E line. Rapidly increasing inbreeding coefficients became a concern; therefore, the 6th generation and thereafter parental pairs were increased to 72. The total increase in inbreeding over 34 generations in the E line was 47.4%, an average of 1.39% per generation. Published estimates by Nestor (1971, 1980) of inbreeding occurring in the E line for the first 18 generations were too low due to an error in calculating variation in family size. The total increase in inbreeding of the RBC1 line was 14.8%, an average of 0.4% per generation.

Direct and Correlated Responses to Selection The direct response to selection for increased egg production, expressed as a deviation from the RBC1 line, is given in Figure 1. For an 84-d production period, the E line exhibited gains until the fifth generation and then appeared to lose egg production relative to the RBC1 line from Generation 5 through Generation 10. A similar result was apparent when egg production was measured for a 180-d production period. Average actual egg production of the E line, plotted by generations, actually increased during Generations 5 to 10. One plausible explanation for these observations is, in Generation 5, breeders of the E and RBC1 lines were moved from a conventional breeder house with windows to a new windowless breeder house. With the change of housing, the method of treating

broody hens was also changed to a more efficient system. It appeared that the more efficient broody-hen management system had a greater impact on the RBC1 line, which expressed a higher incidence of broodiness, than on the E line, in which broodiness was reduced by the selection for increased egg production. The E line hens were exempted from a broody-hen management system in Generation 10 and thereafter, whereas the RBC1 hens were continued on the system. Egg production of the E line relative to the RBC1 line has increased greatly after the management change and shows no consistent indication of slowing down. Based on the linear regression coefficients of response on generations of selection, the average gains in egg production of the E line from the 10th generation onward were 0.76,2.41, and 4.24 eggs, respectively, for 84, 180, and 250 d. The quadratic regression coefficient was significant for 180-d (-0.106, P < 0.01) and 250-d (2.04 P < 0.05) egg production. Large responses in 180-d and 250-d egg production in data from the last two generations of the E line indicate the negative quadratic regression coefficient for 180-d egg production was not signaling a plateau in response to selection. Also, a 180-d egg production was a correlated response in the last 8 generations of the E line. The average phenotypic correlation coefficient between actual selection differentials for 180- and 250-d egg production was 0.73 with a range of 0.61 to 0.91, suggesting that egg production for the two periods of measurement are different traits. All correlation coefficients were highly significant.

SYMPOSIUM: THE EFFECT OF LONG-TERM SELECTION ON GROWTH OF POULTRY

1183

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McCartney et al. (1968) reported the realized h 2 of 84-d egg production was 0.61 + 0.12 (SE) for the first 5 generations of selection. Based on the first 9 generations in the E line, Nestor (1971) reported the realized h 2 of 84-d egg production was 0.33 ± 0.05. After the change in management of broody hens, the realized h 2 of 180-d egg production in the E line was 0.34 ± 0.02 (Generations 10 through 26). Realized h 2 of 250-d egg production in the last 8 generations of the E line was 0.26 ± 0.13. No difference was observed between average intended and actual selection differentials for either 180-d (10.3 eggs) or 250-d (14.7 eggs) egg production, indicating natural selection was not opposing artificial selection. Actual selection differentials for 180-d egg production of the E line decreased from Generation 10 through 26 (-0.58 egg; P < 0.01), indicating a decrease in variation of 180-d egg production in the E line. No significant changes were observed in actual selection differentials for 250-d egg production from Generation 27 through 34. Gains in egg production of the E line were associated with little or no changes in BW at 8, 16, or 24 wk of age during the first four generations of selection (Figures 2 and 3). Body weight of the E line declined greatly during the next few generations of selection. The decline in BW was greater, and occurred sooner, at older ages. No further noticeable change in BW at older ages (16 and 20 or 24 wk of age) occurred until about the 24th generation for males and 27th generation for females when BW of the E line again declined for a few generations. In recent

generations of the E line, no reduction in BW of the E line has been observed. Changes in BW at 8 wk of age exhibited a different pattern. Body weight at 8 wk has been declining since the 22nd generation of selection. There was no significant trend in mortality to 8 wk of age in the E line over generations. Changes observed in egg production and BW of the E line suggest that the genetic correlation between these two traits changed during the course of selection. In the first few generations, the genetic correlation was near zero, became strongly negative the next few generations, returned to near zero for a number of generations, became negative again, and finally returned to near zero for BW at older ages (16 and 20 wk). Previous selection experiments suggested little or no association between BW and egg production in early generations of selection when the selection criterion was BW (Ogasawara et al, 1963; Mukherjee and Friars, 1970) or egg production (Kosin and Becker, 1959; Shoffner and Leighton, 1962). Reported estimates (Cook et al, 1962; Clayton, 1971; Arthur and Abplanalp, 1975) of the genetic correlation between egg production and BW were low (approximately -0.1). Anthony et al. (1990) compared the growth curves of the E and RBC1 lines after 28 generations of selection in the E line. The pattern of growth of the two lines, as described by the Gompertz equation, was different in magnitude of growth (BW at point of inflection and asymptote) but not in form (slope and age at point of inflection and age at asymptote).

1184

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Changes in intensity of lay and broodiness in the E line were summarized for a 180-d production period from Generations 10 through 34. Intensity of lay was estimated by average clutch length, a clutch being defined as the number of eggs laid on consecutive days. Average clutch length increased a total of 5.8 eggs. The rate of increase was 0.17 eggs (P < 0.001) per generation. Broodiness was measured as the total days lost from broodiness and a bird was classified as broody after 5 consecutive d of nonproduction. Broodiness was decreased by 69 d in the E line relative to the RBC1 line over the period of observation. The linear and quadratic regression coefficients were -1.9 and 0.1 d, respectively, both statistically significant. Rate of response to stimulatory lighting (14 h / d) was reduced by a total of 8 d in the E line. The E line also generally exhibited increased fertility, with the deviations from the RBC1 line ranging from 1 to 20% after Generation 5. The linear regression coefficient of response in percentage fertility of the E line on generations (0.23) closely approached significance. Genetic changes in egg production were not associated with changes in hatch of fertile eggs, even though egg weight was greatly reduced (-0.4 g per generation; total of 18 g per egg) in the E line. In the 16th generation of selection in the E line, Strong and Nestor (1980) found that the reduction in egg weight (12.5 g) was due to a disproportionate reduction in albumen. Later studies by Nestor et ol. (1982) (19th generation) and Nestor and Noble (1995) (33rd generation) indicated that the reduction in egg weight of the E line was due to a proportional reduction in all component

parts of the egg. Shell coloration of E-line eggs was changed, with many eggs having no spots.

LONG-TERM SELECTION FOR INCREASED BODY WEIGHT A second RBC line (RBC2) was started from the reciprocal crosses of two commercial turkey lines (Nestor et ah, 1969) and maintained with 36 parental pairs. A subline (F) of the RBC2 line was initiated by mass selection for increased 16-wk BW. From Generations 1 through 21, the F line was also maintained with 36 parental pairs. In Generation 22 and later, the F line was reproduced with 36 males and 72 females (each male being mated with 2 females). Egg production was measured for 180 d throughout the study. The total accumulated inbreeding in the RBC2 and F lines was 12 and 26%, respectively. The respective average increase in inbreeding per generation was 0.42 and 0.93%.

Direct and Correlated Responses to Selection The average number of F-line offspring grown each generation was 451 with a range from 185 to 758. Gains in 16-wk BW of the F line have been consistent over 28 generations of selection (Figure 4) and show no evidence of leveling off. Average gain per generation in 16-wk BW of males and females based on the linear

SYMPOSIUM: THE EFFECT OF LONG-TERM SELECTION ON GROWTH OF POULTRY

1185

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regression coefficient of response on generations was 0.176 and 0.148 kg per generation, respectively. The quadratic regression coefficient was positive and significant for males but not for females. Positive linear and quadratic regression coefficients were also significant for 8- and 20-wk BW changes in the F line. The positive quadratic regression coefficients were probably due to increased selection pressure in the F line in later generations when the number of parents was increased. Mortality to 8 wk of age did not change in the F line. The average intended and actual selection differentials for 16-wk BW in the F line were 0.663 and 0.661 kg, respectively, indicating that natural selection was not an important factor in the F line. The realized h 2 of the 16-wk BW in the F line did not appear to change noticeably over the period of selection. The realized h 2 for Generations 1 through 9 (Nestor, 1977c), 1 through 16 (Nestor, 1984) and 1 through 28 were 0.30 ± 0.04, 0.26 + 0.02, and 0.26 + 0.01, respectively. Arthur and Abplanalp (1975) reported that the average of all published estimates of h 2 of BW was 0.41 based on an average age of 20.7 wk. The actual selection differentials increased with generations (0.018 kg per generation, P < 0.01), which was probably due to the increased number of parents in later generations. Changes in egg production of the F line for two production periods are shown in Figure 5. For both periods, egg production of the F line did not change over the first three generations of selection. During the next 2

generations, a major loss in egg production occurred. No discernable further changes in 84-d egg production were evident through the 14th generation of selection. Since the 14th generation, additional losses in 84-d egg production were evident in the F line. Changes in egg production for 180 d were similar to 84-d egg production except that there were no obvious changes in 180-d egg production after the fifth generation of selection. The genetic correlation between BW during the growing period and egg production changed in the F line similar to the pattern observed in the E line even though the E and F lines started from different base populations and were under different selection criteria. There was no correlation between the two traits during the first three generations of selection in the F line. A strong negative correlation was observed the next two generations of the F line followed by a period when the correlation returned to zero. The two selection studies indicate that the genetic correlation between BW and egg production can change rapidly, reducing the reliability of selection indexes unless the genetic correlation is estimated each generation. The reduction in egg production in the F line was primarily the result of a decrease in intensity of lay (average clutch length) as broodiness only exhibited transitory changes. The loss in average clutch length of the F line was 0.7 eggs over the entire selection period, but the change over generations was positively quadratic. Semen production was reduced in the F line (Nestor, 1977d). Semen volume, spermatozoa concentration, and

1186

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total spermatozoa per ejaculate were reduced relative to the RBC2 line. However, with the mating system used (i.e., insemination with excess numbers of spermatozoa), there was no reduction in percentage fertility. Hatch of fertile eggs was decreased in the F line. The linear regression coefficient was -0.33% (P < 0.001). Walking ability of the F line has declined over generations relative to the RBC2 line. Walking ability was based on a subjective rating of 1 through 5, with a score of 1 indicating the best walking ability with no lateral deviation of the legs and 5 representing birds that could hardly walk or had extreme lateral deviations of the legs or both. Ratings of 2,3, and 4 were intermediates between these extremes. Egg weight increased in the F line. The linear regression coefficient of response on generations was 0.32 g (P < 0.001). The increase in egg weight of the F line was due to a disproportionate increase in albumen (Strong and Nestor, 1980; Nestor et al, 1982; Nestor and Noble, 1995).

Changes in Behavior Foliowing Selection Behavior observations were performed on the RBC2 and F lines in an experiment to study the effect of range and confinement rearing. At all times during the observation periods, birds were classified as eating, drinking, standing, resting, or walking. The number of bouts of each activity per 15-min observation period and the length of each activity bout were recorded. The number of steps taken when birds were walking was recorded. Line effects could not be tested for all behavior traits due to interactions with other main effects (i.e., time of

day, age, and sex). It was possible to test for line differences in number and duration of eating bouts, duration of resting bouts, number of standing bouts, number and duration of walking bouts, and number of steps taken while birds were walking. The lines did not differ in number of eating bouts, duration of resting, number of standing bouts, or number of walking bouts (Table 1). The RBC2 birds had eating bouts of shorter duration than birds from the F line (Table 1). This is in contrast to results with chickens indicating selection for increased BW increases meal number but not meal size (Barbato et

TABLE 1. Changes in behavior traits following selection

Behavior1 Eating, no. Eating, s Resting, s Standing, no. Walking, no. Walking, s Steps, no. Tonic immobility Inductions, no Duration, s

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SYMPOSIUM: THE EFFECT OF LONG-TERM SELECTION ON GROWTH OF POULTRY

1187

TABLE 2. Mortality in various lines of turkeys naturally exposed to fowl cholera and erysipelas Line1 RBC1 E RBC2 F

Fowl cholera (No. males) 73 120 72 77

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al, 1980). Duration of walking bouts was decreased in the F line. When grown on ranges, males from the RBC2 line had improved walking ability scores compared to those of males from the F line. The number of steps taken was less for the F line. Tonic immobility (TI) was measured on a sample of birds from these lines at 20 wk of age. Tonic immobility is generally accepted as an indication of a general state of fearfulness (Beuving et al., 1989). The lines of turkeys differed in both number of inductions required to achieve TI and duration of TI (Table 1). Birds from the F line required fewer inductions to reach a longer duration of TI than birds from the RBC2 line.

Line by Environment Interactions In a study on the effect of range and confinement rearing on different genetic lines of turkeys, line by environment interactions were generally lacking. Range rearing led to increased BW, shank width, and shank depth relative to confinement rearing in both sexes. Rearing environment did not affect shank length of either sex or walking ability scores of females. The response to the two rearing environments was generally similar for the F and RBC2. The only trait influenced by the line by environment interaction was walking ability scores of males. The RBC2 males had improved walking ability scores when range-reared than when confinement-reared, whereas rearing environment did not affect walking ability scores of F males.

CHANGES IN DISEASE RESISTANCE Natural disease outbreaks of erysipelas and fowl cholera occurred involving the RBC1, RBC2, E, and F lines (Saif et al, 1984). The outbreak of fowl cholera, confirmed by isolations of P. multocida, occurred in 34-wk-old males. The males were housed in a single pole-type building, and the outbreak persisted for 3 wk. In the same year, a group of 26-wk-old females from the same lines was intermingled on range where an outbreak of erysipelas, confirmed by isolations of Erysipelas rhusiopathiae, occurred and persisted for 4 wk. The flocks were not vaccinated for either disease, and no complicating secondary infections were detected during the outbreaks.

Mortality observed during the natural disease outbreaks is given in Table 2. During the fowl cholera outbreak, the mortality of E-line males was double (P < 0.05) that for the RBC1 line when the males were housed intermingled. The F line males were housed in pens adjacent to the RBC2 line. Although mortality was higher in the F line than in the RBC2 line (28.5 vs 20.8%), the difference was not significant. During the erysipelas outbreak when all lines were reared intermingled on range, mortality for the F line was 10 times higher than RBC2 line (P < 0.01), but no mortality occurred in the E and RBC1 lines. Because natural disease outbreaks can be influenced by several factors, it was decided to challenge the lines with two disease organisms (P. multocida and Newcastle disease virus) under carefully controlled conditions.

Challenge with P. multocida The culture for challenge trials was obtained from a field isolate of P. multocida, capsular serogroup a, heat stable antigen serotype 3, 4. The challenges were conducted in isolation facilities that restricted the number of birds that could be challenged simultaneously; therefore, multiple challenge trials were utilized. Most challenges were started when the birds were approximately 6 wk of age. The challenge period lasted 2 wk with the birds observed twice daily. Tissues from birds that died during the experiment and live birds at the end of the experimental period were cultured (liver, spleen, and lungs) for the presence of P. multocida. The first series of trials was completed utilizing a small number of birds per group (10 to 22) and unwashed inoculum, thereby allowing inclusion of toxins, if present, with the organisms. In these trials (Sharaf et al, 1988b), it appeared the E line was much more susceptible to P. multocida than the RBC1 line even though the line difference was significant in only one of three trials. The line difference in mortality ranged from 35 to 37% in the three trials. Sharaf et al. (1988a) reported the RBC1 line generally had greater primary and secondary antibody responses than the E line when vaccinated with P. multocida and Newcastle disease virus (NDV) vaccines either alone or in combination, which agreed with the results of the initial challenge trials. However, later challenge trials (Sacco et al, 1991) with washed samples of

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TABLE 3. Mortality following challenge with washed Pasteurella multocida1

TABLE 4. Mortality following challenge with Newcastle disease virus1

Line2

n

Mortality

Line2

n

E

164

(%) 45.7b

E

194

RBCl

165

43.6b

RBCI

196

18.4b

F RBC2

161 165

72.1* 43.6b

F RBC2

194 196

32.5= 15.8b

a b

Mortality (%) 17.5b

a b

- Means with no common superscript differ significantly (P < 0.05). JBirds were inoculated subcutaneously at about 6 wk of age with 1.2 x 107 washed P. multocida, serotype 3, 4. 2 RBC1 and RBC2 = randombred control lines; E = subline of RBCl selected for increased egg production; F = subline of RBC2 selected for increased 16-wk body weight.

- Means with no common superscript differ significantly (P < 0.05). iFour-week-old birds were inoculated with 0.1 mL Texas GB strain containing 1077 mean embryo infectious dose. 2 RBC1 and RBC2 = randombred control lines; E = subline of RBCl selected for increased egg production; F = subline of RBC2 selected for increased 16-wk body weight.

P. multocida (1.2 x 10 7 organisms per bird) and an increased number of birds failed to produce differences between the E and RBCl lines in response to the organism (Table 3). It is possible line differences observed in the first series of trials were the result of chance (due to the small number of birds involved) or the results could be explained by the E line being more susceptible to a P. multocida toxin, a possibility currently being investigated. The F line was more susceptible to challenge with P. multocida than the RBC2 line (Table 3). Mortality in the F line was nearly double that of the RBC2 line. In addition, the number of days from exposure to severe clinical symptoms or death was decreased in the F line compared with the RBC2 line (5.8 vs 8.2 d, P < 0.05).

II genes were identified in the RBCl and RBC2 lines by Emara et al. (1992) using restriction fragment length polymorphism (RFLP) analysis. The haplotypes were found to be in linkage disequilibrium with allelic specificities by mixed lymphocyte reaction, graft-versushost reaction, and skin graft reaction (Emara et al, 1993). All breeders of the RBCl, RBC2, F, and E lines were used for MHC Class II genotyping using a RFLP analysis. The method of DNA isolation was a slight modification of the method used by Emara et al. (1992). A nonradioactive probe w a s prepared from a 2.3-kb fragment of a genomic clone of a chicken Class II (3 gene (Xu et al, 1989). The DNA was digested with the Pvull restriction enzyme. Prehybridization, hybridization, and color development were based on the procedures described in the Genius System User's Guide, 3 except hybridization was conducted without formamide (Maniatis et al, 1986). In addition to the four types (A, B, C, and D) reported previously (Emara et al, 1992), 18 new RFLP patterns were identified with the same restriction enzyme (Pvull). Because the patterns were not known to be from homozygous individuals, the new haplotypes have not yet been determined. However, through examination of the patterns within families from offspring with new patterns, and in the entire populations, it is estimated there were three new frequent haplotypes (Table 5) that occurred more than 15 times in the four lines and some

Challenge with Newcastle Disease Virus The various turkey lines were challenged with a virulent virus (NDV, Texas GB strain) to investigate possible genetic differences to a viral infection. Fourweek-old birds were inoculated by the cloacal route with a 0.1-mL dose containing 107-7 mean embryo infectious virus. Birds were observed twice daily for 2 wk. Line differences in mortality following challenge with the NDV were observed (Table 4; Tsai et al., 1992). As was the case with P. multocida, mortality was higher in the F line than in the RBC2 line and no line difference was observed between the E and RBCl lines.

TABLE 5. Frequencies (percentages) of MHC Class II haplotypes in four turkey lines1

FREQUENCY OF MHC HAPLOTYPES The MHC is associated with resistance or susceptibility of chickens to disease organisms, including NDV (Dunnington et al, 1992) and P. multocida (Lamont et al, 1987). To the authors' knowledge, there has been no published research on the effect of turkey MHC haplotypes on disease resistance, no doubt a result of the general lack of knowledge of MHC haplotypes in existing turkey lines. Four haplotypes of the MHC Class

3

Boehringer Mannheim, Indianapolis, IN 46206.

Haplotype

RBCl

E

RBC2

F

A B C D X Y Z R2

13.9 31.2 9.0 31.9 1.4 9.7 2.8 0

30.0 47.9 0 0.4 20.8 0 0 1.0

34.0 24.3 1.4 10.4 0 0 24.3 5.6

29.6 10.2 8.8 46.8 0.9 0 2.8 0.9

!RBC1 and RBC2 = randombred control lines; E = subline of RBCl selected for increased egg production; F = subline of RBC2 selected for increased 16-wk body weight. 2 Pooled rare haplotypes.

SYMPOSIUM: THE EFFECT OF LONG-TERM SELECTION ON GROWTH OF POULTRY rare types appearing less than five times. There was a totally new band (4.8 kb) in Haplotypes X and Y. Haplotype Z was a new combination pattern shared with some of Haplotypes B and D. The hypothesized haplotypes were used as types for a chi-square test. Haplotype frequencies were significantly (P < 0.01) different between the line comparisons RBCl vs RBC2, RBCl vs E, RBC2 vs F, and E vs F (Table 4). Compared with its control, Haplotypes A, B, and X were greatly increased in the E line, with the increase being greatest for Haplotype X. Haplotypes C, D, Y, and Z were nearly, if not completely, eliminated in the E line. Changes in haplotype frequencies were also noted in the F line relative to its randombred control. Frequencies of Haplotypes C and D increased greatly but frequencies of Haplotypes A, B, and Z decreased in the F line. Differences in predominant haplotypes were evident in the two selected lines (Table 5). In the E line, Haplotype B was predominate with about 48% of the total haplotypes whereas Haplotype D in the F line had a similar percentage. The frequencies of the common haplotypes in the two selected lines changed in opposite directions. It appears that MHC haplotypes or closely linked genes may be associated with traits of economical importance such as egg production and BW in the turkey. Similar associations have been observed in chickens (Simonsen et ah, 1982; Bacon, 1987; Dietert et al, 1991; Abplanalp et al, 1992). Unlike the selected lines, MHC frequencies in the RBC lines were more widely distributed among the haplotypes (Table 5). The RBC lines shared the same haplotypes (A, B, and D), whose frequencies ranged from about 10 to 34%. There was a significant difference in the percentages of homozygotes of MHC haplotypes between the F line (45%) and its RBC (33%). The frequency of homozygotes did not differ between the E line (32%) and its RBC (38%).

HORMONAL MEASUREMENTS IN THE TURKEY LINES Several measurements of hormonal levels have been made over the course of selection in the E and F lines. These measurements were made to evaluate the influence of genetic changes in BW and egg production on hormonal concentration rather than to estimate time trends in the lines. Nestor and Bacon (1982) measured the corticosterone concentration of the lines after cold stressing (4 C for 4 h) the birds at 4 wk of age. Corticosterone concentration was increased in the E line and decreased in the F line relative to their RBC. The ontogeny of plasma growth hormone (GH) has been determined in the lines. Vasilatos-Younkin et al. (1988) found that RBC2 and F lines did not differ in GH concentration from 0 to 14 d of age but GH concentrations were higher in the RBC2 line from 21 to 195 d of

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age. Bacon et al. (1989) also reported GH concentration of the RBC2 line was higher than the F line from 4 to 24 wk of age. Vasilatos-Younkin et al. (1990) found total hepatic GH binding capacity did not differ between the RBC2 and F lines at 2, 4, 8,14, and 24 wk of age. Plasma GH was higher in Line E than in the RBCl line at hatching but higher in the RBCl line than in Line E from Weeks 7 to 28 (Anthony et al, 1990). Bacon et al. (1993) measured plasma concentrations of insulin-like growth factor-I (IGF-I) in the RBC2 and F lines from 1 to 28 wk of age. From 1 to 7 wk, the concentrations of IGF-I were higher in the F than the RBC2 line. From 8 to 28 wk, there was no difference between lines. An interaction between lines and sexes was observed in plasma IGF-I between 16 and 28 wk. The plasma concentration of IGF-I was not different between lines for males, whereas the females of the RBC2 line had a higher concentration than females of the F line.

REFERENCES Abplanalp, H., F. X. Ogasawara, and V. S. Asmundson, 1963. Influence of selection for body weight at different ages on growth of turkeys. Br. Poult. Sci. 4:71-82. Abplanalp, H., K. Sato, D. Napolitano, and J. Reid, 1992. Reproductive performance of inbred congenic Leghorns carrying different haplotypes for the major histocompatibility complex. Poultry Sci. 71:9-17. Anthony, N. B., R. Vasilatos-Younken, D. A. Emmerson, K. E. Nestor, and W. L. Bacon, 1990. Pattern of growth and plasma growth hormone secretion in turkeys selected for increased egg production. Poultry Sci. 69:2057-2063. Arthur, J. A., and H. Abplanalp, 1975. Linear estimates of heritability and genetic correlation for egg production, body weight, conformation and egg weight of turkeys. Poultry Sci. 54:11-23. Asmundson, V. S., and W. E. Lloyd, 1935. Effect of age on reproduction of the turkey hen. Poultry Sci. 14:259-266. Bacon, L. D., 1987. Influence of the major histocompatibility complex on disease resistance and productivity. Poultry Sci. 66:802-811. Bacon, W. L., K. E. Nestor, D. A. Emmerson, R. VasilatosYounken, and D. W. Long, 1993. Circulating IGF-I in plasma of growing male and female turkeys of medium and heavy weight lines. Domest. Anim. Endocrinol. 10: 267-277. Bacon, W. L., R. Vasilatos-Younken, K. E. Nestor, B. J. Andersen, and D. W. Long, 1989. Pulsatile patterns of plasma growth hormone in turkeys: effects of growth rate, age and sex. Gen. Comp. Endocrinol. 75:417-426. Barbato, G. F., J. A. Cherry, P. B. Siegel, and H. P. Van Krey, 1980. Quantitative analysis of the feeding behavior of four populations of chickens. Physiol. Behav. 25:885-891. Beuving, G., R. B. Jones, and H. J. Blokhuis, 1989. Adrenocortical and heterophil/lymphatocyte responses to challenge in hens showing short or long tonic immobility reactions. Br. Poult. Sci. 30:175-184. Clayton, G. A., 1971. Egg production in turkeys. Br. Poult. Sci. 12:463^174. Cook, R. E., W. L. Blow, C. C. Cockerham, and E. W. Glazener, 1962. Improvement of reproductive traits and body measurements of turkeys. Poultry Sci. 41:556-563.

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Dietert, R. R., R. L. Taylor, Jr., and M R. Dietert, 1991. Biological function of the chicken major histocompatibility complex. Crit. Rev. Poult. Biol. 3:111-129. Dunnington, E. A., C. T. Larsen, W. B. Gross, and P. B. Siegel, 1992. Antibody responses to combinations of antigens in White Leghorn chickens of different background genomes and major histocompatibility complex genotypes. Poultry Sci. 71:1801-1806. Emara, M. G., K. E. Nestor, and L. D. Bacon, 1993. The turkey major histocompatibility complex: Characterization by mixed-lymphocyte, graft-versus-host splenomegaly, and skin graft reactions. Poultry Sci. 72:60-66. Emara, M. G., K. E. Nestor, D. N. Foster, and S. J. Lamont, 1992. The turkey major histocompatibility complex: Identification of Class II genotypes by restriction fragment length polymorphism analysis of deoxyribonucleic acid. Poultry Sci. 71:2083-2089. Falconer, D. S., 1964. Introduction to Quantitative Genetics. Oliver and Boyd, Edinburgh, UK. Havenstein, G. B., K. E. Nestor, V. D. Toelle, and W. L. Bacon, 1988. Estimates of genetic parameters in turkeys. 1. Body weight and skeletal characteristics. Poultry Sci. 67: 1378-1387. Knox, C. W., and S. J. Marsden, 1954. Breeding for increased egg production in Beltsville Small White turkeys. Poultry Sci. 33:443-147. Kosin, I. L., and W. A. Becker, 1959. Shifts in the phenotype of lines within a turkey strain, following several generations of single-trait selective breeding. Poultry Sci. 38:1220. (Abstr.) Lamont, S. J., C. Bolin, and N. Cheville, 1987. Genetic resistance to fowl cholera is linked to the major histocompatibility complex. Immunogenetics 25:284-289. Maniatis, T., E. F. Fritsch, and J. Sambrook, 1986. Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Press, Cold Spring Harbor, NY. Marks, H. L., 1990. Genetics of egg production in other galliforms. Pages 761-770 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, New York, NY. McCartney, M. G., 1961. Heritabilities and correlations for body weight and conformation in a randombred population of turkeys. Poultry Sci. 40:1694-1700. McCartney, M. G., 1964. A randombred control population of turkeys. Poultry Sci. 43:730-744. McCartney, M. G., K. E. Nestor, and W. R. Harvey, 1968. Genetics of growth and reproduction in the turkey. 2. Selection for increased body weight and egg production. Poultry Sci. 47:981-990. Mukherjee, T. K., and G. W. Friars, 1970. Heritability estimates and selection responses of some growth and reproductive traits in control and early growth selected strains of turkeys. Poultry Sci. 49:1215-1222. Nestor, K. E., 1971. Genetics of growth and reproduction in the turkey. 3. Further selection for increased egg production. Poultry Sci. 50:1672-1682. Nestor, K. E., 1977a. The use of a paired mating system for the maintenance of experimental populations of turkeys. Poultry Sci. 56:60-65. Nestor, K. E., 1977b. The stability of two randombred control populations of turkeys. Poultry Sci. 56:54-57. Nestor, K. E., 1977c. 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., 1977d. The influence of a genetic change in egg production, body weight, fertility or response to cold stress on semen yield in the turkey. Poultry Sci. 56: 421-125. Nestor, K. E., 1980. Genetics of growth and reproduction in the turkey. 8. Influence of a management change on response to selection for increased egg production. Poultry Sci. 59: 1961-1969. 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., and W. L. Bacon, 1982. Results of cold stress in strains of turkeys selected for growth rate and egg production. Poultry Sci. 61:652-654. Nestor, K. E., M. G. McCartney, and N. Bachev, 1969. Relative contributions of genetics and environment to turkey improvement. Poultry Sci. 48:1944-1949. Nestor, K. E., M. G. McCartney, and W. R. Harvey, 1967. Genetics of growth and reproduction in the turkey. 1. Genetic and non-genetic variation in body weight and body measurements. Poultry Sci. 46:1374-1384. Nestor, K. E., and D. O. Noble, 1995. Influence of selection for increased egg production, body weight, and shank width of turkeys on egg composition and the relationship of the egg traits to hatchability. Poultry Sci. 74:427-433. Nestor, K. E., C. F. Strong, Jr., and W. L. Bacon, 1982. Influence of strain and length of lay on total egg weight and weight of the component parts of turkey eggs. Poultry Sci. 61: 18-24. Noble, D. O., D. A. Emmerson, and K. E. Nestor, 1995. The stability of three randombred control lines of turkeys. Poultry Sci. 74:1074-1078. Ogasawara, F. X., H. Abplanalp, and V. S. Asmundson, 1963. Effect of selection for body weight on reproduction in turkey hens. Poultry Sci. 42:838-842. Sacco, R. E., Y. M. Saif, K. E. Nestor, N. B. Anthony, D. A. Emmerson, and R. N. Dearth, 1991. Genetic variation in resistance of turkeys to experimental challenge with Pasteurella multocida. Avian Dis. 35:950-954. Saif, Y. M., K. E. Nestor, R. N. Dearth, and P. A. Renner, 1984. Case Report—Possible genetic variation in resistance of turkeys to erysipelas and fowl cholera. Avian Dis. 28: 770-773. Shaklee, W. E., C. W. Knox, and S. J. Marsden, 1952. Heritability of egg production in Beltsville Small White turkeys. Poultry Sci. 31:935. (Abstr.) Sharaf, M. M., K. E. Nestor, Y. M. Saif, R. E. Sacco, and G. B. Havenstein, 1988a. Antibody response to Newcastle disease virus and Pasteurella multocida of two strains of turkeys. Poultry Sci. 67:1372-1377. Sharaf, M. M., K. E. Nestor, Y. M. Saif, R. E. Sacco, and G. B. Havenstein, 1988b. Research note: Response of two lines of turkeys to challenge with Pasteurella multocida. Poultry Sci. 67:1807-1809. Shoffner, R. N., and A. T. Leighton, 1962. Photoperiodicity and selection for egg production in the turkey (Meleagris gallapavo). Pages 37-42 in: Proceedings of the 12th World's Poultry Congress, Sydney, Australia. Simonsen, M., N. Kolstad, I. Edfors-Lilja, L.-E. Liljedahl, and P. Sorensen, 1982. Major histocompatibility genes in egglaying hens. Am. J. Reprod. Immunol. 2:148-152. Strong, C. F., Jr., and K. E. Nestor, 1980. Egg quality and reproduction in turkeys. 5. Relationship among traits in medium- and large-bodied lines. Poultry Sci. 59:417-423.

SYMPOSIUM: THE EFFECT OF LONG-TERM SELECTION ON GROWTH OF POULTRY Tsai, H. J., Y. M. Saif, K. E. Nestor, D. A. Emmerson, and R. A. Patterson, 1992. Genetic variation in resistance of turkeys to experimental infection with Newcastle disease virus. Avian Dis. 36:561-565. Toelle, V. D., G. B. Havenstein, K. E. Nestor, and W. L. Bacon, 1990. Estimates of genetic parameters in turkeys. 3. Sexual dimorphism and its implications in selection procedures. Poultry Sci. 69:1634-1643. Vasilatos-Younken, R., W. L. Bacon, and K. E. Nestor, 1988. Relationship of plasma growth hormone to growth within and between turkey lines selected for differential growth rates. Poultry Sci. 67:826-834.

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Vasilatos-Younken, R., K. S. Gray, W. L. Bacon, K. E. Nestor, D. W. Long, and J. L. Rosenberger, 1990. Ontogeny of growth hormone (GH) binding in the domestic turkey: evidence of sexual dimorphism and developmental changes in relationship to plasma GH. J. Endocrinol. 126: 131-139. Xu, Y., J. Pitcovske, L. Person, C. Auffray, Y. Bourlet, B. M. Gerndt, A. W. Nordskog, S. J. Lamont, and C. M. Warner, 1989. Isolation and characterization of three Class II MHC genomic clones from the chicken. J. Immunol. 142: 2122-2132.