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Inbreeding Effects on Reproductive Traits in the Ring-Necked: Pheasant
Inbreeding Effects on Reproductive Traits in the Ring-Necked: Pheasant A. E. WOODARD, HANS ABPLANALP, JACQUELINE M. PISENTI, and LESTER R. SNYDER Department of Avian Sciences, University of California, Davis, California 95616 (Received for publication January 4, 1983)
1983 Poultry Science 62:1725-1730 INTRODUCTION
The effects of inbreeding on reproductive performance have been intensively studied in the domestic chicken by Shoffner (1948) and Wilson (1948) and to a less extent in turkeys (Abplanalp and Woodard, 1967), partridges (Woodard et al., 1982), and quail (Sittman et al., 1966; Kulenkamp et al, 1973); relatively little information is available on other avian species. According to Shoffner (1948), inbreeding in chickens has been found to have a deleterious effect on most reproductive traits, such as egg production, fertility, hatchability, and posthatch mortality. Full-sib inbreeding experiments with Japanese quail by Sittmann et al. (1966) and Kulenkamp et al. (1973) showed a marked depression in most reproductive traits, resulting in a high loss in inbred lines within the first few generations of full-sib inbreeding. Similar results were reported for the Red-legged partridge by Woodard et al. (1982), who found that approximately 80% of established inbred lines become extinct by the second generation of full-sib mating. Woodard and coworkers reported that fertility and hatchability were the two traits most strongly affected. To our knowledge, the effect of inbreeding on reproductive performance in Ring-necked pheasants has not been studied. Because penmated birds allow pedigrees only for the male
parent, full-sib mating was not a feasible mating procedure for pheasants under our conditions. Therefore, it was the objective of this study to determine the effect of inbreeding on reproductive traits in pheasants using a system of successive backcrossing of daughters each generation to a common male ancestor. MATERIALS AND METHODS
This study was based on data collected from 1978 to 1982. Development of inbred lines was attempted from six unselected single males of Mongolian origin (Phasianus c. mongolicus) and four from Chinese origin (Phasianus c. torquatus), respectively. These belonged to closed flocks that were mass mated and maintained at the University of California since 1972. To establish the lines (Go) each of 10 selected sires was mated with 6 randomly selected females of his own flock in 1978. In subsequent generations each male was mated with surviving daughters of the previous year. The general mating plan was to save approximately 30 chicks from each line every generation. However, this effort became more difficult as depression of reproductive traits progressed with each new generation of inbreeding. Whereever the original sire died, surviving daughters were mated to one of their brothers or to a half-brother of the same generation, the latter
1725
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ABSTRACT Ten inbred lines of Ring-necked pheasants were established in 1978 and mated for four generations using a system of repeated backcrossing of daughters to a common sire. In the event the old sire died, the surviving daughters were mated to a surviving brother or half-brother of the same generation. Only 4 of 10 original inbred lines survived four generations of backcrossing; two involved matings with the original sire and two with brothers or half-brothers of Generations 1 and 3, respectively. Egg production, hatchability, and viability were the three traits most affected by inbreeding depression. For 4 generations of inbreeding, the coefficients of regression for all inbred lines on a 10% increase in inbreeding were —5.89, —.42, —1.73, and —3.04 for egg production, egg weight, fertility, and hatchability, respectively. Inbreeding had less severe effects on reproductive traits in two of the four surviving lines. There is evidence that intense early selection among lines for high performance after one generation of inbreeding F = .250 will enhance the success of establishing highly viable inbred lines of pheasants. (Key words: inbreeding, egg production, egg weight, fertility, hatchability)
WOODARD ET AL
1726
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then becoming the new sire for future backcross matings in that line. The random lines consisted of the Chinese variety only. They are generally smaller in size than the Mongolian and lay slightly smaller eggs. Approximately 200 Chinese random chicks were hatched each generation to reproduce the line and maintain at least 100 random breeders per generation. For all years, mixed groups of inbred and randombred chicks of both breeds were brooded on the floor, under electric hovers, and given natural daylight only. At 8 weeks of age, the birds were moved to floor pens located in an opensided building. During the growing period, females were kept separate from males by lines. Males from each inbred line were kept in reserve each generation in event an old sire should die. One month before expected lay of the first egg (about April 1), the old sires were placed in single mating pens with their inbred daughters. Nest boxes were placed in each pen, and the birds were fed a turkey layer diet containing 20% crude protein. All birds were debeaked and specked (a plastic antipick device fastened to the beak). Eggs were gathered twice daily, stored in a cold room at a temperature of 12.8 C and a relative humidity of 70%, and set every 14 days. Data were subjected to curvilinear regression analysis as described by Snedecor and Cochran (1967). Inbreeding coefficients were calculated according to Falconer (1960). The upper level
of inbreeding (F) was used for determining regressions in lines substituted with new males.
RESULTS
After four generations of backcrossing, six inbred lines had become extinct with only four lines remaining to be mated. Of these four, two were matings using the original sires and two with sons of the original sires substituted at Generations 1 and 3, respectively. Because the birds were not pedigreed according to individual hens, it was not possible to determine the exact relationship of a new male to the inbred females of the same line. However, the range of coefficients of inbreeding for the lines substituted with sons of the sires were calculated and given in Figure 1. Egg Production. As shown in Figure 2, average number of eggs per hen over a 12-week period declined in both random and inbred lines at Generations 2 and 3, respectively. However, the greatest decrease occurred in inbred hens at F = .438 when egg production was at a low of about 31 eggs per hen as compared to 47 eggs per hen for the random line. A slight recovery in egg production was noted for the random line in Generation 4. There was good consistency among inbred lines for regression of egg number. The results show a loss of approximately 5.8 eggs for each 10% increase in inbreeding (Table 1). Correla-
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on May 25, 2015
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tion coefficients were significant within lines as well as among lines. Egg Weight. Egg size in the Mongolian strain is normally greater than in Chinese pheasants; thus, egg size is compared between Chinese inbred and Chinese control lines only. Egg weight had decreased about 2.4 g for hens that were 37.5% inbred (Fig. 2). However, a substantial recovery in egg weight was made in the next generation due to the elimination of five lines having an average egg weight of 28.7 vs. 30.5 g for lines surviving three generations of backcrossing to a common sire. Within-line £regression for egg weight was somewhat variable but showed an average decrease of about .42 g for every 10% increase in inbreeding (Table 1). Although most within-line correlations for egg weight were generally high and negative, most values were not statistically significant suggesting that variability within lines was substantial. Fertility. Average fertility in the random line remained relatively constant (91 to 93%) over the 4 years (Fig. 2). A sharp drop in fertility occurred in the inbred lines at .250 and .375 inbreeding followed by a substantial increase in fertility at F = .438 inbreeding. It is noted that lines surviving four generations of backcrossing
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INBREEDING IN PHEASANTS
WOODARD ET AL.
1728
DISCUSSION A system of inbreeding using repeated backcrossing of daughters to a common sire adversely affected all reproductive traits studied but not in the same order of magnitude for all inbred lines. Egg production was the most severely depressed trait, regressing by approximately 5.8% for every 10% increase in inbreeding. The persistent decline in egg production for
TABLE 2. Percent mortality in inbred pheasants
G (F) 1
1
1 .25 2 .375 3 .438 4 .469
8.0 13.6 28.6 22.7
1
2 50.0 100.0 ...
Upper level of inbreeding.
•crossed to a common sire for four generations
7
3
4
5
6
40.7 63.6 100.0
17.9 15.4 12.0 0
33.3 50.0 57.1
20.0 17.9 37.5 17.9 58.3 . ..
8
9
10
27.6 34.8 42.9 41.9
26.7 15.0 60.0
31.0 11.0 28.6
Combined lines
Control
26.1 27.9 37.2 23.1
11.0 15.3 11.8 9.0
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the random line in Generations 2 and 3 does indicate some negative environmental influence that apparently had no adverse carryover to other reproductive traits studied. The greatest loss in reproductive performance occurred in the second generation for most inbred lines. That was to be expected because the greatest increase in the number of deleterious recessive genes are combined at an inbreeding coefficient of 25%. It is noted, however, that some lines survived many generations of inbreeding showing only minor levels of depression for most traits, especially Lines 4 and 8. This agrees with studies of Kulenkamp et al. (1973), Woodard et al. (1982) and, most of all, Shoffner (1948), who postulated that inbreeding has a general depressive effect on most reproductive traits but does not necessarily act in a progressive or cumulative manner in all inbred lines. Thus, our surviving inbred lines were not subject to the deleterious nature of inbreeding to the same extent as were lines lost during Generation 3 or before. To demonstrate this point, the performance of lines surviving four generations of inbreeding was compared to that of lines lost after three generations of inbreeding (excluding Line 2, lost after two generations of inbreeding) and the results given in Table 3. The coefficient of regression for egg number and fertility, respectively, was two and five times greater for lines terminating at F = .375 as compared to those alive at F = .438. This partly may be the reason for the apparent recovery of fertility, hatchability and egg weight given at F = .438 in Fig. 2. For practical purposes, it may be possible to select inbred lines with high survival potential after one generation of backcrossing (F = .250). A comparison of surviving lines and those not surviving is given in Table 4. The surviving inbred lines were found to be superior to nonsurviving lines in all traits at F = .250,
were generally superior to the nonsurviving lines for several reproductive traits including fertility. In fact, Lines 4 and 8 show a remarkable lack of inbreeding depression at F = .438 (Table 1). The degree of variability in fertility among lines certainly is supportive of the lower correlation value for all lines. Hatcbability. Of the traits studied, hatchability showed the second greatest decline after three generations of inbreeding (Fig. 2). There was approximately a 40% difference in hatchability between the inbred and random lines at .250 inbreeding with inbred lines showing only a slight improvement at higher levels of inbreeding. Coefficients of regression for hatchability were markedly variable among lines being as high as - 1 0 . 8 8 and - 1 0 . 8 0 for Lines 6 and 9, respectively, that were lostat .375 inbreeding and as low as —.81 and —2.84, respectively, for Lines 4 and 8 that showed only a slight drop in hatchability (Table 1) over four generations of inbreeding. Mortality. Posthatch mortality to 8 weeks ranged from 9 to 15% in the random line (Table 2). Mortality was highly variable among inbred lines, averaging twice that for the random line at F = .250 and .375 and more than three times greater at F = .438. It is of interest to note that, with exception of Line 8, all surviving lines had less than 30% mortality for any one generation whereas lines that exceeded 50% mortality were generally lost by the following generation.
INBREEDING IN PHEASANTS
1729
TABLE 3. Comparison of coefficient of regression (b) and correlation (r) for egg number, eggweight, percent fertiliy, and hatchability on a 10% increase in inbreeding for inbred hens mated for three and four generations F = .375 (5 lines)
Eggs/hen Eggweight, g Fertility, % Hatchability, % 1
F = .438 (4 lines)
b
r
b
r
-7.75 -.82 -7.09 -5.32
-.912 -.956 -.759 -.932
-4.55 -.44 -1.50 -3.65
-.872 -.836 -.387 -.673
TABLE 4. Comparison of reproductive traits between surviving and nonsurviving inbred lines at F= .250 Eggs/hen
Egg weight
Fertility
Hatchability
Mortality
(no.)
(g)
Surviving lines (4)
(%)
43.8
31.8
82.5
40.6
18.7
Nonsurviving lines (6)
41.3
29.2
65.7
23.8
47.3
TABLE 5. Effect of age of sire and level of inbreeding on several reproductive traits in the pheasants Matings
Dam
Sire
Eggs/hen
lyear(8)' 1 year (8) F = .438 (4)
4 year (1) 3 year (1) 1 year (1)
51.5 50.0 45.0
(no.) 2 1 1 1
Egg weight
Fertility
(g) 28.4 29.1 30.4
Hatchability (%)
71.8 82.3 47.6
72.0 71.0 39.0
( ) = Number of birds.
especially for important traits such as fertility, hatchability, and viability of young chicks. The observed decline in fertility could be due to the advancing age of sires. Therefore, matings were made between sires and young random line females. Other matings were made between highly inbred females (F = .438) and a young random line male. The results are given in Table 5. The performance of the three aged males mated to young random females clearly demonstrates that age, at least up to 4 years, was not an important factor in depressing fertility and hatchability of eggs. The performance of females inbred at F = .438, when crossed with a young male, showed a slight
improvement in fertility and hatchability over the previous generation; the values, however, were twice as low as those of the random females. Because of the limited matings, the results are not conclusive but indicate an adverse effect of inbreeding on female performance as mothers. Also, the age of males, up to 4 years of age, appears unimportant as far as performance of progeny is concerned. Our results support other investigations that egg production, hatchability, and chick viability are three traits most seriously affected by inbreeding depression in avian species such as the partridge (Woodard et al., 1982) and coturnix (Sittmann et al., 1966). The use of
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on May 25, 2015
Upper level of inbreeding.
WOODARD ET AL.
1730
backcrossing as a method of inbreeding does not appear to reduce the deleterious effects of inbreeding even when it is practiced at a slower rate. Our findings do suggest, however, that intense selection for high performance early in the inbreeding program is a satisfactory way of establishing surviving inbred lines.
REFERENCES
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on May 25, 2015
Abplanalp, H., and A. E. Woodard, 1967. Inbreeding effects under continued sib-mating in turkeys. Poultry Sci. 46:1225-1226. Falconer, D. S., 1960. Introduction to Quantitative Genetics. Ronald Press Co., New York, NY.
Kulenkamp, A. W., C. M. Kulenkamp, and T. H. Coleman, 1973. The effects of intense inbreeding (brother X sister) on various traits in Japanese quail. Poultry Sci. 52:1240-1246. Shoffner, R. N., 1948. The reaction of the fowl to inbreeding, Poultry Sci. 27:448-452. Sittmann, K., H. Abplanalp, and R. A. Fraser, 1966. Inbreeding depression in Japanese quail. Genetics 54:371-379. Snedecor, G. W., and W. G. Cochran, 1967. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, IA. Wilson, W. O., 1948. Egg production rate and fertility in inbred chickens. Poultry Sci. 27:719—726. Woodard, A. E., H. Abplanalp, and L. Snyder, 1982. Inbreeding depression in the Red-legged partridge. Poultry Sci. 61:1579-1584.
1983 Poultry Science 62:1725-1730 INTRODUCTION
The effects of inbreeding on reproductive performance have been intensively studied in the domestic chicken by Shoffner (1948) and Wilson (1948) and to a less extent in turkeys (Abplanalp and Woodard, 1967), partridges (Woodard et al., 1982), and quail (Sittman et al., 1966; Kulenkamp et al, 1973); relatively little information is available on other avian species. According to Shoffner (1948), inbreeding in chickens has been found to have a deleterious effect on most reproductive traits, such as egg production, fertility, hatchability, and posthatch mortality. Full-sib inbreeding experiments with Japanese quail by Sittmann et al. (1966) and Kulenkamp et al. (1973) showed a marked depression in most reproductive traits, resulting in a high loss in inbred lines within the first few generations of full-sib inbreeding. Similar results were reported for the Red-legged partridge by Woodard et al. (1982), who found that approximately 80% of established inbred lines become extinct by the second generation of full-sib mating. Woodard and coworkers reported that fertility and hatchability were the two traits most strongly affected. To our knowledge, the effect of inbreeding on reproductive performance in Ring-necked pheasants has not been studied. Because penmated birds allow pedigrees only for the male
parent, full-sib mating was not a feasible mating procedure for pheasants under our conditions. Therefore, it was the objective of this study to determine the effect of inbreeding on reproductive traits in pheasants using a system of successive backcrossing of daughters each generation to a common male ancestor. MATERIALS AND METHODS
This study was based on data collected from 1978 to 1982. Development of inbred lines was attempted from six unselected single males of Mongolian origin (Phasianus c. mongolicus) and four from Chinese origin (Phasianus c. torquatus), respectively. These belonged to closed flocks that were mass mated and maintained at the University of California since 1972. To establish the lines (Go) each of 10 selected sires was mated with 6 randomly selected females of his own flock in 1978. In subsequent generations each male was mated with surviving daughters of the previous year. The general mating plan was to save approximately 30 chicks from each line every generation. However, this effort became more difficult as depression of reproductive traits progressed with each new generation of inbreeding. Whereever the original sire died, surviving daughters were mated to one of their brothers or to a half-brother of the same generation, the latter
1725
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on May 25, 2015
ABSTRACT Ten inbred lines of Ring-necked pheasants were established in 1978 and mated for four generations using a system of repeated backcrossing of daughters to a common sire. In the event the old sire died, the surviving daughters were mated to a surviving brother or half-brother of the same generation. Only 4 of 10 original inbred lines survived four generations of backcrossing; two involved matings with the original sire and two with brothers or half-brothers of Generations 1 and 3, respectively. Egg production, hatchability, and viability were the three traits most affected by inbreeding depression. For 4 generations of inbreeding, the coefficients of regression for all inbred lines on a 10% increase in inbreeding were —5.89, —.42, —1.73, and —3.04 for egg production, egg weight, fertility, and hatchability, respectively. Inbreeding had less severe effects on reproductive traits in two of the four surviving lines. There is evidence that intense early selection among lines for high performance after one generation of inbreeding F = .250 will enhance the success of establishing highly viable inbred lines of pheasants. (Key words: inbreeding, egg production, egg weight, fertility, hatchability)
WOODARD ET AL
1726
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then becoming the new sire for future backcross matings in that line. The random lines consisted of the Chinese variety only. They are generally smaller in size than the Mongolian and lay slightly smaller eggs. Approximately 200 Chinese random chicks were hatched each generation to reproduce the line and maintain at least 100 random breeders per generation. For all years, mixed groups of inbred and randombred chicks of both breeds were brooded on the floor, under electric hovers, and given natural daylight only. At 8 weeks of age, the birds were moved to floor pens located in an opensided building. During the growing period, females were kept separate from males by lines. Males from each inbred line were kept in reserve each generation in event an old sire should die. One month before expected lay of the first egg (about April 1), the old sires were placed in single mating pens with their inbred daughters. Nest boxes were placed in each pen, and the birds were fed a turkey layer diet containing 20% crude protein. All birds were debeaked and specked (a plastic antipick device fastened to the beak). Eggs were gathered twice daily, stored in a cold room at a temperature of 12.8 C and a relative humidity of 70%, and set every 14 days. Data were subjected to curvilinear regression analysis as described by Snedecor and Cochran (1967). Inbreeding coefficients were calculated according to Falconer (1960). The upper level
of inbreeding (F) was used for determining regressions in lines substituted with new males.
RESULTS
After four generations of backcrossing, six inbred lines had become extinct with only four lines remaining to be mated. Of these four, two were matings using the original sires and two with sons of the original sires substituted at Generations 1 and 3, respectively. Because the birds were not pedigreed according to individual hens, it was not possible to determine the exact relationship of a new male to the inbred females of the same line. However, the range of coefficients of inbreeding for the lines substituted with sons of the sires were calculated and given in Figure 1. Egg Production. As shown in Figure 2, average number of eggs per hen over a 12-week period declined in both random and inbred lines at Generations 2 and 3, respectively. However, the greatest decrease occurred in inbred hens at F = .438 when egg production was at a low of about 31 eggs per hen as compared to 47 eggs per hen for the random line. A slight recovery in egg production was noted for the random line in Generation 4. There was good consistency among inbred lines for regression of egg number. The results show a loss of approximately 5.8 eggs for each 10% increase in inbreeding (Table 1). Correla-
Downloaded from http://ps.oxfordjournals.org/ at Purdue University Libraries ADMN on May 25, 2015
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tion coefficients were significant within lines as well as among lines. Egg Weight. Egg size in the Mongolian strain is normally greater than in Chinese pheasants; thus, egg size is compared between Chinese inbred and Chinese control lines only. Egg weight had decreased about 2.4 g for hens that were 37.5% inbred (Fig. 2). However, a substantial recovery in egg weight was made in the next generation due to the elimination of five lines having an average egg weight of 28.7 vs. 30.5 g for lines surviving three generations of backcrossing to a common sire. Within-line £regression for egg weight was somewhat variable but showed an average decrease of about .42 g for every 10% increase in inbreeding (Table 1). Although most within-line correlations for egg weight were generally high and negative, most values were not statistically significant suggesting that variability within lines was substantial. Fertility. Average fertility in the random line remained relatively constant (91 to 93%) over the 4 years (Fig. 2). A sharp drop in fertility occurred in the inbred lines at .250 and .375 inbreeding followed by a substantial increase in fertility at F = .438 inbreeding. It is noted that lines surviving four generations of backcrossing
1
-1.01 -.57 -.56 -.59 -.84 -.42 -1.12 -.63
00
CM NO CM 0 0 NO
-.564 -1.000
FIG. 2. The effect of inbreeding depression on four reproductive traits in two subspecies of Ringnecked pheasants back-crossed to a common sire for four generations.
1
1
-.23
.250
0
NO
m NO
M
00
r~
00
mmim
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70
V^
t-*
NO 00
1
£
CM 0 0
5? Hh r
Fi
1
80
90
\ " \\\
m CM 0 0 00
1
00
F=
R
95
/ l
\
26
NO
*
in 1
^-—-^R
-.903 -.950
\
R
7.
\ .
7. 7.
CM
0
* — - ^
-.979 -.803 -.998 -.978 -.899 -1.000 -.970
-
.438 .375 .375 .219- .375 .406- .438 .375 .219- .375
l ^
* 10 - \
.192 -1.000 -.543 -.241 -.603 -.766 -.981
JC
-1.000 -.997 -.213 -.718 -.984 -.960 -.947 -.999 -.713
INBREEDING IN PHEASANTS
WOODARD ET AL.
1728
DISCUSSION A system of inbreeding using repeated backcrossing of daughters to a common sire adversely affected all reproductive traits studied but not in the same order of magnitude for all inbred lines. Egg production was the most severely depressed trait, regressing by approximately 5.8% for every 10% increase in inbreeding. The persistent decline in egg production for
TABLE 2. Percent mortality in inbred pheasants
G (F) 1
1
1 .25 2 .375 3 .438 4 .469
8.0 13.6 28.6 22.7
1
2 50.0 100.0 ...
Upper level of inbreeding.
•crossed to a common sire for four generations
7
3
4
5
6
40.7 63.6 100.0
17.9 15.4 12.0 0
33.3 50.0 57.1
20.0 17.9 37.5 17.9 58.3 . ..
8
9
10
27.6 34.8 42.9 41.9
26.7 15.0 60.0
31.0 11.0 28.6
Combined lines
Control
26.1 27.9 37.2 23.1
11.0 15.3 11.8 9.0
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the random line in Generations 2 and 3 does indicate some negative environmental influence that apparently had no adverse carryover to other reproductive traits studied. The greatest loss in reproductive performance occurred in the second generation for most inbred lines. That was to be expected because the greatest increase in the number of deleterious recessive genes are combined at an inbreeding coefficient of 25%. It is noted, however, that some lines survived many generations of inbreeding showing only minor levels of depression for most traits, especially Lines 4 and 8. This agrees with studies of Kulenkamp et al. (1973), Woodard et al. (1982) and, most of all, Shoffner (1948), who postulated that inbreeding has a general depressive effect on most reproductive traits but does not necessarily act in a progressive or cumulative manner in all inbred lines. Thus, our surviving inbred lines were not subject to the deleterious nature of inbreeding to the same extent as were lines lost during Generation 3 or before. To demonstrate this point, the performance of lines surviving four generations of inbreeding was compared to that of lines lost after three generations of inbreeding (excluding Line 2, lost after two generations of inbreeding) and the results given in Table 3. The coefficient of regression for egg number and fertility, respectively, was two and five times greater for lines terminating at F = .375 as compared to those alive at F = .438. This partly may be the reason for the apparent recovery of fertility, hatchability and egg weight given at F = .438 in Fig. 2. For practical purposes, it may be possible to select inbred lines with high survival potential after one generation of backcrossing (F = .250). A comparison of surviving lines and those not surviving is given in Table 4. The surviving inbred lines were found to be superior to nonsurviving lines in all traits at F = .250,
were generally superior to the nonsurviving lines for several reproductive traits including fertility. In fact, Lines 4 and 8 show a remarkable lack of inbreeding depression at F = .438 (Table 1). The degree of variability in fertility among lines certainly is supportive of the lower correlation value for all lines. Hatcbability. Of the traits studied, hatchability showed the second greatest decline after three generations of inbreeding (Fig. 2). There was approximately a 40% difference in hatchability between the inbred and random lines at .250 inbreeding with inbred lines showing only a slight improvement at higher levels of inbreeding. Coefficients of regression for hatchability were markedly variable among lines being as high as - 1 0 . 8 8 and - 1 0 . 8 0 for Lines 6 and 9, respectively, that were lostat .375 inbreeding and as low as —.81 and —2.84, respectively, for Lines 4 and 8 that showed only a slight drop in hatchability (Table 1) over four generations of inbreeding. Mortality. Posthatch mortality to 8 weeks ranged from 9 to 15% in the random line (Table 2). Mortality was highly variable among inbred lines, averaging twice that for the random line at F = .250 and .375 and more than three times greater at F = .438. It is of interest to note that, with exception of Line 8, all surviving lines had less than 30% mortality for any one generation whereas lines that exceeded 50% mortality were generally lost by the following generation.
INBREEDING IN PHEASANTS
1729
TABLE 3. Comparison of coefficient of regression (b) and correlation (r) for egg number, eggweight, percent fertiliy, and hatchability on a 10% increase in inbreeding for inbred hens mated for three and four generations F = .375 (5 lines)
Eggs/hen Eggweight, g Fertility, % Hatchability, % 1
F = .438 (4 lines)
b
r
b
r
-7.75 -.82 -7.09 -5.32
-.912 -.956 -.759 -.932
-4.55 -.44 -1.50 -3.65
-.872 -.836 -.387 -.673
TABLE 4. Comparison of reproductive traits between surviving and nonsurviving inbred lines at F= .250 Eggs/hen
Egg weight
Fertility
Hatchability
Mortality
(no.)
(g)
Surviving lines (4)
(%)
43.8
31.8
82.5
40.6
18.7
Nonsurviving lines (6)
41.3
29.2
65.7
23.8
47.3
TABLE 5. Effect of age of sire and level of inbreeding on several reproductive traits in the pheasants Matings
Dam
Sire
Eggs/hen
lyear(8)' 1 year (8) F = .438 (4)
4 year (1) 3 year (1) 1 year (1)
51.5 50.0 45.0
(no.) 2 1 1 1
Egg weight
Fertility
(g) 28.4 29.1 30.4
Hatchability (%)
71.8 82.3 47.6
72.0 71.0 39.0
( ) = Number of birds.
especially for important traits such as fertility, hatchability, and viability of young chicks. The observed decline in fertility could be due to the advancing age of sires. Therefore, matings were made between sires and young random line females. Other matings were made between highly inbred females (F = .438) and a young random line male. The results are given in Table 5. The performance of the three aged males mated to young random females clearly demonstrates that age, at least up to 4 years, was not an important factor in depressing fertility and hatchability of eggs. The performance of females inbred at F = .438, when crossed with a young male, showed a slight
improvement in fertility and hatchability over the previous generation; the values, however, were twice as low as those of the random females. Because of the limited matings, the results are not conclusive but indicate an adverse effect of inbreeding on female performance as mothers. Also, the age of males, up to 4 years of age, appears unimportant as far as performance of progeny is concerned. Our results support other investigations that egg production, hatchability, and chick viability are three traits most seriously affected by inbreeding depression in avian species such as the partridge (Woodard et al., 1982) and coturnix (Sittmann et al., 1966). The use of
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Upper level of inbreeding.
WOODARD ET AL.
1730
backcrossing as a method of inbreeding does not appear to reduce the deleterious effects of inbreeding even when it is practiced at a slower rate. Our findings do suggest, however, that intense selection for high performance early in the inbreeding program is a satisfactory way of establishing surviving inbred lines.
REFERENCES
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Abplanalp, H., and A. E. Woodard, 1967. Inbreeding effects under continued sib-mating in turkeys. Poultry Sci. 46:1225-1226. Falconer, D. S., 1960. Introduction to Quantitative Genetics. Ronald Press Co., New York, NY.
Kulenkamp, A. W., C. M. Kulenkamp, and T. H. Coleman, 1973. The effects of intense inbreeding (brother X sister) on various traits in Japanese quail. Poultry Sci. 52:1240-1246. Shoffner, R. N., 1948. The reaction of the fowl to inbreeding, Poultry Sci. 27:448-452. Sittmann, K., H. Abplanalp, and R. A. Fraser, 1966. Inbreeding depression in Japanese quail. Genetics 54:371-379. Snedecor, G. W., and W. G. Cochran, 1967. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, IA. Wilson, W. O., 1948. Egg production rate and fertility in inbred chickens. Poultry Sci. 27:719—726. Woodard, A. E., H. Abplanalp, and L. Snyder, 1982. Inbreeding depression in the Red-legged partridge. Poultry Sci. 61:1579-1584.