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Effect of Inbreeding on Broiler Weights and Feathering in the Fowl1
Effect of Inbreeding on Broiler Weights and Feathering in the Fowl1 E. W. GLAZENER, W. L. BLOW, C. H. BOSTIAN AND R. S. DEARSTYNE North Carolina State College, Raleigh, N. C. (Received for publication July 6, 1950)
studies have been conducted SEVERAL on the effect of inbreeding on the fowl.
MATERIALS AND PROCEDURE
In 1944 and 1945 eggs were purchased from three breeders of New Hampshires and three breeders of Barred Plymouth Rocks. Single-mated pens of each of the three strains of the two breeds were established the following years. Inbred matings have been made in each strain since the 1 Published as Scientific Paper No. 347. Department of Poultry Science, N.C. Agricultural Experiment Station.
108
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Most of these investigations, however, have dealt with egg production and have not considered broiler traits in detail. Waters and Lambert (1936) concluded from their growth rate studies on inbred White Leghorns that intense inbreeding did not decrease the growth rate of birds materially. The present investigation was undertaken to attempt'to learn more concerning the effect of inbreeding, primarily on growth rate. The following factors were considered: (1) Does inbreeding retard improvement in rate of early feathering? (2) Is genetic uniformity in body weight at broiler age increased by inbreeding? (3) Does inbreeding tend to cause a decline in broiler weight? (4) If inbreeding does result in a decline in growth rate, how effective is selection in overcoming this depression?
beginning of the study. All pen matings have been established on the basis of siband progeny test records after considering the broiler and egg characters. One strain of Barred Plymouth Rocks was culled in the early stages because of poor reproductive performance. The data used in this investigation were on the basis of five strains, three of New Hampshires and two of Barred Plymouth Rocks, collected over a fiveyear period, 1945-49, at the Mountain Experiment Station, Waynesville, North Carolina. During this time approximately 5,000 pedigreed chicks have been observed for body weight at six and twelve weeks of age. Periodic observations were made on the rate of feathering. In the first three years feather observations were made at one day, ten days, six and twelve weeks of age. For the years 1948 and 1949 a record was made of the birds with bare backs at six and twelve weeks. A standard starting and growing mash was fed and environmental conditions were kept as uniform as possible from year to year. The birds were brooded by electrically heated hovers and were raised in confinement. The hatching season extended through the months of February and March, with three to six hatches spaced at regular intervals. The size of two of the inbred lines was enlarged by increasing the number of single matings as the weaknesses of the different lines became apparent. At the end of the five-year period, the more promising lines were being developed from two to three single matings and the
EFFECT OF INBREEDING ON BROILER WEIGHTS AND FEATHERING
to separate the variance into portions due to heredity and environment. He found that inbreeding greatly reduced the hereditary variations for this character in the guinea pigs. Winters, Comstock, and Dailey (1943) observed that inbreeding did not appear to reduce the amount of TABLE 1.—Birds well-feathered at six weeks Year
1945 1946 1947 1948 1949 1945 1946 1947 1948 1949
RESULTS AND DISCUSSION
In a character that apparently is affected by few genes, such as feathering, rapid progress can be made by selection. In the three strains of New Hampshires, NC11, 12, 13, 99 percent of all birds, males and females, were well-feathered at six weeks in 1949. (See Table 1) As the results show, only 16 percent of the eggtype New Hampshires, NC12, were wellfeathered in 1945 at this age. Decided improvement has been made in the two lines of Barred Plymouth Rocks, NC16 and NC17, although the progress was not as rapid as in the New Hampshires. If the effect of inbreeding on feathering is depressing, the result in this study is not pronounced. The next factor considered was the effect of inbreeding on genetic uniformity of growth rate in the fowl. Wright (1920) made a study indicating the relative importance of heredity and environment in the amount of white spotting in guinea pigs. By measuring the likeness between relatives, he was able
1945 1946 1947 1948 1949 1945 1946 1947 1948 1949 1946 1947 1948 1949
Number observed NC11 (NH) ' 107
252 454 457 634 NC12 (NH) 93
86 185 268 320 NC13 (NH) 130
171 197 225 118 NC16 (BPR) 71
117 124 87 185 NC17 (BPR) 106
174 109 199
Percer feather
60 76 93 93 99 16 58 88 94 99 31 70 91 99 99 39 44 48 83 57 43 86 73 88
variability materially for rate of gain within the litters and within the lines of swine in their investigation. Shoffner (1948a), in a flock brought to an average coefficient of inbreeding of 60 percent, found no consistent decline in total variability for egg weight and mature body weight. As was previously explained, the dam and individual variances were calculated. These variances are presented in Table 2 and are used to estimate the relative
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
questionable lines were still confined to a single mating. Analysis of the data was directed at estimation of variance due to dams and of variance among full-sibs of the same hatch and sex. Because sub-class numbers were disproportionate, the least squares method was employed to obtain mean squares for dams adjusted for effects of sire, sex, and hatch. Using this mean square and that for full-sibs it was possible to estimate the variance arising from differences among dams. Four times the variance due to dams was used to estimate the additive genetic variance, though the estimates obtained would contain some upward bias due to dominance. Variance among sires was not used because of the small number of sires involved.
109
110
E. W. GLAZENER, W. L. BLOW, C. H. BOSTIAN AND R. S. DEARSTYNE
change of genetic and environmental variability as the inbreeding progressed. The coefficients of relationships for the dams were used rather than the inbreeding coefficients of the offspring because it was felt that the relationships measured more
difficult to understand if this departure from the theoretical regression is not due to sampling errors, particularly since body weight at twelve weeks has a high degree of heritability. The selection of heterozygotes for breeders seems very
TABLE 2.—Mean weights, variances, and coefficients of relationship for the lines at twelve weeks1 Coefficient of relationship for damsf
1945 1946 1947 1948 1949
0 15 18 38 50
NC11 (NH) 38.4+ .89 39.6+ .38 4 6 . 2 + .24 4 1 . 0 + .22 4 7 . 6 ± .22
4.30 4.52 3.09 5.70
1945 1946 1947 1948 1949
0 10 32 54 57
NC1Z 32.5± 35.6+ 36.8+ 30.1+ 37.4+
1945 1946 1947 1948 1949
0 6 19 39 46
1945 1946 1947 1948 1949 1946 1947 1948 1949
Mean weight ounces
Dam variance
Individual variance
*
77.98 18.52 16.11 23.66 23.10
2.57 5.74 4.62 6.25
*
42.77 13.83 16.53 15.55 27.32
NC13 {NH) 30.2+ .66 32.8+ .40 3 8 . 6 ± .37 32.8+ .43 4 5 . 9 ± .57
10.74 8.18 7.32 3.11 7.21
33.25 16.52 13.90 21.49 33.07
0 10 41 46 56
NC16 {BPR) 35.8±1.09 38.5+ .53 41.2+ .54 3 5 . 4 + .71 4 9 . 6 + .52
15.34 2.94 9.98 5.47 9.29
49.71 26.80 27.67 19.96 37.30
0 15 35 45
NC17 37.6+ 45.3+ 32.1+ 46.0+
9.66 12.89
20.29 26.51 33.02 48.59
{NH) .79 .44 .38 .36 .20
{BPR) .43 .47 .67 .56
*
9.70
1 Environmental difficulties encountered in 1948 affected growth rate. * Dam mean squares smaller than individual mean squares. f The inbreeding coefficients of the progeny of these dams averaged from 35 to 40 percent in 1949.
nearly the genetic constitutions of the lines. The regression of the dam variance on the degree of relationship on a within line basis was .00124+.035, a value that is non-significant. The expected regression which is of the order of —.06 falls well within the confidence limits of the actual regression value. The obtained result is
doubtful since growth rate is considered a multiple gene character. It appears that inbreeding at the rate of approximately 9 percent a year should have reduced the genetic variability. A possibility exists that the birds become more sensitive to the environment as the inbreeding increases, a factor which may affect the size
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
Year
EFFECT OF INBREEDING ON BROILER WEIGHTS AND FEATHERING
Comstock and Winters (1944) used a procedure to determine the efficiency of individual selection in overcoming the depressing effect of inbreeding on some traits in swine. The same formula was used on this data to compare the actual and theoretical change of performance and to determine how rapidly inbreeding could progress at a fixed rate of individual selection without a decline in the original performance. The formula is as follows:
P=bI+sH P is the expected change in performance for each generation due to effects of inbreeding and selection. / is the increase in inbreeding per generation, and b the regression of performance on inbreeding; H is the coefficient of heritability, and s the selection differential. Thus, product bl is the change in performance resulting from inbreeding; the product sH the change in performance resulting from selection. The net change in performance is
the bl and sH values summated. The values obtained from the data were as follows: &=-.1297oz. 7 = 9 percent 5=5.75 oz. (9.5 oz. for males, 2.0 oz. for females) H= 68 percent (corrected for inbreeding) The values for the formula are based on a weighted average of the data from the five strains. The selection differentials in the five strains ranged from 7.8 to 13.2 oz. in the males, 1.0 to 2.8 oz. in the females, and the heritability ranged from 51 to 79 percent. Lerner, Asmundson, and Cruden (1947) found heritability in a stock of New Hampshires to approximate 50 percent at twelve weeks. It is felt that the weighted averages are valid in obtaining a reliable estimate of the values in the formula on the basis of the sample size and the number of strains involved. By solving for the value of P in the equation and. multiplying the result by the number of years, the theoretical net change in body weight was found to be 10.86 ounces for the period. In comparing the means (see Table 2) the actual average gain was 10.40 ounces. When selection is sufficient to overcome the effects of inbreeding, P = 0. By letting P = 0, no increase or decrease in performances, the maximum amount of inbreeding that may be done in any generation without a decline in twelve weeks weight can be estimated in terms of s, H and b; -sH I =— • b The value obtained for I is 30 percent. In accordance with the results, inbreeding may proceed as rapidly as possible at the level of selection practiced in this investigation without a decline in body weight at twelve weeks. This result, however, does not apply to such traits as hatchability and egg production.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
of both the genetic and environmental variation. In 1949, the individual variation tended to increase decidedly in four of the five strains for no apparent reason. The third factor considered was the effect of inbreeding on twelve week body weights. Body weight was plotted as a function of inbreeding. The regression secured was —.1297+ .005, a significant value. This result means that on the basis of this data for every 10 percent increase in inbreeding, the twelve week body weight would decline approximately 1.3 ounces. That inbreeding has a decreasing effect on hatchability and egg production traits has been rather thoroughly established. Cole and Halpin (1916), Dunn (1923), Jull (1929), Dumon (1930), Hays (1934) and Shoffner (1948b) have observed that inbreeding had a depressing effect on hatchability and egg production.
111
1.12
NEWS AND NOTES REFERENCES
Data were analyzed on 5,000 pedigreed chicks hatched from three strains of New Hampshires and two strains of Barred Plymouth Rocks over a five-year period. Genetic variability in body weights at twelve weeks was not consistently reduced as the maternal degree of relationship increased. Inbreeding had no apparent declining effect on feathering, although the regression for broiler weight was -.1297 + .005, the equivalent of 1.3 ounces loss for each 10 percent increase in inbreeding. At the level of selection practiced in this investigation, however, the average gain in body weight for the period was approximately 10 ounces, the actual and theoretical values being about equal. The estimates of heritability for twelve week body weights ranged from 51 to 79 percent. With a selection pressure as strong as that used in this study, inbreeding may proceed as rapidly as possible without effecting a decline in broiler weight.
Cole, L. J., and J. G. Halpin, 1916. Preliminary report of results of an experiment on close inbreeding in fowls. J. Am. Asso. Instruct. Invest. Poultry Hus. 3: 7-8. Comstock, R. E., and L. M. Winters, 1944. A comparison of the effects of inbreeding and selection on performance in swine. J. Animal Sci. 3: 380389. Dumon, A. G., 1930. The effects of inbreeding on hatchability. Report Proc. 4th World's Poultry Congress: 1-5. Dunn, L. C , 1923. Experiments on close inbreeding in fowls. Storrs Agr. Exp. Sta. Bull. I l l : 21-33. Hays, F. A., 1924. Inbreeding in the Rhode Island Red fowl with special reference to winter egg production. Am. Nat. 58: 43-59. Jull, M. A., 1929. Studies in hatchability. I I . Hatchability in relation to the consanguinity of the breeding stock. Poultry Sci. 8: 219-227. Lerner, I. M., V. S. Asmundson and D. M. Cruden, 1947. The improvement of New Hampshire fryers. Poultry Sci. 26: 515-524. Shoffner, R. N., 1948a. The reaction of the fowl to inbreeding. Poultry Sci. 27: 448-452. Shoffner, R. N., 1948b. The variation within a inbred line of S.C. White Leghorns. Poultry Sci. 27: 235-236. Waters, N. F., and W. V. Lambert, 1936. Inbreeding in the White Leghorn fowl. Iowa Agr. Exp. Sta. Res. Bull. 202: 1-55. Winters, L. M., and R. E. Comstock and D. L. Dailey, 1943. The development of an inbred line of swine (Minn. No. 1) from a crossbred foundation. J. Animal Sci. 2: 129-137. Wright, Sewall, 1920. The relative importance of heredity and environment in determining the piebald pattern of guinea pigs. Proc. Nat. Acad. Sci. 6: 320-332.
ACKNOWLEDGMENT
The authors wish to thank Dr. R. E. Comstock, Department of Experimental Statistics, for his consultation in the statistical analysis.
News and Notes {Continued from page 107)
He is a member of the Poultry Science Association, being a Director of the Association and Associate Editor of Poultry Science; of the Marketing Association; and the Economics Association. He is married and has three children. In case any of his friends consider re-
marking "a good chicken man gone wrong," the editor respectfully calls your attention to the fact that Director Gwin was a member of the United States national rifle team in 1929 and was Connecticut State Champion Rifle Shot in 1932.
(Cgntinued on page 115)
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
SUMMARY
studies have been conducted SEVERAL on the effect of inbreeding on the fowl.
MATERIALS AND PROCEDURE
In 1944 and 1945 eggs were purchased from three breeders of New Hampshires and three breeders of Barred Plymouth Rocks. Single-mated pens of each of the three strains of the two breeds were established the following years. Inbred matings have been made in each strain since the 1 Published as Scientific Paper No. 347. Department of Poultry Science, N.C. Agricultural Experiment Station.
108
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
Most of these investigations, however, have dealt with egg production and have not considered broiler traits in detail. Waters and Lambert (1936) concluded from their growth rate studies on inbred White Leghorns that intense inbreeding did not decrease the growth rate of birds materially. The present investigation was undertaken to attempt'to learn more concerning the effect of inbreeding, primarily on growth rate. The following factors were considered: (1) Does inbreeding retard improvement in rate of early feathering? (2) Is genetic uniformity in body weight at broiler age increased by inbreeding? (3) Does inbreeding tend to cause a decline in broiler weight? (4) If inbreeding does result in a decline in growth rate, how effective is selection in overcoming this depression?
beginning of the study. All pen matings have been established on the basis of siband progeny test records after considering the broiler and egg characters. One strain of Barred Plymouth Rocks was culled in the early stages because of poor reproductive performance. The data used in this investigation were on the basis of five strains, three of New Hampshires and two of Barred Plymouth Rocks, collected over a fiveyear period, 1945-49, at the Mountain Experiment Station, Waynesville, North Carolina. During this time approximately 5,000 pedigreed chicks have been observed for body weight at six and twelve weeks of age. Periodic observations were made on the rate of feathering. In the first three years feather observations were made at one day, ten days, six and twelve weeks of age. For the years 1948 and 1949 a record was made of the birds with bare backs at six and twelve weeks. A standard starting and growing mash was fed and environmental conditions were kept as uniform as possible from year to year. The birds were brooded by electrically heated hovers and were raised in confinement. The hatching season extended through the months of February and March, with three to six hatches spaced at regular intervals. The size of two of the inbred lines was enlarged by increasing the number of single matings as the weaknesses of the different lines became apparent. At the end of the five-year period, the more promising lines were being developed from two to three single matings and the
EFFECT OF INBREEDING ON BROILER WEIGHTS AND FEATHERING
to separate the variance into portions due to heredity and environment. He found that inbreeding greatly reduced the hereditary variations for this character in the guinea pigs. Winters, Comstock, and Dailey (1943) observed that inbreeding did not appear to reduce the amount of TABLE 1.—Birds well-feathered at six weeks Year
1945 1946 1947 1948 1949 1945 1946 1947 1948 1949
RESULTS AND DISCUSSION
In a character that apparently is affected by few genes, such as feathering, rapid progress can be made by selection. In the three strains of New Hampshires, NC11, 12, 13, 99 percent of all birds, males and females, were well-feathered at six weeks in 1949. (See Table 1) As the results show, only 16 percent of the eggtype New Hampshires, NC12, were wellfeathered in 1945 at this age. Decided improvement has been made in the two lines of Barred Plymouth Rocks, NC16 and NC17, although the progress was not as rapid as in the New Hampshires. If the effect of inbreeding on feathering is depressing, the result in this study is not pronounced. The next factor considered was the effect of inbreeding on genetic uniformity of growth rate in the fowl. Wright (1920) made a study indicating the relative importance of heredity and environment in the amount of white spotting in guinea pigs. By measuring the likeness between relatives, he was able
1945 1946 1947 1948 1949 1945 1946 1947 1948 1949 1946 1947 1948 1949
Number observed NC11 (NH) ' 107
252 454 457 634 NC12 (NH) 93
86 185 268 320 NC13 (NH) 130
171 197 225 118 NC16 (BPR) 71
117 124 87 185 NC17 (BPR) 106
174 109 199
Percer feather
60 76 93 93 99 16 58 88 94 99 31 70 91 99 99 39 44 48 83 57 43 86 73 88
variability materially for rate of gain within the litters and within the lines of swine in their investigation. Shoffner (1948a), in a flock brought to an average coefficient of inbreeding of 60 percent, found no consistent decline in total variability for egg weight and mature body weight. As was previously explained, the dam and individual variances were calculated. These variances are presented in Table 2 and are used to estimate the relative
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
questionable lines were still confined to a single mating. Analysis of the data was directed at estimation of variance due to dams and of variance among full-sibs of the same hatch and sex. Because sub-class numbers were disproportionate, the least squares method was employed to obtain mean squares for dams adjusted for effects of sire, sex, and hatch. Using this mean square and that for full-sibs it was possible to estimate the variance arising from differences among dams. Four times the variance due to dams was used to estimate the additive genetic variance, though the estimates obtained would contain some upward bias due to dominance. Variance among sires was not used because of the small number of sires involved.
109
110
E. W. GLAZENER, W. L. BLOW, C. H. BOSTIAN AND R. S. DEARSTYNE
change of genetic and environmental variability as the inbreeding progressed. The coefficients of relationships for the dams were used rather than the inbreeding coefficients of the offspring because it was felt that the relationships measured more
difficult to understand if this departure from the theoretical regression is not due to sampling errors, particularly since body weight at twelve weeks has a high degree of heritability. The selection of heterozygotes for breeders seems very
TABLE 2.—Mean weights, variances, and coefficients of relationship for the lines at twelve weeks1 Coefficient of relationship for damsf
1945 1946 1947 1948 1949
0 15 18 38 50
NC11 (NH) 38.4+ .89 39.6+ .38 4 6 . 2 + .24 4 1 . 0 + .22 4 7 . 6 ± .22
4.30 4.52 3.09 5.70
1945 1946 1947 1948 1949
0 10 32 54 57
NC1Z 32.5± 35.6+ 36.8+ 30.1+ 37.4+
1945 1946 1947 1948 1949
0 6 19 39 46
1945 1946 1947 1948 1949 1946 1947 1948 1949
Mean weight ounces
Dam variance
Individual variance
*
77.98 18.52 16.11 23.66 23.10
2.57 5.74 4.62 6.25
*
42.77 13.83 16.53 15.55 27.32
NC13 {NH) 30.2+ .66 32.8+ .40 3 8 . 6 ± .37 32.8+ .43 4 5 . 9 ± .57
10.74 8.18 7.32 3.11 7.21
33.25 16.52 13.90 21.49 33.07
0 10 41 46 56
NC16 {BPR) 35.8±1.09 38.5+ .53 41.2+ .54 3 5 . 4 + .71 4 9 . 6 + .52
15.34 2.94 9.98 5.47 9.29
49.71 26.80 27.67 19.96 37.30
0 15 35 45
NC17 37.6+ 45.3+ 32.1+ 46.0+
9.66 12.89
20.29 26.51 33.02 48.59
{NH) .79 .44 .38 .36 .20
{BPR) .43 .47 .67 .56
*
9.70
1 Environmental difficulties encountered in 1948 affected growth rate. * Dam mean squares smaller than individual mean squares. f The inbreeding coefficients of the progeny of these dams averaged from 35 to 40 percent in 1949.
nearly the genetic constitutions of the lines. The regression of the dam variance on the degree of relationship on a within line basis was .00124+.035, a value that is non-significant. The expected regression which is of the order of —.06 falls well within the confidence limits of the actual regression value. The obtained result is
doubtful since growth rate is considered a multiple gene character. It appears that inbreeding at the rate of approximately 9 percent a year should have reduced the genetic variability. A possibility exists that the birds become more sensitive to the environment as the inbreeding increases, a factor which may affect the size
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
Year
EFFECT OF INBREEDING ON BROILER WEIGHTS AND FEATHERING
Comstock and Winters (1944) used a procedure to determine the efficiency of individual selection in overcoming the depressing effect of inbreeding on some traits in swine. The same formula was used on this data to compare the actual and theoretical change of performance and to determine how rapidly inbreeding could progress at a fixed rate of individual selection without a decline in the original performance. The formula is as follows:
P=bI+sH P is the expected change in performance for each generation due to effects of inbreeding and selection. / is the increase in inbreeding per generation, and b the regression of performance on inbreeding; H is the coefficient of heritability, and s the selection differential. Thus, product bl is the change in performance resulting from inbreeding; the product sH the change in performance resulting from selection. The net change in performance is
the bl and sH values summated. The values obtained from the data were as follows: &=-.1297oz. 7 = 9 percent 5=5.75 oz. (9.5 oz. for males, 2.0 oz. for females) H= 68 percent (corrected for inbreeding) The values for the formula are based on a weighted average of the data from the five strains. The selection differentials in the five strains ranged from 7.8 to 13.2 oz. in the males, 1.0 to 2.8 oz. in the females, and the heritability ranged from 51 to 79 percent. Lerner, Asmundson, and Cruden (1947) found heritability in a stock of New Hampshires to approximate 50 percent at twelve weeks. It is felt that the weighted averages are valid in obtaining a reliable estimate of the values in the formula on the basis of the sample size and the number of strains involved. By solving for the value of P in the equation and. multiplying the result by the number of years, the theoretical net change in body weight was found to be 10.86 ounces for the period. In comparing the means (see Table 2) the actual average gain was 10.40 ounces. When selection is sufficient to overcome the effects of inbreeding, P = 0. By letting P = 0, no increase or decrease in performances, the maximum amount of inbreeding that may be done in any generation without a decline in twelve weeks weight can be estimated in terms of s, H and b; -sH I =— • b The value obtained for I is 30 percent. In accordance with the results, inbreeding may proceed as rapidly as possible at the level of selection practiced in this investigation without a decline in body weight at twelve weeks. This result, however, does not apply to such traits as hatchability and egg production.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
of both the genetic and environmental variation. In 1949, the individual variation tended to increase decidedly in four of the five strains for no apparent reason. The third factor considered was the effect of inbreeding on twelve week body weights. Body weight was plotted as a function of inbreeding. The regression secured was —.1297+ .005, a significant value. This result means that on the basis of this data for every 10 percent increase in inbreeding, the twelve week body weight would decline approximately 1.3 ounces. That inbreeding has a decreasing effect on hatchability and egg production traits has been rather thoroughly established. Cole and Halpin (1916), Dunn (1923), Jull (1929), Dumon (1930), Hays (1934) and Shoffner (1948b) have observed that inbreeding had a depressing effect on hatchability and egg production.
111
1.12
NEWS AND NOTES REFERENCES
Data were analyzed on 5,000 pedigreed chicks hatched from three strains of New Hampshires and two strains of Barred Plymouth Rocks over a five-year period. Genetic variability in body weights at twelve weeks was not consistently reduced as the maternal degree of relationship increased. Inbreeding had no apparent declining effect on feathering, although the regression for broiler weight was -.1297 + .005, the equivalent of 1.3 ounces loss for each 10 percent increase in inbreeding. At the level of selection practiced in this investigation, however, the average gain in body weight for the period was approximately 10 ounces, the actual and theoretical values being about equal. The estimates of heritability for twelve week body weights ranged from 51 to 79 percent. With a selection pressure as strong as that used in this study, inbreeding may proceed as rapidly as possible without effecting a decline in broiler weight.
Cole, L. J., and J. G. Halpin, 1916. Preliminary report of results of an experiment on close inbreeding in fowls. J. Am. Asso. Instruct. Invest. Poultry Hus. 3: 7-8. Comstock, R. E., and L. M. Winters, 1944. A comparison of the effects of inbreeding and selection on performance in swine. J. Animal Sci. 3: 380389. Dumon, A. G., 1930. The effects of inbreeding on hatchability. Report Proc. 4th World's Poultry Congress: 1-5. Dunn, L. C , 1923. Experiments on close inbreeding in fowls. Storrs Agr. Exp. Sta. Bull. I l l : 21-33. Hays, F. A., 1924. Inbreeding in the Rhode Island Red fowl with special reference to winter egg production. Am. Nat. 58: 43-59. Jull, M. A., 1929. Studies in hatchability. I I . Hatchability in relation to the consanguinity of the breeding stock. Poultry Sci. 8: 219-227. Lerner, I. M., V. S. Asmundson and D. M. Cruden, 1947. The improvement of New Hampshire fryers. Poultry Sci. 26: 515-524. Shoffner, R. N., 1948a. The reaction of the fowl to inbreeding. Poultry Sci. 27: 448-452. Shoffner, R. N., 1948b. The variation within a inbred line of S.C. White Leghorns. Poultry Sci. 27: 235-236. Waters, N. F., and W. V. Lambert, 1936. Inbreeding in the White Leghorn fowl. Iowa Agr. Exp. Sta. Res. Bull. 202: 1-55. Winters, L. M., and R. E. Comstock and D. L. Dailey, 1943. The development of an inbred line of swine (Minn. No. 1) from a crossbred foundation. J. Animal Sci. 2: 129-137. Wright, Sewall, 1920. The relative importance of heredity and environment in determining the piebald pattern of guinea pigs. Proc. Nat. Acad. Sci. 6: 320-332.
ACKNOWLEDGMENT
The authors wish to thank Dr. R. E. Comstock, Department of Experimental Statistics, for his consultation in the statistical analysis.
News and Notes {Continued from page 107)
He is a member of the Poultry Science Association, being a Director of the Association and Associate Editor of Poultry Science; of the Marketing Association; and the Economics Association. He is married and has three children. In case any of his friends consider re-
marking "a good chicken man gone wrong," the editor respectfully calls your attention to the fact that Director Gwin was a member of the United States national rifle team in 1929 and was Connecticut State Champion Rifle Shot in 1932.
(Cgntinued on page 115)
Downloaded from http://ps.oxfordjournals.org/ by guest on April 19, 2015
SUMMARY