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The Effect of Genotype-Environment Interactions on Broiler Growth1
The Effect of Genotype-Environment Interactions on Broiler Growth1 K. M . L E W I S AND W. L. B L O W
Department of Poultry Science, North Carolina State of the University of North Carolina at Raleigh (Received for publication August 31, 1964) H E value of a genotype is always defined in terms of its average response over a specific population of environments; therefore, a genotype has no intrinsic value of its own. In particular environments a genotype m a y perform better or worse than expected from its average performance over many environments. Interactions of genotype with environment are of fundamental importance in plant and animal breeding because their involvement influences breeding procedure. I t is very likely t h a t there is a high correlation between an animal's ability to do well in diverse environments, b u t residual variation associated with genotype-environment interactions m a y be an important factor in selecting appropriate testing procedures. The present study was designed to provide further information on the importance of genotype-environment interactions on broiler growth. Generally, experimental evidence has indicated t h a t these interactions do not assume the importance in poultry t h a t they do in plants. Primary interest in poultry in documenting the importance of these interactions has been on certain characters associated with laying birds. A rather extensive review of these results has been presented by Hale (1961). Investigations
devoted
to
analyzing
1 Contribution from the Poultry Science Department, North Carolina Agricultural Experiment Station, Raleigh, North Carolina. Published with the approval of the Director of Research as Paper No. 1864 of the Journal Series.
the importance of interactions between genotype and environment in broilers have been more limited. Gutteridge and O'Neil (1942) found no evidence of a strain-location interaction for skeletal measurements and body weight a t eight weeks of age in three strains of Barred Plymouth Rocks at three locations. Ten strains of broilers were subjected by Merritt and Gowe (1956) to uniform diet and management conditions at three locations. Significant strain X location interactions were obtained for six-week body weight in males and for breast angle at ten weeks of age in females. Observations on groups of birds from ten strains reared separately and intermingled were made b y Hess et al. (1960). Body weights at both 8 and 9 weeks of age showed highly significant second order interactions due to sex, strain and type of rearing. In the same experiment birds grown separately by strain in each of adjacent houses had a significant interaction involving house and strain and a highly significant interaction due to house X strain X sex. Johnson and Abplanalp (1960) found a significant interaction for body weight at 9 weeks for pullets but not for cockerels when 14 strains were fed diets with different caloric levels. Cook et al. (1962) compared the performance of ten strains a t eight experiment stations in the Southeast in three trials. The location X genotype and location X genotype X trial interactions were highly significant for body weights at 2, 4, 6 and 8 weeks of age.
481
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
T
482
K. M. LEWIS AND W. L. BLOW
PROCEDURE
METHODS OF ANALYSIS
Analysis of data in this experiment was designed primarily to provide estimates
Xhijkmn = M+gh+li+ti+r k ( i i ) -r-s m 4-(gl) h i + (gt)hj+(gr)hk(ij)+(gS)hm + (lt)ij+(ls)im+(ts)jm + (rs)km(ij)+(glt)hij+(gls)him
+ (grs)hkm(ii) + (gts) hjm + (Its) i j m + (glts)hijm+ ehijkmn,
where h = 1, 2 • • • 4 genotypes i = 1, 2, 3 locations j = 1, 2, 3 trials k = 1, 2 replications within trials and locations m = 1, 2 sexes n = 1, 2 • • • 32 individuals of each sex per genotype within replications. Then Xhijkmn is the weight of the n th individual in the k th replication of the m th sex of the h th genotype at the i th location
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For each of three hatches, three cases of eggs were shipped from commercial broiler breeders to the North Carolina Experiment Station at Raleigh, North Carolina. The material for this experiment included four strains, two New Hampshires and two White Plymouth Rocks. These eggs were subsequently hatched in Raleigh and day-old chicks were shipped to research farms at Willard and Waynesville, North Carolina. Chicks were started at these locations and Raleigh in April, July and September of the same year. The various hatches of chicks were started on feed at approximately the same time at each location. The birds were housed in replicated pens of 100 unsexed birds of each genotype at each location for each trial in a randomized block design. Floor space at each location was approximately one square foot per bird. The birds were not vaccinated during the grow-out period. The feed used at all locations was the same commercial broiler mash with a coccidiostat added. At ten weeks of age the birds were weighed to the nearest ounce and sex was recorded. No severe disease problem or unusual mortality was encountered in this experiment. The three locations used in this study are representative of the three distinct geographical areas in North Carolina. These areas are the Mountains represented by Waynesville, Piedmont by Raleigh and Coastal Plain by Willard. The mean annual temperatures over a period of thirty years have been 54.5°F., 59.5°F. and 63.1°F., respectively, for the three locations.
of the various components of variance which contribute to the total variation. In order to avoid the difficulties inherent in unequal numbers in the subclasses, the experimental data were restricted to a random sample of 32 individuals of each sex from each genotype in each replication in a trial and location. The analysis was conducted as a factorial experiment involving 4 genotypes, 3 locations, 3 trials and 2 sexes with replications of genotypes nested within trials and locations. A mixed model was assumed with sex considered a fixed variate and the rest random. The assignment of the quality of being fixed or random is to some extent purely arbitrary; however, sex is obviously a fixed effect since the entire population of sexes is drawn when both males and females are represented. The following mathematical model describes the effect of the variables studied:
483
GENOTYPE-ENVIRONMENT AND GROWTH
impact of time and place on the relative performance of these genotypes. In the present study some effort was made to standardize certain factors which may influence performance from location to location. These include such factors as floor space, feed and brooding temperatures. To some extent, however, management varied from location to location and over trials due to differences in personnel and facilities at the various locations. These differences in management and the effects which are an integral part of the geographical locations comprise the location effects of this study. The average body weights in ounces for genotypes, trials and locations over replications and sexes are presented in Table 2. A sex difference characteristic of broilers was observed in this experiment. Strains B and D were superior in performance to A and C. The genotypes sampled in this study weighed the most in Waynesville and the least in Raleigh. Average weights were the largest in the
RESULTS AND DISCUSSION
Logically, in assessing the values of genotypes one is concerned with the
TABLE 1.—Structural analysis and mean square expectations of broiler weights Mean Square Expectations Source
M.S.
c a
% Locations Trials LXT Genotypes GXL GXT GXLXT Rep/L and T RXG/L andT Sexes SXL SXT SXG RXS/LandT SXGXL SXGXT SXLXT SXGXLXT SXGXR/L&T Ind/G, L, T, R, S
M
b
s "M
i
% %
M
b
*M
1
b
b
2 =0
"b
-2 °b
»b
m
%
>b
^
"u
b
M^0
X
X
X
X
Mi,
X
X
X
X
X
M 18 M 17 M16 M16 M I4 M13
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Mj,
X
X
M„
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
M 10 M9 M8 M7 M6 M5 M4 M3 M, Mi
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X X X
X
X
X X
X
X
X X
X
X
X
X
X
X
M
M"M
fc
b
K'
b
«b X
X X
X X
X X
X X
X
°fc
X
x X
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
in the j t h trial. The population mean is represented by n and the effects which are random from individual to individual in the experiment by ehijkmn- Main effects arising from the h th genotype, i th location, j t h trial, k th replication in the i th location and j t h trial, and m th sex are represented by gh, l i; tj, rk(ij) and sm, respectively; while other effects in the model are the various interactions between these main effects. The structural analysis of the broiler weights and the mean square expectations are presented in Table 1. The expectations of the mean squares were derived by using procedures suggested by Schultz (1955). Estimates of the various variance components were obtained by equating the expectations of these mean squares to the mean squares calculated from the data.
484
K. M. LEWIS AND W. L. BLOW
TABLE 2.—Body weights in ounces for genotypes, trials and locations averaged over sexes and replications Genotypes Locations
Trials
B
C
D
Willard
1 2 3
41.66 38.28 41.08
45.24 42.80 45.00
42.91 40.69 41.98
44.42 42.31 46.50
Raleigh
1 2 3
39.00 37.90 41.11
41.78 41.88 44.35
38.84 39.12 40.77
39.33 42.17 44.56
Waynesville
1 2 3
42.80 41.78 43.45
46.12 46.69 47.24
43.49 43.08 43.83
47.30 45.71 47.18
trial conducted in the fall months and the lowest in the summer months. The analysis of variance for body weight and the components of variance due to the sources of variation are presented in Table 3. The only significant interaction involving genotypes was the interaction with replications within locations and trials. Since genotypes were not grown intermingled but in separate pens, this interaction is confounded with pen effects. This may account in part for the significance of this interaction. Although the data were analyzed on the basis of the model presented, the breakdown of the total variance into percent contributions for each variance component is not meaningful as far as breeding techniques are concerned. A cursory examination of these percentages shows that major contributions to variation between birds in this experiment were made by location, sex and random elements of the environment. In terms of the phenotypic model over 93 percent of the total variance was contributed by effects which were common to all genotypes or due to random elements of the environment. These include the variances due to locations, trials, replications, sex and all of the interactions between these primary effects. Although these results demonstrate that birds vary rather widely from location to location and in different
G= — ^ where k is the selection differential in standard deviations and cr2g and
Source
d.l.
2 Locations 2 Trials 4 LXT 3 Genotypes 6 GXL 6 GXT GXLXT 12 9 Rep/L and T R X G / L a n d T 27 1 Sexes SXL 2 2 SXT 3 SXG R X S / L and T 9 6 SXGXL 6 SXGXT SXLXT 4 12 SXGXLXT SXGXR/L and T 27 Ind./G, L, T, S and R 4,464
M.S.
Component of variance
6,115.26** 1,636.17 472.31 4,258.07** 55.73 107.65 59.45 193.00* 80.18** 101,954.36** 330.45 14.56 156.26 20.51 36.98 30.24 127.48** 20.89
3.676 .726 .586 3.606 -.010 .126 -.162 .441 .969 44.110 .240 -.163 .191 .022 .084 .049 .416 .050
17.68
-.014
18.14
18.14
* Indicates significance at the 5% level. ** Indicates significance at the 1% level.
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
A
trials, they are not relevant to the effects of locations and trials on breeding progress when genotypes are tested in common environments. Expected genetic progress from selection is equal to
485
GENOTYPE-ENVIRONMENT AND GROWTH
phenotypic variance. If genotype-environment interactions do exist, this can be accomplished by testing genotypes over more environments. In terms of the present study, the general form of phenotypic variance between selection units would be 2
1 2
C g Is
1 .
im
J 2
0" gts
1.
jm
IJ 2
f g Its
1 .. "t ijm
0- 2 grUt)
'
k
Locations X trials X replications
Locations
1 2 1
2 1 1
1.691 1.622 1.613
3
1 3 1
3 1 1
1.732 1.635 1.623
6 3 3 2 2 1 1
1 6 1 2 1 3 1 3 2
6 1 1 1 2 1 3 2 3
1.775 1.648 1.632 1.644 1.718 1.647 1.748 1.733 1.760
km
with i, j , k, m and n in the denominators representing the number of locations, trials, replications, sexes and individuals per sex of each genotype in the replicates, respectively. The consequences of varying the number of environments can be easily computed when estimates of the parameters are available. A set of different conditions in which numbers of trials, locations and replications were varied but the product of these numbers remained constant was postulated to determine the effects on selecting for increased broiler weight. Although the mean squares for interactions with genotype in the analysis of variance were generally non-significant, the estimates of the variance components derived from this analysis are unbiased estimates of these interactions involving genotype. The expected genetic progress for each set of conditions is presented in Table 4. It is readily apparent from these results that testing genotypes over a number of locations and trials is not a worthwhile endeavor for improving growth rate in broilers. In these testing procedures the maximum gain in efficiency is attained by increased replication in a single year at
Repli±xcpn- Expected cations11 progress 1.586
2
ijkmn
na s
1
As m
ff grs(lt)
™. ,
" The number of individuals (n) of each sex from a genotype in a replication is 32.
one location. Approximately 12 percent additional progress is indicated when six replicates of the genotypes are tested at one location in a single trial. This increase in efficiency arises from the significant replication X genotype interaction observed in this study. Since this variance is confounded with pen effects, intermingling of genotypes rather than separate rearing may afford a more practical approach to testing broiler growth. The futility of testing broiler growth over a large number of environments is apparent when genetic progress with perfect identification of genotypes is only ko-g or 1.899 k. SUMMARY
Four strains of broilers were tested at three locations over three trials with replication of each genotype in trials and locations. Analysis of variance of individual body weights indicated that interactions involving genotype were non-
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
2P
2 2 a gi
TABLE 4.—Expected genetic progress in terms of k when testing with various numbers of trials, locations and replications
486
K. M . L E W I S AND W. L. B L O W
REFERENCES Cook, R. E., C. W. Hess, J. L. Carmon and E. F.
Dembnicki, 1962. Importance of genotype-environment interactions at various ages in broiler type chickens. Poultry Sci. 41: 1637. Gutteridge, H. S., and J. B. O'Neil, 1942. The relative effect of environment and heredity upon body measurments and production characteristics in poultry. Sci. Agr. 22: 482-491. Hale, R. W., 1961. Genotype-environment interactions in a comparison of the cage and semi-intensive systems for laying hens. Brit. Poultry Sci. 2: 145-157. Hess, C. W., E. F. Dembnicki and J. L. Carmon, 1960. Type-of-rearing and location effects on broiler body weights. Poultry Sci. 39: 1086-1091. Johnson, E. A., and H. Abplanalp, 1960. Strain-feed interaction in chicken fryer stock. Poultry Sci. 39: 1263. Merritt, E. S., and R. S. Gowe, 1956. Environment and poultry breeding problems. III. The performance of 8 crossbred and 2 purebred broiler strains at three locations. Canadian J. Agric. Sci. 36: 72-80. Schultz, E. F., 1955. Rules of thumb for determining expectations of mean squares in analysis of variance. Biometrics, 11: 123-135.
Effects of Dosage Level and Length of Feeding Dienestrol Diacetate on Potentiation of Oxytetracycline* J. E. J O N E S , H. R. W I L S O N , P . W. W A L D R O U P AND R. H.
HARMS
Florida Agricultural Experiment Station, Gainesville, Florida (Received for publication August 31, 1964)
V
A R I O U S methods of antibiotic potentiation have been reported including lowering of the dietary calcium level (Price and Zolli, 1959), addition of terephthalic acid (TPA) to the diet (Peterson 1958) or injecting chicks with estradiol (Harms el al., 1963). More recently H a r m s el al. (1964) reported t h a t feeding 35 mg. per kg. of diet of the estrogenic hormone, dienestrol diacetate ( D D ) , was not effective in * Florida Agricultural Experiment Stations Journal series No. 1920.
improving antibiotic utilization; however, a significant increase was obtained when 356 mg. were fed. T h e study reported herein was conducted to determine the effect of feeding various levels of D D for different periods of time upon oxytetracycline blood serum levels. EXPERIMENTAL
PROCEDURE
Two successive experiments were conducted as a 3 X 6 factorial arrangement of treatments with levels of 0, 35, 70, 140, 280 and 560 mg. of D D per kg. of diet.
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significant except for replication X genotype within location and trial. Since the genotypes were not intermingled in replicates, this effect was confounded with pen effects. Expected genetic progress was computed for different selection procedures involving testing with varying numbers of trials, locations and replications. There was a slight increase in the precision of selection associated with increased replication. Expected genetic progress with these procedures indicated t h a t selection of apparently superior genotypes could be made almost as efficiently a t one location in one trial with some replications of genotypes as with the use of several trials, locations and replications.
Department of Poultry Science, North Carolina State of the University of North Carolina at Raleigh (Received for publication August 31, 1964) H E value of a genotype is always defined in terms of its average response over a specific population of environments; therefore, a genotype has no intrinsic value of its own. In particular environments a genotype m a y perform better or worse than expected from its average performance over many environments. Interactions of genotype with environment are of fundamental importance in plant and animal breeding because their involvement influences breeding procedure. I t is very likely t h a t there is a high correlation between an animal's ability to do well in diverse environments, b u t residual variation associated with genotype-environment interactions m a y be an important factor in selecting appropriate testing procedures. The present study was designed to provide further information on the importance of genotype-environment interactions on broiler growth. Generally, experimental evidence has indicated t h a t these interactions do not assume the importance in poultry t h a t they do in plants. Primary interest in poultry in documenting the importance of these interactions has been on certain characters associated with laying birds. A rather extensive review of these results has been presented by Hale (1961). Investigations
devoted
to
analyzing
1 Contribution from the Poultry Science Department, North Carolina Agricultural Experiment Station, Raleigh, North Carolina. Published with the approval of the Director of Research as Paper No. 1864 of the Journal Series.
the importance of interactions between genotype and environment in broilers have been more limited. Gutteridge and O'Neil (1942) found no evidence of a strain-location interaction for skeletal measurements and body weight a t eight weeks of age in three strains of Barred Plymouth Rocks at three locations. Ten strains of broilers were subjected by Merritt and Gowe (1956) to uniform diet and management conditions at three locations. Significant strain X location interactions were obtained for six-week body weight in males and for breast angle at ten weeks of age in females. Observations on groups of birds from ten strains reared separately and intermingled were made b y Hess et al. (1960). Body weights at both 8 and 9 weeks of age showed highly significant second order interactions due to sex, strain and type of rearing. In the same experiment birds grown separately by strain in each of adjacent houses had a significant interaction involving house and strain and a highly significant interaction due to house X strain X sex. Johnson and Abplanalp (1960) found a significant interaction for body weight at 9 weeks for pullets but not for cockerels when 14 strains were fed diets with different caloric levels. Cook et al. (1962) compared the performance of ten strains a t eight experiment stations in the Southeast in three trials. The location X genotype and location X genotype X trial interactions were highly significant for body weights at 2, 4, 6 and 8 weeks of age.
481
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
T
482
K. M. LEWIS AND W. L. BLOW
PROCEDURE
METHODS OF ANALYSIS
Analysis of data in this experiment was designed primarily to provide estimates
Xhijkmn = M+gh+li+ti+r k ( i i ) -r-s m 4-(gl) h i + (gt)hj+(gr)hk(ij)+(gS)hm + (lt)ij+(ls)im+(ts)jm + (rs)km(ij)+(glt)hij+(gls)him
+ (grs)hkm(ii) + (gts) hjm + (Its) i j m + (glts)hijm+ ehijkmn,
where h = 1, 2 • • • 4 genotypes i = 1, 2, 3 locations j = 1, 2, 3 trials k = 1, 2 replications within trials and locations m = 1, 2 sexes n = 1, 2 • • • 32 individuals of each sex per genotype within replications. Then Xhijkmn is the weight of the n th individual in the k th replication of the m th sex of the h th genotype at the i th location
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
For each of three hatches, three cases of eggs were shipped from commercial broiler breeders to the North Carolina Experiment Station at Raleigh, North Carolina. The material for this experiment included four strains, two New Hampshires and two White Plymouth Rocks. These eggs were subsequently hatched in Raleigh and day-old chicks were shipped to research farms at Willard and Waynesville, North Carolina. Chicks were started at these locations and Raleigh in April, July and September of the same year. The various hatches of chicks were started on feed at approximately the same time at each location. The birds were housed in replicated pens of 100 unsexed birds of each genotype at each location for each trial in a randomized block design. Floor space at each location was approximately one square foot per bird. The birds were not vaccinated during the grow-out period. The feed used at all locations was the same commercial broiler mash with a coccidiostat added. At ten weeks of age the birds were weighed to the nearest ounce and sex was recorded. No severe disease problem or unusual mortality was encountered in this experiment. The three locations used in this study are representative of the three distinct geographical areas in North Carolina. These areas are the Mountains represented by Waynesville, Piedmont by Raleigh and Coastal Plain by Willard. The mean annual temperatures over a period of thirty years have been 54.5°F., 59.5°F. and 63.1°F., respectively, for the three locations.
of the various components of variance which contribute to the total variation. In order to avoid the difficulties inherent in unequal numbers in the subclasses, the experimental data were restricted to a random sample of 32 individuals of each sex from each genotype in each replication in a trial and location. The analysis was conducted as a factorial experiment involving 4 genotypes, 3 locations, 3 trials and 2 sexes with replications of genotypes nested within trials and locations. A mixed model was assumed with sex considered a fixed variate and the rest random. The assignment of the quality of being fixed or random is to some extent purely arbitrary; however, sex is obviously a fixed effect since the entire population of sexes is drawn when both males and females are represented. The following mathematical model describes the effect of the variables studied:
483
GENOTYPE-ENVIRONMENT AND GROWTH
impact of time and place on the relative performance of these genotypes. In the present study some effort was made to standardize certain factors which may influence performance from location to location. These include such factors as floor space, feed and brooding temperatures. To some extent, however, management varied from location to location and over trials due to differences in personnel and facilities at the various locations. These differences in management and the effects which are an integral part of the geographical locations comprise the location effects of this study. The average body weights in ounces for genotypes, trials and locations over replications and sexes are presented in Table 2. A sex difference characteristic of broilers was observed in this experiment. Strains B and D were superior in performance to A and C. The genotypes sampled in this study weighed the most in Waynesville and the least in Raleigh. Average weights were the largest in the
RESULTS AND DISCUSSION
Logically, in assessing the values of genotypes one is concerned with the
TABLE 1.—Structural analysis and mean square expectations of broiler weights Mean Square Expectations Source
M.S.
c a
% Locations Trials LXT Genotypes GXL GXT GXLXT Rep/L and T RXG/L andT Sexes SXL SXT SXG RXS/LandT SXGXL SXGXT SXLXT SXGXLXT SXGXR/L&T Ind/G, L, T, R, S
M
b
s "M
i
% %
M
b
*M
1
b
b
2 =0
"b
-2 °b
»b
m
%
>b
^
"u
b
M^0
X
X
X
X
Mi,
X
X
X
X
X
M 18 M 17 M16 M16 M I4 M13
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Mj,
X
X
M„
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
M 10 M9 M8 M7 M6 M5 M4 M3 M, Mi
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X X X
X
X
X X
X
X
X X
X
X
X
X
X
X
M
M"M
fc
b
K'
b
«b X
X X
X X
X X
X X
X
°fc
X
x X
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
in the j t h trial. The population mean is represented by n and the effects which are random from individual to individual in the experiment by ehijkmn- Main effects arising from the h th genotype, i th location, j t h trial, k th replication in the i th location and j t h trial, and m th sex are represented by gh, l i; tj, rk(ij) and sm, respectively; while other effects in the model are the various interactions between these main effects. The structural analysis of the broiler weights and the mean square expectations are presented in Table 1. The expectations of the mean squares were derived by using procedures suggested by Schultz (1955). Estimates of the various variance components were obtained by equating the expectations of these mean squares to the mean squares calculated from the data.
484
K. M. LEWIS AND W. L. BLOW
TABLE 2.—Body weights in ounces for genotypes, trials and locations averaged over sexes and replications Genotypes Locations
Trials
B
C
D
Willard
1 2 3
41.66 38.28 41.08
45.24 42.80 45.00
42.91 40.69 41.98
44.42 42.31 46.50
Raleigh
1 2 3
39.00 37.90 41.11
41.78 41.88 44.35
38.84 39.12 40.77
39.33 42.17 44.56
Waynesville
1 2 3
42.80 41.78 43.45
46.12 46.69 47.24
43.49 43.08 43.83
47.30 45.71 47.18
trial conducted in the fall months and the lowest in the summer months. The analysis of variance for body weight and the components of variance due to the sources of variation are presented in Table 3. The only significant interaction involving genotypes was the interaction with replications within locations and trials. Since genotypes were not grown intermingled but in separate pens, this interaction is confounded with pen effects. This may account in part for the significance of this interaction. Although the data were analyzed on the basis of the model presented, the breakdown of the total variance into percent contributions for each variance component is not meaningful as far as breeding techniques are concerned. A cursory examination of these percentages shows that major contributions to variation between birds in this experiment were made by location, sex and random elements of the environment. In terms of the phenotypic model over 93 percent of the total variance was contributed by effects which were common to all genotypes or due to random elements of the environment. These include the variances due to locations, trials, replications, sex and all of the interactions between these primary effects. Although these results demonstrate that birds vary rather widely from location to location and in different
G= — ^ where k is the selection differential in standard deviations and cr2g and
Source
d.l.
2 Locations 2 Trials 4 LXT 3 Genotypes 6 GXL 6 GXT GXLXT 12 9 Rep/L and T R X G / L a n d T 27 1 Sexes SXL 2 2 SXT 3 SXG R X S / L and T 9 6 SXGXL 6 SXGXT SXLXT 4 12 SXGXLXT SXGXR/L and T 27 Ind./G, L, T, S and R 4,464
M.S.
Component of variance
6,115.26** 1,636.17 472.31 4,258.07** 55.73 107.65 59.45 193.00* 80.18** 101,954.36** 330.45 14.56 156.26 20.51 36.98 30.24 127.48** 20.89
3.676 .726 .586 3.606 -.010 .126 -.162 .441 .969 44.110 .240 -.163 .191 .022 .084 .049 .416 .050
17.68
-.014
18.14
18.14
* Indicates significance at the 5% level. ** Indicates significance at the 1% level.
Downloaded from http://ps.oxfordjournals.org/ at H.E.C. Bibliotheque Myriam & J. Robert Ouimet on June 8, 2015
A
trials, they are not relevant to the effects of locations and trials on breeding progress when genotypes are tested in common environments. Expected genetic progress from selection is equal to
485
GENOTYPE-ENVIRONMENT AND GROWTH
phenotypic variance. If genotype-environment interactions do exist, this can be accomplished by testing genotypes over more environments. In terms of the present study, the general form of phenotypic variance between selection units would be 2
1 2
C g Is
1 .
im
J 2
0" gts
1.
jm
IJ 2
f g Its
1 .. "t ijm
0- 2 grUt)
'
k
Locations X trials X replications
Locations
1 2 1
2 1 1
1.691 1.622 1.613
3
1 3 1
3 1 1
1.732 1.635 1.623
6 3 3 2 2 1 1
1 6 1 2 1 3 1 3 2
6 1 1 1 2 1 3 2 3
1.775 1.648 1.632 1.644 1.718 1.647 1.748 1.733 1.760
km
with i, j , k, m and n in the denominators representing the number of locations, trials, replications, sexes and individuals per sex of each genotype in the replicates, respectively. The consequences of varying the number of environments can be easily computed when estimates of the parameters are available. A set of different conditions in which numbers of trials, locations and replications were varied but the product of these numbers remained constant was postulated to determine the effects on selecting for increased broiler weight. Although the mean squares for interactions with genotype in the analysis of variance were generally non-significant, the estimates of the variance components derived from this analysis are unbiased estimates of these interactions involving genotype. The expected genetic progress for each set of conditions is presented in Table 4. It is readily apparent from these results that testing genotypes over a number of locations and trials is not a worthwhile endeavor for improving growth rate in broilers. In these testing procedures the maximum gain in efficiency is attained by increased replication in a single year at
Repli±xcpn- Expected cations11 progress 1.586
2
ijkmn
na s
1
As m
ff grs(lt)
™. ,
" The number of individuals (n) of each sex from a genotype in a replication is 32.
one location. Approximately 12 percent additional progress is indicated when six replicates of the genotypes are tested at one location in a single trial. This increase in efficiency arises from the significant replication X genotype interaction observed in this study. Since this variance is confounded with pen effects, intermingling of genotypes rather than separate rearing may afford a more practical approach to testing broiler growth. The futility of testing broiler growth over a large number of environments is apparent when genetic progress with perfect identification of genotypes is only ko-g or 1.899 k. SUMMARY
Four strains of broilers were tested at three locations over three trials with replication of each genotype in trials and locations. Analysis of variance of individual body weights indicated that interactions involving genotype were non-
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2P
2 2 a gi
TABLE 4.—Expected genetic progress in terms of k when testing with various numbers of trials, locations and replications
486
K. M . L E W I S AND W. L. B L O W
REFERENCES Cook, R. E., C. W. Hess, J. L. Carmon and E. F.
Dembnicki, 1962. Importance of genotype-environment interactions at various ages in broiler type chickens. Poultry Sci. 41: 1637. Gutteridge, H. S., and J. B. O'Neil, 1942. The relative effect of environment and heredity upon body measurments and production characteristics in poultry. Sci. Agr. 22: 482-491. Hale, R. W., 1961. Genotype-environment interactions in a comparison of the cage and semi-intensive systems for laying hens. Brit. Poultry Sci. 2: 145-157. Hess, C. W., E. F. Dembnicki and J. L. Carmon, 1960. Type-of-rearing and location effects on broiler body weights. Poultry Sci. 39: 1086-1091. Johnson, E. A., and H. Abplanalp, 1960. Strain-feed interaction in chicken fryer stock. Poultry Sci. 39: 1263. Merritt, E. S., and R. S. Gowe, 1956. Environment and poultry breeding problems. III. The performance of 8 crossbred and 2 purebred broiler strains at three locations. Canadian J. Agric. Sci. 36: 72-80. Schultz, E. F., 1955. Rules of thumb for determining expectations of mean squares in analysis of variance. Biometrics, 11: 123-135.
Effects of Dosage Level and Length of Feeding Dienestrol Diacetate on Potentiation of Oxytetracycline* J. E. J O N E S , H. R. W I L S O N , P . W. W A L D R O U P AND R. H.
HARMS
Florida Agricultural Experiment Station, Gainesville, Florida (Received for publication August 31, 1964)
V
A R I O U S methods of antibiotic potentiation have been reported including lowering of the dietary calcium level (Price and Zolli, 1959), addition of terephthalic acid (TPA) to the diet (Peterson 1958) or injecting chicks with estradiol (Harms el al., 1963). More recently H a r m s el al. (1964) reported t h a t feeding 35 mg. per kg. of diet of the estrogenic hormone, dienestrol diacetate ( D D ) , was not effective in * Florida Agricultural Experiment Stations Journal series No. 1920.
improving antibiotic utilization; however, a significant increase was obtained when 356 mg. were fed. T h e study reported herein was conducted to determine the effect of feeding various levels of D D for different periods of time upon oxytetracycline blood serum levels. EXPERIMENTAL
PROCEDURE
Two successive experiments were conducted as a 3 X 6 factorial arrangement of treatments with levels of 0, 35, 70, 140, 280 and 560 mg. of D D per kg. of diet.
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significant except for replication X genotype within location and trial. Since the genotypes were not intermingled in replicates, this effect was confounded with pen effects. Expected genetic progress was computed for different selection procedures involving testing with varying numbers of trials, locations and replications. There was a slight increase in the precision of selection associated with increased replication. Expected genetic progress with these procedures indicated t h a t selection of apparently superior genotypes could be made almost as efficiently a t one location in one trial with some replications of genotypes as with the use of several trials, locations and replications.