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Body Growth Response to Selection and Crossbreeding in Dwarf and Normal Broiler-type Chickens*
Body Growth Response to Selection and Crossbreeding in Dwarf and Normal Broiler-type Chickens* A . G. K H A N , R. G. JAAP AND A . K.
KANOUN
The Ohio State University and The Ohio Agricultural and Development Center, 674 West Lane Columbus, Ohio 43210
Avenue,
(Received for publication November 25, 1974)
POULTRY SCIENCE 54: 1239-1244, 1975
INTRODUCTION
T
HE sex-linked dwarfing gene dw has a potential for development of more efficient broiler breeder dams. When dw dwarf dams are crossed with normal-bodied broiler sire strains, there is only a small reduction in the eight-week body weight of the crossbred broilers (Ricard, 1971; Ricard and Cochez, 1971 ;Mohammadian and Jaap, 1972; Chambers et al., 1974). Dwarf dams lay smaller eggs than their non-dwarf sisters. The effect of this smaller egg size is to reduce eight-week body weight of heterozygous normal sons from dwarf dams about 3 to 3.5 percent. The normal crossbred daughters from dwarf dams approach more closely the broiler weights of those from their normal sisters. Most of the reports to date indicate that there may be a slight growth depressing effect of dwarf allele in crossbred sons which is not accounted for by a smaller egg weight
*Approved for publication as Journal Article No. 116-74 of the Ohio Agricultural Research and Development Center, Wooster, Ohio.
when their mother is a dwarf; however, Ricard and Conan (1974) could not detect a significant difference. Reproductive fitness of dwarf dams appears to be slightly superior to that of normal broiler-type dams. The number of normal eggs produced is greater (Van Middelkoop, 1973) while mortality, fertility and hatchability may not differ from that of their non-dwarf sisters. Chambers et al. (1974) estimated that the reduction in feed cost per dozen eggs produced from dwarf broiler-type dams was 36.3%. In the following experiments response to selection for early rapid growth and increased egg size was compared within dwarf and normal-bodied broiler-type populations. Also, dams selected for within strain superiority were tested for their crossing ability to produce broilers using a commercial broiler-type sire strain. This was a test of whether dwarf dams selected from a rapid growth strain would also produce rapidly growing progeny when the dwarf phenotype was removed by crossing with normal-bodied broiler breeder sires.
1239
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ABSTRACT A normal-bodied broiler population and one dwarfed by the dw sex-linked gene were each sub-divided into two lines. AGB (normal) and D2B (dwarf) were selected only for superior body weight at eight weeks of age. AGE (normal) and D2E (dwarf) were sublines in which prospective dams were selected for large egg weight while prospective sires were selected for eight-week body weight. Selection for large eight-week weight of both sexes in both dwarf and normal populations during each of three generations resulted in superior growth rate to that observed when the dams were selected for egg weight. When the selected dams were tested each generation for their ability to produce superior broiler crossbreds using a commercial broiler sire strain, AGE proved superior to AGB in the second and third generations while D2B and D2E dams produced crossbreds with similar broiler weights. Normal-bodied dams which produced crossbreds having superior growth to that of the dwarf dams in the first generation lost most of this superiority by the third generation in sons and the second generation in daughters. Reproductive fitness was superior within the dwarf lines as well as in their ability to produce more crossbred progeny.
1240
A. G. K H A N , R. G. JAAP AND A. K. K A N O U N MATERIALS AND METHODS
Each of the dwarf and non-dwarf populations was sub-divided into two sublines. One of the sublines was selected for large body weight of both sexes at eight weeks of age. In the other subline, prospective sires were selected for large eight-week weight while prospective dams were selected for large egg size just prior to the reproductive period which began about 30 weeks of age or shortly thereafter. The four sublines will be symbolized as AGB and D2B for the non-dwarf and dwarf populations selected only on eight week weight versus AGE and D2E for those lines in which the prospective dams were selected only for large egg size. Each of the four sublines were reproduced by artificial insemination, primarily paired matings, involving 30 to 40 sires and 35 to 40 dams retained in individual cages each generation. Beginning about 30 weeks of age or shortly thereafter, all normal eggs laid
Y ^ u
+ h. + Sj + gk
+ (hg) ik + (sg) jk ik +' e ^ijkl where, Y ijkl
is the eight-week body weight of the "i"th progeny from the " k " t h line of dam mated to the " j " t h sire in the "l"th hatch, u is the overall mean hj is the effect of the " i " t h hatch Sj is the effect of the " j ' ^ h sire, g k is the effect of the " k " t h line of dam, (hg) ik is the interaction between the "i"th hatch and "k"thlineof dam (sg) jk is the interaction between the " j " t h sire and the " k " t h line of dam eijtd is the residual effect assumed to be distributed normally with zero mean and variance 6\. Crossbreeding Tests. Immediately following reproduction of the sublines, each generation the selected dams used for production of that generation were artificially inseminated with semen from 35 to 40 sires of a non-related commercial sire-line population. The purpose of this crosstesting was to estimate the combining ability as well as reproductive fitness of the various dam sublines with this particular commercial broiler-type sire strain. Statistical analyses were similar to the
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Within Strain Comparisons. A normalbodied broiler strain (AAG) and a dwarf counterpart (D2) were synthesized from the broiler populations utilized by Mohammadian and Jaap (1972). Strain AAG was formed by pooling reciprocal crosses of strains A and AG (Dev et al., 1969). Dams for the D2 base population has 15/ 16ths of A and AG autosomal inheritance as a result of three backcrosses of heterozygous (dw+) sires to A and AG dams. Homozygous dwarf sires for the foundation of the D2 strain were from a mating of heterozygous sires from the second backcross to daughters of the third backcross. Therefore, growth rate of the D2 strain was reduced from that of AAG primarily by a 20% size reduction (Mohammadian and Jaap, 1972) attributable to the dw gene. Also, approximately one-tenth (29/32) of their quantitative inheritance for growth rate was reduced by genes from the smallbodied dwarf Leghorn ancestor which provided the dvvgene.
during a four week period were incubated in two biweekly hatch groups. The dwarf types D2B and D2E were brooded intermingled but in separate pens from the non-dwarfs AGB and AGE which were also intermingled during the brooding period. Data from the first two generations were analyzed within sex and generation using the following model:
1241
GROWTH RESPONSE
within strain analyses. In order to test the significance of line of dam effect, hatches and generations were considered to be a set of cross classified main effects. Since all lines were inseminated with semen from the same sires each generation, the sire effects were considered to be a set of cross classified random effects. Hatch x sire interaction effects were fitted first and were found to be nonsignificant.
Generations
AGE D2B D2E
AGB minus AGE Females
£gB
AGB minus AGE
1
2
3
2002 2001
1881 1859
2096 2012
^n
722
784
1677 1627
1531 1488
1680 1672
+50
+43
+ 18
1230 1161
1308 1271
1433 1357
1
2
3
132 136 130 137 174 172 200 205
192 197 276 286 233 225 247 291
139 128 194 205 220 218 296 300
D2B minus D2E c i Females
D2B T-^p
D2B minus D2E
+69
+37
+65
1039 989
1063 1043
1193 1105
750
720
788
to 160 per generation. Thus inbreeding and genetic drift should have been near minimum for such small populations of breeders. The mean eight-week body weights according to sublines and sex are given in Table 2. Differences between generations within line and sex were highly significant (P > .01). As shown in Table 2, progeny of the B sublines selected for large eight-week weight in both sexes were slightly superior to those from the comparable E-sublines where selection of the dams was only for large egg weight. As expected, mean weights for the dwarf populations (D2B and D2E) were much smaller than those for their normal counterparts (AGB and AGE). The dw gene in these populations reduces eight-week weight about 20% (Mohammadian and Jaap, 1972). In addition, the dwarfs had autosomal inheritance for slightly smaller body size attributable to approximately one-tenth of their inheritance having originated from the smaller slower growing Leghorn ancestry. For these reasons, only comparisons between AGB and AGE and those between D2B and D2E may be used to estimate the effects of selection. Selection to increase maternal egg weight in AGE and D2E produced only small in-
Downloaded from http://ps.oxfordjournals.org/ by Nathalia Oliveira on May 10, 2015
TABLE 1.—Number of progeny available for selection within lines each generation
6 9 J 9 6 9 6 9
Males £ g !
Males Jgg
Within Strain Comparisons. Data for the two hatches in each generation were pooled because hatch effects on mean eight-week weights proved to be statistically non-significant. The numbers of progeny providing the broiler weight data are given in Table 1. The number of chickens of each sex within sublines is a measure of reproductive fitness using artificial insemination because the number of each sex selected as breeders was approximately the same each generation and all normal eggs laid during the same four week period were incubated. The data in Table 1 show that reproductive efficiency was superior in the dwarf lines (D2B and D2E). Since the dwarf types produced more chicks selection intensity for growth rate as well as for egg size in the E-line females was greater than that in their non-dwarf contemporaries. Since most of the matings were paired and full-sib matings avoided, the effective number of parents ranged from 127
AGB
Generations Normals
Dwarfs
RESULTS
Lines
TABLE 2.—Mean eight-week body weights (grams) of progeny from normal (AGB and AGE) and dwarf (D2B and D2E) parents
1242
A. G. KHAN, R. G. JAAP AND A. K. KANOUN
The egg production of dwarf and normal lines may be compared recognizing that there was a slight difference in their ancestry. The number of yolks in all eggs laid as well as the number of single-yolked eggs free from visible shell defects was greater for D2B and D2E pullets than those for their AGB and AGE counterparts. Table 3 gives the average number of yolks and number of normal eggs TABLE 3.—Mean number of yolks in eggs laid and number of normal eggs laid during the first 72 days of production
Line AGB AGE D2B D2E
Pullets 93 157 109 150
Mean number of Normal Yolks eggs 41.9 ± 0.9 37.1 ± 1.0 43.5 ± 0.7 38.6 ± 0.8 48.9 ± 0.9 45.6 ± 0.9 48.3 ± 0.7 44.4 ± 0.8
TABLE 4.—Numbers of crossbred progeny produced from each generation of sleeted normal and dwarf dams Generations Normal dams AGB Sons AGE Daughters
A
g|
Dwarf dams D2B Sons D2E Daughters
jj 2 g
117 117 122 111
146 171 132 201
28 73 12 81
163 208 148 195
193 195 232 212
110 129 117 129
laid by non-selected pullets from the third generation of selected dams during a 72 day period. The average number of eggs laid by the dwarfs exceeded that of the normal pullets by about 7 eggs during this period. At 35 weeks of age, the average weight of eggs laid by the dwarf pullets were 2.8 g. smaller (P < .01) than those from the normal-bodied pullets. Crossbreeding Tests. The numbers of crossbred progeny are given in Table 4. The superior reproductive fitness of the dwarf dams is again illustrated by the larger numbers of crossbred progeny in each of these 3 generations. The cross test data in generation 3 were from eggs laid only during a two-week versus a four-week period for generations 1 and 2. Generation 3 cross tests were also made later in the laying period and many of the AGB dams had ceased egg production. The large normal-bodied dams developed sore feet in wire bottom cages more readily than did the dwarfs which may have been partially responsible for their poorer egg production. Such a great disparity between yields of broilers would probably not occur on floor litter. The number of normal eggs as well as hatchability of all eggs incubated has been superior from these dwarf dams. Most of the hatchability difference would appear to be due to the superior fertility of dwarf dams
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creases. Egg weights of progeny of the third generation of selected parents compared at 35 weeks of age were as follows: AGB, 64.6 ± 0.05; AGE, 65.3 ± 0.4; D2B, 61.2 ± 0.4 and D2E, 63.04 ± 0.4 grams. The 0.7 g. larger egg weight of AGE over that of AGB should have resulted in only a slight increase in weight of their broiler progeny. No linear regression of broiler weight of dwarf sons on egg weight from which they hatched was expected (Khan et al., 1973). However, the 1.8 g. advantage in egg size from D2E dams would have been expected to have increased eight-week weight of their female dwarf progeny about 9 to 10 grams. In view of this previous information, eight-week body weight of both AGB and D2B should have increased more from direct selection and were expected to have been slightly greater than those of their AGE and D2E counterparts. Although many of these differences (Table 2) were small, all were consistent with the expected eight-week weight superiority of the B sublines. Selection of dams for large eightweek weight was superior to that gained from the indirect selection mediated through egg size.
GROWTH RESPONSE
TABLE 5.—Mean body weights (grams) of crossbred progeny from selected normal and dwarf dams at 8 weeks for generations 1 and 2, and at 7 weeks for generation 3 Normal dams <. c Sons
AGB A G E
AGB minus AGE Daughters
AQP
AGB minus AGE
D2E
D2B minus D2E Daughters
T-.2p
D2B minus D2E
3
1788 1766 +22
2000 2064
1456 1524
-64
-68
1563 1488
1639 1653
1247 1293
+75
-14
-46
1625 1657
1933 1901
1488 1447
-32
+32
+41
1439 1442
1609 1566
1234 1247
-3
+43
-13
Progeny of normal minus dwarf dams Sons +136 +125 Daughters +158 +15
+32 +30
when artificial insemination is used. Tests of fertility from natural matings have not been made. Table 5 gives the least square means for eight-week body weights in generations 1 and 2 and actual means for seven-week body weights in generation 3. In generations 2 and 3, crossbreds from the normal dams of the egg weight selection subline AGE produced larger broilers than those from AGB dams. However, within pure strain progeny (Table 2) AGB progeny were superior. Therefore, it appears that the selection of dams on the basis of large egg weight may have improved the broiler weight of their crossbreds but not of their pureline progeny. Crossbred male and female progeny from normal AGB and AGE dams (Table 5) were significantly larger than crossbred progeny from dwarf dams in generation 1. Superiority of crossbreds daughters from normal dams became statistically nonsignificant in generations 2 and 3 and superiority of male crossbreds was nonsignificant only in generation 3. Whether within pureline selection was
more effective in improvement of the crossbred performance of dwarf than of normal dams needs further verification from experiments designed for that purpose. Since dwarf dams produced more progeny, selection intensity for larger eight-week weight was higher in the dwarf populations. Whether heritability for growth rate in the dwarf phenotype is similar to that in the normal is not known at this time. It is doubtful that the slight difference in ancestry of the dwarf and non-dwarf populations could have contributed more to genetic diversity in the dwarfs. These data indicate that improvement of crossing ability of dwarf dam populations might be more rapid than that of non-dwarf populations to be used as mothers of broiler chickens. Females of an inferior dwarf broiler-type strain (Dl) having part of their inheritance similar to that of D2 were crosstested using semen from the same commercial broiler sires used for the test of the second generation of D2. While no direct within strain growth comparisons between Dl and D2 were available, eight-week body weight of both sexes of the Dl strain has averaged about 140 g. less than those for D2. The mean weight of 397 male and 429 female crossbreds from Dl dams was 1782 ± 13 g. and 1476 ± 9 g., respectively. The average weight of these crossbreds from Dl dams was approximately 100 g. less than the average D2B and D2E crossbred progenies in that generation (Generation 2—Table 5). This comparison of crossbred progenies from Dl and D2 dams favors the expectation that, where there are large differences in growth rate between dwarf broiler-type strains, dams from the more rapidly growing dwarf strains should produce superior crossbred broilers. In this comparison of Dl and D2, most of the additive genetic effects in the dwarf appeared to be additive in the normal-bodied crossbred phenotype. Therefore, selection for superior growth in the
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Dwarf dams c ™ , D2B Sons
Generations 2
1
1243
1244
A. G. KHAN, R. G. JAAP AND A. K. KANOUN
dwarf dam strain should improve the growth rate of their normal-bodied crossbred progeny. REFERENCES
Distribution of Selenium in Egg White and Yolk after Feeding Natural and Synthetic Selenium Compounds J. D . LATSHAW AND M . OSMAN
Department of Poultry Science, Ohio Agricultural Research and Development Center, and Ohio State University, Columbus, Ohio 43210 (Received for publication November 25, 1974)
ABSTRACT Practical diets containing various selenium levels, with and without selenite supplementation, were fed to hens. Eggs were then collected over a 14-day period to determine how quickly changes in dietary selenium affected egg white and yolk selenium. Changes in egg white selenium content were rapid and essentially completed seven days after changing the selenium content of a practical diet. Changes in egg yolk were not yet completed by 14 days. When selenium from practical feedstuffs was fed, the selenium content of dried egg white was about equal to or greater than the selenium content of dried egg yolk. When selenite was fed, the selenium content of dried yolk was higher. Feeding selenomethionine resulted in more selenium in egg white than in egg yolk. Feeding selenocystine resulted in more selenium in egg yolk than egg white, a pattern similar to that from feeding selenite. The data suggest that selenocystine is not incorporated into protein but is metabolized to an inorganic selenium compound. POULTRY SCIENCE 54: 1244-1252, 1975
INTRODUCTION
S
from ingredients generally used for formulating practical diets, the selenium in a given
TUDIES with monogastric animals have shown that the form of selenium in the
diet has a significant effect on the amount of selenium which will be present in tissues of the body. If the dietary selenium comes
tissue is approximately proportional to the amount found in the diet (Ku et al., 1972b; Scott and Thompson, 1971; and Latshaw, 1975). If the dietary selenium is provided by sodium selenite, then the selenium content of tissues is not proportional to dietary sele-
Ohio Agricultural Research and Development Center Journal Article Series No. 113-74.
nium. Less selenium is retained from selenite, with the effect being especially prominent
Downloaded from http://ps.oxfordjournals.org/ by Nathalia Oliveira on May 10, 2015
Chambers, J. R., A. D. Smith, I. McMillan and G. W. Friars, 1974. Comparison of normal and dwarf broiler breeder hens. Poultry Sci. 53: 864-870. Dev, D. S., R. G. Jaap and W. R. Harvey, 1969. Results of selection for eight-week body weight in three broiler populations of chickens. Poultry Sci. 48: 1336-1348. Khan, A. G., R. G. Jaap and W. R. Harvey, 1973. The effect of egg weight on eight-week body weight of normal and dwarf progeny from dwarf dams. Poultry Sci. 53: 211-218.
Mohammadian, M., and R. G. Jaap, 1972. Effect of the sex-linked dw dwarfing gene on body growth of chickens. Poultry Sci. 51: 1701-1707. Ricard, F. H., 1971. Growth rate and carcass characters of chicken broilers obtained from normal or dwarf (dw) dams. World's Poultry Sci. J. 27: 278279. Ricard, F. H., and L. P. Cochez, 1971. Effects of the sex-linked dwarf gene, dw, on performance of hens in a meat-type strain of domestic fowl. World's Poultry Sci. J. 27: 292. Ricard, F. H., and L. Conan, 1974. Performances zootechniques de poulets normaux fils de meres normales ou naines. Proc. XV World's Poultry Congress: 24-26. VanMiddlekoop, J. H., 1973. Influence of the dwarfing gene on egg laying pattern. 4th Europ. Poultry Conf., London: 563-567.
KANOUN
The Ohio State University and The Ohio Agricultural and Development Center, 674 West Lane Columbus, Ohio 43210
Avenue,
(Received for publication November 25, 1974)
POULTRY SCIENCE 54: 1239-1244, 1975
INTRODUCTION
T
HE sex-linked dwarfing gene dw has a potential for development of more efficient broiler breeder dams. When dw dwarf dams are crossed with normal-bodied broiler sire strains, there is only a small reduction in the eight-week body weight of the crossbred broilers (Ricard, 1971; Ricard and Cochez, 1971 ;Mohammadian and Jaap, 1972; Chambers et al., 1974). Dwarf dams lay smaller eggs than their non-dwarf sisters. The effect of this smaller egg size is to reduce eight-week body weight of heterozygous normal sons from dwarf dams about 3 to 3.5 percent. The normal crossbred daughters from dwarf dams approach more closely the broiler weights of those from their normal sisters. Most of the reports to date indicate that there may be a slight growth depressing effect of dwarf allele in crossbred sons which is not accounted for by a smaller egg weight
*Approved for publication as Journal Article No. 116-74 of the Ohio Agricultural Research and Development Center, Wooster, Ohio.
when their mother is a dwarf; however, Ricard and Conan (1974) could not detect a significant difference. Reproductive fitness of dwarf dams appears to be slightly superior to that of normal broiler-type dams. The number of normal eggs produced is greater (Van Middelkoop, 1973) while mortality, fertility and hatchability may not differ from that of their non-dwarf sisters. Chambers et al. (1974) estimated that the reduction in feed cost per dozen eggs produced from dwarf broiler-type dams was 36.3%. In the following experiments response to selection for early rapid growth and increased egg size was compared within dwarf and normal-bodied broiler-type populations. Also, dams selected for within strain superiority were tested for their crossing ability to produce broilers using a commercial broiler-type sire strain. This was a test of whether dwarf dams selected from a rapid growth strain would also produce rapidly growing progeny when the dwarf phenotype was removed by crossing with normal-bodied broiler breeder sires.
1239
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ABSTRACT A normal-bodied broiler population and one dwarfed by the dw sex-linked gene were each sub-divided into two lines. AGB (normal) and D2B (dwarf) were selected only for superior body weight at eight weeks of age. AGE (normal) and D2E (dwarf) were sublines in which prospective dams were selected for large egg weight while prospective sires were selected for eight-week body weight. Selection for large eight-week weight of both sexes in both dwarf and normal populations during each of three generations resulted in superior growth rate to that observed when the dams were selected for egg weight. When the selected dams were tested each generation for their ability to produce superior broiler crossbreds using a commercial broiler sire strain, AGE proved superior to AGB in the second and third generations while D2B and D2E dams produced crossbreds with similar broiler weights. Normal-bodied dams which produced crossbreds having superior growth to that of the dwarf dams in the first generation lost most of this superiority by the third generation in sons and the second generation in daughters. Reproductive fitness was superior within the dwarf lines as well as in their ability to produce more crossbred progeny.
1240
A. G. K H A N , R. G. JAAP AND A. K. K A N O U N MATERIALS AND METHODS
Each of the dwarf and non-dwarf populations was sub-divided into two sublines. One of the sublines was selected for large body weight of both sexes at eight weeks of age. In the other subline, prospective sires were selected for large eight-week weight while prospective dams were selected for large egg size just prior to the reproductive period which began about 30 weeks of age or shortly thereafter. The four sublines will be symbolized as AGB and D2B for the non-dwarf and dwarf populations selected only on eight week weight versus AGE and D2E for those lines in which the prospective dams were selected only for large egg size. Each of the four sublines were reproduced by artificial insemination, primarily paired matings, involving 30 to 40 sires and 35 to 40 dams retained in individual cages each generation. Beginning about 30 weeks of age or shortly thereafter, all normal eggs laid
Y ^ u
+ h. + Sj + gk
+ (hg) ik + (sg) jk ik +' e ^ijkl where, Y ijkl
is the eight-week body weight of the "i"th progeny from the " k " t h line of dam mated to the " j " t h sire in the "l"th hatch, u is the overall mean hj is the effect of the " i " t h hatch Sj is the effect of the " j ' ^ h sire, g k is the effect of the " k " t h line of dam, (hg) ik is the interaction between the "i"th hatch and "k"thlineof dam (sg) jk is the interaction between the " j " t h sire and the " k " t h line of dam eijtd is the residual effect assumed to be distributed normally with zero mean and variance 6\. Crossbreeding Tests. Immediately following reproduction of the sublines, each generation the selected dams used for production of that generation were artificially inseminated with semen from 35 to 40 sires of a non-related commercial sire-line population. The purpose of this crosstesting was to estimate the combining ability as well as reproductive fitness of the various dam sublines with this particular commercial broiler-type sire strain. Statistical analyses were similar to the
Downloaded from http://ps.oxfordjournals.org/ by Nathalia Oliveira on May 10, 2015
Within Strain Comparisons. A normalbodied broiler strain (AAG) and a dwarf counterpart (D2) were synthesized from the broiler populations utilized by Mohammadian and Jaap (1972). Strain AAG was formed by pooling reciprocal crosses of strains A and AG (Dev et al., 1969). Dams for the D2 base population has 15/ 16ths of A and AG autosomal inheritance as a result of three backcrosses of heterozygous (dw+) sires to A and AG dams. Homozygous dwarf sires for the foundation of the D2 strain were from a mating of heterozygous sires from the second backcross to daughters of the third backcross. Therefore, growth rate of the D2 strain was reduced from that of AAG primarily by a 20% size reduction (Mohammadian and Jaap, 1972) attributable to the dw gene. Also, approximately one-tenth (29/32) of their quantitative inheritance for growth rate was reduced by genes from the smallbodied dwarf Leghorn ancestor which provided the dvvgene.
during a four week period were incubated in two biweekly hatch groups. The dwarf types D2B and D2E were brooded intermingled but in separate pens from the non-dwarfs AGB and AGE which were also intermingled during the brooding period. Data from the first two generations were analyzed within sex and generation using the following model:
1241
GROWTH RESPONSE
within strain analyses. In order to test the significance of line of dam effect, hatches and generations were considered to be a set of cross classified main effects. Since all lines were inseminated with semen from the same sires each generation, the sire effects were considered to be a set of cross classified random effects. Hatch x sire interaction effects were fitted first and were found to be nonsignificant.
Generations
AGE D2B D2E
AGB minus AGE Females
£gB
AGB minus AGE
1
2
3
2002 2001
1881 1859
2096 2012
^n
722
784
1677 1627
1531 1488
1680 1672
+50
+43
+ 18
1230 1161
1308 1271
1433 1357
1
2
3
132 136 130 137 174 172 200 205
192 197 276 286 233 225 247 291
139 128 194 205 220 218 296 300
D2B minus D2E c i Females
D2B T-^p
D2B minus D2E
+69
+37
+65
1039 989
1063 1043
1193 1105
750
720
788
to 160 per generation. Thus inbreeding and genetic drift should have been near minimum for such small populations of breeders. The mean eight-week body weights according to sublines and sex are given in Table 2. Differences between generations within line and sex were highly significant (P > .01). As shown in Table 2, progeny of the B sublines selected for large eight-week weight in both sexes were slightly superior to those from the comparable E-sublines where selection of the dams was only for large egg weight. As expected, mean weights for the dwarf populations (D2B and D2E) were much smaller than those for their normal counterparts (AGB and AGE). The dw gene in these populations reduces eight-week weight about 20% (Mohammadian and Jaap, 1972). In addition, the dwarfs had autosomal inheritance for slightly smaller body size attributable to approximately one-tenth of their inheritance having originated from the smaller slower growing Leghorn ancestry. For these reasons, only comparisons between AGB and AGE and those between D2B and D2E may be used to estimate the effects of selection. Selection to increase maternal egg weight in AGE and D2E produced only small in-
Downloaded from http://ps.oxfordjournals.org/ by Nathalia Oliveira on May 10, 2015
TABLE 1.—Number of progeny available for selection within lines each generation
6 9 J 9 6 9 6 9
Males £ g !
Males Jgg
Within Strain Comparisons. Data for the two hatches in each generation were pooled because hatch effects on mean eight-week weights proved to be statistically non-significant. The numbers of progeny providing the broiler weight data are given in Table 1. The number of chickens of each sex within sublines is a measure of reproductive fitness using artificial insemination because the number of each sex selected as breeders was approximately the same each generation and all normal eggs laid during the same four week period were incubated. The data in Table 1 show that reproductive efficiency was superior in the dwarf lines (D2B and D2E). Since the dwarf types produced more chicks selection intensity for growth rate as well as for egg size in the E-line females was greater than that in their non-dwarf contemporaries. Since most of the matings were paired and full-sib matings avoided, the effective number of parents ranged from 127
AGB
Generations Normals
Dwarfs
RESULTS
Lines
TABLE 2.—Mean eight-week body weights (grams) of progeny from normal (AGB and AGE) and dwarf (D2B and D2E) parents
1242
A. G. KHAN, R. G. JAAP AND A. K. KANOUN
The egg production of dwarf and normal lines may be compared recognizing that there was a slight difference in their ancestry. The number of yolks in all eggs laid as well as the number of single-yolked eggs free from visible shell defects was greater for D2B and D2E pullets than those for their AGB and AGE counterparts. Table 3 gives the average number of yolks and number of normal eggs TABLE 3.—Mean number of yolks in eggs laid and number of normal eggs laid during the first 72 days of production
Line AGB AGE D2B D2E
Pullets 93 157 109 150
Mean number of Normal Yolks eggs 41.9 ± 0.9 37.1 ± 1.0 43.5 ± 0.7 38.6 ± 0.8 48.9 ± 0.9 45.6 ± 0.9 48.3 ± 0.7 44.4 ± 0.8
TABLE 4.—Numbers of crossbred progeny produced from each generation of sleeted normal and dwarf dams Generations Normal dams AGB Sons AGE Daughters
A
g|
Dwarf dams D2B Sons D2E Daughters
jj 2 g
117 117 122 111
146 171 132 201
28 73 12 81
163 208 148 195
193 195 232 212
110 129 117 129
laid by non-selected pullets from the third generation of selected dams during a 72 day period. The average number of eggs laid by the dwarfs exceeded that of the normal pullets by about 7 eggs during this period. At 35 weeks of age, the average weight of eggs laid by the dwarf pullets were 2.8 g. smaller (P < .01) than those from the normal-bodied pullets. Crossbreeding Tests. The numbers of crossbred progeny are given in Table 4. The superior reproductive fitness of the dwarf dams is again illustrated by the larger numbers of crossbred progeny in each of these 3 generations. The cross test data in generation 3 were from eggs laid only during a two-week versus a four-week period for generations 1 and 2. Generation 3 cross tests were also made later in the laying period and many of the AGB dams had ceased egg production. The large normal-bodied dams developed sore feet in wire bottom cages more readily than did the dwarfs which may have been partially responsible for their poorer egg production. Such a great disparity between yields of broilers would probably not occur on floor litter. The number of normal eggs as well as hatchability of all eggs incubated has been superior from these dwarf dams. Most of the hatchability difference would appear to be due to the superior fertility of dwarf dams
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creases. Egg weights of progeny of the third generation of selected parents compared at 35 weeks of age were as follows: AGB, 64.6 ± 0.05; AGE, 65.3 ± 0.4; D2B, 61.2 ± 0.4 and D2E, 63.04 ± 0.4 grams. The 0.7 g. larger egg weight of AGE over that of AGB should have resulted in only a slight increase in weight of their broiler progeny. No linear regression of broiler weight of dwarf sons on egg weight from which they hatched was expected (Khan et al., 1973). However, the 1.8 g. advantage in egg size from D2E dams would have been expected to have increased eight-week weight of their female dwarf progeny about 9 to 10 grams. In view of this previous information, eight-week body weight of both AGB and D2B should have increased more from direct selection and were expected to have been slightly greater than those of their AGE and D2E counterparts. Although many of these differences (Table 2) were small, all were consistent with the expected eight-week weight superiority of the B sublines. Selection of dams for large eightweek weight was superior to that gained from the indirect selection mediated through egg size.
GROWTH RESPONSE
TABLE 5.—Mean body weights (grams) of crossbred progeny from selected normal and dwarf dams at 8 weeks for generations 1 and 2, and at 7 weeks for generation 3 Normal dams <. c Sons
AGB A G E
AGB minus AGE Daughters
AQP
AGB minus AGE
D2E
D2B minus D2E Daughters
T-.2p
D2B minus D2E
3
1788 1766 +22
2000 2064
1456 1524
-64
-68
1563 1488
1639 1653
1247 1293
+75
-14
-46
1625 1657
1933 1901
1488 1447
-32
+32
+41
1439 1442
1609 1566
1234 1247
-3
+43
-13
Progeny of normal minus dwarf dams Sons +136 +125 Daughters +158 +15
+32 +30
when artificial insemination is used. Tests of fertility from natural matings have not been made. Table 5 gives the least square means for eight-week body weights in generations 1 and 2 and actual means for seven-week body weights in generation 3. In generations 2 and 3, crossbreds from the normal dams of the egg weight selection subline AGE produced larger broilers than those from AGB dams. However, within pure strain progeny (Table 2) AGB progeny were superior. Therefore, it appears that the selection of dams on the basis of large egg weight may have improved the broiler weight of their crossbreds but not of their pureline progeny. Crossbred male and female progeny from normal AGB and AGE dams (Table 5) were significantly larger than crossbred progeny from dwarf dams in generation 1. Superiority of crossbreds daughters from normal dams became statistically nonsignificant in generations 2 and 3 and superiority of male crossbreds was nonsignificant only in generation 3. Whether within pureline selection was
more effective in improvement of the crossbred performance of dwarf than of normal dams needs further verification from experiments designed for that purpose. Since dwarf dams produced more progeny, selection intensity for larger eight-week weight was higher in the dwarf populations. Whether heritability for growth rate in the dwarf phenotype is similar to that in the normal is not known at this time. It is doubtful that the slight difference in ancestry of the dwarf and non-dwarf populations could have contributed more to genetic diversity in the dwarfs. These data indicate that improvement of crossing ability of dwarf dam populations might be more rapid than that of non-dwarf populations to be used as mothers of broiler chickens. Females of an inferior dwarf broiler-type strain (Dl) having part of their inheritance similar to that of D2 were crosstested using semen from the same commercial broiler sires used for the test of the second generation of D2. While no direct within strain growth comparisons between Dl and D2 were available, eight-week body weight of both sexes of the Dl strain has averaged about 140 g. less than those for D2. The mean weight of 397 male and 429 female crossbreds from Dl dams was 1782 ± 13 g. and 1476 ± 9 g., respectively. The average weight of these crossbreds from Dl dams was approximately 100 g. less than the average D2B and D2E crossbred progenies in that generation (Generation 2—Table 5). This comparison of crossbred progenies from Dl and D2 dams favors the expectation that, where there are large differences in growth rate between dwarf broiler-type strains, dams from the more rapidly growing dwarf strains should produce superior crossbred broilers. In this comparison of Dl and D2, most of the additive genetic effects in the dwarf appeared to be additive in the normal-bodied crossbred phenotype. Therefore, selection for superior growth in the
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Dwarf dams c ™ , D2B Sons
Generations 2
1
1243
1244
A. G. KHAN, R. G. JAAP AND A. K. KANOUN
dwarf dam strain should improve the growth rate of their normal-bodied crossbred progeny. REFERENCES
Distribution of Selenium in Egg White and Yolk after Feeding Natural and Synthetic Selenium Compounds J. D . LATSHAW AND M . OSMAN
Department of Poultry Science, Ohio Agricultural Research and Development Center, and Ohio State University, Columbus, Ohio 43210 (Received for publication November 25, 1974)
ABSTRACT Practical diets containing various selenium levels, with and without selenite supplementation, were fed to hens. Eggs were then collected over a 14-day period to determine how quickly changes in dietary selenium affected egg white and yolk selenium. Changes in egg white selenium content were rapid and essentially completed seven days after changing the selenium content of a practical diet. Changes in egg yolk were not yet completed by 14 days. When selenium from practical feedstuffs was fed, the selenium content of dried egg white was about equal to or greater than the selenium content of dried egg yolk. When selenite was fed, the selenium content of dried yolk was higher. Feeding selenomethionine resulted in more selenium in egg white than in egg yolk. Feeding selenocystine resulted in more selenium in egg yolk than egg white, a pattern similar to that from feeding selenite. The data suggest that selenocystine is not incorporated into protein but is metabolized to an inorganic selenium compound. POULTRY SCIENCE 54: 1244-1252, 1975
INTRODUCTION
S
from ingredients generally used for formulating practical diets, the selenium in a given
TUDIES with monogastric animals have shown that the form of selenium in the
diet has a significant effect on the amount of selenium which will be present in tissues of the body. If the dietary selenium comes
tissue is approximately proportional to the amount found in the diet (Ku et al., 1972b; Scott and Thompson, 1971; and Latshaw, 1975). If the dietary selenium is provided by sodium selenite, then the selenium content of tissues is not proportional to dietary sele-
Ohio Agricultural Research and Development Center Journal Article Series No. 113-74.
nium. Less selenium is retained from selenite, with the effect being especially prominent
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Chambers, J. R., A. D. Smith, I. McMillan and G. W. Friars, 1974. Comparison of normal and dwarf broiler breeder hens. Poultry Sci. 53: 864-870. Dev, D. S., R. G. Jaap and W. R. Harvey, 1969. Results of selection for eight-week body weight in three broiler populations of chickens. Poultry Sci. 48: 1336-1348. Khan, A. G., R. G. Jaap and W. R. Harvey, 1973. The effect of egg weight on eight-week body weight of normal and dwarf progeny from dwarf dams. Poultry Sci. 53: 211-218.
Mohammadian, M., and R. G. Jaap, 1972. Effect of the sex-linked dw dwarfing gene on body growth of chickens. Poultry Sci. 51: 1701-1707. Ricard, F. H., 1971. Growth rate and carcass characters of chicken broilers obtained from normal or dwarf (dw) dams. World's Poultry Sci. J. 27: 278279. Ricard, F. H., and L. P. Cochez, 1971. Effects of the sex-linked dwarf gene, dw, on performance of hens in a meat-type strain of domestic fowl. World's Poultry Sci. J. 27: 292. Ricard, F. H., and L. Conan, 1974. Performances zootechniques de poulets normaux fils de meres normales ou naines. Proc. XV World's Poultry Congress: 24-26. VanMiddlekoop, J. H., 1973. Influence of the dwarfing gene on egg laying pattern. 4th Europ. Poultry Conf., London: 563-567.