- Email: [email protected]
Parental Effects on Performance of Broiler Chicken Progenies1
ENVIRONMENT AND HEALTH Parental Effects on Performance of Broiler Chicken Progenies 1 F. G. PROUDFOOT and H. W. HULAN Agriculture Canada, Research Station, Kentville, Nova Scotia, B4N IJ5 (Received for publication May 5, 1986)
1987 Poultry Science 66:1119-1122 INTRODUCTION
MATERIALS AND METHODS
Parental genotypes can have substantial effects on the performance of broiler progeny (Proudfoot et al., 1985; Proudfoot and Hulan, 1986). Such diverse characteristics as resistance to Northern Fowl mite infestation (DeVaney, 1984) and the heritability of abdominal fat (Gyles and Maeza, 1981) demonstrate parental genotypic effects on the performance of progeny. For meat-type birds, information concerning parental environmental effects on progeny performance is more limited. It has, however, been established that photoperiod of parental housing and dietary treatments can result in an increase in the size of hatching eggs which, in turn, can have a significant effect on broiler progeny performance (Proudfoot et al., 1980, 1982a,b, 1985; Proudfoot and Hulan, 1986). The parental transmission of passive immunity to specific diseases as well as congenital diseases to progeny also constitutes a form of parental effect on progeny performance (Harris et al., 1984). The purpose of the present study was to provide further information on parental genotypic effects and effects of parental dietary treatment of broilers on the subsequent performance of progeny involving a wide range of genotypic differences and diets which had significant (P<.05) effects on the performance of the parental stock (Proudfoot et al., 1987).
Hatching eggs were obtained from four adult, maternal meat-breeder genotypes which were housed in a 48-pen windowless breeder house with 12 pens per genotype. The maternal parents were two normal and two dwarf genotypes which had been mated with normal Cornish White males (with rate of feather growth, autosexing capability) and Cornish Gold males (with color, auto-sexing capability) in all combinations (Proudfoot et al., 1987). These eight matings had been randomly assigned to the 24 pens in each end (block) of the building with three adult breeder diets randomly assigned to the three pens of each mating group in each block. Parent stocks had been reared on a regular feeding program to 140 days of age (Proudfoot et al., 1985) and thereafter on three different breeder diets (Table 1). One hundred and eighty eggs per pen were collected over a 7-day period commencing at 225 days of age. They were subsequently incubated and upon hatching, 40 male and 40 female chicks from each sample were wingbanded, vaccinated for Marek's disease, intermingled in each pen of a 48-pen brooding and rearing house (same floor plan as adult breeder building) in the same relative pen position as their parental breeders, and reared as broiler chickens to 42 days of age. The chicks were subjected to continuous light for the first 48 hr and thereafter cycles of intermittent light (4 hr on and 2 hr off) to slaughter. Lights were dimmed linearly from 20 lx at Day
'Contribution No. 1879.
1119
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
ABSTRACT Mortality among broiler progeny from a meat-type parent population, consisting of four maternal genotypes (two normal and two dwarf) mated with two normal paternal genotypes (White and Gold) and fed three different breeder diets was not significantly (P>.05) affected by genotypes or parental dietary treatments. Body weights of male and female progenies from matings with White males were significantly (P<.05) heavier at both 21 and 42 days than those sired by Gold males but progeny sired by Gold males exhibited the best feed conversion. The progeny from normal hens were heavier, had a better feed conversion up to 21 days, and yielded higher monetary returns than those from dwarf hens. Parental diets had no significant effect on progeny weights, feed conversion, or monetary returns. A low magnitude first-order interaction, involving paternal and maternal genotypes, occurred for feed conversion and monetary returns.
PROUDFOOT AND HULAN
1120
TABLE 1. Percentage composition of adult breeder diets HPLE1 (with canola)
Ingredients Ground corn Ground wheat Ground barley Soybean meal (49%) Canola meal (38%) Fishmeal (63%) Salt (NaCl) Ground limestone Dicalcium phosphate Vitamin mineral mix 2 Calculated analysis: Crude protein, % Metabolizable energy, kcal/kg
10.00 53.98 10.00 .80
10.10 41.95 25.00 12.50
9.90 41.95 30.00 7.30
15.00 2.50
2.50
2.50
.30
.20
.30
5.70
5.82
5.64 1.41 1.00
.72
.93
1.00
1.00
17.0 2,650
17.0 2,650
15.0 2,650
HPLE = High protein and low energy, LPLE = low protein and low energy.
2
Amount per kilogram of diet: 10,000 IU vitamin A; 2,000 ICU vitamin D 3 ; 2 mg vitamin K;8 mg riboflavin; 30 mg niacin; 10 mg d-calcium pantothenate; 2 mg folic acid; 15 Mg vitamin B 12 ; 13 IU vitamin E; 500 Mg biotin; 6 mg pyridoxine; 3 mg thiamine; 100 mg ethoxyquin; 130 mg manganese oxide (56% Mn); 90 mg zinc oxide (80% Zn); 30 mg copper sulfate (25% Cu); 300 Mg calcium iodate (62% I); 300 Mg sodium selenite (45% Se); 500 mg choline chloride.
1 to .2 lx at 14 days, which was maintained to the end of the test. The dietary program consisted of feeding a starter diet as crumbles, with 24% protein and metabolizable energy (ME) of 3,000-kcal/kg to 21 days and a finisher diet, as pellets, with 16% protein and an ME of 3,200 kcal/kg from 22 to 42 days. Traits measured were: mortality, live body weights at 21 and 42 days, feed conversion ratio (unit weight of feed consumed divided by unit live weight) and monetary returns per bird started divided by the cost of 1 -day-old chicks and feed. .Chicks were priced at 37.50 each. Starter and finisher diets were priced at 30.851 and 30.2580/kg, respectively. Meat revenue was based on a price of 114.75c7kg (live weight) less weight of birds condemned at time of slaughter. RESULTS AND DISCUSSION
Survival was generally good for the entire population; male and female mortality were 3.6 and 2.5%, respectively. As there were no significant (P>.05) genotypic or parental dietary effects on mortality among the broiler progeny mortality data are not presented in tabular form. Paternal genotype had a significant effect on the weights of male and female progeny at both
21 and 42 days of age, with the White males producing male and female progeny which were heavier compared with progeny sired by the Gold males (Table 2). The normal maternal parents also produced male and female progeny which weighed significantly more than those produced by dwarf maternal parents. This difference in body weight may be associated with the smaller-sized hatching eggs produced by the dwarf maternal parents (Proudfoot et al., 1982a). This egg size effect on progeny performance would be expected to largely disappear as the breeder flock ages and minimum egg size reaches or exceeds 46 g (Proudfoot and Hulan, 1981). The different diets fed during the laying period to parental stocks had no effect (P>.05) on the weight of broiler progeny. Feed conversion was significantly affected by the paternal genotype, with progeny sired by the Gold male exhibiting the best feed conversion rates at both 21 and 42 days of age (Table 2.) Normal maternal parents produced progeny which had better feed conversion rates up to 21 days of age than those from dwarf parents but not at 42 days of age. Feed conversion was not affected (P> .05) by maternal genotype or parental breeder diets. The importance of a first-order interaction between paternal and maternal genotypes for feed conversion at both 21 and
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
1
LPLE1
HPLE
1.35 1.37 .006
* 1.35 1.36 1.37 1.37 .008 NS 1.36 1.36 1.36 .007 NS PG X MG 1.36
1,884 1,815 10.0
** 1,903 1,864 1,835 1,796 14.2
* 1,848 1,851 1,851 12.3 NS 1,850
2,249 2,119 9.8
** 2,250 2,248 2,156 2,083 13.9
* 2,171 2,184 2,197 12.1 NS 2,184
683 663 3.6
**
682 683 665 661 5.1 NS
665 675 679 4.4 NS
673
762 734 3.5
**
764 760 743 726 4.9 NS
741 749 755 4.2 NS
748
See Table 3 for data on interactions.
HPLE = High protein, low energy; LPLE = low protein, low energy.
NS = Not significantly different (P>.05).
SEM = Standard error of the mean.
**
**
*
**
*
21 days
*'Significantly different (P<.01).
(.kg/
Feed con
1.39 1.34 .006
Female
1,883 1,816 10.0
42 days
2,209 2,159 9.8
\g)
(tr\
Male
685 661 3.6
Female
Mean live body weight
757 740 3.5
Male
'Significantly different (P<.05).
4
3
2
1
Paternal genotype A (White) B (Gold) SEM1 Significance Maternal size Normal Dwarf SEM Significance Maternal genotypes Normal 1 Normal 2 Dwarf 1 Dwarf 2 SEM Significance Breeder diets 3 HPLE + canola HPLE LPLE SEM Significance Interaction 4 Overall
Source of variation
21 days
TABLE 2. Parental effects on body weight, feed conversion, and monetary returns of broile
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
PROUDFOOT AND HULAN
1122
TABLE 3. Effect of paternal genotypes (PC) and maternal genotypes (MG) on feed conversion at 21 and 42 days and monetary returns for broiler chicken progeny Maternal genotypes
Performance measure
Paternal genotype
Feed consumed per unit of body weight to 21 days, kg/kg1
White Gold
1.37 1.32
1.39 1.33
1.37 1.37
1.41 1.33
Feed consumed per unit of body weight to 42 days, kg/kg2
White Gold
1.87 1.80
1.89 1.80
1.85 1.83
1.89 1.79
Monetary returns over the cost of chicks and feed, i
White Gold
Nl
75.6 82.3
Standard error of the mean (SEM) = .011 of PG X MG interaction. SEM = .010 of PG X MG interaction.
3
SEM = 1.6 of PG X MG interaction.
42 days of age probably should be discounted because feed conversion was equal or better among progeny from all four maternal genotypes sired by the Gold male than from those sired by White males; only one mating was not significantly different (P>.05) (Table 3). This low magnitude interaction may therefore not be repeatable. Maternal size had a significant effect on monetary returns, with normal parents producing progeny which had higher monetary returns compared with progeny from dwarf maternal parents (Table 2). However, a first-order interaction revealed that the Gold male mated with one of the normal maternal genotypes exhibited higher monetary returns compared with the White male mated with the same normal maternal genotype (Table 3). Other matings showed no evidence of differential combining ability. It should be noted that progeny produced by mating the White male with each of the two normal and one of the dwarf maternal genotypes showed no difference (P>.05) in monetary returns. Although paternal and maternal genotypic effects on the performance of broiler chickens were frequently quite pronounced, parental environmental effects appeared to be minimal. Parental dietary treatments had no significant effect on the progeny, even though those diets had significant effects on the general performance of the parental stocks, including parental mortality (Proudfoot ef al., 1982b, 1985,1986,1987).
ACKNOWLEDGMENT
The authors wish to acknowledge that the
Dl
76.1 75.1
73.5 68.4
D2
68.3 70.7
breeding stock for this experiment was provided by Shaver Poultry Breeding Farms, Ontario, Canada. REFERENCES DeVaney, J. A., 1984. Influence of Northern Fowl mite populations of parent chickens on Fl progeny. Poultry Sci. 63:589-591. Gyles, N. R., and A. Maeza, 1981. Abdominal fat in parents and broiler progeny. Poultry Sci. 60:1663. (Abstr.) Harris, D. L., V. A. Garwood, P. C. Lowe, P. Y. Hestor, L. B. Crittenden, and A. M. Fadly, 1984. Influence of sex-linked feathering phenotypes of parents and progeny upon Lymphoid Leukosis virus infection status and egg production. Poultry Sci. 63:401^413. Proudfoot, F. G., and H. W. Hulan, 1981. The influence of hatching egg size on the subsequent performance of broiler chickens. Poultry Sci. 60:2167-2170. Proudfoot, F. G., and H. W. Hulan, 1986. The performance of one normal and two dwarf meat maternal genotypes and their progeny as affected by rearing and adult dietary treatments. Can. J. Anim. Sci. 66:245-256. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1980. The effects of several different photoperiods on the performance of meat-parent genotypes. Can. J. Anim. Sci. 60:21-31. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1982a. Effect of hatching egg size from dwarf and normal maternal meat parent genotypes on the performance of broiler chickens. Poultry Sci. 61:655-660. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1982b. The effects of diets supplemented with Tower and/or Candle rapeseed meals on performance of meat chicken breeders. Can. J. Anim. Sci. 62:239-247. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1985. Effects of age at photoperiod change and dietary protein on performances of four dwarf maternal meat parent genotypes and their broiler chicken progeny. Can. J. Anim. Sci. 65:113-124. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1987. The performance of two paternal and four maternal meat breeder genotypes as affected by three adult breeder diets to 266 days of age. Can. J. Anim. Sci. 67:127-132.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
1 2
N2
1987 Poultry Science 66:1119-1122 INTRODUCTION
MATERIALS AND METHODS
Parental genotypes can have substantial effects on the performance of broiler progeny (Proudfoot et al., 1985; Proudfoot and Hulan, 1986). Such diverse characteristics as resistance to Northern Fowl mite infestation (DeVaney, 1984) and the heritability of abdominal fat (Gyles and Maeza, 1981) demonstrate parental genotypic effects on the performance of progeny. For meat-type birds, information concerning parental environmental effects on progeny performance is more limited. It has, however, been established that photoperiod of parental housing and dietary treatments can result in an increase in the size of hatching eggs which, in turn, can have a significant effect on broiler progeny performance (Proudfoot et al., 1980, 1982a,b, 1985; Proudfoot and Hulan, 1986). The parental transmission of passive immunity to specific diseases as well as congenital diseases to progeny also constitutes a form of parental effect on progeny performance (Harris et al., 1984). The purpose of the present study was to provide further information on parental genotypic effects and effects of parental dietary treatment of broilers on the subsequent performance of progeny involving a wide range of genotypic differences and diets which had significant (P<.05) effects on the performance of the parental stock (Proudfoot et al., 1987).
Hatching eggs were obtained from four adult, maternal meat-breeder genotypes which were housed in a 48-pen windowless breeder house with 12 pens per genotype. The maternal parents were two normal and two dwarf genotypes which had been mated with normal Cornish White males (with rate of feather growth, autosexing capability) and Cornish Gold males (with color, auto-sexing capability) in all combinations (Proudfoot et al., 1987). These eight matings had been randomly assigned to the 24 pens in each end (block) of the building with three adult breeder diets randomly assigned to the three pens of each mating group in each block. Parent stocks had been reared on a regular feeding program to 140 days of age (Proudfoot et al., 1985) and thereafter on three different breeder diets (Table 1). One hundred and eighty eggs per pen were collected over a 7-day period commencing at 225 days of age. They were subsequently incubated and upon hatching, 40 male and 40 female chicks from each sample were wingbanded, vaccinated for Marek's disease, intermingled in each pen of a 48-pen brooding and rearing house (same floor plan as adult breeder building) in the same relative pen position as their parental breeders, and reared as broiler chickens to 42 days of age. The chicks were subjected to continuous light for the first 48 hr and thereafter cycles of intermittent light (4 hr on and 2 hr off) to slaughter. Lights were dimmed linearly from 20 lx at Day
'Contribution No. 1879.
1119
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
ABSTRACT Mortality among broiler progeny from a meat-type parent population, consisting of four maternal genotypes (two normal and two dwarf) mated with two normal paternal genotypes (White and Gold) and fed three different breeder diets was not significantly (P>.05) affected by genotypes or parental dietary treatments. Body weights of male and female progenies from matings with White males were significantly (P<.05) heavier at both 21 and 42 days than those sired by Gold males but progeny sired by Gold males exhibited the best feed conversion. The progeny from normal hens were heavier, had a better feed conversion up to 21 days, and yielded higher monetary returns than those from dwarf hens. Parental diets had no significant effect on progeny weights, feed conversion, or monetary returns. A low magnitude first-order interaction, involving paternal and maternal genotypes, occurred for feed conversion and monetary returns.
PROUDFOOT AND HULAN
1120
TABLE 1. Percentage composition of adult breeder diets HPLE1 (with canola)
Ingredients Ground corn Ground wheat Ground barley Soybean meal (49%) Canola meal (38%) Fishmeal (63%) Salt (NaCl) Ground limestone Dicalcium phosphate Vitamin mineral mix 2 Calculated analysis: Crude protein, % Metabolizable energy, kcal/kg
10.00 53.98 10.00 .80
10.10 41.95 25.00 12.50
9.90 41.95 30.00 7.30
15.00 2.50
2.50
2.50
.30
.20
.30
5.70
5.82
5.64 1.41 1.00
.72
.93
1.00
1.00
17.0 2,650
17.0 2,650
15.0 2,650
HPLE = High protein and low energy, LPLE = low protein and low energy.
2
Amount per kilogram of diet: 10,000 IU vitamin A; 2,000 ICU vitamin D 3 ; 2 mg vitamin K;8 mg riboflavin; 30 mg niacin; 10 mg d-calcium pantothenate; 2 mg folic acid; 15 Mg vitamin B 12 ; 13 IU vitamin E; 500 Mg biotin; 6 mg pyridoxine; 3 mg thiamine; 100 mg ethoxyquin; 130 mg manganese oxide (56% Mn); 90 mg zinc oxide (80% Zn); 30 mg copper sulfate (25% Cu); 300 Mg calcium iodate (62% I); 300 Mg sodium selenite (45% Se); 500 mg choline chloride.
1 to .2 lx at 14 days, which was maintained to the end of the test. The dietary program consisted of feeding a starter diet as crumbles, with 24% protein and metabolizable energy (ME) of 3,000-kcal/kg to 21 days and a finisher diet, as pellets, with 16% protein and an ME of 3,200 kcal/kg from 22 to 42 days. Traits measured were: mortality, live body weights at 21 and 42 days, feed conversion ratio (unit weight of feed consumed divided by unit live weight) and monetary returns per bird started divided by the cost of 1 -day-old chicks and feed. .Chicks were priced at 37.50 each. Starter and finisher diets were priced at 30.851 and 30.2580/kg, respectively. Meat revenue was based on a price of 114.75c7kg (live weight) less weight of birds condemned at time of slaughter. RESULTS AND DISCUSSION
Survival was generally good for the entire population; male and female mortality were 3.6 and 2.5%, respectively. As there were no significant (P>.05) genotypic or parental dietary effects on mortality among the broiler progeny mortality data are not presented in tabular form. Paternal genotype had a significant effect on the weights of male and female progeny at both
21 and 42 days of age, with the White males producing male and female progeny which were heavier compared with progeny sired by the Gold males (Table 2). The normal maternal parents also produced male and female progeny which weighed significantly more than those produced by dwarf maternal parents. This difference in body weight may be associated with the smaller-sized hatching eggs produced by the dwarf maternal parents (Proudfoot et al., 1982a). This egg size effect on progeny performance would be expected to largely disappear as the breeder flock ages and minimum egg size reaches or exceeds 46 g (Proudfoot and Hulan, 1981). The different diets fed during the laying period to parental stocks had no effect (P>.05) on the weight of broiler progeny. Feed conversion was significantly affected by the paternal genotype, with progeny sired by the Gold male exhibiting the best feed conversion rates at both 21 and 42 days of age (Table 2.) Normal maternal parents produced progeny which had better feed conversion rates up to 21 days of age than those from dwarf parents but not at 42 days of age. Feed conversion was not affected (P> .05) by maternal genotype or parental breeder diets. The importance of a first-order interaction between paternal and maternal genotypes for feed conversion at both 21 and
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
1
LPLE1
HPLE
1.35 1.37 .006
* 1.35 1.36 1.37 1.37 .008 NS 1.36 1.36 1.36 .007 NS PG X MG 1.36
1,884 1,815 10.0
** 1,903 1,864 1,835 1,796 14.2
* 1,848 1,851 1,851 12.3 NS 1,850
2,249 2,119 9.8
** 2,250 2,248 2,156 2,083 13.9
* 2,171 2,184 2,197 12.1 NS 2,184
683 663 3.6
**
682 683 665 661 5.1 NS
665 675 679 4.4 NS
673
762 734 3.5
**
764 760 743 726 4.9 NS
741 749 755 4.2 NS
748
See Table 3 for data on interactions.
HPLE = High protein, low energy; LPLE = low protein, low energy.
NS = Not significantly different (P>.05).
SEM = Standard error of the mean.
**
**
*
**
*
21 days
*'Significantly different (P<.01).
(.kg/
Feed con
1.39 1.34 .006
Female
1,883 1,816 10.0
42 days
2,209 2,159 9.8
\g)
(tr\
Male
685 661 3.6
Female
Mean live body weight
757 740 3.5
Male
'Significantly different (P<.05).
4
3
2
1
Paternal genotype A (White) B (Gold) SEM1 Significance Maternal size Normal Dwarf SEM Significance Maternal genotypes Normal 1 Normal 2 Dwarf 1 Dwarf 2 SEM Significance Breeder diets 3 HPLE + canola HPLE LPLE SEM Significance Interaction 4 Overall
Source of variation
21 days
TABLE 2. Parental effects on body weight, feed conversion, and monetary returns of broile
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
PROUDFOOT AND HULAN
1122
TABLE 3. Effect of paternal genotypes (PC) and maternal genotypes (MG) on feed conversion at 21 and 42 days and monetary returns for broiler chicken progeny Maternal genotypes
Performance measure
Paternal genotype
Feed consumed per unit of body weight to 21 days, kg/kg1
White Gold
1.37 1.32
1.39 1.33
1.37 1.37
1.41 1.33
Feed consumed per unit of body weight to 42 days, kg/kg2
White Gold
1.87 1.80
1.89 1.80
1.85 1.83
1.89 1.79
Monetary returns over the cost of chicks and feed, i
White Gold
Nl
75.6 82.3
Standard error of the mean (SEM) = .011 of PG X MG interaction. SEM = .010 of PG X MG interaction.
3
SEM = 1.6 of PG X MG interaction.
42 days of age probably should be discounted because feed conversion was equal or better among progeny from all four maternal genotypes sired by the Gold male than from those sired by White males; only one mating was not significantly different (P>.05) (Table 3). This low magnitude interaction may therefore not be repeatable. Maternal size had a significant effect on monetary returns, with normal parents producing progeny which had higher monetary returns compared with progeny from dwarf maternal parents (Table 2). However, a first-order interaction revealed that the Gold male mated with one of the normal maternal genotypes exhibited higher monetary returns compared with the White male mated with the same normal maternal genotype (Table 3). Other matings showed no evidence of differential combining ability. It should be noted that progeny produced by mating the White male with each of the two normal and one of the dwarf maternal genotypes showed no difference (P>.05) in monetary returns. Although paternal and maternal genotypic effects on the performance of broiler chickens were frequently quite pronounced, parental environmental effects appeared to be minimal. Parental dietary treatments had no significant effect on the progeny, even though those diets had significant effects on the general performance of the parental stocks, including parental mortality (Proudfoot ef al., 1982b, 1985,1986,1987).
ACKNOWLEDGMENT
The authors wish to acknowledge that the
Dl
76.1 75.1
73.5 68.4
D2
68.3 70.7
breeding stock for this experiment was provided by Shaver Poultry Breeding Farms, Ontario, Canada. REFERENCES DeVaney, J. A., 1984. Influence of Northern Fowl mite populations of parent chickens on Fl progeny. Poultry Sci. 63:589-591. Gyles, N. R., and A. Maeza, 1981. Abdominal fat in parents and broiler progeny. Poultry Sci. 60:1663. (Abstr.) Harris, D. L., V. A. Garwood, P. C. Lowe, P. Y. Hestor, L. B. Crittenden, and A. M. Fadly, 1984. Influence of sex-linked feathering phenotypes of parents and progeny upon Lymphoid Leukosis virus infection status and egg production. Poultry Sci. 63:401^413. Proudfoot, F. G., and H. W. Hulan, 1981. The influence of hatching egg size on the subsequent performance of broiler chickens. Poultry Sci. 60:2167-2170. Proudfoot, F. G., and H. W. Hulan, 1986. The performance of one normal and two dwarf meat maternal genotypes and their progeny as affected by rearing and adult dietary treatments. Can. J. Anim. Sci. 66:245-256. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1980. The effects of several different photoperiods on the performance of meat-parent genotypes. Can. J. Anim. Sci. 60:21-31. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1982a. Effect of hatching egg size from dwarf and normal maternal meat parent genotypes on the performance of broiler chickens. Poultry Sci. 61:655-660. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1982b. The effects of diets supplemented with Tower and/or Candle rapeseed meals on performance of meat chicken breeders. Can. J. Anim. Sci. 62:239-247. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1985. Effects of age at photoperiod change and dietary protein on performances of four dwarf maternal meat parent genotypes and their broiler chicken progeny. Can. J. Anim. Sci. 65:113-124. Proudfoot, F. G., H. W. Hulan, and K. B. McRae, 1987. The performance of two paternal and four maternal meat breeder genotypes as affected by three adult breeder diets to 266 days of age. Can. J. Anim. Sci. 67:127-132.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 28, 2015
1 2
N2