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Embryonic Mortality in Chicken Eggs as Influenced by Egg Weight and Inbreeding
Embryonic Mortality in Chicken Eggs as Influenced by Egg Weight and Inbreeding C. HAGGER, D. STEIGER-STAFL, and C. MARGUERAT Institute of Animal Production, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland (Received for publication September 19, 1985)
1986 Poultry Science 65:812-814 INTRODUCTION
The influence of either egg weight or amount of inbreeding on the survival rate of chicken embryos has long been known. An extensive review of these and other effects on the hatchability is given by Landauer (1967). Amount of inbreeding in the hen and in the embryo must be distinguished in an analysis of embryonic mortality (Hagger and Steiger-Stafl, 1982). The combined effect of egg weight and inbreeding has received little attention, particularly in populations with extremes of egg weight. This study presents information from an experiment where two lines of chickens with large egg size and moderate inbreeding were crossed with birds from an inbred, small egg weight population. MATERIALS AND METHODS
Birds of two lines (LI, L2) selected for large early egg size (Hagger and Abplanalp, 1978) and birds from a backcross (BC) system among five highly inbred lines (Hagger, 1985, 1986) were used in the experiment. All lines were of the Leghorn type and were developed and kept on the experimental farm "Chamau" of the Swiss Federal Institute of Technology. Selection for egg weight was performed during 13 generations in a single population, which was then split into two lines and selection continued on a index for an additional five generations. After this, the two lines were propagated without selection. All birds had a complete pedigree back to the foundation population. This information allowed calculation of the ex-
pected inbreeding level according to Cruden (1949). Four types of matings were used: 1) 10 males of LI each with 2 females of L I , 2) 10 males of L2 each with 2 females of L2, 3) the same 20 males from 1 and 2 each with 3 backcross females (L X BC), 4) 20 backcross males each with three females, i.e., 1 or 2 from LI and L2 (BC x L). Matings were by artificial insemination with undiluted semen during a 4-week breeding season when all hens were 55 weeks of age. The BC hens produced at a higher rate than hens of the other lines. Thus, eggs had to be collected for a shorter time than from the hens of the egg weight lines. As far as possible, eggs from all breeding types together were incubated in four weekly batches. Fertility was checked at the 9th day of incubation by candling. Eggs that then showed no sign of embryonic development were considered as unfertilized, and eggs that showed a blood ring were considered as early embryonic death. These early death figures were biased downward to some extent, because embryos that died in the first few days of incubation were not detected. All remaining eggs that did not hatch were considered as late embryonic death. Average egg weight between 41 and 60 weeks of age was available from all hens, including the weight of the eggs used in this experiment. RESULTS AND DISCUSSION
Table 1 shows the average egg weight and inbreeding of the breeder hens together with
812
Downloaded from http://ps.oxfordjournals.org/ at University of Wisconsin-Oshkosh on June 8, 2015
ABSTRACT The influence of egg weight (average between 41 and 60 weeks) and of inbreeding of the embryo on viability of the embryos was investigated with two lines of large egg weight (LI, L2) and their reciprocal crosses to a small egg weight population (L X BC, BC X L). Average egg weights of breeder hens for LI, L2, L X BC, and BC X L were 69.0, 74.5, 53.4, and 70.7 g, respectively. Inbreeding of embryos was 23.8 and 25.3% for LI and L2 and ~0 for the other two groups. The different late embryonic death rates of the groups, i.e., 14.0, 23.6, 5.0, and 17.6%, could be explained by the different egg weights. Extent of inbreeding was not important for embryonic viability in the extreme egg weight range considered. (Key words: embryonic mortality, egg weight, inbreeding level)
RESEARCH NOTE
813
TABLE 1. Egg weight, amount of inbreeding, and embryonic mortality of various lines Mating type L2
21 397
20 369
23.2 23.8 69.0a 6.5a 14.0*
24.7 25.3 74.8 b 7.1* 23.6b
.94
LX BC 60 1002
-45 ~0 53.4C 5.5* 5.0C -.189
BC X L 60 935 24.0 ~0 70.7 a 10.3 b 17.6 a .084
' ' Means with different superscript within a row are significantly different (P<.05), t for egg weight, X2 for mortality rates.
amount of inbreeding of embryos studied. The difference in egg weight between LI and L2 was only partly due to a different selection response, as LI was somewhat lower in this trait because of the splitting of the original population. A large difference in this trait of about 18 g existed between the hens from the egg weight lines and the backcross hens. The other important difference between the mating types was the extent of inbreeding of the pure line and the crossed embryos, i.e., 24.5% vs ~0%. Only a very small variation of this trait was found in the egg weight lines. The BC X L embryos showed significantly (P<.05) higher early mortality rate than either embryos from eggs with similar weights but different amount of inbreeding (pure LI and L2) or embryos from eggs with different weights but equal amount of inbreeding (L X BC). Thus, a third, yet unknown, factor must have been responsible for this result. Eggs from the two egg weight lines differed significantly in late embryonic mortality and in weight, whereas the difference in inbreeding (1.5%) was very small. The same relationship could be observed for L x BC vs. BC X L, where the large difference in late embryonic mortality was associated with a large difference in egg weight and no difference in inbreeding. The third point of relevance comes from the comparison of LI with BC X L. The differences in late mortality and in egg weight between these two groups were not significant, but there was a large difference in inbreeding (23.8% vs ~0%). Additional maternal effects should be absent in this particular comparison. A slight linear increase of the late mortality (logits of
percentages) with increasing egg weights (g) could be found in both the combined set of LI and L2 and in BC X L (Table 1). In the small egg weight group, L X BC, this relationship was negative. These findings point to an optimum egg weight for hatchability as discussed by Landauer (1967). Data in Table 1 indicate that the late embryonic mortality of the four groups is influenced almost completely through the egg weight and not through extent of inbreeding. This statement holds true if no other maternal effects than egg weight, which affects the viability of the embryos, were present in LI and L2. Not even such an effect would bias the comparisons between LI, L2, and BC X L. Embryonic mortality can be regarded as a direct fitness trait. It is well-known that an increase in the amount of inbreeding and intense selection for metric traits reduces overall fitness (Falconer, 1982). It was further shown by Landauer (1967) that egg weight has an optimum of around 55 g for maximum hatchability. Our data suggest that inbreeding, up to a certain degree, is not of great importance for fertility in populations far from the optimum for egg weight.
REFERENCES Cruden, D., 1949. The computation of inbreeding coefficients in closed populations. Heredity 40:248-251. Falconer, D. S., 1982. Introduction to Quantitative Genetics, 2nd edition. Longman, London and New York. Hagger, C , 1985. Line and crossing effects in a diallel mating system with highly inbred lines of White
Downloaded from http://ps.oxfordjournals.org/ at University of Wisconsin-Oshkosh on June 8, 2015
No. of matings, No. of fertile eggs, Average inbreeding of hen, % Average inbreeding of embryo, % Average egg weight of breeder hens, 41 to 60 week, g Early embryonic mortality (until 9th day), % Late embryonic mortality (9th day until hatch), % Repression of logits of late mortality on egg weight
LI
814
HAGGER ET AL.
Leghorn chickens. Theor. Appl. Genet., 69: 555-560. Hagger, C , 1986. Genetic effects of heterosis in F l and backcrosses of inbred lines of White Leghorns. J. Anim. Breedg. Genet. 103:26—32. Hagger, C , and H. Abplanalp, 1978. Food consumption records for the genetic improvement of income over food costs in laying flocks of White Leghorns. Br. Poult. Sci. 19:651-667.
Hagger, C. and D. Steiger-StafI, 1982. Befruchtungsrate und embryonale Sterblichkeit bei hoch ingeziichteten Gefliigellinien des Typs Weisse Leghorn in Reinzucht und Kreuzung. Schweiz. Landwirtsch. Monatsh. 60:269-275. Landauer, W., 1967. The hatchability of chicken eggs as influenced by environment and heredity. Monogr. 1 rev. Storrs Agric. Exp. Sta., Univ. Connecticut, Storrs, CT.
Downloaded from http://ps.oxfordjournals.org/ at University of Wisconsin-Oshkosh on June 8, 2015
1986 Poultry Science 65:812-814 INTRODUCTION
The influence of either egg weight or amount of inbreeding on the survival rate of chicken embryos has long been known. An extensive review of these and other effects on the hatchability is given by Landauer (1967). Amount of inbreeding in the hen and in the embryo must be distinguished in an analysis of embryonic mortality (Hagger and Steiger-Stafl, 1982). The combined effect of egg weight and inbreeding has received little attention, particularly in populations with extremes of egg weight. This study presents information from an experiment where two lines of chickens with large egg size and moderate inbreeding were crossed with birds from an inbred, small egg weight population. MATERIALS AND METHODS
Birds of two lines (LI, L2) selected for large early egg size (Hagger and Abplanalp, 1978) and birds from a backcross (BC) system among five highly inbred lines (Hagger, 1985, 1986) were used in the experiment. All lines were of the Leghorn type and were developed and kept on the experimental farm "Chamau" of the Swiss Federal Institute of Technology. Selection for egg weight was performed during 13 generations in a single population, which was then split into two lines and selection continued on a index for an additional five generations. After this, the two lines were propagated without selection. All birds had a complete pedigree back to the foundation population. This information allowed calculation of the ex-
pected inbreeding level according to Cruden (1949). Four types of matings were used: 1) 10 males of LI each with 2 females of L I , 2) 10 males of L2 each with 2 females of L2, 3) the same 20 males from 1 and 2 each with 3 backcross females (L X BC), 4) 20 backcross males each with three females, i.e., 1 or 2 from LI and L2 (BC x L). Matings were by artificial insemination with undiluted semen during a 4-week breeding season when all hens were 55 weeks of age. The BC hens produced at a higher rate than hens of the other lines. Thus, eggs had to be collected for a shorter time than from the hens of the egg weight lines. As far as possible, eggs from all breeding types together were incubated in four weekly batches. Fertility was checked at the 9th day of incubation by candling. Eggs that then showed no sign of embryonic development were considered as unfertilized, and eggs that showed a blood ring were considered as early embryonic death. These early death figures were biased downward to some extent, because embryos that died in the first few days of incubation were not detected. All remaining eggs that did not hatch were considered as late embryonic death. Average egg weight between 41 and 60 weeks of age was available from all hens, including the weight of the eggs used in this experiment. RESULTS AND DISCUSSION
Table 1 shows the average egg weight and inbreeding of the breeder hens together with
812
Downloaded from http://ps.oxfordjournals.org/ at University of Wisconsin-Oshkosh on June 8, 2015
ABSTRACT The influence of egg weight (average between 41 and 60 weeks) and of inbreeding of the embryo on viability of the embryos was investigated with two lines of large egg weight (LI, L2) and their reciprocal crosses to a small egg weight population (L X BC, BC X L). Average egg weights of breeder hens for LI, L2, L X BC, and BC X L were 69.0, 74.5, 53.4, and 70.7 g, respectively. Inbreeding of embryos was 23.8 and 25.3% for LI and L2 and ~0 for the other two groups. The different late embryonic death rates of the groups, i.e., 14.0, 23.6, 5.0, and 17.6%, could be explained by the different egg weights. Extent of inbreeding was not important for embryonic viability in the extreme egg weight range considered. (Key words: embryonic mortality, egg weight, inbreeding level)
RESEARCH NOTE
813
TABLE 1. Egg weight, amount of inbreeding, and embryonic mortality of various lines Mating type L2
21 397
20 369
23.2 23.8 69.0a 6.5a 14.0*
24.7 25.3 74.8 b 7.1* 23.6b
.94
LX BC 60 1002
-45 ~0 53.4C 5.5* 5.0C -.189
BC X L 60 935 24.0 ~0 70.7 a 10.3 b 17.6 a .084
' ' Means with different superscript within a row are significantly different (P<.05), t for egg weight, X2 for mortality rates.
amount of inbreeding of embryos studied. The difference in egg weight between LI and L2 was only partly due to a different selection response, as LI was somewhat lower in this trait because of the splitting of the original population. A large difference in this trait of about 18 g existed between the hens from the egg weight lines and the backcross hens. The other important difference between the mating types was the extent of inbreeding of the pure line and the crossed embryos, i.e., 24.5% vs ~0%. Only a very small variation of this trait was found in the egg weight lines. The BC X L embryos showed significantly (P<.05) higher early mortality rate than either embryos from eggs with similar weights but different amount of inbreeding (pure LI and L2) or embryos from eggs with different weights but equal amount of inbreeding (L X BC). Thus, a third, yet unknown, factor must have been responsible for this result. Eggs from the two egg weight lines differed significantly in late embryonic mortality and in weight, whereas the difference in inbreeding (1.5%) was very small. The same relationship could be observed for L x BC vs. BC X L, where the large difference in late embryonic mortality was associated with a large difference in egg weight and no difference in inbreeding. The third point of relevance comes from the comparison of LI with BC X L. The differences in late mortality and in egg weight between these two groups were not significant, but there was a large difference in inbreeding (23.8% vs ~0%). Additional maternal effects should be absent in this particular comparison. A slight linear increase of the late mortality (logits of
percentages) with increasing egg weights (g) could be found in both the combined set of LI and L2 and in BC X L (Table 1). In the small egg weight group, L X BC, this relationship was negative. These findings point to an optimum egg weight for hatchability as discussed by Landauer (1967). Data in Table 1 indicate that the late embryonic mortality of the four groups is influenced almost completely through the egg weight and not through extent of inbreeding. This statement holds true if no other maternal effects than egg weight, which affects the viability of the embryos, were present in LI and L2. Not even such an effect would bias the comparisons between LI, L2, and BC X L. Embryonic mortality can be regarded as a direct fitness trait. It is well-known that an increase in the amount of inbreeding and intense selection for metric traits reduces overall fitness (Falconer, 1982). It was further shown by Landauer (1967) that egg weight has an optimum of around 55 g for maximum hatchability. Our data suggest that inbreeding, up to a certain degree, is not of great importance for fertility in populations far from the optimum for egg weight.
REFERENCES Cruden, D., 1949. The computation of inbreeding coefficients in closed populations. Heredity 40:248-251. Falconer, D. S., 1982. Introduction to Quantitative Genetics, 2nd edition. Longman, London and New York. Hagger, C , 1985. Line and crossing effects in a diallel mating system with highly inbred lines of White
Downloaded from http://ps.oxfordjournals.org/ at University of Wisconsin-Oshkosh on June 8, 2015
No. of matings, No. of fertile eggs, Average inbreeding of hen, % Average inbreeding of embryo, % Average egg weight of breeder hens, 41 to 60 week, g Early embryonic mortality (until 9th day), % Late embryonic mortality (9th day until hatch), % Repression of logits of late mortality on egg weight
LI
814
HAGGER ET AL.
Leghorn chickens. Theor. Appl. Genet., 69: 555-560. Hagger, C , 1986. Genetic effects of heterosis in F l and backcrosses of inbred lines of White Leghorns. J. Anim. Breedg. Genet. 103:26—32. Hagger, C , and H. Abplanalp, 1978. Food consumption records for the genetic improvement of income over food costs in laying flocks of White Leghorns. Br. Poult. Sci. 19:651-667.
Hagger, C. and D. Steiger-StafI, 1982. Befruchtungsrate und embryonale Sterblichkeit bei hoch ingeziichteten Gefliigellinien des Typs Weisse Leghorn in Reinzucht und Kreuzung. Schweiz. Landwirtsch. Monatsh. 60:269-275. Landauer, W., 1967. The hatchability of chicken eggs as influenced by environment and heredity. Monogr. 1 rev. Storrs Agric. Exp. Sta., Univ. Connecticut, Storrs, CT.
Downloaded from http://ps.oxfordjournals.org/ at University of Wisconsin-Oshkosh on June 8, 2015