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Effect of Environmental Temperature on the Life Span of Red Blood Cells in Domestic Fowl
Effect of Environmental Temperature on the Life Span of Red Blood Cells in Domestic Fowl KARAM F. A. SOLIMAN AND TILL M. HUSTON Department of Poultry Science, University of Georgia, Athens, Georgia 30601 (Received for publication October 25, 1971)
ABSTRACT The mean red blood cell life span was determined to two groups of 18 week old Athens Randombred male birds using a "Cr labeling procedure. There were eight birds in each group. One group was raised at 8°C. and the other at 30°C. There were no statistical differences due to temperature between the two groups which had mean red blood cell life spans of 27.4 and 26.7 days at 8° and 30°C, respectively. POULTRY SCIENCE 51: 1198-1201,
INTRODUCTION
T
HE effect of environmental temperature on thyroid activity has been studied and established (Hoffmann and Shaffner, 1950; Stahl et al., 1961; Huston and Carmon, 1962; Garren and Shaffner, 1956). Moreover, thyroxin hormone has been shown to have erythropoietic activity in addition to its regulation of the basal metabolic rate (Turner, 1966). Relationships between basal metabolic and red blood cells life span in poikilothermic animals have been established (Berlin, 1964). If the environmental temperature of the alligator was changed from 31°C. to 16°C, there was an apparent prolongation of the red cell life span. There is, however, considerable reduction if not complete suppression of red cell synthesis (Cline and Waldmann, 1962a). Brace (1953) reported similar results in the hibernating marmot. There are many reports on the relationship between thyroxin level in blood and life span of the red cells in homeothermic animals (human, McClellan et al., 1958; dog, Waldmann et al., 1962; Cline and Berlin, 1963). There is a dearth of information concerning the direct effect of environmental temperature on the survival of the erythrocytes in homeothermic animals. The object of this study is to determine the relationship between environmental tem-
1972
perature and the life span of the red blood cells. MATERIALS AND METHODS
Two groups of Athens Randombred males, 18 weeks of age, were raised from hatching in controlled temperatures. The mean temperature of the two environments studied were 8° or 30°C. with a diurnal cycle of 4°-12°C. or 26°-34°C, respectively. Eight birds were in each group, and their body weight ranged from 2.00 to 2.60 kg. In the determination of the red blood cells (R.B.C.) life span, the labeling of R.B.C. was achieved with the use of 51Cr. This technique was developed by Gray and Sterling (1950) and modified by Rodnan et al. (1957). In the labeling procedure 400 JXC. of 51Cr (Na2 61 Cr0 4 ) with specific activity of .167 mc./mg. Cr in .4 ml. saline solution was injected intravenously. Two millilitres of blood were taken 24 hours after injection and at weekly intervals for the next four weeks for determination of the decline of the radioactivity of R.B.C. The blood samples were washed three times using 7.0 ml. of 0.75% saline each time to remove the extracorpuscular radioactivity. The emission of r>1Cr was counted in an Isomatic Well Counter (Baird Atomic Company, Model 709). Blood hematocrit was measured by the microhematocrit method 198
1199
ERYTHROCYTE SURVIVAL
(Johnson, 1955) and radioactivity expressed as counts per minute per millilitre of packed R.B.C. corrected for physical decay of the isotope (half life 26.5 days). The counts of the initial blood samples taken at 24 hours were used as a standard and were taken as 1.0. The counts of the standard on other counting days were used to obtain a correction factor (CF = counts of standard on day zero/counts of standard on day x) which was used to correct the counts of each sample. The corrected values were calculated as a percentage of the initial counts at zero days for each bird. The regression line of corrected counts on days elapsed was calculated for each chicken. The interception on the days coordinate was considered as the mean life span of the red blood cells in a chicken (Cline and Waldmann, 1962b). RESULTS AND DISCUSSION
The average decline in the radioactivity of the red blood cells of the chicken as corrected for physical decay of chromium51 is
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2
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WEEKS AFTER INJECTION
FIG. 1. Decline in MCr counts in relation to time for prediction of the mean life span of red blood cells. The graph represents the two different groups in two different environmental temperatures.
TABLE 1.—Effect of environmental temperature on the body weight, hematocrit and the red cell life span of A thens Randombred
Temperature 8°C. 30°C.
Body Weight in kgm.
Hematocrit
R.B.C. Life Span days
2.69* 2.13
36.5* 34.1
27.36 26.73
* Different significantly (P<0.05).
depicted in Figure 1. Tests for the regression coefficient (bi) of the corrected counts on days after 51Cr injection of these two groups at 8° and 30°C. show no significant effect of temperature on the life span of the red blood cells (Table 1). The life span of red blood cells was 27.4 days at 8°C. and 26.7 days at 30°C. A significant difference was observed between the two groups in hematocrit and body size. There was no correlation observed between R.B.C. life span and body size or hematocrit. The non-significant effect of environmental temperature on the life span of red blood cells is supported by the analogous result of an increased rate of production of dogs since it has been established that environmental temperature affects the thyroid activity. Waldmann et al. (1962) found that dogs with experimentally induced hyperthyroidism became polycythemic as a result of an increased rate of production of R.B.C. but there was no change in the R.B.C. life span. Also in the hypothyroid dog Cline and Berlin (1963) found that there was 38% decrease in hematocrit and there was no change in R.B.C. life span. On the other hand McClellan et al. (1958) found that R.B.C. from hypothyroid and hyperthyroid patients have a normal survival period in normal recipients, but autologous 51 Cr labeled cells in hyperthyroid patients have diminished survival. The significant effect of environmental temperature on hematocrit is in agreement with Huston (1965), Washburn and Hu-
1200
K. F. A. SOLIMAN AND T. M. HUSTON
ston (1968), Moye et al. (1970) and Deaton et al. (1970). It is apparent that the effect of temperature on hematocrit is neither due to the life span of R.B.C. nor due to hemodilution (Soliman and Huston, (1972). The direct effect of environmental temperature on the thyroid activity which in turn controls the erythropoiesis may have a major effect. Also it might be that the effect of ambient temperature and, consequently, thyroxin on erythropoiesis comes through an indirect route. Thyroxin stimulates oxygen consumption by uncoupling the oxidative phosphorylation in the mitochondria of the cells in the animal body (Turner, 1966). It was reported that in cold weather chickens have a higher thyroxin level and a greater oxygen consumption than those in hot weather (Huston and Carmon, 1962). The need of oxygen to be used for the high metabolic rate might induce erythropoietin to be secreted from the kidney which will in turn induce the production of the red blood cells (Turner, 1966). Allison (1960) reported an equation for predicting the R.B.C. life span using the animal body weight. In the present work no correlation was found between body weight and the R.B.C. life span indicating that this equation might be applied among species but not within species. The life span of red blood cells reported in this work (27 day) is very close to the value obtained by Hevesy and Ottesen (1945) using 32P and two birds. They found that the R.B.C. life span was 28 days. Shemin (1948) found that the R.B.C. life span on one individual chicken by using glycine15N to be 28 days. Rodnan et al. (1957) by using 51Cr and six chickens found that the maximum R.B.C. life span value to be 35 days. On the other hand Brace and Atland (1956), using the random destruction method and glycine14C, reported a mean life span of 20 days for
chickens. There would seem to be at least two major reasons for the various life spans reported in the literature. First, the small numbers of individuals used in these experiments and second the different labeling procedure used for each experiment. REFERENCES Allison, A. C , I960. Turnovers of erythrocytes and plasma proteins in mammals. Nature, 188: 3740. Berlin, N. I., 1964. Life span of the red cell. p. 423-450. In C. Bishop and D. M. Surgenor, The Red Blood Cell. Academic Press, New York and London. Brace, K., 19S3. Life span of the marmot erythrocyte. Blood, 8: 648-650. Brace, K., and P. D. Atland, 1956. Life span of the duck and chicken erythrocyte as determined with "C. Proc. Soc. Exp. Biol. Med. 92: 615617. Cline, M. J., and T. A. Waldmann, 1962a. Effect of temperature on red cell survival in the alligator. Proc. Soc. Exp. Biol. Med. I l l : 716-718. Cline, M. J., and T. A. Waldmann, 1962b. Effect of temperature on erythropoiesis and red cell survival in the frog. Amer. J. Physiol. 203: 401-403. Cline, M. J., and N. I. Berlin, 1963. Erythropoiesis and red cell survival in the hypothyroid dog. Amer. J. Physiol. 204: 415-418. Deaton, J. W., F. N. Reece and W. J. Traver, 1970. Hematocrit hemoglobin and plasma-protein levels of broilers under constant temperature. Poultry Sci. 49: 1993-1996. Garren, H. W., and C. S. Shaffner, 1956. How the period of exposure to different stress stimuli affects the endocrine and lymphatic gland weights of young chickens. Poultry Sci. 35: 266-272. Gray, S. J., and K. Sterling, 1950. The tagging of red cells and plasma protein with radioactive chromium. J. Clin. Invest. 29: 1604-1615. Hevesy, G., and J. Ottesen, 1945. Life cycle of the red corpuscles of the hen. Nature, 156: 534. Hoffmann, E., and C. S. Shaffner, 1950. Thyroid weight and functions as influenced by environmental temperature. Poultry Sci. 29: 365-376. Huston, T. M., and J. L. Carmon, 1962. The influence of high environmental temperature on thyroid size of domestic fowl. Poultry Sci. 4 1 : 175-179. Huston, T. M., 1965. The influence of different environmental temperatures on immature fowl. Poultry Sci. 44: 1032-1036.
ERYTHROCYTE
Johnson, P. M., 1955. Hematocrit values for the chick embryos at various ages. Amer. J. Physiol. 180:361-362. McClellan, J. E., C. Donegan, O. A. Thorup and B. S. Leavell, 1958. Survival time of the erythrocyte in myxedema and hyperthyroidism. J. Lab. Clin. Med. 51: 91-96. Moye, R. J., Jr., K. W. Washburn and T. M. Huston, 1970. Effect of environmental temperature on erythrocyte number and size. Poultry Sci. 49: 1683-1686. Rodnan, G. P., F. G. Ebaugh, Jr. and M. R. S. Fox, 1957. The life span of the red blood cell and the red blood cell volume in the chicken, pigeon and duck as estimated by the use of Na251Cr04. Blood, 12: 355-366. Shemin, D., 1948. The biosynthesis of prophyrins. Cold Spring Harbor Symp. Quant. Biol. 13: 185-192.
SURVIVAL
1201
Soliman, K. F. A., and T. M. Huston, 1972. Effect of dietary protein and fat on the hematocrit and plasma cholesterol of chickens at different environmental temperature. Poultry Sci. (In press). Stahl, P., G. W. Pipes and C. W. Turner, 1961. Time required for low temperature to influence thyroid secretion rate in fowls. Poultry Sci. 40: 646-650. Turner, C. D., 1966. General Endocrinology. 4th ed. W. B. Saunders Co., Phil. Lond. p. 579. Waldmann, T. A., S. M. Weissman and E. H. Levin, 1962. Effect of thyroid administration of erythropoiesis in the dog. J. Lab. Clin. Med. 59: 926-931. Washburn, K. W., and T. M. Huston, 1968. Effect of environmental temperature on iron deficiency anemia in Athens-Canadian Randombred. Poultry Sci. 47: 1532-1535.
Evaluation of Certain Reproductive Traits in Lines of Chickens Selected for Mating Ability W. T. C O O K 1 AND P . B.
SIEGEL
Department of Poultry Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication October 25, 1971) ABSTRACT An evaluation was made of age at sexual maturity, egg production, egg weight, fertility and hatchability in lines of chickens divergently selected for 10 to 12 generations for cumulative number of completed matings of males. Males of the low mating line matured at earlier ages than those of the unselected control and high mating lines. The four comb phenotypes involving the rose and the pea loci did not influence age at sexual maturity in males. In females no differences were found among lines for age at sexual maturity, hen-day egg production, and egg weights. The selected lines were not different for percentage fertility and hatchability of fertile eggs. POULTRY SCIENCE 51: 1201-1206, 1972
" D I D I R E C T I O N A L selection for com•*-* ponents of sexual behavior results in lines of chickens in which males have different mating propensities (Wood-Gush, 1960; Tindell and Arze, 1965). Siegel (1965, 1972) using the Athens-Canadian (AC) R a n d o m b r e d population as a base, established distinct high and low mating lines by selecting for number of complete
matings. T h e AC randombreds exhibit segregation of alleles at the rose and pea loci (Hess, 1962; Merritt and Gowe, 1962). Reported here are the effects of Siegel's continuous selection for high and low male mating behavior on certain reproductive traits, and the effects of comb phenotypes on one of those traits. MATERIALS AND METHODS
1 Present address, Research Headquarters, HyLine Poultry Farm, Johnston, Iowa 50131.
General. T h e d a t a used in this paper are from the 5 1 0 , S H and Si 2 generations
ABSTRACT The mean red blood cell life span was determined to two groups of 18 week old Athens Randombred male birds using a "Cr labeling procedure. There were eight birds in each group. One group was raised at 8°C. and the other at 30°C. There were no statistical differences due to temperature between the two groups which had mean red blood cell life spans of 27.4 and 26.7 days at 8° and 30°C, respectively. POULTRY SCIENCE 51: 1198-1201,
INTRODUCTION
T
HE effect of environmental temperature on thyroid activity has been studied and established (Hoffmann and Shaffner, 1950; Stahl et al., 1961; Huston and Carmon, 1962; Garren and Shaffner, 1956). Moreover, thyroxin hormone has been shown to have erythropoietic activity in addition to its regulation of the basal metabolic rate (Turner, 1966). Relationships between basal metabolic and red blood cells life span in poikilothermic animals have been established (Berlin, 1964). If the environmental temperature of the alligator was changed from 31°C. to 16°C, there was an apparent prolongation of the red cell life span. There is, however, considerable reduction if not complete suppression of red cell synthesis (Cline and Waldmann, 1962a). Brace (1953) reported similar results in the hibernating marmot. There are many reports on the relationship between thyroxin level in blood and life span of the red cells in homeothermic animals (human, McClellan et al., 1958; dog, Waldmann et al., 1962; Cline and Berlin, 1963). There is a dearth of information concerning the direct effect of environmental temperature on the survival of the erythrocytes in homeothermic animals. The object of this study is to determine the relationship between environmental tem-
1972
perature and the life span of the red blood cells. MATERIALS AND METHODS
Two groups of Athens Randombred males, 18 weeks of age, were raised from hatching in controlled temperatures. The mean temperature of the two environments studied were 8° or 30°C. with a diurnal cycle of 4°-12°C. or 26°-34°C, respectively. Eight birds were in each group, and their body weight ranged from 2.00 to 2.60 kg. In the determination of the red blood cells (R.B.C.) life span, the labeling of R.B.C. was achieved with the use of 51Cr. This technique was developed by Gray and Sterling (1950) and modified by Rodnan et al. (1957). In the labeling procedure 400 JXC. of 51Cr (Na2 61 Cr0 4 ) with specific activity of .167 mc./mg. Cr in .4 ml. saline solution was injected intravenously. Two millilitres of blood were taken 24 hours after injection and at weekly intervals for the next four weeks for determination of the decline of the radioactivity of R.B.C. The blood samples were washed three times using 7.0 ml. of 0.75% saline each time to remove the extracorpuscular radioactivity. The emission of r>1Cr was counted in an Isomatic Well Counter (Baird Atomic Company, Model 709). Blood hematocrit was measured by the microhematocrit method 198
1199
ERYTHROCYTE SURVIVAL
(Johnson, 1955) and radioactivity expressed as counts per minute per millilitre of packed R.B.C. corrected for physical decay of the isotope (half life 26.5 days). The counts of the initial blood samples taken at 24 hours were used as a standard and were taken as 1.0. The counts of the standard on other counting days were used to obtain a correction factor (CF = counts of standard on day zero/counts of standard on day x) which was used to correct the counts of each sample. The corrected values were calculated as a percentage of the initial counts at zero days for each bird. The regression line of corrected counts on days elapsed was calculated for each chicken. The interception on the days coordinate was considered as the mean life span of the red blood cells in a chicken (Cline and Waldmann, 1962b). RESULTS AND DISCUSSION
The average decline in the radioactivity of the red blood cells of the chicken as corrected for physical decay of chromium51 is
100 90
<;o
h-
" \
•
\
\
Z60 50
^. N
\
•
i—
z ill 4 0
£ 30
"
P
•
\\ *%\
20
^
10 1
2
3
\? 4
5
WEEKS AFTER INJECTION
FIG. 1. Decline in MCr counts in relation to time for prediction of the mean life span of red blood cells. The graph represents the two different groups in two different environmental temperatures.
TABLE 1.—Effect of environmental temperature on the body weight, hematocrit and the red cell life span of A thens Randombred
Temperature 8°C. 30°C.
Body Weight in kgm.
Hematocrit
R.B.C. Life Span days
2.69* 2.13
36.5* 34.1
27.36 26.73
* Different significantly (P<0.05).
depicted in Figure 1. Tests for the regression coefficient (bi) of the corrected counts on days after 51Cr injection of these two groups at 8° and 30°C. show no significant effect of temperature on the life span of the red blood cells (Table 1). The life span of red blood cells was 27.4 days at 8°C. and 26.7 days at 30°C. A significant difference was observed between the two groups in hematocrit and body size. There was no correlation observed between R.B.C. life span and body size or hematocrit. The non-significant effect of environmental temperature on the life span of red blood cells is supported by the analogous result of an increased rate of production of dogs since it has been established that environmental temperature affects the thyroid activity. Waldmann et al. (1962) found that dogs with experimentally induced hyperthyroidism became polycythemic as a result of an increased rate of production of R.B.C. but there was no change in the R.B.C. life span. Also in the hypothyroid dog Cline and Berlin (1963) found that there was 38% decrease in hematocrit and there was no change in R.B.C. life span. On the other hand McClellan et al. (1958) found that R.B.C. from hypothyroid and hyperthyroid patients have a normal survival period in normal recipients, but autologous 51 Cr labeled cells in hyperthyroid patients have diminished survival. The significant effect of environmental temperature on hematocrit is in agreement with Huston (1965), Washburn and Hu-
1200
K. F. A. SOLIMAN AND T. M. HUSTON
ston (1968), Moye et al. (1970) and Deaton et al. (1970). It is apparent that the effect of temperature on hematocrit is neither due to the life span of R.B.C. nor due to hemodilution (Soliman and Huston, (1972). The direct effect of environmental temperature on the thyroid activity which in turn controls the erythropoiesis may have a major effect. Also it might be that the effect of ambient temperature and, consequently, thyroxin on erythropoiesis comes through an indirect route. Thyroxin stimulates oxygen consumption by uncoupling the oxidative phosphorylation in the mitochondria of the cells in the animal body (Turner, 1966). It was reported that in cold weather chickens have a higher thyroxin level and a greater oxygen consumption than those in hot weather (Huston and Carmon, 1962). The need of oxygen to be used for the high metabolic rate might induce erythropoietin to be secreted from the kidney which will in turn induce the production of the red blood cells (Turner, 1966). Allison (1960) reported an equation for predicting the R.B.C. life span using the animal body weight. In the present work no correlation was found between body weight and the R.B.C. life span indicating that this equation might be applied among species but not within species. The life span of red blood cells reported in this work (27 day) is very close to the value obtained by Hevesy and Ottesen (1945) using 32P and two birds. They found that the R.B.C. life span was 28 days. Shemin (1948) found that the R.B.C. life span on one individual chicken by using glycine15N to be 28 days. Rodnan et al. (1957) by using 51Cr and six chickens found that the maximum R.B.C. life span value to be 35 days. On the other hand Brace and Atland (1956), using the random destruction method and glycine14C, reported a mean life span of 20 days for
chickens. There would seem to be at least two major reasons for the various life spans reported in the literature. First, the small numbers of individuals used in these experiments and second the different labeling procedure used for each experiment. REFERENCES Allison, A. C , I960. Turnovers of erythrocytes and plasma proteins in mammals. Nature, 188: 3740. Berlin, N. I., 1964. Life span of the red cell. p. 423-450. In C. Bishop and D. M. Surgenor, The Red Blood Cell. Academic Press, New York and London. Brace, K., 19S3. Life span of the marmot erythrocyte. Blood, 8: 648-650. Brace, K., and P. D. Atland, 1956. Life span of the duck and chicken erythrocyte as determined with "C. Proc. Soc. Exp. Biol. Med. 92: 615617. Cline, M. J., and T. A. Waldmann, 1962a. Effect of temperature on red cell survival in the alligator. Proc. Soc. Exp. Biol. Med. I l l : 716-718. Cline, M. J., and T. A. Waldmann, 1962b. Effect of temperature on erythropoiesis and red cell survival in the frog. Amer. J. Physiol. 203: 401-403. Cline, M. J., and N. I. Berlin, 1963. Erythropoiesis and red cell survival in the hypothyroid dog. Amer. J. Physiol. 204: 415-418. Deaton, J. W., F. N. Reece and W. J. Traver, 1970. Hematocrit hemoglobin and plasma-protein levels of broilers under constant temperature. Poultry Sci. 49: 1993-1996. Garren, H. W., and C. S. Shaffner, 1956. How the period of exposure to different stress stimuli affects the endocrine and lymphatic gland weights of young chickens. Poultry Sci. 35: 266-272. Gray, S. J., and K. Sterling, 1950. The tagging of red cells and plasma protein with radioactive chromium. J. Clin. Invest. 29: 1604-1615. Hevesy, G., and J. Ottesen, 1945. Life cycle of the red corpuscles of the hen. Nature, 156: 534. Hoffmann, E., and C. S. Shaffner, 1950. Thyroid weight and functions as influenced by environmental temperature. Poultry Sci. 29: 365-376. Huston, T. M., and J. L. Carmon, 1962. The influence of high environmental temperature on thyroid size of domestic fowl. Poultry Sci. 4 1 : 175-179. Huston, T. M., 1965. The influence of different environmental temperatures on immature fowl. Poultry Sci. 44: 1032-1036.
ERYTHROCYTE
Johnson, P. M., 1955. Hematocrit values for the chick embryos at various ages. Amer. J. Physiol. 180:361-362. McClellan, J. E., C. Donegan, O. A. Thorup and B. S. Leavell, 1958. Survival time of the erythrocyte in myxedema and hyperthyroidism. J. Lab. Clin. Med. 51: 91-96. Moye, R. J., Jr., K. W. Washburn and T. M. Huston, 1970. Effect of environmental temperature on erythrocyte number and size. Poultry Sci. 49: 1683-1686. Rodnan, G. P., F. G. Ebaugh, Jr. and M. R. S. Fox, 1957. The life span of the red blood cell and the red blood cell volume in the chicken, pigeon and duck as estimated by the use of Na251Cr04. Blood, 12: 355-366. Shemin, D., 1948. The biosynthesis of prophyrins. Cold Spring Harbor Symp. Quant. Biol. 13: 185-192.
SURVIVAL
1201
Soliman, K. F. A., and T. M. Huston, 1972. Effect of dietary protein and fat on the hematocrit and plasma cholesterol of chickens at different environmental temperature. Poultry Sci. (In press). Stahl, P., G. W. Pipes and C. W. Turner, 1961. Time required for low temperature to influence thyroid secretion rate in fowls. Poultry Sci. 40: 646-650. Turner, C. D., 1966. General Endocrinology. 4th ed. W. B. Saunders Co., Phil. Lond. p. 579. Waldmann, T. A., S. M. Weissman and E. H. Levin, 1962. Effect of thyroid administration of erythropoiesis in the dog. J. Lab. Clin. Med. 59: 926-931. Washburn, K. W., and T. M. Huston, 1968. Effect of environmental temperature on iron deficiency anemia in Athens-Canadian Randombred. Poultry Sci. 47: 1532-1535.
Evaluation of Certain Reproductive Traits in Lines of Chickens Selected for Mating Ability W. T. C O O K 1 AND P . B.
SIEGEL
Department of Poultry Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication October 25, 1971) ABSTRACT An evaluation was made of age at sexual maturity, egg production, egg weight, fertility and hatchability in lines of chickens divergently selected for 10 to 12 generations for cumulative number of completed matings of males. Males of the low mating line matured at earlier ages than those of the unselected control and high mating lines. The four comb phenotypes involving the rose and the pea loci did not influence age at sexual maturity in males. In females no differences were found among lines for age at sexual maturity, hen-day egg production, and egg weights. The selected lines were not different for percentage fertility and hatchability of fertile eggs. POULTRY SCIENCE 51: 1201-1206, 1972
" D I D I R E C T I O N A L selection for com•*-* ponents of sexual behavior results in lines of chickens in which males have different mating propensities (Wood-Gush, 1960; Tindell and Arze, 1965). Siegel (1965, 1972) using the Athens-Canadian (AC) R a n d o m b r e d population as a base, established distinct high and low mating lines by selecting for number of complete
matings. T h e AC randombreds exhibit segregation of alleles at the rose and pea loci (Hess, 1962; Merritt and Gowe, 1962). Reported here are the effects of Siegel's continuous selection for high and low male mating behavior on certain reproductive traits, and the effects of comb phenotypes on one of those traits. MATERIALS AND METHODS
1 Present address, Research Headquarters, HyLine Poultry Farm, Johnston, Iowa 50131.
General. T h e d a t a used in this paper are from the 5 1 0 , S H and Si 2 generations