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Physiological Differences Associated with Genetic Differences in Egg Production
Physiological Differences Associated with Genetic Differences in Egg Production 3. GONADOTROPHIN SENSITIVITY R.
F R A N K H A M 1 AND H.
DOORNENBAL
Canada Department of Agriculture, Research Station, Lacombe, Alberta, Canada (Received for publication June 4, 1970)
HE pituitary gonadotrophic hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are generally believed to control ovulation and egg production (Sturkie, 196S). Other hormones and biological substances are known to influence egg production but their effects are generally considered to be through effects on general body metabolism. It is then likely that a genetic increase in egg production achieved through selection may involve either an increase in the secretion of the gonadotrophic hormones and/or an increase in target organ sensitivity to them. The object of this experiment was to determine whether gonadotrophin sensitivity, as measured by male chick response to gonadotrophin, had increased in two lines of poultry selected for increased egg production as compared to their base population.
T
MATERIALS AND METHODS
S27S and S% are two lines of White Leghorns selected for increased egg production and OCS is their base population. These lines and their development, production characteristics and management have been described previously (Frankham and Doornenbal, 1970). The method used to determine gonadotrophin sensitivity was the standard chick testes weight response to gonadotrophin method of Breneman et al. (19S9) as used 1 Present address: Department of Biology, University of Chicago, Chicago, Illinois 60637.
by Siegel and Siegel (1964) and Siegel et al. (1968). The gonadotrophin source was anterior pituitaries from selected line cockerels of approximately 12 months of age. The pituitaries were removed, weighed, placed in a 0.9% saline solution and deep frozen until required. Prior to use the pituitaries were homogenized, diluted with 0.9% saline, centrifuged, and the concentration of the supernatant adjusted such that 0.2 ml. of solution contained the equivalent of 1.5 mg. of fresh anterior pituitary. Twenty-four hours old male chicks were injected subcutaneously in the dorsal neck region with 0.2 ml. of pituitary extract (treated) or 0.2 ml. of saline (control) twice at 12 hour intervals and after a further 12 hours all chicks were weighed, sacrificed, and their testes removed and weighed. Eighty male chicks per strain were used. These were obtained from each strain by taking two full sibs from each of two dam families within each of twenty sire families. One full sib was then placed in the treated group and the other in the control group. The chicks were maintained without food or water and kept in darkness for the duration of the experiment. The testes weights were expressed as milligrams of testes per 100 gm. of body weight as suggested by Siegel and Siegel (1964). The testes weight responses and their standard errors were calculated from the difference between full-sibs in the treated and control groups (i.e. a paired
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1620
R. FRANKHAM AND H. DOORNENBAL TABLE 1.—Testes weight response to gonadotrophin for the three strains Testes weight (mg.) per 100 g. body weight
Strain
Number
1
Treated
Control
1.311 1.09 .84* 1.10
29.13 + 1.47 30.40+1.16
14.29±.81 15.88i.60
Response
s% S275
32 32 64 31
14.84 + 14.52 + 14.68+ 12.17 +
St 27.12 + 1.42 14.95+.83 OCS 1 Response of treated over control. % Standard errors. f S is the combined value for the two selected strains. * and ** differ from OCS at the P < 0 . 1 0 and P < 0 . 0 5 levels. comparison). Difference between strains were tested using the t test. RESULTS AND DISCUSSION
Testes weights and body weights for the control and treated groups and the testes weight response (deviation between treated and control groups) for each strain are presented in Table 1. Both selected strains responded more to the gonadotrophin injections than did the control, but the differences were not significant. As the response was similar in the two selected strains they were combined (Table 1). The response of the selected lines combined was significantly (P < 0.10) greater by 20.6% than that of the control. Thus gonadotrophin sensitivity increased under selection for increased part-record egg production. The selected lines used in this study have higher egg production, lower mature body weight and earlier age at first egg than their base population (Frankham and Doornenbal, 1970). Siegel et al. (1968) and Van Krey and Siegel (1968) reported differences in gonadotrophin secretion and gonadotrophin sensitivity between two lines of White Rocks which differed in age at first egg, egg production and body weight. They found that gonadotrophin secretion was higher and gonadotrophin sensitivity lower in the line with earlier sexual maturity, lower egg production and higher body weight. Since the lines in their experi-
Body weight (g.) Treated
Control
28.85+.38 28.39+.35**
30.07+.34 2 9 . 1 3 + . 35
29.75+.44
30.20+.48
ments and ours were of different breeds and the lines differed in several traits it is difficult to draw parallels between them. The only consistency between the two was that mature body weight was negatively associated with gonadotrophin sensitivity. Because the heritability of gonadotrophin sensitivity is high (Siegel and Siegel, 1964), it may be possible to improve egg production (which has a low heritability) more rapidly by selection on gonadotrophin sensitivity than on egg production itself. The potential of such a procedure depends on the importance of gonadotrophin sensitivity as a component of egg production. In our population gonadotrophin sensitivity was probably an important component of egg production as it changed under selection for egg production. However, this may not be the case in other populations. It would be necessary to establish that gonadotrophin sensitivity was an important component of egg production in a variety of populations and to establish that egg production was increased by selection for gonadotrophin sensitivity before direct selection on gonadotrophin sensitivity could be advocated as means of improving egg production. Research into these questions is warranted on the basis of our results. SUMMARY The gonadotrophin sensitivity of two lines selected for increased part-record egg
GENETIC DIFFERENCES IN PRODUCTION
production was compared with that of their base population. Gonadotrophin sensitivity was determined as the change in male chick testes weight due to injection of the equivalent of 3 mg. of fresh cockerel anterior pituitary (given in two injections) as compared to that of their saline injected full sibs. The gonadotrophin sensitivity of the selected lines was significantly (P < 0.10) greater by 20.6% than that of their base population. Thus gonadotrophin sensitivity increased under selection for increased part-record egg production. The possibility of selecting directly on gonadotrophin sensitivity as a means of increasing egg production is discussed. ACKNOWLEDGEMENTS
We are indebted to I. Friesen, W. E. Sage, A. S. Schonheiter and A. W. Wilson for assistance in carrying out this experi-
1621
ment and to H. T. Fredeen, T. Fujishima and J. G. Stothart for their comments on the manuscript. REFERENCES Breneman, W. R., F. J. Zeller and B. E. Beekman, 1959. Gonadotrophin assay in chicks. Poultry Sci. 38: 152-158. Frankham, R., and H. Doornenbal, 1970. Physiological differences associated with genetic differences in egg production. 1. Organ and endocrine gland weights. Poultry Sci. 49: 1610-1615. Siegel, P. B., and H. S. Siegel, 1964. Genetic variation in chick bioassays for gonadotrophins. I. Testis weight and response. Virginia J. Sci. 15: 187-203. Siegel, P. B., H. P. Van Krey and H. S. Siegel, 1968. Pituitary-gonad relationships in weight selected lines differing in sexual maturity. Poultry Sci. 47: 771-776. Sturkie, P. D., 1965. Avian Physiology. Cornell Univ. Press, Ithaca, N.Y. Van Krey, H. P., and P. B. Siegel, 1968. Pituitarygonadal relationships in chickens selected for high and low body weight. Poultry Sci. 47: 480-487.
Increased Incidence of Encephalomalacia in the Chick by Dietary Phytol1 W. J. PUDELKIEWICZ, SANDRA M. THOMSON AND C. F. HELMBOLDT Departments of Poultry Science and Animal Diseases, University of Connecticut, Storrs, Connecticut 06268 (Received for publication June 6, 1970)
T
HE role of linoleic acid in the etiology of encephalomalacia has been reported (Dam et al., 1958; Century and Horwitt, 1959; Machlin and Gordon, 1960). Substances such as inositol, ascorbic acid, methylene blue, and a number of synthetic antioxidants have been shown to alleviate the incidence of encephalomalacia either partially or completely. Century and Horwitt (1959), and Century et al. (1959) 1 Scientific Contribution No. 424, Agricultural Experiment Station, University of Connecticut, Storrs.
reported that certain saturated fatty acids such as lauric and myristic caused an increase in the incidence of this disorder. In a preliminary experiment, cis-trans phytol was fed on the assumption that it would prevent the development of encephalomalacia. This hypothesis was based upon the results of our previous work where phytol was found to increase the concentration of vitamin E in liver tissue 2to 3-fold over controls (Pudelkiewicz et al., 1964). It was felt that the phytol would preserve the residual tocopherol in the feed ingredients and delay the occurrence of en-
F R A N K H A M 1 AND H.
DOORNENBAL
Canada Department of Agriculture, Research Station, Lacombe, Alberta, Canada (Received for publication June 4, 1970)
HE pituitary gonadotrophic hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are generally believed to control ovulation and egg production (Sturkie, 196S). Other hormones and biological substances are known to influence egg production but their effects are generally considered to be through effects on general body metabolism. It is then likely that a genetic increase in egg production achieved through selection may involve either an increase in the secretion of the gonadotrophic hormones and/or an increase in target organ sensitivity to them. The object of this experiment was to determine whether gonadotrophin sensitivity, as measured by male chick response to gonadotrophin, had increased in two lines of poultry selected for increased egg production as compared to their base population.
T
MATERIALS AND METHODS
S27S and S% are two lines of White Leghorns selected for increased egg production and OCS is their base population. These lines and their development, production characteristics and management have been described previously (Frankham and Doornenbal, 1970). The method used to determine gonadotrophin sensitivity was the standard chick testes weight response to gonadotrophin method of Breneman et al. (19S9) as used 1 Present address: Department of Biology, University of Chicago, Chicago, Illinois 60637.
by Siegel and Siegel (1964) and Siegel et al. (1968). The gonadotrophin source was anterior pituitaries from selected line cockerels of approximately 12 months of age. The pituitaries were removed, weighed, placed in a 0.9% saline solution and deep frozen until required. Prior to use the pituitaries were homogenized, diluted with 0.9% saline, centrifuged, and the concentration of the supernatant adjusted such that 0.2 ml. of solution contained the equivalent of 1.5 mg. of fresh anterior pituitary. Twenty-four hours old male chicks were injected subcutaneously in the dorsal neck region with 0.2 ml. of pituitary extract (treated) or 0.2 ml. of saline (control) twice at 12 hour intervals and after a further 12 hours all chicks were weighed, sacrificed, and their testes removed and weighed. Eighty male chicks per strain were used. These were obtained from each strain by taking two full sibs from each of two dam families within each of twenty sire families. One full sib was then placed in the treated group and the other in the control group. The chicks were maintained without food or water and kept in darkness for the duration of the experiment. The testes weights were expressed as milligrams of testes per 100 gm. of body weight as suggested by Siegel and Siegel (1964). The testes weight responses and their standard errors were calculated from the difference between full-sibs in the treated and control groups (i.e. a paired
1619
1620
R. FRANKHAM AND H. DOORNENBAL TABLE 1.—Testes weight response to gonadotrophin for the three strains Testes weight (mg.) per 100 g. body weight
Strain
Number
1
Treated
Control
1.311 1.09 .84* 1.10
29.13 + 1.47 30.40+1.16
14.29±.81 15.88i.60
Response
s% S275
32 32 64 31
14.84 + 14.52 + 14.68+ 12.17 +
St 27.12 + 1.42 14.95+.83 OCS 1 Response of treated over control. % Standard errors. f S is the combined value for the two selected strains. * and ** differ from OCS at the P < 0 . 1 0 and P < 0 . 0 5 levels. comparison). Difference between strains were tested using the t test. RESULTS AND DISCUSSION
Testes weights and body weights for the control and treated groups and the testes weight response (deviation between treated and control groups) for each strain are presented in Table 1. Both selected strains responded more to the gonadotrophin injections than did the control, but the differences were not significant. As the response was similar in the two selected strains they were combined (Table 1). The response of the selected lines combined was significantly (P < 0.10) greater by 20.6% than that of the control. Thus gonadotrophin sensitivity increased under selection for increased part-record egg production. The selected lines used in this study have higher egg production, lower mature body weight and earlier age at first egg than their base population (Frankham and Doornenbal, 1970). Siegel et al. (1968) and Van Krey and Siegel (1968) reported differences in gonadotrophin secretion and gonadotrophin sensitivity between two lines of White Rocks which differed in age at first egg, egg production and body weight. They found that gonadotrophin secretion was higher and gonadotrophin sensitivity lower in the line with earlier sexual maturity, lower egg production and higher body weight. Since the lines in their experi-
Body weight (g.) Treated
Control
28.85+.38 28.39+.35**
30.07+.34 2 9 . 1 3 + . 35
29.75+.44
30.20+.48
ments and ours were of different breeds and the lines differed in several traits it is difficult to draw parallels between them. The only consistency between the two was that mature body weight was negatively associated with gonadotrophin sensitivity. Because the heritability of gonadotrophin sensitivity is high (Siegel and Siegel, 1964), it may be possible to improve egg production (which has a low heritability) more rapidly by selection on gonadotrophin sensitivity than on egg production itself. The potential of such a procedure depends on the importance of gonadotrophin sensitivity as a component of egg production. In our population gonadotrophin sensitivity was probably an important component of egg production as it changed under selection for egg production. However, this may not be the case in other populations. It would be necessary to establish that gonadotrophin sensitivity was an important component of egg production in a variety of populations and to establish that egg production was increased by selection for gonadotrophin sensitivity before direct selection on gonadotrophin sensitivity could be advocated as means of improving egg production. Research into these questions is warranted on the basis of our results. SUMMARY The gonadotrophin sensitivity of two lines selected for increased part-record egg
GENETIC DIFFERENCES IN PRODUCTION
production was compared with that of their base population. Gonadotrophin sensitivity was determined as the change in male chick testes weight due to injection of the equivalent of 3 mg. of fresh cockerel anterior pituitary (given in two injections) as compared to that of their saline injected full sibs. The gonadotrophin sensitivity of the selected lines was significantly (P < 0.10) greater by 20.6% than that of their base population. Thus gonadotrophin sensitivity increased under selection for increased part-record egg production. The possibility of selecting directly on gonadotrophin sensitivity as a means of increasing egg production is discussed. ACKNOWLEDGEMENTS
We are indebted to I. Friesen, W. E. Sage, A. S. Schonheiter and A. W. Wilson for assistance in carrying out this experi-
1621
ment and to H. T. Fredeen, T. Fujishima and J. G. Stothart for their comments on the manuscript. REFERENCES Breneman, W. R., F. J. Zeller and B. E. Beekman, 1959. Gonadotrophin assay in chicks. Poultry Sci. 38: 152-158. Frankham, R., and H. Doornenbal, 1970. Physiological differences associated with genetic differences in egg production. 1. Organ and endocrine gland weights. Poultry Sci. 49: 1610-1615. Siegel, P. B., and H. S. Siegel, 1964. Genetic variation in chick bioassays for gonadotrophins. I. Testis weight and response. Virginia J. Sci. 15: 187-203. Siegel, P. B., H. P. Van Krey and H. S. Siegel, 1968. Pituitary-gonad relationships in weight selected lines differing in sexual maturity. Poultry Sci. 47: 771-776. Sturkie, P. D., 1965. Avian Physiology. Cornell Univ. Press, Ithaca, N.Y. Van Krey, H. P., and P. B. Siegel, 1968. Pituitarygonadal relationships in chickens selected for high and low body weight. Poultry Sci. 47: 480-487.
Increased Incidence of Encephalomalacia in the Chick by Dietary Phytol1 W. J. PUDELKIEWICZ, SANDRA M. THOMSON AND C. F. HELMBOLDT Departments of Poultry Science and Animal Diseases, University of Connecticut, Storrs, Connecticut 06268 (Received for publication June 6, 1970)
T
HE role of linoleic acid in the etiology of encephalomalacia has been reported (Dam et al., 1958; Century and Horwitt, 1959; Machlin and Gordon, 1960). Substances such as inositol, ascorbic acid, methylene blue, and a number of synthetic antioxidants have been shown to alleviate the incidence of encephalomalacia either partially or completely. Century and Horwitt (1959), and Century et al. (1959) 1 Scientific Contribution No. 424, Agricultural Experiment Station, University of Connecticut, Storrs.
reported that certain saturated fatty acids such as lauric and myristic caused an increase in the incidence of this disorder. In a preliminary experiment, cis-trans phytol was fed on the assumption that it would prevent the development of encephalomalacia. This hypothesis was based upon the results of our previous work where phytol was found to increase the concentration of vitamin E in liver tissue 2to 3-fold over controls (Pudelkiewicz et al., 1964). It was felt that the phytol would preserve the residual tocopherol in the feed ingredients and delay the occurrence of en-