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Dwarfism in Diverse Genetic Backgrounds: Diet-Egg Production Relationships
BREEDING AND GENETICS Dwarfism in Diverse Genetic Backgrounds: Diet-Egg Production Relationships J. A. CHERRY and P. B. SIEGEL Poultry Science Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication August 2, 1977)
INTRODUCTION
Genetic influences on the nutrient requirements of the fowl are well documented. Surprisingly, however, there has been a lack of research on the genetic-nutritional relationships involved in the expression of the sex-linked dwarf gene, dw, in meat-type chickens. We previously reported that the depressive effect of dw on egg weight was partially prevented by diet (Cherry et al, 1977). This paper contains comparisons of body size and egg production between dwarf and normal pullets of diverse genetic backgrounds fed different diets. MATERIALS AND METHODS
Stocks and Husbandry. The pullets utilized in this study were obtained from the fifth successive backcross generation following the introduction of the dw gene into the S 1 3 generation of lines selected bidirectionally for high and low eight-week body weight (Reddy and Siegel, 1977). The genotypes were designated as high-weight normals (HWN), highweight dwarfs (HWD), low-weight normals (LWN) and low-weight dwarfs (LWD). Chicks hatched in March, 1976, were vaccinated for Marek's disease and reared in heterosexual flocks on litter floors. Lighting was continuous until the chicks were seven days of age, after which rearing continued under the natural photoperiod. At 134 days of age, 40 pullets from each of the four genotypes were 1978 Poultry Sci 57:325-329
placed into individual cages within blocks of five cages sharing a common feeder. At this time they were subjected to a 14-hr photoperiod from 0700 to 2100 hr. Four blocks of pullets from each of the four genotypes (HWN, HWD, LWN, LWD) were randomly assigned either the "high" or the "low" diet previously described by Cherry et al. (1977). The high diet contained 23% protein, 2795 kcal/kg of metabolizable energy, 4% calcium, .77% available phosphorus, and .42% methionine. The low diet (used during the course of selection of these lines) contained 16% protein, 2785 kcal/kg of metabolizable energy, 3.5% Ca, .45% available phosphorus, and .28% methionine. The feed intake of the HWN pullets was restricted to approximately 65% of full consumption while the other genotypes received feed ad lib. Traits Measured and Analysis. Individual body weights to the nearest 10 g were obtained at several ages commencing at 140 days of age, and the length of the right shank was measured, in mm, at 168, 224, and 266 days of age. Feed consumption was measured biweekly for each block of five pullets, considered the observational unit. The ovipositions of each pullet were classified daily by the procedure of Reddy and Siegel (1976) from the date of first egg to December 27, 1976. In addition, extra-calcified eggs were identified according to the description of van Middelkoop and Simons (1970). Egg production was measured as percentage hen-day pro-
325
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ABSTRACT The effect of diet on phenotypic expressions of the sex-linked dwarf gene, dw, was studied in lines of chickens selected for high and for low juvenile body weight. The relative reduction of body weight and shank length due to dw was consistently greater in the low-weight than in the high-weight line regardless of diet. The hen-day egg production of high-weight dwarf pullets was greater than that of their normal siblings while the opposite relationship was found in the low-weight line. Feeding a diet containing increased levels of protein, calcium, phosphorus, and metabolizable energy increased the egg production of dwarf pullets, regardless of their background genome, but did not significantly affect the egg production of normal pullets. This diet also partially prevented the reduction in shell thickness associated with dwarfism in the low-weight line. In addition, the tendency of dw to reduce the incidence of defective eggs in the high-weight line and to increase the incidence of the low-weight line varied with diet. Dwarf pullets of both rapid and slow growing populations require different diets for the maximum realization of their genetic potential.
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RESULTS AND DISCUSSION Body Weight and Shank Length. Pullets from t h e HW line were significantly heavier and had longer shanks t h a n t h o s e from the LW line. Similarly, n o r m a l pullets were significantly heavier and had longer shanks t h a n dwarfs. These results were e x p e c t e d and are consistent with previous observations. A significant effect of diet on b o d y weight was n o t observed until 2 2 4 days of age ( 9 0 days after feeding t h e t w o
e x p e r i m e n t a l diets c o m m e n c e d ) with pullets fed t h e high diet being heavier t h a n t h o s e fed t h e l o w diet. N o differences b e t w e e n diets were observed for shank length, indicating t h a t skeletal g r o w t h had been essentially c o m p l e t e d . Primary interest in this e x p e r i m e n t involved t h e interactions a m o n g t h e variables. N o n e of t h e interactions involving diet as a main variable was significant for b o d y size parameters, indicating t h a t t h e responses of t h e HW and LW lines as well as t h e dwarf and n o r m a l pullets were similar u n d e r b o t h diets. T h e depressive effect of dw on b o t h weight and shank length was greater in t h e LW t h a n in t h e HW line (Table 1), resulting in significant line X dwarfnondwarf interactions. This depressive effect was consistently greater for b o d y weight t h a n for shank length and was in accord with t h e observations of R e d d y and Siegel ( 1 9 7 7 ) . Differences b e t w e e n diets for feed c o n s u m p tion were n o t significant. Also, n o n e of t h e interactions of diet with o t h e r main variables were significant for feed c o n s u m p t i o n . T h e HW pullets c o n s u m e d significantly more feed t h a n t h e LW pullets, and n o r m a l pullets c o n s u m e d significantly m o r e feed than their dwarf siblings. This would be expected from t h e differences in b o d y size. Egg Production and Shell Thickness. Means and standard deviations for percentage hen-day p r o d u c t i o n of n o r m a l eggs were 59 ± 15 for t h e HW line and 52 ± 18 for t h e LW line with t h e difference b e t w e e n lines significant. Corre-
TABLE 1 .—Comparisons3- between dwarf and normal pullets for body weight and shank length at various ages by line and diet HW line
LW line
Age (days)
High diet
Low diet
High diet
Low diet
Body weight 140 168 196 224 252 266 308
65 68 68 68 67 68 68
69 73 69 71 68 68 66
60 60 55 51 50 50 48
70 64 59 50 49 48 47
Shank length 168 224 266
75 77 77
77 76 77
68 67 65
68 65 65
(Dwarf/normal) X 100.
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d u c t i o n of n o r m a l eggs. E x t r a calcified, d o u b l e yolked, and total defective eggs (all oviposits o t h e r t h a n n o r m a l eggs) were considered as t h e percentage of n o r m a l eggs and converted t o arc sin v % prior t o analysis. When t h e r e were less t h a n 5 0 observations per pullet, t h e percentages were transformed t o F r e e m a n - T u k e y arc sines (Mosteller and Y o u t z , 1 9 6 1 ) . Shell thickness was measured for all eggs laid during a period of three consecutive days when t h e pullets reached 2 4 5 days of age, and t h e mean value for each individual pullet was used in analysis. Data were analyzed b y analysis of variance with lines, diets, and dwarf-nondwarf as fixed effects. T h e statistical m o d e l was: Y;. k i = (X + L; Dj + G k + (LD)ij + ( L G ) i k + ( D G ) j k + ( L D G ) ; j k + ejjk) where i = 1, 2 lines, j = 1, 2 diets, k = 1, 2 dwarf-nondwarf, and 1 = 1 , 2 . . . 2 0 individuals per line-diet-dwarf subclass (4 blocks for feed c o n s u m p t i o n analysis).
327
DIET AND DWARF PHENOTYPE
FIG. 1. Interactions of pullet's genotype with line and with diet for percentage hen-day production of normal eggs.
F 320 3 co 310 CK
hi T
300
T" V-
290
\
m
CO
280
t
HW LINE
LW LINE
FIG. 2. Interaction of pullet's genotype with line for shell thickness (Mm).
inconsistent results obtained by other investigators (Merat, 1972; Silber and Merat, 1974; Guillame, 1976). These data also provide additional evidence that the nutritional requirements of dwarf chickens are quite different from those of their normal siblings. This is not unexpected. Although the physiological basis of dwarfism is poorly understood, phenotypic manifestations of dwarfism are well documented. A characteristic hypothyroidism associated with dwarfism was observed by several investigators (reviewed by Guillame, 1976). Dwarfs have significantly lower levels of blood glucose, total lipids, cholesterol, and free amino acids in their muscles when compared with normal chickens (Guillame, 1972). The dw gene also results in enhanced glycogen and fat storage (Grandhi et al., 1975; Guillame, 1976). Lipogenesis is stimulated and lipolysis inhibited by dw (Touchburn and Blum, 1972), and protein metabolism is altered by dwarfism (Wood et al., 1971; Guillame, 1972; Brown et al., 1972). It was also postulated that dw influences the basic mechanisms controlling appetite (Cherry et al., 1977). Despite these physiological differences, all of which could conceivably affect nutrient requirements, the relationship between diet and the reproductive performance of dwarf pullets is poorly understood. Protein and caloric requirements were evaluated by Guillame (1969, 1971), Arscott and Bernier (1970), Leclercq and Blum (1971), Summers (1971), Quisenberry (1972), and Waldroup and Hazen (1975, 1976). Dwarfs generally appeared to require
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sponding percentages for the high diet were 58 ± 15, and for the low diet 53 ± 18 with the differences again significant. Of interest are the significant dwarf-nondwarf interactions with line and diet (Fig. 1). The HWD pullets produced more normal eggs than their nondwarf siblings, while the egg production of the LWD pullets was severely depressed. There were no differences in the percentage egg production of normal pullets due to diet, but the egg production of the dwarf pullets fed the low diet was considerably less than those fed the high diet. There were no significant differences between diets for shell thickness. Means and standard deviations were 315 ± 25 jUm for the HW line and 297 ± 28 Mm for the LW line with the difference being significant. Also, the shells of eggs from normal pullets were significantly thicker than those from dwarf pullets (310 ± 23 flmvs. 302 ± 30 Mm). The only significant first order interaction between variables for shell thickness was for line X dwarf-nondwarf (Fig. 2). Values were similar for normal pullets from both lines, while the shells of eggs from the LWD pullets were considerably thinner than those from the HWD pullets. This observation is consistent with that of Reddy and Siegel (1977). Furthermore, the significant diet X line x dwarf-nondwarf interaction demonstrates the involvement of diet in this phenomenon. The feeding of the high diet to LWD pullets partially prevented the reduction in shell thickness (mean = 292 /mi)- This was consistent with our previous observation of an increase in egg shell weight, expressed as a percentage of egg weight, from feeding the high diet to LWD pullets (Cherry et al., 1977). This divergence in response between the HW and LW lines as a result of dw and diet may explain the
328
J. A. CHERRY AND P. B. SIEGEL
Defective Eggs. Introduction of the dw gene into certain populations of chickens reduces the frequency of abnormal eggs (Jaap and Mohammadian, 1969; Jaap, 1971; van Middelkoop, 1973). Conversely, this gene provokes the opposite effect in stocks with optimum ovarian activity (Reddy and Siegel, 1977). The results of the present experiment appear to substantiate these observations. Moreover, it appears that the incidence of defective eggs laid by dwarf pullets varies with the diet fed. The % of extra-calcified eggs laid by pullets of the LW line was negligible (.02%), whereas HWD pullets laid a significantly lower percentage of extra-calcified eggs than their nondwarf sisters (.44% vs. 1.45%). No incidence of double yolked eggs was recorded for either dwarf or nondwarf pullets in the LW line. HWD pullets laid only .45% double yolked eggs while 2.54% of the eggs laid by HWN pullets were double yolked. Diet had no apparent effect on the incidence of either extra-calcified or double yolked eggs. As anticipated from previous work (Reddy and Siegel, 1977), dwarfism reduced the incidence of total defective eggs in the HW line and increased their incidence in the LW line. The
8r PHWN
16-
1
LOW DIET
DHWD
HIGH DIET
FIG. 3. Interaction of pullet's genotype with diet for percentage defective eggs oviposited.
significant diet X line X dwarf-nondwarf interaction, however, indicates that these responses deviate with diet (Fig. 3). The LWD pullets receiving the high diet did not lay any more defective eggs than did their normal siblings. When fed the low diet, however, the LWD pullets produced substantially more defective eggs than did their counterparts. This suggests that a nutrient deficiency may be involved in the increased incidence of defective eggs in this population. Opposite tendencies were observed in the HW line where the high diet increased the percentage of defective eggs laid by dwarf pullets while reducing their incidence in nondwarf pullets. These observations provide further evidence that the phenotypic expression of the dw gene is modified by its background genome (French and Nordskog, 1973; Jaap and Forssido, 1976; Reddy and Siegel, 1977) and by diet (Cherry et al., 1977). Dwarf pullets with diverse genetic backgrounds apparently require different diets for the maximum realization of their genetic potential. Additional studies are needed to identify and more precisely define the requirements of the specific nutrients involved. REFERENCES Arscott, G. H., and P. E. Bernier, 1970. Proteins and amino acid needs of the mini hen. Proc. 5th Ann.
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diets with more protein and low calorie-to-protein ratios than do nondwarf chickens, however, these higher nutrient requirements have usually been observed with egg laying dwarf stocks. Guillame (1976) concluded that meattype dwarf strains did not require a special diet. Similarly, dwarf Leghorn-type strains appear to require a higher percentage of dietary calcium (Arscott et al., 1961; Bernier and Arscott, 1972; Austic et al., 1977), while there is little evidence that heavy dw lines need additional calcium (Prod'homme and Merat, 1969; Guillame, 1976). The increased egg production resulting from feeding the high diet to the HWD as well as to the LWD pullets in this experiment indicates that meat-type dwarf stocks also require different dietary regimes for maximum egg production. This observation, along with the previous report that diet attenuated the depressive effect of dw on egg weight (Cherry et al., 1977), indicates that the development of proper nutritional programs will improve the performance of dwarf pullets. Improved performance could give the dwarf broiler breeder mother a competitive advantage over nondwarf hens in the commercial production of hatching eggs-
DIET AND DWARF PHENOTYPE
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restriction during the growing period on the Pacific Northwest Animal Nutr. Conf. Richland, performance of dwarf breeders. World's Poultry Washington, pp. 52—59. Sci. J. 27:288-289. Arscott, G. H., P. Rachapaetayakom, and P. E. Bernier, 1961. Observations on gross requirements Merat, P., 1972. Quelques effects du gene dw sur la for certain nutrients in dwarf White Leghorn hens. pointe et sur la qualite dws oeufs. Ann. Genet. Sel. Poultry Sci. 40:1372-1373. Anim. 4 : 2 1 7 - 2 2 3 . Austic, R. E., D. J. Baker, and R. K. Cole, 1977. Mosteller, F., and C. Youtz, 1961. Tables of the Susceptibility of a dwarf strain of chickens to Freeman-Tukey transformation for the binomial rickets. Poultry Sci. 56:285-291. and poissan distribution. Biometrika48:433—440. Bernier, P. E., and G. H. Arscott, 1972. Fifteen years Prod'homme, J., and P. Merat, 1969. Etude d'un gene of observation on the dwarf gene in the domestic de nanisme lie au sexe chez la poule III. Consomfowl. Ann. Genet. Sel. Anim. 4:183-215. mation alimentaire et production suivant la teneur Brown, R. G., A. S. Wood, B. S. Reinhart, and D. en calcium de la ration. Ann. Genet. Sel. Anim. Longworth, 1972. Differences in amino acid activa1:135-145. tion found between dwarf and non dwarf White Quisenberry, J. H., 1972. High density diets for dwarf Leghorn chickens. Poultry Sci. 51:1067—1068. layers. Ann. Genet. Sel. Anim. 4:271-279. Cherry, J. A., M. Z. Ghitelman, and P. B. Siegel, 1977. Reddy, P. R. K., and P. B. Siegel, 1976. Selection for The relationship between diet and dwarfism in body weight at eight weeks of age. 11. Ovulation diverse genetic backgrounds on egg parameters. and o v i p o s i t i o n p a t t e r n s . P o u l t r y Sci. Poultry Sci. (In press.) 55:1518-1530. French, H. L., and A. W. Nordskog, 1973. PerformReddy, P. R. K., and P. B. Siegel, 1977. Selection for ance of dwarf chickens compared with normal body weight at eight weeks of age. 14. Effects of small-bodied c h i c k e n s . Poultry Sci. t h e s e x - l i n k e d dwarf gene. Poultry Sci. 52:1318-1328. 56:1004-1013. Grandhi, R., R. G. Brown, and J. D. Summers, 1975. Silber, J., and P. Merat, 1974. Etude genitique de la A study of thyroid activity in dwarf and non-dwarf ponte d'oeufs mous chez la poule. XV World's female chicks during key physiological states of Poultry Cong., New Orleans, pp. 491—493. growth and reproduction. Poultry Sci. 54:47—53. Summers, J. D., 1971. Nutrition of the dwarf layer. Guillame, J., 1969. Consequences de l'introduction du World's Poultry Sci. J. 27:287-288. gene de nanisme dw sur ['utilisation alimentaire chez le poussin femelle. Ann. Biol. Biochem. Touchburn, S. P., and J. C. Blum, 1972. Effects of the genes for dwarfism (dw) and naked neck (Na) on Biophys. 9:369-378. chick growth and lipid metabolism. Ann. Genet. Guillame, J., 1971. Some nutritional and physiological Sel. Anim. 4:311-316. traits of the dw chick. World's Poultry Sci. J. van Middelkoop, J. H., 1973. Influence of the dwarf 27:284-285. gene on yolk production and its consequence for Guillame, J., 1972. Donnees complementaires sur normal egg laying of White Plymouth Rock pullets. les besoins nutritionnels de la reproductrice Archiv. fur Geflugelkunde 5:192-196. naine Vedette. Ann. Genet. Sel Anim. 4:281 — van Middelkoop, J. H., and P. C. M. Simmons, 1970. 295. Abnormal eggs due to the presence of two eggs in Guillame, J., 1976. The dwarfing gene dw: Its effect the uterus at the same time. Tijdschr. Diergeneesk. on anatomy, physiology, nutrition, management. 95:21-23. Its application in poultry industry. World's Poultry Waldroup, P. W., and K. R. Hazen, 1975. Energy needs Sci. J. 32:285-304. of dwarf (dw) broiler breeder hens. Poultry Sci. Jaap, R. G., 1971. Selection for body size and repro ; 54:1931-1935. ductive fitness in chickens. World's Poultry Sci. J. Waldroup, P. W., and K. R. Hazen, 1976. A compari27:372-379. son of the daily energy needs of the normal and Jaap, R. G., and T. Forssido, 1976. Exceptionally dwarf b r o i l e r breeder hen. Poultry Sci. large eggs from dwarf leghorn pullets. Poultry Sci. 55:1383-1393. 55:1120-1121. Jaap, R. G., and M. Mohammadian, 1969. Sex-linked Wood, A. S., B. S. Reinhart, G. Rajaratnam, and J. D. dwarfism and egg production in broiler dams. Summers, 1971. A comparison of the blood Poultry Sci. 48:344-346. constituents of dwarf versus non-dwarf birds. Leclercq, B., and J. C. Blum, 1971. Effects of nutrient Poultry Sci. 50:804-807.
INTRODUCTION
Genetic influences on the nutrient requirements of the fowl are well documented. Surprisingly, however, there has been a lack of research on the genetic-nutritional relationships involved in the expression of the sex-linked dwarf gene, dw, in meat-type chickens. We previously reported that the depressive effect of dw on egg weight was partially prevented by diet (Cherry et al, 1977). This paper contains comparisons of body size and egg production between dwarf and normal pullets of diverse genetic backgrounds fed different diets. MATERIALS AND METHODS
Stocks and Husbandry. The pullets utilized in this study were obtained from the fifth successive backcross generation following the introduction of the dw gene into the S 1 3 generation of lines selected bidirectionally for high and low eight-week body weight (Reddy and Siegel, 1977). The genotypes were designated as high-weight normals (HWN), highweight dwarfs (HWD), low-weight normals (LWN) and low-weight dwarfs (LWD). Chicks hatched in March, 1976, were vaccinated for Marek's disease and reared in heterosexual flocks on litter floors. Lighting was continuous until the chicks were seven days of age, after which rearing continued under the natural photoperiod. At 134 days of age, 40 pullets from each of the four genotypes were 1978 Poultry Sci 57:325-329
placed into individual cages within blocks of five cages sharing a common feeder. At this time they were subjected to a 14-hr photoperiod from 0700 to 2100 hr. Four blocks of pullets from each of the four genotypes (HWN, HWD, LWN, LWD) were randomly assigned either the "high" or the "low" diet previously described by Cherry et al. (1977). The high diet contained 23% protein, 2795 kcal/kg of metabolizable energy, 4% calcium, .77% available phosphorus, and .42% methionine. The low diet (used during the course of selection of these lines) contained 16% protein, 2785 kcal/kg of metabolizable energy, 3.5% Ca, .45% available phosphorus, and .28% methionine. The feed intake of the HWN pullets was restricted to approximately 65% of full consumption while the other genotypes received feed ad lib. Traits Measured and Analysis. Individual body weights to the nearest 10 g were obtained at several ages commencing at 140 days of age, and the length of the right shank was measured, in mm, at 168, 224, and 266 days of age. Feed consumption was measured biweekly for each block of five pullets, considered the observational unit. The ovipositions of each pullet were classified daily by the procedure of Reddy and Siegel (1976) from the date of first egg to December 27, 1976. In addition, extra-calcified eggs were identified according to the description of van Middelkoop and Simons (1970). Egg production was measured as percentage hen-day pro-
325
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ABSTRACT The effect of diet on phenotypic expressions of the sex-linked dwarf gene, dw, was studied in lines of chickens selected for high and for low juvenile body weight. The relative reduction of body weight and shank length due to dw was consistently greater in the low-weight than in the high-weight line regardless of diet. The hen-day egg production of high-weight dwarf pullets was greater than that of their normal siblings while the opposite relationship was found in the low-weight line. Feeding a diet containing increased levels of protein, calcium, phosphorus, and metabolizable energy increased the egg production of dwarf pullets, regardless of their background genome, but did not significantly affect the egg production of normal pullets. This diet also partially prevented the reduction in shell thickness associated with dwarfism in the low-weight line. In addition, the tendency of dw to reduce the incidence of defective eggs in the high-weight line and to increase the incidence of the low-weight line varied with diet. Dwarf pullets of both rapid and slow growing populations require different diets for the maximum realization of their genetic potential.
J. A. CHERRY AND P. B. SIEGEL
326
RESULTS AND DISCUSSION Body Weight and Shank Length. Pullets from t h e HW line were significantly heavier and had longer shanks t h a n t h o s e from the LW line. Similarly, n o r m a l pullets were significantly heavier and had longer shanks t h a n dwarfs. These results were e x p e c t e d and are consistent with previous observations. A significant effect of diet on b o d y weight was n o t observed until 2 2 4 days of age ( 9 0 days after feeding t h e t w o
e x p e r i m e n t a l diets c o m m e n c e d ) with pullets fed t h e high diet being heavier t h a n t h o s e fed t h e l o w diet. N o differences b e t w e e n diets were observed for shank length, indicating t h a t skeletal g r o w t h had been essentially c o m p l e t e d . Primary interest in this e x p e r i m e n t involved t h e interactions a m o n g t h e variables. N o n e of t h e interactions involving diet as a main variable was significant for b o d y size parameters, indicating t h a t t h e responses of t h e HW and LW lines as well as t h e dwarf and n o r m a l pullets were similar u n d e r b o t h diets. T h e depressive effect of dw on b o t h weight and shank length was greater in t h e LW t h a n in t h e HW line (Table 1), resulting in significant line X dwarfnondwarf interactions. This depressive effect was consistently greater for b o d y weight t h a n for shank length and was in accord with t h e observations of R e d d y and Siegel ( 1 9 7 7 ) . Differences b e t w e e n diets for feed c o n s u m p tion were n o t significant. Also, n o n e of t h e interactions of diet with o t h e r main variables were significant for feed c o n s u m p t i o n . T h e HW pullets c o n s u m e d significantly more feed t h a n t h e LW pullets, and n o r m a l pullets c o n s u m e d significantly m o r e feed than their dwarf siblings. This would be expected from t h e differences in b o d y size. Egg Production and Shell Thickness. Means and standard deviations for percentage hen-day p r o d u c t i o n of n o r m a l eggs were 59 ± 15 for t h e HW line and 52 ± 18 for t h e LW line with t h e difference b e t w e e n lines significant. Corre-
TABLE 1 .—Comparisons3- between dwarf and normal pullets for body weight and shank length at various ages by line and diet HW line
LW line
Age (days)
High diet
Low diet
High diet
Low diet
Body weight 140 168 196 224 252 266 308
65 68 68 68 67 68 68
69 73 69 71 68 68 66
60 60 55 51 50 50 48
70 64 59 50 49 48 47
Shank length 168 224 266
75 77 77
77 76 77
68 67 65
68 65 65
(Dwarf/normal) X 100.
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 5, 2015
d u c t i o n of n o r m a l eggs. E x t r a calcified, d o u b l e yolked, and total defective eggs (all oviposits o t h e r t h a n n o r m a l eggs) were considered as t h e percentage of n o r m a l eggs and converted t o arc sin v % prior t o analysis. When t h e r e were less t h a n 5 0 observations per pullet, t h e percentages were transformed t o F r e e m a n - T u k e y arc sines (Mosteller and Y o u t z , 1 9 6 1 ) . Shell thickness was measured for all eggs laid during a period of three consecutive days when t h e pullets reached 2 4 5 days of age, and t h e mean value for each individual pullet was used in analysis. Data were analyzed b y analysis of variance with lines, diets, and dwarf-nondwarf as fixed effects. T h e statistical m o d e l was: Y;. k i = (X + L; Dj + G k + (LD)ij + ( L G ) i k + ( D G ) j k + ( L D G ) ; j k + ejjk) where i = 1, 2 lines, j = 1, 2 diets, k = 1, 2 dwarf-nondwarf, and 1 = 1 , 2 . . . 2 0 individuals per line-diet-dwarf subclass (4 blocks for feed c o n s u m p t i o n analysis).
327
DIET AND DWARF PHENOTYPE
FIG. 1. Interactions of pullet's genotype with line and with diet for percentage hen-day production of normal eggs.
F 320 3 co 310 CK
hi T
300
T" V-
290
\
m
CO
280
t
HW LINE
LW LINE
FIG. 2. Interaction of pullet's genotype with line for shell thickness (Mm).
inconsistent results obtained by other investigators (Merat, 1972; Silber and Merat, 1974; Guillame, 1976). These data also provide additional evidence that the nutritional requirements of dwarf chickens are quite different from those of their normal siblings. This is not unexpected. Although the physiological basis of dwarfism is poorly understood, phenotypic manifestations of dwarfism are well documented. A characteristic hypothyroidism associated with dwarfism was observed by several investigators (reviewed by Guillame, 1976). Dwarfs have significantly lower levels of blood glucose, total lipids, cholesterol, and free amino acids in their muscles when compared with normal chickens (Guillame, 1972). The dw gene also results in enhanced glycogen and fat storage (Grandhi et al., 1975; Guillame, 1976). Lipogenesis is stimulated and lipolysis inhibited by dw (Touchburn and Blum, 1972), and protein metabolism is altered by dwarfism (Wood et al., 1971; Guillame, 1972; Brown et al., 1972). It was also postulated that dw influences the basic mechanisms controlling appetite (Cherry et al., 1977). Despite these physiological differences, all of which could conceivably affect nutrient requirements, the relationship between diet and the reproductive performance of dwarf pullets is poorly understood. Protein and caloric requirements were evaluated by Guillame (1969, 1971), Arscott and Bernier (1970), Leclercq and Blum (1971), Summers (1971), Quisenberry (1972), and Waldroup and Hazen (1975, 1976). Dwarfs generally appeared to require
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 5, 2015
sponding percentages for the high diet were 58 ± 15, and for the low diet 53 ± 18 with the differences again significant. Of interest are the significant dwarf-nondwarf interactions with line and diet (Fig. 1). The HWD pullets produced more normal eggs than their nondwarf siblings, while the egg production of the LWD pullets was severely depressed. There were no differences in the percentage egg production of normal pullets due to diet, but the egg production of the dwarf pullets fed the low diet was considerably less than those fed the high diet. There were no significant differences between diets for shell thickness. Means and standard deviations were 315 ± 25 jUm for the HW line and 297 ± 28 Mm for the LW line with the difference being significant. Also, the shells of eggs from normal pullets were significantly thicker than those from dwarf pullets (310 ± 23 flmvs. 302 ± 30 Mm). The only significant first order interaction between variables for shell thickness was for line X dwarf-nondwarf (Fig. 2). Values were similar for normal pullets from both lines, while the shells of eggs from the LWD pullets were considerably thinner than those from the HWD pullets. This observation is consistent with that of Reddy and Siegel (1977). Furthermore, the significant diet X line x dwarf-nondwarf interaction demonstrates the involvement of diet in this phenomenon. The feeding of the high diet to LWD pullets partially prevented the reduction in shell thickness (mean = 292 /mi)- This was consistent with our previous observation of an increase in egg shell weight, expressed as a percentage of egg weight, from feeding the high diet to LWD pullets (Cherry et al., 1977). This divergence in response between the HW and LW lines as a result of dw and diet may explain the
328
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Defective Eggs. Introduction of the dw gene into certain populations of chickens reduces the frequency of abnormal eggs (Jaap and Mohammadian, 1969; Jaap, 1971; van Middelkoop, 1973). Conversely, this gene provokes the opposite effect in stocks with optimum ovarian activity (Reddy and Siegel, 1977). The results of the present experiment appear to substantiate these observations. Moreover, it appears that the incidence of defective eggs laid by dwarf pullets varies with the diet fed. The % of extra-calcified eggs laid by pullets of the LW line was negligible (.02%), whereas HWD pullets laid a significantly lower percentage of extra-calcified eggs than their nondwarf sisters (.44% vs. 1.45%). No incidence of double yolked eggs was recorded for either dwarf or nondwarf pullets in the LW line. HWD pullets laid only .45% double yolked eggs while 2.54% of the eggs laid by HWN pullets were double yolked. Diet had no apparent effect on the incidence of either extra-calcified or double yolked eggs. As anticipated from previous work (Reddy and Siegel, 1977), dwarfism reduced the incidence of total defective eggs in the HW line and increased their incidence in the LW line. The
8r PHWN
16-
1
LOW DIET
DHWD
HIGH DIET
FIG. 3. Interaction of pullet's genotype with diet for percentage defective eggs oviposited.
significant diet X line X dwarf-nondwarf interaction, however, indicates that these responses deviate with diet (Fig. 3). The LWD pullets receiving the high diet did not lay any more defective eggs than did their normal siblings. When fed the low diet, however, the LWD pullets produced substantially more defective eggs than did their counterparts. This suggests that a nutrient deficiency may be involved in the increased incidence of defective eggs in this population. Opposite tendencies were observed in the HW line where the high diet increased the percentage of defective eggs laid by dwarf pullets while reducing their incidence in nondwarf pullets. These observations provide further evidence that the phenotypic expression of the dw gene is modified by its background genome (French and Nordskog, 1973; Jaap and Forssido, 1976; Reddy and Siegel, 1977) and by diet (Cherry et al., 1977). Dwarf pullets with diverse genetic backgrounds apparently require different diets for the maximum realization of their genetic potential. Additional studies are needed to identify and more precisely define the requirements of the specific nutrients involved. REFERENCES Arscott, G. H., and P. E. Bernier, 1970. Proteins and amino acid needs of the mini hen. Proc. 5th Ann.
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diets with more protein and low calorie-to-protein ratios than do nondwarf chickens, however, these higher nutrient requirements have usually been observed with egg laying dwarf stocks. Guillame (1976) concluded that meattype dwarf strains did not require a special diet. Similarly, dwarf Leghorn-type strains appear to require a higher percentage of dietary calcium (Arscott et al., 1961; Bernier and Arscott, 1972; Austic et al., 1977), while there is little evidence that heavy dw lines need additional calcium (Prod'homme and Merat, 1969; Guillame, 1976). The increased egg production resulting from feeding the high diet to the HWD as well as to the LWD pullets in this experiment indicates that meat-type dwarf stocks also require different dietary regimes for maximum egg production. This observation, along with the previous report that diet attenuated the depressive effect of dw on egg weight (Cherry et al., 1977), indicates that the development of proper nutritional programs will improve the performance of dwarf pullets. Improved performance could give the dwarf broiler breeder mother a competitive advantage over nondwarf hens in the commercial production of hatching eggs-
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restriction during the growing period on the Pacific Northwest Animal Nutr. Conf. Richland, performance of dwarf breeders. World's Poultry Washington, pp. 52—59. Sci. J. 27:288-289. Arscott, G. H., P. Rachapaetayakom, and P. E. Bernier, 1961. Observations on gross requirements Merat, P., 1972. Quelques effects du gene dw sur la for certain nutrients in dwarf White Leghorn hens. pointe et sur la qualite dws oeufs. Ann. Genet. Sel. Poultry Sci. 40:1372-1373. Anim. 4 : 2 1 7 - 2 2 3 . Austic, R. E., D. J. Baker, and R. K. Cole, 1977. Mosteller, F., and C. Youtz, 1961. Tables of the Susceptibility of a dwarf strain of chickens to Freeman-Tukey transformation for the binomial rickets. Poultry Sci. 56:285-291. and poissan distribution. Biometrika48:433—440. Bernier, P. E., and G. H. Arscott, 1972. Fifteen years Prod'homme, J., and P. Merat, 1969. Etude d'un gene of observation on the dwarf gene in the domestic de nanisme lie au sexe chez la poule III. Consomfowl. Ann. Genet. Sel. Anim. 4:183-215. mation alimentaire et production suivant la teneur Brown, R. G., A. S. Wood, B. S. Reinhart, and D. en calcium de la ration. Ann. Genet. Sel. Anim. Longworth, 1972. Differences in amino acid activa1:135-145. tion found between dwarf and non dwarf White Quisenberry, J. H., 1972. High density diets for dwarf Leghorn chickens. Poultry Sci. 51:1067—1068. layers. Ann. Genet. Sel. Anim. 4:271-279. Cherry, J. A., M. Z. Ghitelman, and P. B. Siegel, 1977. Reddy, P. R. K., and P. B. Siegel, 1976. Selection for The relationship between diet and dwarfism in body weight at eight weeks of age. 11. Ovulation diverse genetic backgrounds on egg parameters. and o v i p o s i t i o n p a t t e r n s . P o u l t r y Sci. Poultry Sci. (In press.) 55:1518-1530. French, H. L., and A. W. Nordskog, 1973. PerformReddy, P. R. K., and P. B. Siegel, 1977. Selection for ance of dwarf chickens compared with normal body weight at eight weeks of age. 14. Effects of small-bodied c h i c k e n s . Poultry Sci. t h e s e x - l i n k e d dwarf gene. Poultry Sci. 52:1318-1328. 56:1004-1013. Grandhi, R., R. G. Brown, and J. D. Summers, 1975. Silber, J., and P. Merat, 1974. Etude genitique de la A study of thyroid activity in dwarf and non-dwarf ponte d'oeufs mous chez la poule. XV World's female chicks during key physiological states of Poultry Cong., New Orleans, pp. 491—493. growth and reproduction. Poultry Sci. 54:47—53. Summers, J. D., 1971. Nutrition of the dwarf layer. Guillame, J., 1969. Consequences de l'introduction du World's Poultry Sci. J. 27:287-288. gene de nanisme dw sur ['utilisation alimentaire chez le poussin femelle. Ann. Biol. Biochem. Touchburn, S. P., and J. C. Blum, 1972. Effects of the genes for dwarfism (dw) and naked neck (Na) on Biophys. 9:369-378. chick growth and lipid metabolism. Ann. Genet. Guillame, J., 1971. Some nutritional and physiological Sel. Anim. 4:311-316. traits of the dw chick. World's Poultry Sci. J. van Middelkoop, J. H., 1973. Influence of the dwarf 27:284-285. gene on yolk production and its consequence for Guillame, J., 1972. Donnees complementaires sur normal egg laying of White Plymouth Rock pullets. les besoins nutritionnels de la reproductrice Archiv. fur Geflugelkunde 5:192-196. naine Vedette. Ann. Genet. Sel Anim. 4:281 — van Middelkoop, J. H., and P. C. M. Simmons, 1970. 295. Abnormal eggs due to the presence of two eggs in Guillame, J., 1976. The dwarfing gene dw: Its effect the uterus at the same time. Tijdschr. Diergeneesk. on anatomy, physiology, nutrition, management. 95:21-23. Its application in poultry industry. World's Poultry Waldroup, P. W., and K. R. Hazen, 1975. Energy needs Sci. J. 32:285-304. of dwarf (dw) broiler breeder hens. Poultry Sci. Jaap, R. G., 1971. Selection for body size and repro ; 54:1931-1935. ductive fitness in chickens. World's Poultry Sci. J. Waldroup, P. W., and K. R. Hazen, 1976. A compari27:372-379. son of the daily energy needs of the normal and Jaap, R. G., and T. Forssido, 1976. Exceptionally dwarf b r o i l e r breeder hen. Poultry Sci. large eggs from dwarf leghorn pullets. Poultry Sci. 55:1383-1393. 55:1120-1121. Jaap, R. G., and M. Mohammadian, 1969. Sex-linked Wood, A. S., B. S. Reinhart, G. Rajaratnam, and J. D. dwarfism and egg production in broiler dams. Summers, 1971. A comparison of the blood Poultry Sci. 48:344-346. constituents of dwarf versus non-dwarf birds. Leclercq, B., and J. C. Blum, 1971. Effects of nutrient Poultry Sci. 50:804-807.