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Lipid and Energy Metabolism in Chicks Affected by Dwarfism (dw) and Naked-Neck (Na)12
Lipid and Energy Metabolism in Chicks Affected by Dwarfism (dw) and Naked-Neck (Na)1'2 S. P. TOUCHBURN3 Department of Poultry Science, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 and J. GUILLAUME, B. LECLERCQ, and J. C. BLUM Station de Recherches Avicoles, Centre de Recherches de Tours, Institut National de la Recherche Agronomique, 37380 Nouzilly, France
ABSTRACT In two experiments, sister pairs of chicks, one dwarf (dw) and one nondwarf (Dw+), were reared in individual cages to 5 weeks of age. Chicks carrying the sex-linked recessive dw gene were identified at hatching by the closely linked fast feathering gene (k). The dwarf chicks showed a 27% reduction in weight gain, a reduced body temperature, increased carcass content of lipid, and increased lipid , 4 C activity from injected ""C-labeled acetate. The augmented accumulation of carcass lipid in the dwarf chicks was shown to be a result of increased lipogenesis and decreased energy expenditure. An autosomal dominant gene for naked-neck (Na), present in half of the pairs of chicks, also caused increased lipogenesis. Naked-neck birds showed increased energy expenditure in a cool environment and perhaps a greater flexibility of body temperature regulation. An interaction between the dw and Na genes was apparent under cool environmental conditions and may have been due to a suppression by the dw gene of the Na gene's effect on thermoregulation, possibly by slowing down lipid degradation. (Key words: lipid synthesis, energy metabolism, dw, Na, thermoregulation) 1980 Poultry Science 59:2189-2197 INTRODUCTION
Poultry breeders in France have exploited the use of a sex-linked recessive gene for dwarfism (dw) to provide broiler-breeder hens which, when crossed with nondwarf (Dw+) males, yield normal broiler progeny. The dwarf phenotype appeared in the experimental flock at Jouy-en-Josas France, and was reported by Merat (1969). Considered to be the same as that first discovered by Hutt (1953), it caused a reduction in body weight of 30% in females and 40% in males, shortened the long bones, and reduced the number and weight of eggs produced
'This work was accomplished while the senior author was on leave from the Ohio Agricultural Research and Development Center. 2 Approved for publication as Journal Article No. 143-79 of die Ohio Agricultural Research and Development Center, Wooster, OH 44691. 3 Present address: Department of Animal Science, Macdonald Campus of McGill University, Ste. Anne de Bellevue, P.Q. Canada H9X ICO.
by 10%. Jaap and Mohammadian (1969) reported that the dw gene reduced the rate of yolk deposition without reducing the rate of egg production in birds in which mature body weights were considerably greater than those of Merat's flock. The dwarf hens, by virtue of their reduced size, also introduce considerable economies of feed and space into the production of commercial broiler chicks, especially if feed intake is restricted. Guillaume (1969) showed that introduction of the dw gene in chickens not only reduced growth but also reduced feed utilization efficiency and increased the energy storage in the body. On a weight basis the dwarf pullets consumed almost as much feed as their normal sisters. Leclercq et al. (1970) reported that the feed consumption of Cornish x White Rock commercial dwarf pullets was practically independent of the energy level of the diet and that they could withstand severe restriction of energy intake without ill effects. The original intention of the current work was to investigate lipid metabolism in normal chicks and in chicks in which this function was
2189
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(Received for publication October 26, 1979)
TOUCHBURN ET AL.
2190
altered or perturbed. The dwarfing gene appeared to be an excellent tool for this purpose. Another gene, an autosomal dominant gene for naked-neck (Na), entered the experimental design inadvertently and added another dimension to the research. Some of the current research has been reported previously (Touchburn, 1971a,b; Touchburn and Blum, 1971, 1972). A review on the nature and practical applications of the dw gene was presented by Guillaume(1976). EXPERIMENTAL PROCEDURES
The diets fed were based on corn, soybean meal and fish meal (Table 1). They were
Individual body weights and feed consumption data were recorded weekly. Oxygen consumption and carbon dioxide production were measured for each chick on two or three occasions between the ages of 3 and 5 weeks and were taken between 0800 and 1200 hr so that the birds were in the absorptive state. For this measurement the chick was placed for .5 hr in a flow-through chamber equipped for measurement of the differentials between entering and exhaust air for both oxygen and carbon dioxide contents. The differential for oxygen, recorded potentiometrically, was detected by paramagnetic sensing. Infrared absorption was used to measure the absolute levels of carbon dioxide. All measurements were corrected for the effect of atmospheric pressure on flow rate. The instruments employed were: for O2, Oxygor-1; for C 0 2 , Unor-S-2. They were manufactured by H. Maihak-AG., 2000 Hamburg 39, West Germany, and sold in France by Schlumberger Controle Industriel, 92140 Clamart, France. At 5 weeks of age body temperature was measured cloacally toward the end of the 4 hr fast period. Approximately 1.5 hr after they had been refed on the final day, each chick was injected intraperitoneally with 10 /iCi of 14 C-labeled acetate in 1 ml of .9% sodium chloride solution. In Experiment 1, sodium acetate-2- 14 C (Specific activity 20.7 /xCi per /UM) was used; in Experiment 2, sodium acetate-l- 1 4 C (specific activity of 22.7 H& per /iM) was used. In Experiment 1, five sister pairs of chicks were killed by exsanguination at intervals of .5, 1, 2, and 3 hr postinjection. In Experiment 2, they were all killed 2 hr after radioisotope
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To provide the experimental chicks and to identify dwarf andnondwarf chicks at hatching, special matings were made using cocks from the experimental flock at Jouy-en-Josas. These sires were heterozygous for dwarfism (Dw+dw) and for early feathering rate (Kk) and contained chromosomes Dw+K or dwk so that either dominant or recessive genes were transmitted together. By chance, three of the four sires also carried the dominant autosomal gene for naked-neck (Na) The cocks were mated by artificial insemination with females of a commercial dwarfed broiler strain, JA57, of the Institut National de la Recherche Agronomique which carried the recessive genes dw and k. At time of hatching the chicks were sexed by the vent method and the females were chosen for these studies. Females, rather than males were used because Ricard (1971) had observed that heterozygous male chicks were 3% smaller than their homozygous brothers, indicating incomplete recessiveness of the dw gene. The females, being hemizygous dw- or Dw+-, should be expected to yield more clearcut differences. They were separated by rate of early feathering as indicated by relative lengths of primary and covert feathers. Classification by feathering rate was verified at 5 weeks of age—the chicks classified as slow feathering being nondwarfs and those classified as fast feathering being dwarfs. They were further segregated for the normal neck or naked neck condition. Full sister pairs, one dwarf and one nondwarf, were placed in adjacent individual wire-floored cages in electrically heated battery brooders in a heated room. The first experiment comprised 19 pairs, 11 of which were normal neck and 8 naked neck pairs. The second experiment included 5 to 8 normal neck or naked-neck pairs on each of two diets.
calculated to provide 3.03 kcal (12.7 kj) ME/g. The analyzed crude protein contents of diet A were 18.6% and 19.2% in Experiments 1 and 2, respectively. Diet B, fed only in Experiment 2, contained 24.9% crude protein. These relatively high energy diets were intended to stimulate lipogenesis. The greater protein content of diet B was an attempt to satisfy the possibly increased protein requirement of the dwarf chicks. Feed and water were provided ad libitum, except that from 2 to 5 weeks of age the chicks were deprived of feed for 4 hr daily from 1000 to 1400 hr. This was intended to condition the birds so that they would eat at a maximum rate immediately preceding the injection of 14 C-labeled acetate on the final day of the trial.
LIPID METABOLISM IN DWARF AND NAKED-NECK CHICKS TABLE 1. Composition of experimental chick diets
2191
RESULTS
Out of 19 pairs of dwarf:nondwarf (Dw+ •. dw) sisters in Experiment 1 and 24 pairs in Experiment 2, one chick exhibiting fast feathering turned out not to be a dwarf according to (%) weight gain, carcass lipid content, and all other Ground yellow corn 63.15 52.2 metabolic parameters measured. This bird Soybean meal (49% protein) 26.5 36.5 undoubtedly represents a case of crossingNorwegian herring meal (70% protein) 1.0 1.0 over of the chromosome near the k locus Peanut oil 3.0 4.0 which, according to Hutt (1960), occurs at an Dicalcium phosphate 2.5 2.5 average frequency of 7%. The data for this pair Ground limestone 1.5 1.25 were discarded (Experiment 1). .5 .5 Sodium chloride The mean values for body weight gain and DL-methionine .15 .35 1.5 1.5 Vitamin premix a feed conversion to 5 weeks of age are presented Trace mineral premix 0 .2 .2 in Table 2. The weight gain of dwarfs was Total 100.00 100.00 depressed (P<.001) and averaged roughly 73% of normal. Their feed conversion was poorer Crude protein (analyzed, N X 6.25) 19.2 24.9 (P<.02) than that of their nondwarf sisters kcal/kg 3028 3017 except when they were fed diet A in Experiment kj/kg 12672 12626 2. The Na gene reduced mean body weight in two instances: the nondwarf birds fed Diet A in vitamin premix provides per kilogram of diet: Experiment 1 (P<.3) and the nondwarf birds vitamin A, 8,000 IU; vitamin D 3 , 1,000 ICU; vitamin fed diet B in Experiment 2 (P<.01). The Na E, 2.5 IU; vitamin K, 2 mg; riboflavin, 10 mg; niacin, gene had no apparent effect on feed conversion. 20 mg; calcium pantothenate, 8 mg; cyanocobalamin, 10 Mg; choline chloride, 1250 mg; folacin, 1.5 mg; Feeding the higher protein diet B had a marked effect of improving the feed conversion over butylated hydroxytoluene, 25 mg. that on diet A in the nondwarf birds only. Trace mineral premix provides per kilogram of The carcass lipid content and the radioactivity diet (mg): manganese, 86.6; zinc, 77.2; iron, 28; copper, 2.8; iodine, 1.4; cobalt, .27. of carcass and liver lipids are presented in Table 3. When carcass lipid content was expressed as a percent of body weight, the dwarf birds contained almost half again as much fat as their injection. The livers were removed, frozen, and normal sisters. These differences were significant stored at —20 C for future analysis. The car- in all instances (P<.05 to .001). Carcass lipid casses were weighed, frozen, then later ground content was slightly reduced by feeding diet B. and freeze dried. Total lipids were extracted In Experiment 1, extreme variability was from duplicate samples of the lyophilized encountered in carcass lipid 1 4 C content; when carcasses by the method of Folch et al. (1957). coupled with the limited number of animals The 1 4 C activities of duplicate aliquots of used, no differences were found in relation to carcass and liver lipid were measured in a liquid time elapsed after injection. For example, scintillation counter. The quantities of lipid and maximum values were obtained as early as .5 hr the 1 4 C content were related to the fresh-killed postinjection in some cases. As a consequence, body weight. The data were analyzed using the lipid- 14 C values for Experiment 1 represent Students t test: the method of paired com- the means over all intervals. For Experiment 2 parisons for the effect of dv> gene (sister pairs), the postinjection interval was held constant at the simple t test for the Na gene (comparison of 2 hr. The specific radioactivities of both carcass two means). The likelihood of obtaining and liver lipids showed no significant differences significant differences in the latter comparisons due to treatment. There was, however, a was poor because of the limited numbers of consistent finding of higher specific activities in animals and of the variability among families the lipids of the dwarf birds. due to the heterogeneity of the sires. Under In Experiment 1, the naked-neck birds these conditions, probability levels of .1 and .2 showed a marked increase in specific activity of were taken as indicating tendencies, particularly carcass lipids and a marked decrease for that of when all of the traits were considered in relation liver lipids. The radioactivity in total carcass to each other. lipids in this experiment appeared to be inDiet A
Diet B
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TOUCHBURN ET AL.
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creased by the Na gene only in the dwarf birds. Birds fed diet A in Experiment 2 showed a slight increase in specific activity of carcass and liver lipid. The total radioactivity in the total carcass lipids was significantly increased by the presence of the Na gene. The feeding of diet B elimated the response of the Na gene and tended to minimize the response of the dw gene in carcass lipid radioactivity. The presence of the dw gene depressed (P<.05 to .001) body temperature when measured at 5 weeks of age (Table 4). Feeding the high protein diet caused an increase in body temperature (P<.001) in the nondwarf birds. The respiratory quotient (C0 2 expired :C>2 consumed) was increased (P<.05) in the dwarf birds as compared to their nondwarf sisters, indicating that the dwarfs were oxidizing more carbohydrate and less lipid. This parameter was not discernibly affected by either the Na gene or the feeding of diet B. The mean values for resting metabolic rate were much higher in Experiment 1 than in Experiment 2. In both experiments the dwarfs had consistently lower values than their nondwarf sisters. The differences were significant in most instances in spite of the limited number of comparisons. The naked-neck birds were completely consistent in showing a marked increase in resting metabolic rate over that of their non-nakedneck counterparts. This effect was most pronounced in the nondwarf birds of Experiment 1. Based on dietary intake and carcass analyses for lipid and protein content, a thermochemical efficiency value was calculated [(calories retained/calories ingested) X 100, Table 5)]. The dwarf birds had an increased (P<.01) thermochemical efficiency. The Na gene appeared to reduce this efficiency only in the first experiment and most markedly in the nondwarf birds. Feeding the higher protein diet, diet B, appeared to reduce thermochemical efficiency of the dwarf birds only. These dwarf birds fed diet B, however, were still superior (P<.001) in energy retention to their nondwarf sisters consuming the same diet. Nitrogen retention (Table 5) was poorer (P<.05) for the dwarf birds fed diet A in the first experiment. In the second experiment for the birds fed diet B, the dwarf birds again showed slightly poorer nitrogen retention, but the differences were not significant. On diet A in this experiment the dwarf birds showed slightly superior nitrogen retention values over those of their normal
na Na P<
Thousand dpm in total carcass lipid
na Na
Specific activity (dpm/mg) of liver lipid
na Na
Specific activity (dpm/mg) of carcass lipid
na Na P<
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1977 2089
1548 1137
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TABLE 3. Effect of genes for dwarfism (dw) and naked neck (Na) and of diet on carcass lipid content, to activities of carcass and liver lipids from injected acetate- ' 4 C
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No. of pairs
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Experiment 1
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.91 .87
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TABLE 4. Effect of genes for dwarfism (dw), naked neck (Na), and of diet on body temperature, respi metabolic rate of chicks (3 to 5 weeks of age).
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LIPID METABOLISM IN DWARF AND NAKED-NECK CHICKS
2195
sisters. The Na gene exerted no apparent effect on this trait. Feeding the higher protein diet resulted in a marked decrease in the percentage nitrogen retention. DISCUSSION 3
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Experiment 1, ended January 21, was conducted during very cold weather while Experiment 2, which ended March 23, was conducted during warmer weather. Although the chicks were housed in a heated building in heated battery brooders, the seasonal difference was discernible in the room and appears to have reduced the ambient temperature during the first experiment below a critical point, which greatly influenced the results. The Na gene was observed to cause a denudation far beyond a simple lack of neck feathers. Greenwood (1927) found that birds carrying the Na gene had no feathers in the intertract spaces (apteria), almost no ventral feather tract, and a reduced lateral breast tract. The naked neck birds were, thus, much more susceptible to the cooler conditions existing in Experiment 1. The reduced growth and feed efficiencies shown by the dwarf chicks in this study (Table 2) generally confirm previous observations on growth (Hutt, 1953; Merat, 1969) and feed efficiency (Guillaume, 1969). In the one exception, when the dwarf birds fed diet A in the second experiment showed a feed conversion slightly superior to their nondwarf sisters, it was paralleled by unexpectedly high values for nitrogen retention (Table 5). No explanation is apparent for this deviation from the general pattern of response. The nondwarf birds fed diet B showed feed conversions superior to those fed diet A. This was to be expected because the calorie-protein ratio of diet A was deliberately wider than optimal. The dwarf birds gained more weight on diet B and the ratio of their weight to that of their nondwarf sisters was greater on diet B than on diet A. This response had been reported by Guillaume (1969) and observed in several subsequent experiments. Thus, the presence of the dw gene appears to result in an increased protein requirement. This conclusion was recently supported by Cherry and Siegel (1978), who measured the effect of the dw gene in heavy and light weight birds. However, it was contradicted in a subsequent experiment (Cherry and Siegel, 1979). The presence of the dw gene increased the specific activity of carcass and liver lipids in all
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TOUCHBURN ET AL.
The metabolic responses to diet B closely resemble those on diet A in the cool environment, suggesting that dietary calorie-protein ratio played an important role in relation to energy needs. The latter effect was true for the nondwarf birds but had only a moderate effect on the dwarf birds. This tends to confirm the earlier observations by Leclercq et al. (1970) that the feed consumption of dwarfs was almost independent of the energy level of the diet. Likewise, Simon (1972) observed that even after a 36-day training period initiated at 19 days of age, dwarf cockerels, in contrast to their normal brothers, showed no signs of adaptation to a regimen of 2 days of fast followed by 4 days of repletion feeding. Dwarf birds showed an energy metabolism considerably altered from normal (Table 4).
Compared to their nondwarf sisters, the dwarfs had significantly lower body temperatures and resting metabolic rates which indicate a reduced metabolic activity. The significantly greater respiratory quotient indicates that relatively more carbohydrate and less lipid was being oxidized by the dwarf birds. Thus, the dw gene appeared to spare or conserve depot lipids. In comparison with their normal-feathered counterparts the naked-neck birds showed elevated resting metabolic rates in all instances. This difference was most pronounced in the nondwarf birds under the influence of the cooler environment of Experiment 1. The naked-neck dwarf birds, however, were much less sensitive in terms of metabolic response to environmental temperature. The dwarfs were perhaps incapable of mobilizing and subsequently oxidizing their excesses of stored lipid to maintain body temperatures at the same level as their nondwarf sisters. This reduced lipid mobilization and oxidation is definitely an important factor contributing to the obesity in the dwarf chick. Growth hormone is known to enhance fatty acid mobilization and metabolism (Young, 1945; Goodman and Knobil, 1961; Goldman and Bressler, 1967). In fact, lipid may be an absolutely required source of energy for the growth process (Greenbaum, 1953). The apparent inability of dwarf chicks to utilize stored lipid suggests that the dwarfism caused by the dw gene results from a lack of growth hormone or a reduction in its function. The inferior nitrogen retention of the dwarf chicks could also be explained by an insufficiency of growth hormone since this hormone definitely promotes protein accretion (Young, 1945). The significantly greater values for thermochemical efficiency exhibited by the dwarf chicks confirm the earlier results of Guillaume (1969). The current work has shown that this enhanced retention of ingested energy by the dwarf chicks was mediated through a definitely reduced resting metabolic rate, lower body temperature, and a diminished utilization of depot fat. The naked-neck birds showed a definitely inferior thermochemical efficiency only in the cool environment of Experiment 1. This undoubtedly represents the greater heat loss to the surrounding air by these partially naked birds. In an environment close to thermoneutrality for the chick (Experiment 2) the Na gene was observed to mediate an increase in
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cases after injection with 14 C-labeled acetate. This suggests that the gene is associated with increased lipid synthesis from acetate. The lack of statistically significant differences, however, leaves this conclusion open to question. The Na gene was also associated with increased lipid synthesis from acetate under certain conditions as shown by the values for specific activity of carcass and liver lipids of birds fed diet A in Experiment 2. The greater total radioactivity in total carcass lipids reflecting increased lipid synthesis was associated with the dw gene in practically all instances and with the Na gene in all but the nondwarf chicks fed diet A in Experiment 1 and diet B in Experiment 2. In the first experiment, under cooler conditions, the effects of the Na gene on specific activities of carcass and liver lipids are opposite. Carcass lipid specific activity was elevated in the nakedneck birds while that of liver was reduced. This was probably due to a higher rate of transport of synthesized lipid from the liver to the tissues in the naked-neck chicks in the cool environment. In the present instance the lack of increased radioactivity in total carcass lipids of the naked-neck chicks may reflect an increased rate at which the acetate or the synthesized lipids are oxidized to maintain body temperature in these partially denuded birds. In this first experiment, the increased radioactivity in total carcass lipids of the naked-neck dwarf birds suggests that the dw gene had the effect of inhibiting the use of stored lipid as a source of energy for maintaining body temperature and/or enhancing the incorporation of R e labeled acetate into lipid.
LIPID METABOLISM IN DWARF AND NAKED-NECK CHICKS
ACKNOWLEDGMENTS The senior author wishes to acknowledge the generosity of the Ministry of Agriculture of France for the financial support which helped make this work possible and Claude Calet, then Director of the Poultry Research Center of Tours, for the opportunity to work there. Thanks are also expressed to W. L. Bacon, R. G. Jaap, and E. C. Naber of Ohio for helpful criticisms of the manuscript. REFERENCES Cherry, J. A., and P. B. Siegel, 1978. Dwarfism in diverse genetic backgrounds:diet-egg production relationships. Poultry Sci. 57:325-329. Cherry, J. A., and P. B. Siegel, 1979. Dwarfism in diverse genetic backgrounds 3. Effects of dietary protein. Poultry Sci. 58:991-993. Folch, J., N. Lees, and Ch. H. Sloane-Stanley, 1957. A simple method for isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226:497-509. Goldman, J. K., and R. Bressler, 1967. Growth hormone stimulation of fatty acid utilization by adipose tissue. Endocrinology 81:1306—1310. Goodman, H. M., and E. Knobil, 1961. Growth hormone and fatty acid mobilization. The role of the pituitary, adrenal and thyroid. Endocrinology 69:187-189. Greenbaum, A. L., 1953. Changes in body composition
and respiratory quotient of adult female rats treated with purified growth hormone. Biochem. J. 54:400-407. Greenwood, A. W., 1927. The hackleless fowl. Proc. Roy. Phys. Soc. (Edinburgh) 21:123-129. Hutt, F. B., 1949. Pages 117-119 in Genetics of the fowl. McGraw Hill Book Co., Inc. New York NY. Guillaume, J., 1969. Consequences de 1'introduction du gene de nanisme An sur l'utilisation alimentaire chez le poussin femelle. Ann. Biol. Anim. Bioch. Biophys. 9:369-378. Guillaume, J., 1976. The dwarfing gene dw: its effects on anatomy, physiology, nutrition and management. Its application in poultry industry. World's Poultry Sci. J. 32:285-304. Hutt, F. B., 1953. Sex linked dwarfism in the fowl. Genetics 38:670. Hutt, F. B., 1960. New loci in the sex chromosome of the fowl. Heredity 15:97-110. Jaap, R. G., and M. Mohammadian, 1969. Sex linked dwarfism and egg production of broiler dams. Poultry Sci. 48:344-346. Leclercq, B., J. Guillaume, and J-C. Blum, 1970. Donnees sur les besoins alimentaires de la reproductrice naine Vedette INRA (dw) durant les periodes de croissance et de ponte. I. Periode de croissance. Proc. 14th World's Poultry Cong., (Madrid) 2 : 7 8 7 - 7 9 5 . Me'rat, P., 1969. Etude d'un gene de nanisme lie au sexe chez la poule. I. Description sommaire et performances. Ann. Genet. Sel. Anim. 1:19—26. Ricard, F. H., 1971. Croissance et caracteristiques de carcasse de poulets issus de poules normales ou naines (dw). Ann. Genet. Sel. Anim. 3:377—393. Simon, J., 1972. Influence du gene de nanisme (dw) du gene cou nu (Na) et du rythme d'alimentation sur la croissance et le comportement alimentaire du poulet. Ann. Gene't. Sel. Anim. 4:305-310. Touchburn, S. P., 1971a. A study of lipogenesis using 14 C-labeled acetate in full sister pairs of normal and dwarf chicks. World's Poultry Sci. J. 27: 285-286. Touchburn, S. P., 1971b. Etude de la lipogenese a l'aide d'un acetate marqe au 1 4 C chez des paires de soeurs normales et naines. Ann. Genet. Sel. Anim. 3:386. Touchburn, S. P., and J-C. Blum, 1971. Action des genes de nanisme (dw) et de cou nu (Na) sur la croissance du poussin et le metabolisme lipidique. Ann. Genet. Sel. Anim. 3:393. Touchburn, S. P., and J-C. Blum, 1972. Effects of the genes for dwarfism (dw) and naked neck (Na) on chick growth and lipid metabolism. Ann. Genet. Sel. Anim. 4:311-316. Young, F. G., 1945. Growth and diabetes in normal animals treated with pituitary (anterior lobe) diabetogenic extract. Biochem. J. 39:515—536.
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lipid synthesis, and this effect was additive with that of the dw gene so that the naked-neck dwarf chicks showed the greatest incorporation 4 of injected C-labeled acetate into carcass lipid. This augmented lipid synthesis was more obvious under suboptimal temperature conditions (Experiment 1) when it contrasted with a diminished specific radioactivity of carcass lipids shown by the normal neck chicks. Under these conditions the accumulation of lipid was precluded by the increased resting metabolic rates and higher body temperatures sustained by the naked-neck birds. In this case an apparent interaction between the two genes occurred when the dw gene inhibited the effects of the Na gene, preventing the increases in metabolic rate, lipid oxidation, and body temperature.
2197
ABSTRACT In two experiments, sister pairs of chicks, one dwarf (dw) and one nondwarf (Dw+), were reared in individual cages to 5 weeks of age. Chicks carrying the sex-linked recessive dw gene were identified at hatching by the closely linked fast feathering gene (k). The dwarf chicks showed a 27% reduction in weight gain, a reduced body temperature, increased carcass content of lipid, and increased lipid , 4 C activity from injected ""C-labeled acetate. The augmented accumulation of carcass lipid in the dwarf chicks was shown to be a result of increased lipogenesis and decreased energy expenditure. An autosomal dominant gene for naked-neck (Na), present in half of the pairs of chicks, also caused increased lipogenesis. Naked-neck birds showed increased energy expenditure in a cool environment and perhaps a greater flexibility of body temperature regulation. An interaction between the dw and Na genes was apparent under cool environmental conditions and may have been due to a suppression by the dw gene of the Na gene's effect on thermoregulation, possibly by slowing down lipid degradation. (Key words: lipid synthesis, energy metabolism, dw, Na, thermoregulation) 1980 Poultry Science 59:2189-2197 INTRODUCTION
Poultry breeders in France have exploited the use of a sex-linked recessive gene for dwarfism (dw) to provide broiler-breeder hens which, when crossed with nondwarf (Dw+) males, yield normal broiler progeny. The dwarf phenotype appeared in the experimental flock at Jouy-en-Josas France, and was reported by Merat (1969). Considered to be the same as that first discovered by Hutt (1953), it caused a reduction in body weight of 30% in females and 40% in males, shortened the long bones, and reduced the number and weight of eggs produced
'This work was accomplished while the senior author was on leave from the Ohio Agricultural Research and Development Center. 2 Approved for publication as Journal Article No. 143-79 of die Ohio Agricultural Research and Development Center, Wooster, OH 44691. 3 Present address: Department of Animal Science, Macdonald Campus of McGill University, Ste. Anne de Bellevue, P.Q. Canada H9X ICO.
by 10%. Jaap and Mohammadian (1969) reported that the dw gene reduced the rate of yolk deposition without reducing the rate of egg production in birds in which mature body weights were considerably greater than those of Merat's flock. The dwarf hens, by virtue of their reduced size, also introduce considerable economies of feed and space into the production of commercial broiler chicks, especially if feed intake is restricted. Guillaume (1969) showed that introduction of the dw gene in chickens not only reduced growth but also reduced feed utilization efficiency and increased the energy storage in the body. On a weight basis the dwarf pullets consumed almost as much feed as their normal sisters. Leclercq et al. (1970) reported that the feed consumption of Cornish x White Rock commercial dwarf pullets was practically independent of the energy level of the diet and that they could withstand severe restriction of energy intake without ill effects. The original intention of the current work was to investigate lipid metabolism in normal chicks and in chicks in which this function was
2189
Downloaded from http://ps.oxfordjournals.org/ at Gazi Universitesi on May 6, 2015
(Received for publication October 26, 1979)
TOUCHBURN ET AL.
2190
altered or perturbed. The dwarfing gene appeared to be an excellent tool for this purpose. Another gene, an autosomal dominant gene for naked-neck (Na), entered the experimental design inadvertently and added another dimension to the research. Some of the current research has been reported previously (Touchburn, 1971a,b; Touchburn and Blum, 1971, 1972). A review on the nature and practical applications of the dw gene was presented by Guillaume(1976). EXPERIMENTAL PROCEDURES
The diets fed were based on corn, soybean meal and fish meal (Table 1). They were
Individual body weights and feed consumption data were recorded weekly. Oxygen consumption and carbon dioxide production were measured for each chick on two or three occasions between the ages of 3 and 5 weeks and were taken between 0800 and 1200 hr so that the birds were in the absorptive state. For this measurement the chick was placed for .5 hr in a flow-through chamber equipped for measurement of the differentials between entering and exhaust air for both oxygen and carbon dioxide contents. The differential for oxygen, recorded potentiometrically, was detected by paramagnetic sensing. Infrared absorption was used to measure the absolute levels of carbon dioxide. All measurements were corrected for the effect of atmospheric pressure on flow rate. The instruments employed were: for O2, Oxygor-1; for C 0 2 , Unor-S-2. They were manufactured by H. Maihak-AG., 2000 Hamburg 39, West Germany, and sold in France by Schlumberger Controle Industriel, 92140 Clamart, France. At 5 weeks of age body temperature was measured cloacally toward the end of the 4 hr fast period. Approximately 1.5 hr after they had been refed on the final day, each chick was injected intraperitoneally with 10 /iCi of 14 C-labeled acetate in 1 ml of .9% sodium chloride solution. In Experiment 1, sodium acetate-2- 14 C (Specific activity 20.7 /xCi per /UM) was used; in Experiment 2, sodium acetate-l- 1 4 C (specific activity of 22.7 H& per /iM) was used. In Experiment 1, five sister pairs of chicks were killed by exsanguination at intervals of .5, 1, 2, and 3 hr postinjection. In Experiment 2, they were all killed 2 hr after radioisotope
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To provide the experimental chicks and to identify dwarf andnondwarf chicks at hatching, special matings were made using cocks from the experimental flock at Jouy-en-Josas. These sires were heterozygous for dwarfism (Dw+dw) and for early feathering rate (Kk) and contained chromosomes Dw+K or dwk so that either dominant or recessive genes were transmitted together. By chance, three of the four sires also carried the dominant autosomal gene for naked-neck (Na) The cocks were mated by artificial insemination with females of a commercial dwarfed broiler strain, JA57, of the Institut National de la Recherche Agronomique which carried the recessive genes dw and k. At time of hatching the chicks were sexed by the vent method and the females were chosen for these studies. Females, rather than males were used because Ricard (1971) had observed that heterozygous male chicks were 3% smaller than their homozygous brothers, indicating incomplete recessiveness of the dw gene. The females, being hemizygous dw- or Dw+-, should be expected to yield more clearcut differences. They were separated by rate of early feathering as indicated by relative lengths of primary and covert feathers. Classification by feathering rate was verified at 5 weeks of age—the chicks classified as slow feathering being nondwarfs and those classified as fast feathering being dwarfs. They were further segregated for the normal neck or naked neck condition. Full sister pairs, one dwarf and one nondwarf, were placed in adjacent individual wire-floored cages in electrically heated battery brooders in a heated room. The first experiment comprised 19 pairs, 11 of which were normal neck and 8 naked neck pairs. The second experiment included 5 to 8 normal neck or naked-neck pairs on each of two diets.
calculated to provide 3.03 kcal (12.7 kj) ME/g. The analyzed crude protein contents of diet A were 18.6% and 19.2% in Experiments 1 and 2, respectively. Diet B, fed only in Experiment 2, contained 24.9% crude protein. These relatively high energy diets were intended to stimulate lipogenesis. The greater protein content of diet B was an attempt to satisfy the possibly increased protein requirement of the dwarf chicks. Feed and water were provided ad libitum, except that from 2 to 5 weeks of age the chicks were deprived of feed for 4 hr daily from 1000 to 1400 hr. This was intended to condition the birds so that they would eat at a maximum rate immediately preceding the injection of 14 C-labeled acetate on the final day of the trial.
LIPID METABOLISM IN DWARF AND NAKED-NECK CHICKS TABLE 1. Composition of experimental chick diets
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RESULTS
Out of 19 pairs of dwarf:nondwarf (Dw+ •. dw) sisters in Experiment 1 and 24 pairs in Experiment 2, one chick exhibiting fast feathering turned out not to be a dwarf according to (%) weight gain, carcass lipid content, and all other Ground yellow corn 63.15 52.2 metabolic parameters measured. This bird Soybean meal (49% protein) 26.5 36.5 undoubtedly represents a case of crossingNorwegian herring meal (70% protein) 1.0 1.0 over of the chromosome near the k locus Peanut oil 3.0 4.0 which, according to Hutt (1960), occurs at an Dicalcium phosphate 2.5 2.5 average frequency of 7%. The data for this pair Ground limestone 1.5 1.25 were discarded (Experiment 1). .5 .5 Sodium chloride The mean values for body weight gain and DL-methionine .15 .35 1.5 1.5 Vitamin premix a feed conversion to 5 weeks of age are presented Trace mineral premix 0 .2 .2 in Table 2. The weight gain of dwarfs was Total 100.00 100.00 depressed (P<.001) and averaged roughly 73% of normal. Their feed conversion was poorer Crude protein (analyzed, N X 6.25) 19.2 24.9 (P<.02) than that of their nondwarf sisters kcal/kg 3028 3017 except when they were fed diet A in Experiment kj/kg 12672 12626 2. The Na gene reduced mean body weight in two instances: the nondwarf birds fed Diet A in vitamin premix provides per kilogram of diet: Experiment 1 (P<.3) and the nondwarf birds vitamin A, 8,000 IU; vitamin D 3 , 1,000 ICU; vitamin fed diet B in Experiment 2 (P<.01). The Na E, 2.5 IU; vitamin K, 2 mg; riboflavin, 10 mg; niacin, gene had no apparent effect on feed conversion. 20 mg; calcium pantothenate, 8 mg; cyanocobalamin, 10 Mg; choline chloride, 1250 mg; folacin, 1.5 mg; Feeding the higher protein diet B had a marked effect of improving the feed conversion over butylated hydroxytoluene, 25 mg. that on diet A in the nondwarf birds only. Trace mineral premix provides per kilogram of The carcass lipid content and the radioactivity diet (mg): manganese, 86.6; zinc, 77.2; iron, 28; copper, 2.8; iodine, 1.4; cobalt, .27. of carcass and liver lipids are presented in Table 3. When carcass lipid content was expressed as a percent of body weight, the dwarf birds contained almost half again as much fat as their injection. The livers were removed, frozen, and normal sisters. These differences were significant stored at —20 C for future analysis. The car- in all instances (P<.05 to .001). Carcass lipid casses were weighed, frozen, then later ground content was slightly reduced by feeding diet B. and freeze dried. Total lipids were extracted In Experiment 1, extreme variability was from duplicate samples of the lyophilized encountered in carcass lipid 1 4 C content; when carcasses by the method of Folch et al. (1957). coupled with the limited number of animals The 1 4 C activities of duplicate aliquots of used, no differences were found in relation to carcass and liver lipid were measured in a liquid time elapsed after injection. For example, scintillation counter. The quantities of lipid and maximum values were obtained as early as .5 hr the 1 4 C content were related to the fresh-killed postinjection in some cases. As a consequence, body weight. The data were analyzed using the lipid- 14 C values for Experiment 1 represent Students t test: the method of paired com- the means over all intervals. For Experiment 2 parisons for the effect of dv> gene (sister pairs), the postinjection interval was held constant at the simple t test for the Na gene (comparison of 2 hr. The specific radioactivities of both carcass two means). The likelihood of obtaining and liver lipids showed no significant differences significant differences in the latter comparisons due to treatment. There was, however, a was poor because of the limited numbers of consistent finding of higher specific activities in animals and of the variability among families the lipids of the dwarf birds. due to the heterogeneity of the sires. Under In Experiment 1, the naked-neck birds these conditions, probability levels of .1 and .2 showed a marked increase in specific activity of were taken as indicating tendencies, particularly carcass lipids and a marked decrease for that of when all of the traits were considered in relation liver lipids. The radioactivity in total carcass to each other. lipids in this experiment appeared to be inDiet A
Diet B
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TOUCHBURN ET AL.
2192
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creased by the Na gene only in the dwarf birds. Birds fed diet A in Experiment 2 showed a slight increase in specific activity of carcass and liver lipid. The total radioactivity in the total carcass lipids was significantly increased by the presence of the Na gene. The feeding of diet B elimated the response of the Na gene and tended to minimize the response of the dw gene in carcass lipid radioactivity. The presence of the dw gene depressed (P<.05 to .001) body temperature when measured at 5 weeks of age (Table 4). Feeding the high protein diet caused an increase in body temperature (P<.001) in the nondwarf birds. The respiratory quotient (C0 2 expired :C>2 consumed) was increased (P<.05) in the dwarf birds as compared to their nondwarf sisters, indicating that the dwarfs were oxidizing more carbohydrate and less lipid. This parameter was not discernibly affected by either the Na gene or the feeding of diet B. The mean values for resting metabolic rate were much higher in Experiment 1 than in Experiment 2. In both experiments the dwarfs had consistently lower values than their nondwarf sisters. The differences were significant in most instances in spite of the limited number of comparisons. The naked-neck birds were completely consistent in showing a marked increase in resting metabolic rate over that of their non-nakedneck counterparts. This effect was most pronounced in the nondwarf birds of Experiment 1. Based on dietary intake and carcass analyses for lipid and protein content, a thermochemical efficiency value was calculated [(calories retained/calories ingested) X 100, Table 5)]. The dwarf birds had an increased (P<.01) thermochemical efficiency. The Na gene appeared to reduce this efficiency only in the first experiment and most markedly in the nondwarf birds. Feeding the higher protein diet, diet B, appeared to reduce thermochemical efficiency of the dwarf birds only. These dwarf birds fed diet B, however, were still superior (P<.001) in energy retention to their nondwarf sisters consuming the same diet. Nitrogen retention (Table 5) was poorer (P<.05) for the dwarf birds fed diet A in the first experiment. In the second experiment for the birds fed diet B, the dwarf birds again showed slightly poorer nitrogen retention, but the differences were not significant. On diet A in this experiment the dwarf birds showed slightly superior nitrogen retention values over those of their normal
na Na P<
Thousand dpm in total carcass lipid
na Na
Specific activity (dpm/mg) of liver lipid
na Na
Specific activity (dpm/mg) of carcass lipid
na Na P<
Lipid % of body weight
1977 2089
1548 1137
34.5 50.4
12.3 9.2 .02
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37.7 51.4
2056 2646
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10 8
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No. of pairs
Diet A
Experiment 1
.02
.01 .01
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1866 3350
1014 1254
.02
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11.1
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53.2 55.2
15.6 15.8
1239 1384
dw
4 4
No. of pairs
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.05 .05
P<
TABLE 3. Effect of genes for dwarfism (dw) and naked neck (Na) and of diet on carcass lipid content, to activities of carcass and liver lipids from injected acetate- ' 4 C
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Resting metabolic rate, kcal 0 2 / H/kg body weight •"
na Na
Respiratory quotient
na Na P<
Body temperature, °C
6.32 7.28
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.88 .89
.10
.20
.85 .84
41.19 41.01
dw
41.25 41.35
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5 5
10 8
No. of pairs
Diet A
Experiment 1
.05
.3 .05
.001
.10
P<
5.36 5.48
.85 .85
41.36 41.25
DW1
4.18 4.59
.91 .87
.3
41.05
41 .14
dw
4 4
7 4
No. of pairs
Diet A
.10
.05 .05
.05 .05
P<
TABLE 4. Effect of genes for dwarfism (dw), naked neck (Na), and of diet on body temperature, respi metabolic rate of chicks (3 to 5 weeks of age).
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LIPID METABOLISM IN DWARF AND NAKED-NECK CHICKS
2195
sisters. The Na gene exerted no apparent effect on this trait. Feeding the higher protein diet resulted in a marked decrease in the percentage nitrogen retention. DISCUSSION 3
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Experiment 1, ended January 21, was conducted during very cold weather while Experiment 2, which ended March 23, was conducted during warmer weather. Although the chicks were housed in a heated building in heated battery brooders, the seasonal difference was discernible in the room and appears to have reduced the ambient temperature during the first experiment below a critical point, which greatly influenced the results. The Na gene was observed to cause a denudation far beyond a simple lack of neck feathers. Greenwood (1927) found that birds carrying the Na gene had no feathers in the intertract spaces (apteria), almost no ventral feather tract, and a reduced lateral breast tract. The naked neck birds were, thus, much more susceptible to the cooler conditions existing in Experiment 1. The reduced growth and feed efficiencies shown by the dwarf chicks in this study (Table 2) generally confirm previous observations on growth (Hutt, 1953; Merat, 1969) and feed efficiency (Guillaume, 1969). In the one exception, when the dwarf birds fed diet A in the second experiment showed a feed conversion slightly superior to their nondwarf sisters, it was paralleled by unexpectedly high values for nitrogen retention (Table 5). No explanation is apparent for this deviation from the general pattern of response. The nondwarf birds fed diet B showed feed conversions superior to those fed diet A. This was to be expected because the calorie-protein ratio of diet A was deliberately wider than optimal. The dwarf birds gained more weight on diet B and the ratio of their weight to that of their nondwarf sisters was greater on diet B than on diet A. This response had been reported by Guillaume (1969) and observed in several subsequent experiments. Thus, the presence of the dw gene appears to result in an increased protein requirement. This conclusion was recently supported by Cherry and Siegel (1978), who measured the effect of the dw gene in heavy and light weight birds. However, it was contradicted in a subsequent experiment (Cherry and Siegel, 1979). The presence of the dw gene increased the specific activity of carcass and liver lipids in all
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TOUCHBURN ET AL.
The metabolic responses to diet B closely resemble those on diet A in the cool environment, suggesting that dietary calorie-protein ratio played an important role in relation to energy needs. The latter effect was true for the nondwarf birds but had only a moderate effect on the dwarf birds. This tends to confirm the earlier observations by Leclercq et al. (1970) that the feed consumption of dwarfs was almost independent of the energy level of the diet. Likewise, Simon (1972) observed that even after a 36-day training period initiated at 19 days of age, dwarf cockerels, in contrast to their normal brothers, showed no signs of adaptation to a regimen of 2 days of fast followed by 4 days of repletion feeding. Dwarf birds showed an energy metabolism considerably altered from normal (Table 4).
Compared to their nondwarf sisters, the dwarfs had significantly lower body temperatures and resting metabolic rates which indicate a reduced metabolic activity. The significantly greater respiratory quotient indicates that relatively more carbohydrate and less lipid was being oxidized by the dwarf birds. Thus, the dw gene appeared to spare or conserve depot lipids. In comparison with their normal-feathered counterparts the naked-neck birds showed elevated resting metabolic rates in all instances. This difference was most pronounced in the nondwarf birds under the influence of the cooler environment of Experiment 1. The naked-neck dwarf birds, however, were much less sensitive in terms of metabolic response to environmental temperature. The dwarfs were perhaps incapable of mobilizing and subsequently oxidizing their excesses of stored lipid to maintain body temperatures at the same level as their nondwarf sisters. This reduced lipid mobilization and oxidation is definitely an important factor contributing to the obesity in the dwarf chick. Growth hormone is known to enhance fatty acid mobilization and metabolism (Young, 1945; Goodman and Knobil, 1961; Goldman and Bressler, 1967). In fact, lipid may be an absolutely required source of energy for the growth process (Greenbaum, 1953). The apparent inability of dwarf chicks to utilize stored lipid suggests that the dwarfism caused by the dw gene results from a lack of growth hormone or a reduction in its function. The inferior nitrogen retention of the dwarf chicks could also be explained by an insufficiency of growth hormone since this hormone definitely promotes protein accretion (Young, 1945). The significantly greater values for thermochemical efficiency exhibited by the dwarf chicks confirm the earlier results of Guillaume (1969). The current work has shown that this enhanced retention of ingested energy by the dwarf chicks was mediated through a definitely reduced resting metabolic rate, lower body temperature, and a diminished utilization of depot fat. The naked-neck birds showed a definitely inferior thermochemical efficiency only in the cool environment of Experiment 1. This undoubtedly represents the greater heat loss to the surrounding air by these partially naked birds. In an environment close to thermoneutrality for the chick (Experiment 2) the Na gene was observed to mediate an increase in
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cases after injection with 14 C-labeled acetate. This suggests that the gene is associated with increased lipid synthesis from acetate. The lack of statistically significant differences, however, leaves this conclusion open to question. The Na gene was also associated with increased lipid synthesis from acetate under certain conditions as shown by the values for specific activity of carcass and liver lipids of birds fed diet A in Experiment 2. The greater total radioactivity in total carcass lipids reflecting increased lipid synthesis was associated with the dw gene in practically all instances and with the Na gene in all but the nondwarf chicks fed diet A in Experiment 1 and diet B in Experiment 2. In the first experiment, under cooler conditions, the effects of the Na gene on specific activities of carcass and liver lipids are opposite. Carcass lipid specific activity was elevated in the nakedneck birds while that of liver was reduced. This was probably due to a higher rate of transport of synthesized lipid from the liver to the tissues in the naked-neck chicks in the cool environment. In the present instance the lack of increased radioactivity in total carcass lipids of the naked-neck chicks may reflect an increased rate at which the acetate or the synthesized lipids are oxidized to maintain body temperature in these partially denuded birds. In this first experiment, the increased radioactivity in total carcass lipids of the naked-neck dwarf birds suggests that the dw gene had the effect of inhibiting the use of stored lipid as a source of energy for maintaining body temperature and/or enhancing the incorporation of R e labeled acetate into lipid.
LIPID METABOLISM IN DWARF AND NAKED-NECK CHICKS
ACKNOWLEDGMENTS The senior author wishes to acknowledge the generosity of the Ministry of Agriculture of France for the financial support which helped make this work possible and Claude Calet, then Director of the Poultry Research Center of Tours, for the opportunity to work there. Thanks are also expressed to W. L. Bacon, R. G. Jaap, and E. C. Naber of Ohio for helpful criticisms of the manuscript. REFERENCES Cherry, J. A., and P. B. Siegel, 1978. Dwarfism in diverse genetic backgrounds:diet-egg production relationships. Poultry Sci. 57:325-329. Cherry, J. A., and P. B. Siegel, 1979. Dwarfism in diverse genetic backgrounds 3. Effects of dietary protein. Poultry Sci. 58:991-993. Folch, J., N. Lees, and Ch. H. Sloane-Stanley, 1957. A simple method for isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226:497-509. Goldman, J. K., and R. Bressler, 1967. Growth hormone stimulation of fatty acid utilization by adipose tissue. Endocrinology 81:1306—1310. Goodman, H. M., and E. Knobil, 1961. Growth hormone and fatty acid mobilization. The role of the pituitary, adrenal and thyroid. Endocrinology 69:187-189. Greenbaum, A. L., 1953. Changes in body composition
and respiratory quotient of adult female rats treated with purified growth hormone. Biochem. J. 54:400-407. Greenwood, A. W., 1927. The hackleless fowl. Proc. Roy. Phys. Soc. (Edinburgh) 21:123-129. Hutt, F. B., 1949. Pages 117-119 in Genetics of the fowl. McGraw Hill Book Co., Inc. New York NY. Guillaume, J., 1969. Consequences de 1'introduction du gene de nanisme An sur l'utilisation alimentaire chez le poussin femelle. Ann. Biol. Anim. Bioch. Biophys. 9:369-378. Guillaume, J., 1976. The dwarfing gene dw: its effects on anatomy, physiology, nutrition and management. Its application in poultry industry. World's Poultry Sci. J. 32:285-304. Hutt, F. B., 1953. Sex linked dwarfism in the fowl. Genetics 38:670. Hutt, F. B., 1960. New loci in the sex chromosome of the fowl. Heredity 15:97-110. Jaap, R. G., and M. Mohammadian, 1969. Sex linked dwarfism and egg production of broiler dams. Poultry Sci. 48:344-346. Leclercq, B., J. Guillaume, and J-C. Blum, 1970. Donnees sur les besoins alimentaires de la reproductrice naine Vedette INRA (dw) durant les periodes de croissance et de ponte. I. Periode de croissance. Proc. 14th World's Poultry Cong., (Madrid) 2 : 7 8 7 - 7 9 5 . Me'rat, P., 1969. Etude d'un gene de nanisme lie au sexe chez la poule. I. Description sommaire et performances. Ann. Genet. Sel. Anim. 1:19—26. Ricard, F. H., 1971. Croissance et caracteristiques de carcasse de poulets issus de poules normales ou naines (dw). Ann. Genet. Sel. Anim. 3:377—393. Simon, J., 1972. Influence du gene de nanisme (dw) du gene cou nu (Na) et du rythme d'alimentation sur la croissance et le comportement alimentaire du poulet. Ann. Gene't. Sel. Anim. 4:305-310. Touchburn, S. P., 1971a. A study of lipogenesis using 14 C-labeled acetate in full sister pairs of normal and dwarf chicks. World's Poultry Sci. J. 27: 285-286. Touchburn, S. P., 1971b. Etude de la lipogenese a l'aide d'un acetate marqe au 1 4 C chez des paires de soeurs normales et naines. Ann. Genet. Sel. Anim. 3:386. Touchburn, S. P., and J-C. Blum, 1971. Action des genes de nanisme (dw) et de cou nu (Na) sur la croissance du poussin et le metabolisme lipidique. Ann. Genet. Sel. Anim. 3:393. Touchburn, S. P., and J-C. Blum, 1972. Effects of the genes for dwarfism (dw) and naked neck (Na) on chick growth and lipid metabolism. Ann. Genet. Sel. Anim. 4:311-316. Young, F. G., 1945. Growth and diabetes in normal animals treated with pituitary (anterior lobe) diabetogenic extract. Biochem. J. 39:515—536.
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lipid synthesis, and this effect was additive with that of the dw gene so that the naked-neck dwarf chicks showed the greatest incorporation 4 of injected C-labeled acetate into carcass lipid. This augmented lipid synthesis was more obvious under suboptimal temperature conditions (Experiment 1) when it contrasted with a diminished specific radioactivity of carcass lipids shown by the normal neck chicks. Under these conditions the accumulation of lipid was precluded by the increased resting metabolic rates and higher body temperatures sustained by the naked-neck birds. In this case an apparent interaction between the two genes occurred when the dw gene inhibited the effects of the Na gene, preventing the increases in metabolic rate, lipid oxidation, and body temperature.
2197