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Selection for Body Weight at Eight Weeks of Age
Selection for Body Weight at Eight Weeks of Age. 15. Feed Passage and Intestinal Size of Normal and Dwarf Chicks1 J. A. CHERRY and P. B. SIEGEL Poultry Science Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received for publication August 24, 1977)
INTRODUCTION Artificial selection during t h e last quarter c e n t u r y has c o n t r i b u t e d genetically t o t h e r e d u c t i o n in t h e growing cycle of broilers from 14 t o less t h a n eight weeks with a c o n c o m i t a n t i m p r o v e m e n t in t h e efficiency of feed utilizat i o n . It m a y be reasoned t h a t selection for b o d y weight has also altered gastrointestinal (GI) functions which could influence t h e efficiency of feed utilization. Several recent studies have utilized electron m i c r o s c o p y t o describe t h e intestine of t h e fowl ( H u m p h r e y and T u r k , 1 9 7 4 a , 1 9 7 4 b ; Bayer et al., 1 9 7 5 ) . Others have a t t e m p t e d t o correlate t h e improved feed efficiency resulting from antibiotic supplementation t o intestinal function (National A c a d e m y of Sciences, 1 9 6 9 ; Franti et al., 1 9 7 1 ; J o h n s t o n and Arscott, 1 9 7 4 ; March etal, 1 9 7 5 ) . Similarly, t h e rate of feed passage t h r o u g h t h e GI tract of t h e fowl has been investigated (Heuser, 1 9 4 5 ; Jensen et al., 1 9 6 2 ; Hillerman et al., 1 9 5 3 ; T u c k e y et al., 1 9 5 8 ) , as has t h e relative g r o w t h of internal organs (Dror et al., 1 9 7 7 ) .
1 This project was supported by a grant from the Virginia Agricultural Foundation.
1978 Poultry Sci 57:336-340
Of these investigations, however, only Dror et al. (1977) considered t h e relationship of t h e g e n o m e of t h e p o p u l a t i o n t o t h e observed responses. T h e e x p e r i m e n t reported here was designed t o c o m p a r e t h e m o r p h o l o g y of t h e GI tract a n d feed passage rates of populations of chickens exhibiting wide differences in g r o w t h rate as a result of dwarfism and of selection for growth. MATERIALS AND METHODS Stocks. T h e g e n o t y p e s used in the experim e n t were derived from White P l y m o u t h R o c k lines selected bidirectionally for eight-week b o d y weight (Siegel, 1 9 7 0 ) . T h e sex-linked recessive dwarf gene, dw, from a commercial m e a t strain was i n t r o d u c e d into t h e S! 3 generation of b o t h t h e high-weight (HW) and lowweight (LW) lines ( R e d d y and Siegel, 1 9 7 7 ) . S u b s e q u e n t generations were o b t a i n e d b y repeated backcrossing t h r o u g h t h e B 6 generation. T h e resulting g e n o t y p e s , h o m o z y g o u s n o r m a l males (DwDw), h e t e r o z y g o u s normal males (Dwdw), dwarf males (dwdw), n o r m a l females (Dw—) and dwarf females (dw—) from t h e HW and from t h e LW lines were used in t h e experiment.
336
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ABSTRACT Comparisons were made of feed passage rates and size of the gastrointestinal tract components among populations of chickens exhibiting wide differences in growth rate. The populations consisted of White Plymouth Rock stocks selected bidirectionally for high and low juvenile body weight. Comparisons included males heterozygous for the sex-linked gene for dwarfism, as well as normal and dwarf males and females. The indigestible marker, ferric oxide, appeared earlier and disappeared later in the excreta of males from the low-weight line than in those from the high-weight line. Results with female chicks were similar, except that line differences in the time to the first appearance in the excreta were not significant. There were no significant differences in feed passage rates due to the dwarf gene. The weights of the crop, gizzard, duodenum, and the total gastrointestinal tract were, when expressed as a percentage of body weight, significantly heavier for male chicks from the low-weight than for those from the high-weight line. Duodenum weights of female chicks from the low-weight line were also significantly larger than those from the high-weight line. Effects of the dwarfing gene on various components of the gastrointestinal tract, when expressed as percentage weights, were not significant with one exception. Dwarf females from the high-weight line had lower duodenum weights than normals while the reverse was true in the low weight line. In general, the proportionately larger intestinal weights appeared to correspond with a slower clearance of feed through the gastrointestinal tract and may be indicative of altered digestive or absorptive functions resulting from selection for growth.
337
FEED PASSAGE AND INTESTINAL SIZE
analysis of variance. Each sex was analyzed separately and the statistical model was the same as that used for feed passage, except that all chicks came from a single trial. RESULTS AND DISCUSSION Ferric Oxide Clearance. Ferric oxide appeared significantly earlier and disappeared significantly later in the excreta of males from the LW line than in the excreta of male chicks from the HW line (Fig. 1). Consequently, the duration of time between the appearance and disappearance of this indigestible marker was also significantly longer in the LW than in the HW males. The pattern for females resembled that for males for the time of disappearance and the duration of time between the appearance and disappearance of Fe2C>3 i n the excreta, with the differences between lines being significant. The difference in the appearance time of F e 2 0 3 , however, was not significant. Differences in the clearance of F e 2 0 3 in the excreta as a result of the dw gene were not significant, nor were there significant line-dwarf genotype interactions suggesting that the genotypes responded similarly in both lines. The concentration of an indigestible marker in the excreta generally follows a normal
APP
OUR
DIS
APP
DUR
DIS
FIG. 1. Means and standard errors for the time to appearance (APP), time to disappearance (DIS), and the interval between the appearance and disappearance (DUR) of ferric oxide in the excreta of chickens by selection line.
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Ferric Oxide Clearance. Day-old chicks were wingbanded, sexed, vaccinated for Marek's Disease, and reared in heterosexual flocks on a dry mash feed containing 20% protein and 2685 kcal/kg of metabolizable energy. During the seventh week of age the chicks were randomly assigned to individual wire cages. Subsequently, when approximately eight weeks of age, the chicks were individually weighed to the nearest 5 g and access to feed was discontinued. At 0600 the follow day, the chicks were returned to feed and each bird was administered a gelatin capsule containing .3 g of ferric oxide ( F e 2 0 3 ) directly into the esophagus. The dropping papers beneath each cage were periodically replaced and visually monitored at 15-min intervals to record the time of the appearance and disappearance of the F e 2 0 3 in the excreta. The data were collected in two trials for males and two trials for females. There were 30 male and 30 female chicks from each of the selection line-dwarf genotype subclasses (180 males and 120 females). Data, in min, were analyzed separately for each sex by analysis of variance. The statistical model was: Yjjk] = /j. + T; + Lj + D k + (TL);: + (TD) i k + (LD) j k + (LTD) i j k + e i j k i where i = 1, 2 trials; j = 1, 2 lines; k = 1, 2, 3 dwarf genotypes; and 1 = 1, 2 . . . n individuals. The statistical model for females was similar, except that there were only 2 genotypes since dvi is sex-linked. Gastrointestinal Tract Morphology. Following determination of ferric oxide clearance rates, ten male and ten female chicks from each of the ten populations were selected at random, sacrificed, and the total GI tract dissected from the caudal extreme of the pharynx to the anterior extreme of the cloaca. The GI tract was then separated into the following parts and each component was weighed to the nearest 10 mg: a) crop including the upper esophagus with the pharynx differentiating the anterior limit, b) proventriculus with the limits defined by the esophagus and the isthmus, c) gizzard from the isthmus to the pyloric glands, d) duodenum with the limits being the pyloric glands and the hepatic, cystic and pancreatic ducts, and e) intestine consisting of both the small and large intestine from the hepatic, cystic and pancreatic ducts to the cloaca. The weight of the GI tract was determined by totaling the component parts. Parts of the GI tract were expressed as percentage of total body weight. Percentages were transformed to arc sin v % prior to
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J. A. CHERRY AND P. B. SIEGEL
ly, in a variety of ways. Passage rate may increase nutrient absorption by simply prolonging the time during which nutrients are in proximity to the specific intestinal absorptive cells. Our data do not support this hypothesis. Microbial populations of the intestine may also be altered by the availability of substrate resulting in differences in the synthesis or utilization of nutrients (Tuckey et al, 1958). In addition, feed transit times may reflect the efficiency of the digestive and absorptive processes so that a faster clearance rate would be indicative of more efficient feed utilization and more rapid growth. Our data are consistent with this hypothesis, since it is well documented that the chicks from the HW line grow faster and utilize feed more efficiently than chicks from the LW line (Siegel and Wisman,
TABLE 1. —Means and standard deviations for gastrointestinal tract weights as a percentage of body weights of male chicks by selection line and dwarf genotypec Line LW
Pooled x
7.88 2.25 7.44 1.33 .64 7.53 7.62 b
7.08 a 7.20 a 7.43 a
.99 .93 .89 .94°
.3 5 .29 .14
.84 a .87 a .86 a
.39 .05 .43 .07 .46 .09 .43 a
.48 .44 .51 .48 a
.17 .12 .09
.44 a .44 a .48 a
DwDw Dwdw dwdw Pooled x
2.84 .31 3.04 .24 3.47 .39 3.12 a
3.58 3.18 3.48 3.4lt>
.01 .46 .44
3.21 a 3.11 a 3.48 a
Duodenum
DwDw Dwdw dwdw Pooled x
.75 .10 .83 .21 .92 .12 .83 a
1.04 .91 .93 .96 b
.31 .19 .11
.90 a .87 a .92 a
Intestine
DwDw Dwdw dwdw Pooled x
1.60 .22 1.83 .31 1.67' .17 1.70 a
1.77 1.98 1.72 1.82 a
.69 .59 .29
1.68 a 1.90 a 1.70 a
Component
Genotype
HW
GI tract
DwDw Dwdw dwdw Pooled x
6.27 .56 6.95 .98 7.33 .76 6.85 a
Crop
DwDw Dwdw dwdw Pooled x
.69 .13 .81 .31 .82 .18 .77 a
Proventriculus
DwDw Dwdw dwdw Pooled x
Gizzard
(means ± SD)
a,b Within main variables, any two means with the same superscript are not significantly different (P=S.05). There was a significant selection line-dwarf genotype interaction for gizzard weight (P<.05).
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distribution from first appearance to complete disappearance (Jensen et al., 1962). The time to first appearance, which is often used as an indicator of feed passage rates (Hillerman et al., 1953; Tuckey et al., 1958) would, therefore, seem to be a reliable index of gastrointestinal clearance rates. However, these data suggest that the complete clearance of F e 2 0 3 does not correspond with the time to first appearance in different genetic stocks. Chicks from the HW line appeared to completely clear F e 2 0 3 from the GI tract at a faster rate than did chicks from the LW line, although the initial appearance of this marker in the excreta was earlier in the LW male chicks and not significantly different in LW female chicks. The rate of feed passage may theoretically influence feed utilization, directly and indirect-
FEED PASSAGE AND INTESTINAL SIZE
was significant but there was a significant selection line-dwarf genotype interaction for the weight of the gizzard. When compared to the HW homozygous normal males, the heterozygous males and dwarf males had larger gizzards. Conversely, in the LW line the gizzard weights were reduced by dw in both the homozygous and heterozygous state. This interaction was not observed with the female chicks, but there was a similar selection line-dwarf genotype interaction for duodenum weights. The dw gene significantly reduced the duodenum weights of female chicks in the HW line and increased their weights as a percentage of body weight in the LW line (Table 2). The biological significance of these interactions is not clear. It would be surprising if all components were equal on a percentage basis because of the very large differences in body size among these populations. However, these observations do provide additional evidence that the phenotypic expression of dwarfism varies according to the background genome (French and Nordskog, 1973; Reddy and Siegel, 1977; Cherry et
TABLE 2.—Means and standard deviations for gastrointestinal tract component weights as a percentage of body weights of female chicks by selection line and dwarf genotype0 Line Component
Genotype
GI tract
Dw
dw Pooled x Crop
Proventriculus
Gizzard
Dw
.97
.77 .86 a
Dw
.60
dw Pooled x
.49 .54a
Dw
Dw
dw Pooled x Intestine
Dw
dw Pooled x
Pooled x
LW
" (means ± SD) ~ 8.66 4.22 7.94 .92 7.13 .93 8.65 1.27 a 7.90* 8.30
dw Pooled x
dw Pooled x Duodenum
HW
.49 .12
.39 .10
.94
1.11 1.02 a .52
.59 .56 a
8.30 a 7.89 a
.18 .29
.95 a .94 a
.14 .08
.56 a .54 a
3.74 1.92 .37 3.09 3.42a
3.48 3.58 3.53 a
.58 .45
3.61 a 3.34a
1.06 .79 .92a
.58 .09
1.03 1.21 1.12b
.19 .24
1.04a l.OOa
2.30 1.99 2.14a
.91 .61
1.93 2.19 2.06 a
.26 .76
2.12a 2.09a
a,b Within main variables, any two means with the same superscript are not significantly different (P<.05). There was a significant selection line-dwarf genotype interaction for duodenum weight (P<.05).
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1966; Proudman et al., 1970; Owens et al., 1971). It is also interesting that female chicks, which are poorer converters of feedstuffs into body weight (Scott et al, 1976), appeared to clear F e 2 0 3 in the excreta at a slower rate than did the male chicks (Fig. 1). The dw gene also affects body weight and the efficiency of feed utilization (Guillame, 1976) but, in this experiment, had no significant influence on feed transit rates. Gastrointestinal Tract Component Weights. Expressed as a percentage of body weight, the GI tract and its specific components varied widely between males from the HW and LW lines. The LW males, where the clearance of F e 2 0 3 from the GI tract was slower, had significantly larger GI tract weights than did the males from the HW line (Table 1). Weights of the crop, gizzard and duodenum were also significantly larger for the LW males, while the differences in the weights of the intestine (jejunem to cloaca) and for the proventriculus were not significant. None of the main effects due to the dwarf genotypes in the male chicks
339
340
J. A. CHERRY AND P. B. SIEGEL
al, 1978). Differences in the percentage weights of GI tract components of female chicks, with the exception of duodenum weight, were not significant (Table 2). These data indicate that selection for growth has altered the weights of the GI tract and some of the specific components of the GI tract of male chickens. Furthermore, the larger intestinal weights appear to correspond with a slower clearance of food from the intestinal tract and may be indicative of an alteration in the digestive and absorptive functions.
The authors wish to thank Mrs. Kay Criner and Mrs. Janice Scearce for their technical assistance. REFERENCES Bayer, R. C , C. B. Chawan, F. H. Bird, and S. D. Musgrave, 1975. Characteristics of die absorptive surface of the small intestine of die chicken from 1 day to 14 weeks of age. Poultry Sci. 54:155—169. Cherry, J. A., M. Z. Ghitelman, and P. B. Siegel, 1978. The relationship between diet and dwarfism in diverse genetic backgrounds on egg parameters. Poultry Sci. 57:171-179. Dror, Y., I. Nir, and Z. Nitsan, 1977. The relative growth of internal organs in light and heavy breeds. Br. Poultry Sci. 18:493-496. Franti, C. E., H. E. Adler, and L. M. Julian, 1971. Antibiotic growth promotion: Effects of bacitracin and oxytetracyclines on intestines and selected lymphoid tissues of New Hampshire cockerels. Poultry Sci. 50:94-99. French, H. L., and A. W. Nordskog, 1973. Performance of dwarf chickens compared with normal small-bodied c h i c k e n s . P o u l t r y Sci. 52:1318-1328. Guillame, J., 1976. The dwaring gene dw. Its effects on anatomy, physiology, nutrition, management. Its application to poultry industry. World's Poultry Sci. J. 32:285-304. Heuser, G. F., 1945. The rate of passage of feed from
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
ACKNOWLEDGEMENTS
the crop of the hen. Poultry Sci. 24:20—24. Hillerman, J. P., F. H. Kratzer and W. O. Wilson, 1953. Food passage through chickens and turkeys and some regulating factors. Poultry Sci. 32:332—335. Humphrey, C. B., and D. E. Turk, 1974a. The ultrastructure of normal chick intestinal epithelium. Poultry Sci. 53:990-1000. Humphrey, C. D., and D. E. Turk, 1974b. The ultrastructure of chick intestinal absorptive cells during Eimeria acervulina infection. Poultry Sci. 53:1001-1008. Jensen, L. S., L. H. Merrill, C. V. Reddy, and J. McGinnis, 1962. Observations on eating patterns and rate of food passage of birds fed pelleted and unpelleted diets. Poultry Sci. 41:1414-1419. Johnston, N. P., and G. H. Arscott, 1974. Effect of a fermentation residue and an antibiotic on growth of chickens fed rations containing corn or wheat. Poultry Sci. 53:1335-1341. March, B. E., T. Smith, and M. Sadiq, 1975. Factors affecting estimates of metabolizable energy values of rapeseed meal for poultry. Poultry Sci. 54:538-546. National Academy of Sciences, 1969. The use of drugs in animal feeds. National Academy of Sciences, Washington, DC. Owens, C. A., P. B. Siegel, and H. P. Van Krey, 1971. Selection for body weight at eight weeks of age. 8. Growth and metabolism in two light environments. Poultry Sci. 50:548-553. Proudman, J. A., W. J. Mellen, and D. L. Anderson, 1970. Utilization of feed in fast and slow growing lines of chickens. Poultry Sci. 49:961-972. Reddy, P. R. K., and P. B. Siegel, 1977. Selection for body weight at eight weeks of age. 14. Effects of the sex-linked dwarf gene. Poultry Sci. 56:1004— 1013. Scott, M. L., M. C. Nesheim, and R. J. Young, 1976. Nutrition of the chicken. 2nd ed. M. L. Scott and Associates, Ithaca, New York. Siegel, P. B., 1970. Selection for juvenile body weight in chickens. XIV World's Poultry Cong. Madrid pp. 465-471. Siegel, P. B., and E. L. Wisman, 1966. Selection for body weight at eight weeks of age. 6. Changes in appetite and feed utilization. Poultry Sci. 45:1391-1397. Tuckey, R., B. E. March, and J. Biely, 1958. Diet and the rate of food passage in the growing chick. Poultry Sci. 37:787-792.
INTRODUCTION Artificial selection during t h e last quarter c e n t u r y has c o n t r i b u t e d genetically t o t h e r e d u c t i o n in t h e growing cycle of broilers from 14 t o less t h a n eight weeks with a c o n c o m i t a n t i m p r o v e m e n t in t h e efficiency of feed utilizat i o n . It m a y be reasoned t h a t selection for b o d y weight has also altered gastrointestinal (GI) functions which could influence t h e efficiency of feed utilization. Several recent studies have utilized electron m i c r o s c o p y t o describe t h e intestine of t h e fowl ( H u m p h r e y and T u r k , 1 9 7 4 a , 1 9 7 4 b ; Bayer et al., 1 9 7 5 ) . Others have a t t e m p t e d t o correlate t h e improved feed efficiency resulting from antibiotic supplementation t o intestinal function (National A c a d e m y of Sciences, 1 9 6 9 ; Franti et al., 1 9 7 1 ; J o h n s t o n and Arscott, 1 9 7 4 ; March etal, 1 9 7 5 ) . Similarly, t h e rate of feed passage t h r o u g h t h e GI tract of t h e fowl has been investigated (Heuser, 1 9 4 5 ; Jensen et al., 1 9 6 2 ; Hillerman et al., 1 9 5 3 ; T u c k e y et al., 1 9 5 8 ) , as has t h e relative g r o w t h of internal organs (Dror et al., 1 9 7 7 ) .
1 This project was supported by a grant from the Virginia Agricultural Foundation.
1978 Poultry Sci 57:336-340
Of these investigations, however, only Dror et al. (1977) considered t h e relationship of t h e g e n o m e of t h e p o p u l a t i o n t o t h e observed responses. T h e e x p e r i m e n t reported here was designed t o c o m p a r e t h e m o r p h o l o g y of t h e GI tract a n d feed passage rates of populations of chickens exhibiting wide differences in g r o w t h rate as a result of dwarfism and of selection for growth. MATERIALS AND METHODS Stocks. T h e g e n o t y p e s used in the experim e n t were derived from White P l y m o u t h R o c k lines selected bidirectionally for eight-week b o d y weight (Siegel, 1 9 7 0 ) . T h e sex-linked recessive dwarf gene, dw, from a commercial m e a t strain was i n t r o d u c e d into t h e S! 3 generation of b o t h t h e high-weight (HW) and lowweight (LW) lines ( R e d d y and Siegel, 1 9 7 7 ) . S u b s e q u e n t generations were o b t a i n e d b y repeated backcrossing t h r o u g h t h e B 6 generation. T h e resulting g e n o t y p e s , h o m o z y g o u s n o r m a l males (DwDw), h e t e r o z y g o u s normal males (Dwdw), dwarf males (dwdw), n o r m a l females (Dw—) and dwarf females (dw—) from t h e HW and from t h e LW lines were used in t h e experiment.
336
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ABSTRACT Comparisons were made of feed passage rates and size of the gastrointestinal tract components among populations of chickens exhibiting wide differences in growth rate. The populations consisted of White Plymouth Rock stocks selected bidirectionally for high and low juvenile body weight. Comparisons included males heterozygous for the sex-linked gene for dwarfism, as well as normal and dwarf males and females. The indigestible marker, ferric oxide, appeared earlier and disappeared later in the excreta of males from the low-weight line than in those from the high-weight line. Results with female chicks were similar, except that line differences in the time to the first appearance in the excreta were not significant. There were no significant differences in feed passage rates due to the dwarf gene. The weights of the crop, gizzard, duodenum, and the total gastrointestinal tract were, when expressed as a percentage of body weight, significantly heavier for male chicks from the low-weight than for those from the high-weight line. Duodenum weights of female chicks from the low-weight line were also significantly larger than those from the high-weight line. Effects of the dwarfing gene on various components of the gastrointestinal tract, when expressed as percentage weights, were not significant with one exception. Dwarf females from the high-weight line had lower duodenum weights than normals while the reverse was true in the low weight line. In general, the proportionately larger intestinal weights appeared to correspond with a slower clearance of feed through the gastrointestinal tract and may be indicative of altered digestive or absorptive functions resulting from selection for growth.
337
FEED PASSAGE AND INTESTINAL SIZE
analysis of variance. Each sex was analyzed separately and the statistical model was the same as that used for feed passage, except that all chicks came from a single trial. RESULTS AND DISCUSSION Ferric Oxide Clearance. Ferric oxide appeared significantly earlier and disappeared significantly later in the excreta of males from the LW line than in the excreta of male chicks from the HW line (Fig. 1). Consequently, the duration of time between the appearance and disappearance of this indigestible marker was also significantly longer in the LW than in the HW males. The pattern for females resembled that for males for the time of disappearance and the duration of time between the appearance and disappearance of Fe2C>3 i n the excreta, with the differences between lines being significant. The difference in the appearance time of F e 2 0 3 , however, was not significant. Differences in the clearance of F e 2 0 3 in the excreta as a result of the dw gene were not significant, nor were there significant line-dwarf genotype interactions suggesting that the genotypes responded similarly in both lines. The concentration of an indigestible marker in the excreta generally follows a normal
APP
OUR
DIS
APP
DUR
DIS
FIG. 1. Means and standard errors for the time to appearance (APP), time to disappearance (DIS), and the interval between the appearance and disappearance (DUR) of ferric oxide in the excreta of chickens by selection line.
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
Ferric Oxide Clearance. Day-old chicks were wingbanded, sexed, vaccinated for Marek's Disease, and reared in heterosexual flocks on a dry mash feed containing 20% protein and 2685 kcal/kg of metabolizable energy. During the seventh week of age the chicks were randomly assigned to individual wire cages. Subsequently, when approximately eight weeks of age, the chicks were individually weighed to the nearest 5 g and access to feed was discontinued. At 0600 the follow day, the chicks were returned to feed and each bird was administered a gelatin capsule containing .3 g of ferric oxide ( F e 2 0 3 ) directly into the esophagus. The dropping papers beneath each cage were periodically replaced and visually monitored at 15-min intervals to record the time of the appearance and disappearance of the F e 2 0 3 in the excreta. The data were collected in two trials for males and two trials for females. There were 30 male and 30 female chicks from each of the selection line-dwarf genotype subclasses (180 males and 120 females). Data, in min, were analyzed separately for each sex by analysis of variance. The statistical model was: Yjjk] = /j. + T; + Lj + D k + (TL);: + (TD) i k + (LD) j k + (LTD) i j k + e i j k i where i = 1, 2 trials; j = 1, 2 lines; k = 1, 2, 3 dwarf genotypes; and 1 = 1, 2 . . . n individuals. The statistical model for females was similar, except that there were only 2 genotypes since dvi is sex-linked. Gastrointestinal Tract Morphology. Following determination of ferric oxide clearance rates, ten male and ten female chicks from each of the ten populations were selected at random, sacrificed, and the total GI tract dissected from the caudal extreme of the pharynx to the anterior extreme of the cloaca. The GI tract was then separated into the following parts and each component was weighed to the nearest 10 mg: a) crop including the upper esophagus with the pharynx differentiating the anterior limit, b) proventriculus with the limits defined by the esophagus and the isthmus, c) gizzard from the isthmus to the pyloric glands, d) duodenum with the limits being the pyloric glands and the hepatic, cystic and pancreatic ducts, and e) intestine consisting of both the small and large intestine from the hepatic, cystic and pancreatic ducts to the cloaca. The weight of the GI tract was determined by totaling the component parts. Parts of the GI tract were expressed as percentage of total body weight. Percentages were transformed to arc sin v % prior to
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J. A. CHERRY AND P. B. SIEGEL
ly, in a variety of ways. Passage rate may increase nutrient absorption by simply prolonging the time during which nutrients are in proximity to the specific intestinal absorptive cells. Our data do not support this hypothesis. Microbial populations of the intestine may also be altered by the availability of substrate resulting in differences in the synthesis or utilization of nutrients (Tuckey et al, 1958). In addition, feed transit times may reflect the efficiency of the digestive and absorptive processes so that a faster clearance rate would be indicative of more efficient feed utilization and more rapid growth. Our data are consistent with this hypothesis, since it is well documented that the chicks from the HW line grow faster and utilize feed more efficiently than chicks from the LW line (Siegel and Wisman,
TABLE 1. —Means and standard deviations for gastrointestinal tract weights as a percentage of body weights of male chicks by selection line and dwarf genotypec Line LW
Pooled x
7.88 2.25 7.44 1.33 .64 7.53 7.62 b
7.08 a 7.20 a 7.43 a
.99 .93 .89 .94°
.3 5 .29 .14
.84 a .87 a .86 a
.39 .05 .43 .07 .46 .09 .43 a
.48 .44 .51 .48 a
.17 .12 .09
.44 a .44 a .48 a
DwDw Dwdw dwdw Pooled x
2.84 .31 3.04 .24 3.47 .39 3.12 a
3.58 3.18 3.48 3.4lt>
.01 .46 .44
3.21 a 3.11 a 3.48 a
Duodenum
DwDw Dwdw dwdw Pooled x
.75 .10 .83 .21 .92 .12 .83 a
1.04 .91 .93 .96 b
.31 .19 .11
.90 a .87 a .92 a
Intestine
DwDw Dwdw dwdw Pooled x
1.60 .22 1.83 .31 1.67' .17 1.70 a
1.77 1.98 1.72 1.82 a
.69 .59 .29
1.68 a 1.90 a 1.70 a
Component
Genotype
HW
GI tract
DwDw Dwdw dwdw Pooled x
6.27 .56 6.95 .98 7.33 .76 6.85 a
Crop
DwDw Dwdw dwdw Pooled x
.69 .13 .81 .31 .82 .18 .77 a
Proventriculus
DwDw Dwdw dwdw Pooled x
Gizzard
(means ± SD)
a,b Within main variables, any two means with the same superscript are not significantly different (P=S.05). There was a significant selection line-dwarf genotype interaction for gizzard weight (P<.05).
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distribution from first appearance to complete disappearance (Jensen et al., 1962). The time to first appearance, which is often used as an indicator of feed passage rates (Hillerman et al., 1953; Tuckey et al., 1958) would, therefore, seem to be a reliable index of gastrointestinal clearance rates. However, these data suggest that the complete clearance of F e 2 0 3 does not correspond with the time to first appearance in different genetic stocks. Chicks from the HW line appeared to completely clear F e 2 0 3 from the GI tract at a faster rate than did chicks from the LW line, although the initial appearance of this marker in the excreta was earlier in the LW male chicks and not significantly different in LW female chicks. The rate of feed passage may theoretically influence feed utilization, directly and indirect-
FEED PASSAGE AND INTESTINAL SIZE
was significant but there was a significant selection line-dwarf genotype interaction for the weight of the gizzard. When compared to the HW homozygous normal males, the heterozygous males and dwarf males had larger gizzards. Conversely, in the LW line the gizzard weights were reduced by dw in both the homozygous and heterozygous state. This interaction was not observed with the female chicks, but there was a similar selection line-dwarf genotype interaction for duodenum weights. The dw gene significantly reduced the duodenum weights of female chicks in the HW line and increased their weights as a percentage of body weight in the LW line (Table 2). The biological significance of these interactions is not clear. It would be surprising if all components were equal on a percentage basis because of the very large differences in body size among these populations. However, these observations do provide additional evidence that the phenotypic expression of dwarfism varies according to the background genome (French and Nordskog, 1973; Reddy and Siegel, 1977; Cherry et
TABLE 2.—Means and standard deviations for gastrointestinal tract component weights as a percentage of body weights of female chicks by selection line and dwarf genotype0 Line Component
Genotype
GI tract
Dw
dw Pooled x Crop
Proventriculus
Gizzard
Dw
.97
.77 .86 a
Dw
.60
dw Pooled x
.49 .54a
Dw
Dw
dw Pooled x Intestine
Dw
dw Pooled x
Pooled x
LW
" (means ± SD) ~ 8.66 4.22 7.94 .92 7.13 .93 8.65 1.27 a 7.90* 8.30
dw Pooled x
dw Pooled x Duodenum
HW
.49 .12
.39 .10
.94
1.11 1.02 a .52
.59 .56 a
8.30 a 7.89 a
.18 .29
.95 a .94 a
.14 .08
.56 a .54 a
3.74 1.92 .37 3.09 3.42a
3.48 3.58 3.53 a
.58 .45
3.61 a 3.34a
1.06 .79 .92a
.58 .09
1.03 1.21 1.12b
.19 .24
1.04a l.OOa
2.30 1.99 2.14a
.91 .61
1.93 2.19 2.06 a
.26 .76
2.12a 2.09a
a,b Within main variables, any two means with the same superscript are not significantly different (P<.05). There was a significant selection line-dwarf genotype interaction for duodenum weight (P<.05).
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1966; Proudman et al., 1970; Owens et al., 1971). It is also interesting that female chicks, which are poorer converters of feedstuffs into body weight (Scott et al, 1976), appeared to clear F e 2 0 3 in the excreta at a slower rate than did the male chicks (Fig. 1). The dw gene also affects body weight and the efficiency of feed utilization (Guillame, 1976) but, in this experiment, had no significant influence on feed transit rates. Gastrointestinal Tract Component Weights. Expressed as a percentage of body weight, the GI tract and its specific components varied widely between males from the HW and LW lines. The LW males, where the clearance of F e 2 0 3 from the GI tract was slower, had significantly larger GI tract weights than did the males from the HW line (Table 1). Weights of the crop, gizzard and duodenum were also significantly larger for the LW males, while the differences in the weights of the intestine (jejunem to cloaca) and for the proventriculus were not significant. None of the main effects due to the dwarf genotypes in the male chicks
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340
J. A. CHERRY AND P. B. SIEGEL
al, 1978). Differences in the percentage weights of GI tract components of female chicks, with the exception of duodenum weight, were not significant (Table 2). These data indicate that selection for growth has altered the weights of the GI tract and some of the specific components of the GI tract of male chickens. Furthermore, the larger intestinal weights appear to correspond with a slower clearance of food from the intestinal tract and may be indicative of an alteration in the digestive and absorptive functions.
The authors wish to thank Mrs. Kay Criner and Mrs. Janice Scearce for their technical assistance. REFERENCES Bayer, R. C , C. B. Chawan, F. H. Bird, and S. D. Musgrave, 1975. Characteristics of die absorptive surface of the small intestine of die chicken from 1 day to 14 weeks of age. Poultry Sci. 54:155—169. Cherry, J. A., M. Z. Ghitelman, and P. B. Siegel, 1978. The relationship between diet and dwarfism in diverse genetic backgrounds on egg parameters. Poultry Sci. 57:171-179. Dror, Y., I. Nir, and Z. Nitsan, 1977. The relative growth of internal organs in light and heavy breeds. Br. Poultry Sci. 18:493-496. Franti, C. E., H. E. Adler, and L. M. Julian, 1971. Antibiotic growth promotion: Effects of bacitracin and oxytetracyclines on intestines and selected lymphoid tissues of New Hampshire cockerels. Poultry Sci. 50:94-99. French, H. L., and A. W. Nordskog, 1973. Performance of dwarf chickens compared with normal small-bodied c h i c k e n s . P o u l t r y Sci. 52:1318-1328. Guillame, J., 1976. The dwaring gene dw. Its effects on anatomy, physiology, nutrition, management. Its application to poultry industry. World's Poultry Sci. J. 32:285-304. Heuser, G. F., 1945. The rate of passage of feed from
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ACKNOWLEDGEMENTS
the crop of the hen. Poultry Sci. 24:20—24. Hillerman, J. P., F. H. Kratzer and W. O. Wilson, 1953. Food passage through chickens and turkeys and some regulating factors. Poultry Sci. 32:332—335. Humphrey, C. B., and D. E. Turk, 1974a. The ultrastructure of normal chick intestinal epithelium. Poultry Sci. 53:990-1000. Humphrey, C. D., and D. E. Turk, 1974b. The ultrastructure of chick intestinal absorptive cells during Eimeria acervulina infection. Poultry Sci. 53:1001-1008. Jensen, L. S., L. H. Merrill, C. V. Reddy, and J. McGinnis, 1962. Observations on eating patterns and rate of food passage of birds fed pelleted and unpelleted diets. Poultry Sci. 41:1414-1419. Johnston, N. P., and G. H. Arscott, 1974. Effect of a fermentation residue and an antibiotic on growth of chickens fed rations containing corn or wheat. Poultry Sci. 53:1335-1341. March, B. E., T. Smith, and M. Sadiq, 1975. Factors affecting estimates of metabolizable energy values of rapeseed meal for poultry. Poultry Sci. 54:538-546. National Academy of Sciences, 1969. The use of drugs in animal feeds. National Academy of Sciences, Washington, DC. Owens, C. A., P. B. Siegel, and H. P. Van Krey, 1971. Selection for body weight at eight weeks of age. 8. Growth and metabolism in two light environments. Poultry Sci. 50:548-553. Proudman, J. A., W. J. Mellen, and D. L. Anderson, 1970. Utilization of feed in fast and slow growing lines of chickens. Poultry Sci. 49:961-972. Reddy, P. R. K., and P. B. Siegel, 1977. Selection for body weight at eight weeks of age. 14. Effects of the sex-linked dwarf gene. Poultry Sci. 56:1004— 1013. Scott, M. L., M. C. Nesheim, and R. J. Young, 1976. Nutrition of the chicken. 2nd ed. M. L. Scott and Associates, Ithaca, New York. Siegel, P. B., 1970. Selection for juvenile body weight in chickens. XIV World's Poultry Cong. Madrid pp. 465-471. Siegel, P. B., and E. L. Wisman, 1966. Selection for body weight at eight weeks of age. 6. Changes in appetite and feed utilization. Poultry Sci. 45:1391-1397. Tuckey, R., B. E. March, and J. Biely, 1958. Diet and the rate of food passage in the growing chick. Poultry Sci. 37:787-792.