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The Influence of Genetic Changes in Body Weight, Egg Production, and Body Conformation on Organ Growth of Turkeys1
The Influence of Genetic Changes in Body Weight, Egg Production, and Body Conformation on Organ Growth of Turkeys1 KARL E. NESTOR, Y. M. SAIF, D. A. EMMERSON,2 and N. B. ANTHONY3 Department of Poultry Science, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio 44691
1995 Poultry Science 74:601-611
development of various supply and demand organs. Katanbaf et al. (1988b) Growth of the total body influences the compared the organ growth of chicken growth of individual organs in chickens lines selected for high or low 56-d BW at a and turkeys (Latimer, 1924, 1925, 1927; common age (56 d) or at common BW. The Burger et al, 1962). Large genetic gains in weight of various organs differed between BW, egg production, and conformation lines in both comparisons, indicating that may have a differential impact on the divergent selection for increased BW had modified the growth of the organs. Katanbaf et al. (1988a) studied the allomorphic relationship of the high- and low-BW lines Received for publication July 25, 1994. of chickens from hatch to 56 d of age. In Accepted for publication December 14, 1994. Claries and research support provided by State the high- and low-BW lines, the organs and Federal Funds appropriated to the Ohio Agricul- whose relationships to BW that were most tural Research and Development Center, The Ohio divergent were the gizzard, small intesState University. Manuscript Number 105-94. tine, breast, legs, feathers, and abdominal 2 Present address: Hybrid Turkeys Inc., Kitchner, fat. The relationships of specific organs to ON, Canada, N2E 2P8. total BW varied with age and were 'Present address: Department of Poultry Science, influenced by BW selection. University of Arkansas, Fayetteville, AR 72701. INTRODUCTION
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ABSTRACT Measurements were made on the breast with bone (BWB), a demand organ, and various supply organs in mature turkeys (approximately 40 wk of age) from various lines of turkeys to determine the influence of selection for increased egg production, BW, and body conformation on resource allocation. Comparisons made were: 1) a line (E) selected long-term for increased egg production and its randombred control (RBC1); 2) a line (F) selected long-term for increased 16-wk BW and its control (RBC2); 3) the F line with a commercial sire line (C); and 4) the RBC1 line and a randombred control (RBC3) that was formed from the F and C lines. Data were analyzed on an absolute basis and after adjustment to a common BW by covariance analysis. The only major change in organ sizes that occurred that could not be accounted for by differences in BW was in the E line. The actual and relative weights of total supply organs decreased and the relative weight of the BWB increased in the E line when compared with its randombred control. Selection for increased BW in the F line did not result in a relative change in BWB. The BWB weight was relatively heavier in the C line than in the F line. The relative amount of BWB was slightly but significantly different in the two randombreds (RBC1 and RBC3) formed 29 yr apart. Weight of the gizzard did not increase at the same rate as BW in two large-bodied lines (F and RBC3). (Key words: organ weight, genetic changes, egg production, body weight, turkey)
602
NESTOR ET AL.
In recent years, commercial turkey breeders have made large genetic improvements in growth rate, relative breast meat yield, and egg production. The objective of the present study was to investigate the influence of major genetic changes in BW, relative amount of breast meat, and egg production on the growth of various organs and tissues of adult turkeys. MATERIALS AND METHODS
RESULTS AND DISCUSSION
Body weights were obtained before and after bleeding and bled weights were expressed as a percentage of BW before killing. The bled weight averaged 97.1% of the weight before bleeding and there was no effect of line, sex, or line by sex interaction.
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Adult males and females (approximately 40 wk of age) of various lines were used in the study. The lines included a line (E) selected long-term (30 generations) for increased egg production (Anthony et ah, 1991); a randombred control population (RBC1; Nestor, 1977a) that served as the base population of E; a line (F) selected long-term (24 generations) for increased 16-wk BW (Nestor, 1984); a randombred control population (RBC2; Nestor, 1977a) that served as the base population for F; a sire line (C) obtained from a commercial breeder in 1986; and a third randombred control population (RBC3) that was formed by reciprocally crossing Lines F and C in 1987 (in the 20th generation of F). The C line was maintained with minimal selection for increased 16-wk BW and increased breast width. The RBC3 line had been bred without conscious selection for four generations. The number of observations for each line-sex subgroup varied from 8 to 11. All lines were reproduced in four weekly hatches in April, 1990, grown in confinement until 8 wk of age, and then range-reared until 20 wk of age. All birds were fed a declining protein six-ration system (Naber and Touchburn, 1970) based on the schedule for males during the growing period. Selected males and females were housed in confinement after 20 wk of age. Females were housed in floor pens in a windowless breeder house and given 6 h of light/d. Males were housed in an open-sided pole shelter and exposed to natural daylight conditions until December 1, when they were moved into the same building as the females and provided 6 h of light/d. Other details of the feeding and management of the
breeder males and females are given by Nestor (1984). Measurements were made on the birds on January 16 and 17,1991 when the birds were subjected to an overnight feed withdrawal, weighed, and killed by exsanguination. After bleeding, the birds were reweighed and the following weight measurements were recorded: breast muscle plus bone without skin (BWB); lungs; trachea (from tongue to bifurcation); heart; spleen; esophagus, crop, and proventriculus combined (ECP); gizzard; small and large intestines combined; ceca; and pancreas. The contents of the intestinal system were carefully removed prior to weighing. In addition, the lengths of the trachea, ceca, and small and large intestines combined were measured. The weight of the BWB was used as a measure of a demand organ, whereas the total weight of the trachea, heart, spleen, ECP, gizzard, intestines, ceca, and pancreas was used as a measure of supply organs. The data were analyzed by ANOVA with line and sex as main effects using SAS® software (SAS Institute, 1985). The interaction between the main effects was also calculated. Line means were compared by orthogonal contrasts. Contrasts were used to make the following planned comparisons: RBC1 vs E (effect of selection for increased egg production), RBC2 vs F (effect of selection solely for increased BW), F vs C (comparison of two largebodied lines differing greatly in conformation), and RBC1 vs RBC3 (comparison of randombred populations formed from commercial turkey lines 29 yr apart, 1957 vs 1987). The interactions of sex by line contrasts were also computed. Data for supply and demand organs were analyzed on an absolute basis and after adjusting to a common BW by covariance analysis.
603
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
Effect of Selection for Increased Egg Production
Sex Differences
Body weight was lower (P < .001) in the E line relative to the RBC1 line (Table 1). Nestor (1971, 1980) reported that mature BW (at 50% production) was reduced by selection for increased egg production. Bacon and Nestor (1982) found that BW changes during the laying period were similar for the E and RBC1 lines. The average weight of BWB (a measure of demand organs) was lighter in the E line than in the RBC1 line (Table 1). Adjusted weight of the BWB was higher in the E line than in the RBC1 line. Similar differences between lines were observed in both sexes for there was no interaction of sex with the contrast of RBC1 vs E. The line comparison
TABLE 1. Effect of line and sex on weight of total body, breast muscle with bone, and total supply organs of mature turkeys
Variable 1 Line RBC1
E RBC2
F C RBC3
Live body weight
Total supply organs 3
Breast with bone Actual
Adjusted 2
Adjusted 2
Actual
n.~\ vKgJ
(r\
Vb>
2.90 2.53 3.54 5.27 5.96 5.41
3.96 4.23 3.98 3.76 5.02 4.36
419 343 468 570 510 535
484 448 496 477 452 472
5.49 3.05*** .044
4.32 4.12
576
504
373***
439***
444
4
4
444
44
444
444
NS
444
444
NS
444
4
444
444
444
444
NS NS NS NS
NS NS
NS NS
NS NS NS
NS NS NS NS NS NS
11.5
9.5 13.5 19.7 17.9 18.2
Sex Male Female
18.6 11.5***
SEM Contrasts RBC1 vs E RBC2 vs F F vs C RBC1 vs RBC3 Sex by RBC1 vs E Sex by RBC2 vs F Sex by F vs C Sex by RBC1 vs RBC3
.11
3.7
44
44
NS
NS
*
4
1 RBC1 = randombred control line; E = subline of RBC1 developed by selecting for increased egg production; RBC2 = randombred control line; F = subline of RBC2 selected for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by reciprocally crossing Lines F and C. 2 Adjusted to a common body weight by covariance analysis. 3 The supply organs included the lungs, trachea, heart, liver, pancreas, spleen, esophagus, crop, proventriculus, gizzard, intestines, and ceca. *P < .05. **P < .01. h P < .001.
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The sexes differed in BW and the actual weight of all organs and tissues measured (Tables 1 to 4 ). In all cases, the values for males were higher than that for females. After adjustment for BW differences between sexes, weights of the lungs, trachea, heart, liver, spleen, ECP, intestines, and total supply organs remained larger in males than in females. The adjusted weights of the BWB and ceca did not differ between the sexes. The weights of the pancreas and gizzard were larger in females than in males after adjustment for BW. The actual lengths of the intestines and ceca were longer in males than in females (Table 5). However, after adjustment to a common BW, intestines and ceca were longer in females.
604
NESTOR ET AL. TABLE 2. Effect of line and sex on the respiratory system of mature turkeys Lung weight 1
Variable
Actual
Adjusted
2
Adjusted
30.1 22.1 33.5 39.7 34.0 39.0
30.5 22.7 33.6 39.2 33.6 38.6
14.6 12.2 16.4 24.0 19.4 19.7
41.5 24.6*** .50
41.1 25.0**
23.3 21.8 12.1*** 13.5*** .23 Prol NS **
NS X-
NS NS NS NS
••+
NS NS NS NS NS NS NS
Adjusted2
____ (cm)
f» VS/
*** »*»
Actual
*** *** »**
NS
** **
NS
16.0 14.5 17.0 21.9 18.1 18.4
*** ***
NS NS *4
**
NS
29.9 28.6 29.9 33.3 30.4 31.1
31.9 31.9 30.8 30.4 28.6 29.1
34.7 26.4*** .19
32.5 28.4***
NS
NS NS NS
** **
NS NS
**
*
*
NS NS
NS NS NS
1
RBC1 = randombred control line; E = subline of RBCl developed by selecting for increased egg production; RBC2 = randombred control line; F = subline of RBC2 selected for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by reciprocally crossing Lines F and C. 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. ***P < .001.
indicates that the line difference in actual weights of BWB was due to the differences in BW between the lines. The E line was apparently directing relatively more resources to the breast than other parts of the body. The total weight of the supply organs measured was reduced in the E fine both on an actual basis and after adjustment for differences in BW. There was no interaction between sex and the comparison between the E vs RBCl lines for weight of supply organs. The E line individuals are apparently diverting more resources to demand organs than to supply organs. Egg production of turkeys is positively correlated genetically with body depth (McCartney et al., 1968), that could influence the breast muscles and keel bone. The E line had reduced lung weights relative to the RBCl line before and after adjusting for BW (Table 2). Actual trachea weight was lower in the E than in the RBCl
line (P < .01). However, the line difference was due to differences in BW, as no line differences were evident when the data were adjusted for BW by covariance analysis. The trachea was longer in the RBCl line than the E line. The line difference in trachea length was not significant after adjustment for BW. The absolute weights of the heart, liver, pancreas, and spleen were larger in the RBCl line than in the E line (Table 3). Differences between lines remained significant for all the above organs except for the liver after adjustment for differences in BW. There was a significant interaction between sex and the line contrast for actual and adjusted heart weights. The magnitude of the sex difference was larger in the RBCl line than in the E line. Differences in weights of the ECP and the weights of the gizzard and ceca between lines were significant on an absolute basis
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Line RBCl E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBCl vs E RBC2 vs F F vs C RBCl vs RBC3 Sex by RBCl vs E Sex by RBC2 vs F Sex by F vs C Sex by RBCl vs RBC3
Actual
Trachea length
Trachea weight 2
**
NS
*
*
444
444
NS NS
44
NS
* *
68.2 50.0***
78.0 41.0*** .73
NS NS NS
NS
56.7 49.7 58.1 64.9 53.7 71.5
2
Adjusted
47.8 35.4 54.5 77.5 61.5 80.3
Actual
Heart
NS NS NS NS
444
NS NS NS NS NS NS
4
4
NS
44
444
80.2 73.5**
82.0 80.7 83.3 67.3 72.9 74.9
(8)
• Probabi
2
Adjusted
97.7 57.3*** 1.12
66.0 55.0 76.6 90.0 87.0 90.6
Actual
Liver
*
NS NS NS NS NS NS
444
8.45 7.43*** .142
7.90 5.47 8.22 8.82 8.35 8.89
Actual
Pan
^RBCl = randombred control line; E = subline of RBCl developed by selecting for increased egg production; RBC2 = ra for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by re 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. ***P < .001.
Line RBCl E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBCl vs E RBC2 vs F F vs C RBCl vs RBC3 Sex by RBCl vs E Sex by RBC2 vs F Sex by F vs C Sex by RBCl vs RBC3
Variable
1
TABLE 3. Effect of line and sex on weight of the heart, hver, pancreas, and sp
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***
NS NS NS NS
NS NS NS
*
NS
**
NS NS NS
»*
»*
**
**
NS NS
Probabi NS
***
NS NS NS NS NS NS NS NS
** »»* ** **
NS
*
NS NS
NS
NS
67.1 46.8*** .12
90.5 111.4***
107.9 95.4*** 1.26
112.7 78.4***
49.9 45.7 55.4 66.3 62.5 62.1
125.8 66.4*'* 1.68
(g)
Actual
108.0 102.0 117.1 93.2 94.3 91.2
Adjusted
92.2 76.6 110.4 115.6 108.3 106.7
Actual
2
101.1 91.9 94.3 102.1 93.9 89.9
Adjusted
Gizzard
89.1 72.7 89.4 119.1 104.5 101.7
Actual
2
Int
RBC1 = randombred control line; E = subline of RBCl developed by selecting for increased egg production; RBC2 = ra for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by re 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. T < .001.
1
Line RBCl E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBCl vs E RBC2 vs F F vs C RBCl vs RBC3 Sex by RBCl vs E Sex by RBC2 vs F Sex by E vs C Sex by RBCl vs RBC2
Variable
1
Esophagus, crop, and proventriculus
TABLE 4. Effect of line and sex on the weight of the gastrointestinal tract
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607
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
TABLE 5. Influence of line and sex on the length of the intestines and ceca of adult turkeys
(2eca
Intestines Variable1
Actual
Adjusted2
Actual
Adjusted2
(cm) 170 169 188 210 196 198
188 197 195 184 180 180
21.7 23.0 27.1 28.8 26.7 27.8
22.2 23.8 27.3 28.0 26.3 27.7
202 175*** 1.5
182 192***
29.0 22.7*** .26
21.5 23.2*
NS
NS NS NS NS NS NS NS NS
NS NS NS
NS NS NS
**
*
- Probabil *#•
* ***
NS NS NS NS
NS NS NS NS
NS NS NS NS
!RBC1 = randombred control line; E = subline of RBC1 developed by selecting for increased egg production; RBC2 = randombred control line; F = subline of RBC2 selected for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by reciprocally crossing Lines F and C. 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. ***P < .001.
(Table 4). Adjustment for BW removed line differences. The weight of intestines did not differ on an absolute or relative basis. There was no sex by RBC1 vs E interaction for any part of the gastrointestinal tract. Lengths of the intestines and ceca did not differ between lines (Table 5). Influence of Selecting Solely for Increased Body Weight Selecting only for increased BW in the F line resulted in greatly increased mature BW and, as a result, weights of BWB and total supply organs (RBC2 vs F line contrast, Table 1). Adjustment for BW differences between F and RBC2 lines resulted in nonsignificant line differences in weights of BWB and total supply organs. Nestor (1977c, 1984) previously reported that BW at maturity was greater for females of the F line than those of the RBC2 line in earlier
generations of the F line. Bacon and Nestor (1982) observed that the change in BW during the egg production period was similar in the F and RBC2 lines. During the growing period, Nestor et al. (1987, 1988) and Emmerson et al. (1991) observed that the F line had higher breast muscle weight than the RBC2 line at 16 wk of age and older on an actual and percentage BW basis. The increases in breast muscle size in the F line were associated with decreases in percentage of leg muscles. Lung weight on an absolute basis was greater in the F line than in the RBC2 control line (Table 2). The line difference was due to the large difference in BW because there was no line difference after adjustment for BW. Timmwood et al. (1987a) studied lung growth on an unidentified unselected stock of turkeys. Three birds were killed at 22 and 25 d of incubation, on hatch day, and at 1,4,
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Line RBC1 E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBC1 vs E RBC2 vs F F vs C RBC1 vs RBC3 Sex by RBC1 vs E Sex by RBC2 vs F Sex by F vs C Sex by RBC1 vs RBC3
608
NESTOR ET AL.
The weights of the ECP, intestines, and ceca were larger in the F line than in the RBC2 line (Table 4). These line differences were due to differences in BW. Actual gizzard weights were similar in the two lines, but when adjustments were made for BW differences, gizzard weight was smaller in the F line. Sex interacted with the line comparisons for adjusted gizzard weights. In the 11th generation of the F line, Nestor et al. (1981) found that the actual weights of the crop plus thoracic esophagus, proventriculus, small intestines, large intestines plus ceca, and total digestive tract were larger in the F than the RBC2 line at the beginning of lay. In addition, when weights of the digestive tract were expressed as a percentage of BW, the values were lowered in the F line. In the study of Nestor et al. (1981), the actual and relative weights of the gizzard were smaller in the F line. The differences in results obtained in the present study and in the earlier study (Nestor et al, 1981) may have been the result of genetic changes occurring in the F line since the 11th generation and the different method of adjusting for BW differences. Based on actual weights, the ceca were heavier in F than in RBC2, but this line difference was removed by adjustment for BW. The line comparison of the length of the intestine was similar to that observed with the weight data. The length of the intestines was greater in the F line than in the RBC2 line before adjustment for weight differences (Table 5). After adjustment, there was no line difference. There was no line difference in length of the ceca. Effect of Differences in Body Conformation in Large-Bodied Turkeys The contrast of the F and C lines compares two large-bodied lines varying in body conformation. Although the BW of the F and C lines differed by 1.8 kg (Table 1), the BW of these two lines were much greater than the BW of the RBC1, RBC2, and E lines. The weight of the BWB was larger in C than in F (5.96 vs 5.27 kg), but the difference between lines was not significant. After adjustment for BW differences, there was a large line difference (1.26 kg) in weight of breast with bone. The F line was selected
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7, 10,14, 21, 28, 112, and 420 d of age. The growth of the lung was divided into three stages: 1) tissue proliferation, in which explosive growth occurred in lung volume relative to BW and in the gas-exchange compartment within the lung (22 d of incubation to hatch); 2) equilibrated growth, in which most lung compartments grew evenly with lung volume (hatch day to 28 d of age); and 3) regulated growth, in which all lung compartments except large vessels and the exchange compartment grew evenly and at a slower rate than BW (from 28 d of age to adult). In another paper, Timmwood et al. (1987b) compared the growth of the lungs of the unimproved stock and a commercial line selected for increased growth and conformation. No qualitative histological differences were observed between the lungs of the two lines but there were morphometric differences in lung growth relative to BW. During equilibrated lung growth, there was less rapid growth of air and blood capillary volumes and surfaces relative to BW in the selected than in the unselected turkey. The gas exchange compartment did not enlarge concomitant with the large increase in muscle mass of the selected turkeys, whereas large-vessel volume and small-airway volume grew similarly to BW in both turkey lines. Trachea weight was greater in the F line than in the RBC2 line but there was an interaction between sex and the F vs RBC2 contrast (Table 2). The magnitude of the sex difference in trachea weight was greater in the F line than in the RBC2 line. The trachea was longer in the F line than in the RBC2 line on an absolute basis but not relative to BW. The interaction of sex and the F vs RBC2 contrast was significant in both the actual and adjusted lengths. The size of the sex difference was greater for the F line in both comparisons. The weights of the heart, liver, and spleen were greater in the F than RBC2 line (Table 3). Adjustment for BW differences removed the line differences for heart weight and changed the direction of the difference for liver weight. There were no line differences in pancreas weight. The interaction of sex and the F vs RBC2 contrast was significant only for actual heart weight. The sex difference was larger in the F than in the RBC2 line.
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
the F and C lines (Table 4). Only the actual weight of ECP differed between lines. The length of the intestines was greater in the F line than in the C line but the difference was due to a difference in BW (Table 5). There was no line difference in the length of the ceca. Comparison of Two Randombred Control Lines The comparison of the RBC1 and RBC3 lines should represent a conservative estimate of the progress made in the commercial turkey over a 29-yr period (1957 to 1987) through genetic selection. The RBC1 line was formed by the crossing of four commercial strains that were popular at the time (McCartney, 1964) and the RBC3 line was formed by reciprocally crossing the C line and the F line selected only for increased BW. The two randombred control lines differed by 6.7 kg in BW (Table 1). Weight of the BWB was almost twice as large in RBC3 as in RBC1. After adjustment for the large differences in BW, the difference in the weight of the BWB between lines was reduced but remained greater in the RBC3 line. These results indicate that commercial turkey breeders have made progress in improving the relative amount of breast muscle in addition to increasing total BW. The actual weight of the supply organs was greater in RBC3 than in RBC1. After adjustment for BW differences, the line difference was not significant. Differences between the RBC1 and RBC3 lines in weights of the lungs and trachea were not significant after adjustment for BW (Table 2). Trachea length adjusted for BW was longer in RBC1 than RBC3. Heart weight and adjusted liver weight were not different between the RBC1 and RBC3 lines (Table 2). Adjusted pancreas and spleen weights were different between lines but there was an interaction of sex with the comparison. The interaction for the adjusted spleen weight was the result of the sex difference being larger in the RBC3 line than in the RBC1 line. For adjusted pancreas weight, males had larger weights than females in the RBC1 line whereas the reverse was true for the RBC3 line. The RBC1 and RBC3 lines differed in the actual weights of parts (ECP, gizzard, and
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solely for increased 16-wk BW. The selection criteria in the C line were unknown but a major emphasis was probably placed on breast size. Nestor et ah (1988) reported similar findings in that the actual weight of the breast muscles and the weight expressed as a percentage of BW were greater in C than in F at 16 wk of age. The interaction of sex with the contrast of F vs C was significant for the weight of the BWB on an actual and relative basis (Table 1). The interaction for the actual weight of the BWB was due to a larger sex difference occurring in the F line than in the C line. The interaction in the weight of the BWB after adjustment of BW was due to the lack of a sex difference in the F line (3.76 vs 3.77 kg for males and females, respectively) whereas a sex difference existed in the C line (5.20 vs 4.84 kg for males and females, respectively). The total weight of all supply organs measured differed between the F and C lines on an absolute basis but not after adjustment for BW differences. Trachea weight of the F line was greater than that of the C line but the comparison was complicated by an interaction with sex (Table 2). Actual trachea were longer in the F line than in the C line but the line differences were due to BW differences between the lines. The interaction of sex with the F vs C contrast was significant for actual and adjusted trachea length. In both cases, the sex differences were larger in F than in C. The line differences in trachea weight and length were probably the result of differences in neck length. Individuals of the F line are noticeably taller, have longer shanks (Nestor et al., 1988), and appear to have longer necks than individuals of the C line. No line differences were observed in lung weight. Spleen weight (both actual and relative) was greater in the F line than in the C line (Table 3) and the interaction with sex was significant in both cases. There was no difference between lines for the actual weights of the heart, liver, and pancreas. Adjustment for BW differences resulted in significant line differences in the heart and liver. The hearts were smaller in the C line than in the F line but the reverse was true for the liver. The weights of the parts of the gastrointestinal trait did not differ greatly between
609
610
NESTOR ET AL.
General Discussion All of the turkey lines were maintained using at least 36 parental pairs (Nestor, 1977b) so genetic drift should not greatly influence the results (Nestor, 1977a). The possible effects of natural selection in the selected and control lines cannot be ruled out. The lines of turkeys used in the present study were very diverse. This allowed for the comparison of the effects of selection for increased egg production, BW, and conformation on various tissues and organs in mature turkeys. The only major reallocation of resources mat could not be accounted for by differences in BW was for the comparison of the E line and its corresponding randombred control line. The weight of supply organs measured decreased and the weight of the BWB increased. There were some differences in individual supply organs in the various comparisons. Most notably, gizzard weight was relative smaller in faster growing birds (RBC2 vs F and RBC1 vs RBC3). It appeared from the results of the current study that selection for increased growth and conformation did not greatly modify the distribution of resources in mature turkeys other than changes associated with BW per se. It is possible that transient changes in resource allocations occurred during the growing period but were not evident in mature turkeys.
REFERENCES Anthony, N. B., D. A. Emmerson, and K. E. Nestor, 1991. Genetics of growth and reproduction in the
turkey. 12. Results of long-term selection for increased 180-day egg production. Poultry Sci. 70: 1314-1322. Bacon, W. L., and K. E. Nestor, 1982. Body weight changes during the reproductive period in four strains of turkey hens. Poultry Sci. 61:575-577. Burger, R. E., F. W. Lorenz, and C. E. Gates, 1962. Relationships of organ weight to body weight. Poultry Sci. 41:1762-1773. Emmerson, D. A., N. B. Anthony, K. E. Nestor, and Y. M. Saif, 1991. Genetic association of selection for increased leg muscle and increased shank diameter with body composition and walking ability. Poultry Sci. 70:739-745. Katanbaf, M. N., E. A. Dunnington, and P. B. Siegel, 1988a. Allomorphic relationships from hatching to 56 days in parental lines and Fj crosses of chickens selected 27 generations for high or low body weight. Growth Dev. Aging 52:11-22. Katanbaf, M. N., P. B. Siegel, and E. A. Dunnington, 1988b. Organ growth of selected lines of chickens and their Fj crosses to a common body weight or age. Theor. Appl. Genet. 76:540-544. Latimer, H. B., 1924. Postnatal growth of the body, systems, and organs of the Single-Comb White Leghorn. J. Agric. Res. 29:363-397. Latimer, H. B., 1925. The relative postnatal growth of the systems and organs of the chicken. Anat. Rec. 31:233-253. Latimer, H. B., 1927. Correlations of the weights and lengths of the body, systems, and organs of the turkey hen. Anat. Rec. 35:365-377. McCartney, M. G., 1964. A randombred control population of turkeys. Poultry Sci. 43:739-744. McCartney, M. G., K. E. Nestor, and W. R. Harvey, 1968. Genetics of growth and reproduction in the turkey. 2. Selection for increased body weight and egg production. Poultry Sci. 47:981-990. Naber, E. C , and S. P. Touchbum, 1970. Ohio Poultry Rations. Ohio Cooperative Extension Service Bulletin 343. The Ohio State University, Columbus, OH. Nestor, K. E., 1971. Genetics of growth and reproduction in the turkey. 3. Further selection for increased egg production. Poultry Sci. 50: 1672-1682. Nestor, K. E., 1977a. The stability of two randombred control populations of turkeys. Poultry Sci. 56: 54-57. Nestor, K. E., 1977b. The use of a paired mating system for the maintenance of experimental populations of turkeys. Poultry Sci. 56:60-65. Nestor, K. E., 1977c. Genetics of growth and reproduction in the turkey. 5. Selection for increased body weight alone and in combination with increased egg production. Poultry Sci. 56:337-347. Nestor, K. E., 1980. Genetics of growth and reproduction in the turkey. 8. Influence of a management change on response to selection for increased egg production. Poultry Sci. 59:1961-1969. Nestor, K. E., 1984. Genetics of growth and reproduction in the turkey. 9. Long-term selection for increased 16-week body weight. Poultry Sci. 63: 2114-2122. Nestor, K. E., W. L. Bacon, G. B. Havenstein, Y. M. Saif, and P. A. Renner, 1988. Carcass traits of turkeys from lines selected for increased growth rate or increased shank width. Poultry Sci. 67:1660-1667.
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intestines) of the gastrointestinal system but the line differences were removed by covariance analysis to adjust for BW differences (Table 4). Gizzard weight was larger in the RBC3 before adjustment for BW but was larger (P > .05) in RBC1 after adjustment. This result supports the data from the RBC2 vs F comparison in that gizzard weight is reduced in large birds after BW differences are taken into consideration. The length of the intestines was not different between the RBC1 and RBC3 lines after adjustment for differences in BW (Table 5). The ceca were longer in RBC3 than in RBC1 even after adjustment for differences in BW.
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
611
Nestor, K. E., W. L. Bacon, P. D. Moorhead, Y. M. Saif, SAS Institute, 1985. SAS® User's Guide: Statistics. G. B. Havenstein, and P. A. Renner, 1987. Version 5 Edition. SAS Institute Inc., Cary, NC. Comparison of bone and muscle growth in turkey Timmwood, K. I., D. M. Hyde, and C. G. Plopper, lines selected for increased body weight and 1987a. Lung growth of the turkey, Meleagris increased shank width. Poultry Sri. 66:1421-1428. gallopavo: I. Morphologic and morphometric Nestor, K. E., A. H. Cantor, W. L. Bacon, and K. I. description. Am. J. Anat. 178:144-157. Brown, 1981. The influence of body weight restriction during the growing and holding Timmwood, K. I., D. M. Hyde, and C. G. Plopper, 1987b. Lung growth of the turkey, Meleagris periods on reproduction of turkey females from gallopavo: n. Comparison of two genetic lines. strains differing in body weight. Poultry Sci. 60: 1458-1467. Am. J. Anat. 178:158-169.
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1995 Poultry Science 74:601-611
development of various supply and demand organs. Katanbaf et al. (1988b) Growth of the total body influences the compared the organ growth of chicken growth of individual organs in chickens lines selected for high or low 56-d BW at a and turkeys (Latimer, 1924, 1925, 1927; common age (56 d) or at common BW. The Burger et al, 1962). Large genetic gains in weight of various organs differed between BW, egg production, and conformation lines in both comparisons, indicating that may have a differential impact on the divergent selection for increased BW had modified the growth of the organs. Katanbaf et al. (1988a) studied the allomorphic relationship of the high- and low-BW lines Received for publication July 25, 1994. of chickens from hatch to 56 d of age. In Accepted for publication December 14, 1994. Claries and research support provided by State the high- and low-BW lines, the organs and Federal Funds appropriated to the Ohio Agricul- whose relationships to BW that were most tural Research and Development Center, The Ohio divergent were the gizzard, small intesState University. Manuscript Number 105-94. tine, breast, legs, feathers, and abdominal 2 Present address: Hybrid Turkeys Inc., Kitchner, fat. The relationships of specific organs to ON, Canada, N2E 2P8. total BW varied with age and were 'Present address: Department of Poultry Science, influenced by BW selection. University of Arkansas, Fayetteville, AR 72701. INTRODUCTION
601
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ABSTRACT Measurements were made on the breast with bone (BWB), a demand organ, and various supply organs in mature turkeys (approximately 40 wk of age) from various lines of turkeys to determine the influence of selection for increased egg production, BW, and body conformation on resource allocation. Comparisons made were: 1) a line (E) selected long-term for increased egg production and its randombred control (RBC1); 2) a line (F) selected long-term for increased 16-wk BW and its control (RBC2); 3) the F line with a commercial sire line (C); and 4) the RBC1 line and a randombred control (RBC3) that was formed from the F and C lines. Data were analyzed on an absolute basis and after adjustment to a common BW by covariance analysis. The only major change in organ sizes that occurred that could not be accounted for by differences in BW was in the E line. The actual and relative weights of total supply organs decreased and the relative weight of the BWB increased in the E line when compared with its randombred control. Selection for increased BW in the F line did not result in a relative change in BWB. The BWB weight was relatively heavier in the C line than in the F line. The relative amount of BWB was slightly but significantly different in the two randombreds (RBC1 and RBC3) formed 29 yr apart. Weight of the gizzard did not increase at the same rate as BW in two large-bodied lines (F and RBC3). (Key words: organ weight, genetic changes, egg production, body weight, turkey)
602
NESTOR ET AL.
In recent years, commercial turkey breeders have made large genetic improvements in growth rate, relative breast meat yield, and egg production. The objective of the present study was to investigate the influence of major genetic changes in BW, relative amount of breast meat, and egg production on the growth of various organs and tissues of adult turkeys. MATERIALS AND METHODS
RESULTS AND DISCUSSION
Body weights were obtained before and after bleeding and bled weights were expressed as a percentage of BW before killing. The bled weight averaged 97.1% of the weight before bleeding and there was no effect of line, sex, or line by sex interaction.
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Adult males and females (approximately 40 wk of age) of various lines were used in the study. The lines included a line (E) selected long-term (30 generations) for increased egg production (Anthony et ah, 1991); a randombred control population (RBC1; Nestor, 1977a) that served as the base population of E; a line (F) selected long-term (24 generations) for increased 16-wk BW (Nestor, 1984); a randombred control population (RBC2; Nestor, 1977a) that served as the base population for F; a sire line (C) obtained from a commercial breeder in 1986; and a third randombred control population (RBC3) that was formed by reciprocally crossing Lines F and C in 1987 (in the 20th generation of F). The C line was maintained with minimal selection for increased 16-wk BW and increased breast width. The RBC3 line had been bred without conscious selection for four generations. The number of observations for each line-sex subgroup varied from 8 to 11. All lines were reproduced in four weekly hatches in April, 1990, grown in confinement until 8 wk of age, and then range-reared until 20 wk of age. All birds were fed a declining protein six-ration system (Naber and Touchburn, 1970) based on the schedule for males during the growing period. Selected males and females were housed in confinement after 20 wk of age. Females were housed in floor pens in a windowless breeder house and given 6 h of light/d. Males were housed in an open-sided pole shelter and exposed to natural daylight conditions until December 1, when they were moved into the same building as the females and provided 6 h of light/d. Other details of the feeding and management of the
breeder males and females are given by Nestor (1984). Measurements were made on the birds on January 16 and 17,1991 when the birds were subjected to an overnight feed withdrawal, weighed, and killed by exsanguination. After bleeding, the birds were reweighed and the following weight measurements were recorded: breast muscle plus bone without skin (BWB); lungs; trachea (from tongue to bifurcation); heart; spleen; esophagus, crop, and proventriculus combined (ECP); gizzard; small and large intestines combined; ceca; and pancreas. The contents of the intestinal system were carefully removed prior to weighing. In addition, the lengths of the trachea, ceca, and small and large intestines combined were measured. The weight of the BWB was used as a measure of a demand organ, whereas the total weight of the trachea, heart, spleen, ECP, gizzard, intestines, ceca, and pancreas was used as a measure of supply organs. The data were analyzed by ANOVA with line and sex as main effects using SAS® software (SAS Institute, 1985). The interaction between the main effects was also calculated. Line means were compared by orthogonal contrasts. Contrasts were used to make the following planned comparisons: RBC1 vs E (effect of selection for increased egg production), RBC2 vs F (effect of selection solely for increased BW), F vs C (comparison of two largebodied lines differing greatly in conformation), and RBC1 vs RBC3 (comparison of randombred populations formed from commercial turkey lines 29 yr apart, 1957 vs 1987). The interactions of sex by line contrasts were also computed. Data for supply and demand organs were analyzed on an absolute basis and after adjusting to a common BW by covariance analysis.
603
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
Effect of Selection for Increased Egg Production
Sex Differences
Body weight was lower (P < .001) in the E line relative to the RBC1 line (Table 1). Nestor (1971, 1980) reported that mature BW (at 50% production) was reduced by selection for increased egg production. Bacon and Nestor (1982) found that BW changes during the laying period were similar for the E and RBC1 lines. The average weight of BWB (a measure of demand organs) was lighter in the E line than in the RBC1 line (Table 1). Adjusted weight of the BWB was higher in the E line than in the RBC1 line. Similar differences between lines were observed in both sexes for there was no interaction of sex with the contrast of RBC1 vs E. The line comparison
TABLE 1. Effect of line and sex on weight of total body, breast muscle with bone, and total supply organs of mature turkeys
Variable 1 Line RBC1
E RBC2
F C RBC3
Live body weight
Total supply organs 3
Breast with bone Actual
Adjusted 2
Adjusted 2
Actual
n.~\ vKgJ
(r\
Vb>
2.90 2.53 3.54 5.27 5.96 5.41
3.96 4.23 3.98 3.76 5.02 4.36
419 343 468 570 510 535
484 448 496 477 452 472
5.49 3.05*** .044
4.32 4.12
576
504
373***
439***
444
4
4
444
44
444
444
NS
444
444
NS
444
4
444
444
444
444
NS NS NS NS
NS NS
NS NS
NS NS NS
NS NS NS NS NS NS
11.5
9.5 13.5 19.7 17.9 18.2
Sex Male Female
18.6 11.5***
SEM Contrasts RBC1 vs E RBC2 vs F F vs C RBC1 vs RBC3 Sex by RBC1 vs E Sex by RBC2 vs F Sex by F vs C Sex by RBC1 vs RBC3
.11
3.7
44
44
NS
NS
*
4
1 RBC1 = randombred control line; E = subline of RBC1 developed by selecting for increased egg production; RBC2 = randombred control line; F = subline of RBC2 selected for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by reciprocally crossing Lines F and C. 2 Adjusted to a common body weight by covariance analysis. 3 The supply organs included the lungs, trachea, heart, liver, pancreas, spleen, esophagus, crop, proventriculus, gizzard, intestines, and ceca. *P < .05. **P < .01. h P < .001.
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The sexes differed in BW and the actual weight of all organs and tissues measured (Tables 1 to 4 ). In all cases, the values for males were higher than that for females. After adjustment for BW differences between sexes, weights of the lungs, trachea, heart, liver, spleen, ECP, intestines, and total supply organs remained larger in males than in females. The adjusted weights of the BWB and ceca did not differ between the sexes. The weights of the pancreas and gizzard were larger in females than in males after adjustment for BW. The actual lengths of the intestines and ceca were longer in males than in females (Table 5). However, after adjustment to a common BW, intestines and ceca were longer in females.
604
NESTOR ET AL. TABLE 2. Effect of line and sex on the respiratory system of mature turkeys Lung weight 1
Variable
Actual
Adjusted
2
Adjusted
30.1 22.1 33.5 39.7 34.0 39.0
30.5 22.7 33.6 39.2 33.6 38.6
14.6 12.2 16.4 24.0 19.4 19.7
41.5 24.6*** .50
41.1 25.0**
23.3 21.8 12.1*** 13.5*** .23 Prol NS **
NS X-
NS NS NS NS
••+
NS NS NS NS NS NS NS
Adjusted2
____ (cm)
f» VS/
*** »*»
Actual
*** *** »**
NS
** **
NS
16.0 14.5 17.0 21.9 18.1 18.4
*** ***
NS NS *4
**
NS
29.9 28.6 29.9 33.3 30.4 31.1
31.9 31.9 30.8 30.4 28.6 29.1
34.7 26.4*** .19
32.5 28.4***
NS
NS NS NS
** **
NS NS
**
*
*
NS NS
NS NS NS
1
RBC1 = randombred control line; E = subline of RBCl developed by selecting for increased egg production; RBC2 = randombred control line; F = subline of RBC2 selected for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by reciprocally crossing Lines F and C. 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. ***P < .001.
indicates that the line difference in actual weights of BWB was due to the differences in BW between the lines. The E line was apparently directing relatively more resources to the breast than other parts of the body. The total weight of the supply organs measured was reduced in the E fine both on an actual basis and after adjustment for differences in BW. There was no interaction between sex and the comparison between the E vs RBCl lines for weight of supply organs. The E line individuals are apparently diverting more resources to demand organs than to supply organs. Egg production of turkeys is positively correlated genetically with body depth (McCartney et al., 1968), that could influence the breast muscles and keel bone. The E line had reduced lung weights relative to the RBCl line before and after adjusting for BW (Table 2). Actual trachea weight was lower in the E than in the RBCl
line (P < .01). However, the line difference was due to differences in BW, as no line differences were evident when the data were adjusted for BW by covariance analysis. The trachea was longer in the RBCl line than the E line. The line difference in trachea length was not significant after adjustment for BW. The absolute weights of the heart, liver, pancreas, and spleen were larger in the RBCl line than in the E line (Table 3). Differences between lines remained significant for all the above organs except for the liver after adjustment for differences in BW. There was a significant interaction between sex and the line contrast for actual and adjusted heart weights. The magnitude of the sex difference was larger in the RBCl line than in the E line. Differences in weights of the ECP and the weights of the gizzard and ceca between lines were significant on an absolute basis
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Line RBCl E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBCl vs E RBC2 vs F F vs C RBCl vs RBC3 Sex by RBCl vs E Sex by RBC2 vs F Sex by F vs C Sex by RBCl vs RBC3
Actual
Trachea length
Trachea weight 2
**
NS
*
*
444
444
NS NS
44
NS
* *
68.2 50.0***
78.0 41.0*** .73
NS NS NS
NS
56.7 49.7 58.1 64.9 53.7 71.5
2
Adjusted
47.8 35.4 54.5 77.5 61.5 80.3
Actual
Heart
NS NS NS NS
444
NS NS NS NS NS NS
4
4
NS
44
444
80.2 73.5**
82.0 80.7 83.3 67.3 72.9 74.9
(8)
• Probabi
2
Adjusted
97.7 57.3*** 1.12
66.0 55.0 76.6 90.0 87.0 90.6
Actual
Liver
*
NS NS NS NS NS NS
444
8.45 7.43*** .142
7.90 5.47 8.22 8.82 8.35 8.89
Actual
Pan
^RBCl = randombred control line; E = subline of RBCl developed by selecting for increased egg production; RBC2 = ra for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by re 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. ***P < .001.
Line RBCl E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBCl vs E RBC2 vs F F vs C RBCl vs RBC3 Sex by RBCl vs E Sex by RBC2 vs F Sex by F vs C Sex by RBCl vs RBC3
Variable
1
TABLE 3. Effect of line and sex on weight of the heart, hver, pancreas, and sp
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***
NS NS NS NS
NS NS NS
*
NS
**
NS NS NS
»*
»*
**
**
NS NS
Probabi NS
***
NS NS NS NS NS NS NS NS
** »»* ** **
NS
*
NS NS
NS
NS
67.1 46.8*** .12
90.5 111.4***
107.9 95.4*** 1.26
112.7 78.4***
49.9 45.7 55.4 66.3 62.5 62.1
125.8 66.4*'* 1.68
(g)
Actual
108.0 102.0 117.1 93.2 94.3 91.2
Adjusted
92.2 76.6 110.4 115.6 108.3 106.7
Actual
2
101.1 91.9 94.3 102.1 93.9 89.9
Adjusted
Gizzard
89.1 72.7 89.4 119.1 104.5 101.7
Actual
2
Int
RBC1 = randombred control line; E = subline of RBCl developed by selecting for increased egg production; RBC2 = ra for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by re 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. T < .001.
1
Line RBCl E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBCl vs E RBC2 vs F F vs C RBCl vs RBC3 Sex by RBCl vs E Sex by RBC2 vs F Sex by E vs C Sex by RBCl vs RBC2
Variable
1
Esophagus, crop, and proventriculus
TABLE 4. Effect of line and sex on the weight of the gastrointestinal tract
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607
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
TABLE 5. Influence of line and sex on the length of the intestines and ceca of adult turkeys
(2eca
Intestines Variable1
Actual
Adjusted2
Actual
Adjusted2
(cm) 170 169 188 210 196 198
188 197 195 184 180 180
21.7 23.0 27.1 28.8 26.7 27.8
22.2 23.8 27.3 28.0 26.3 27.7
202 175*** 1.5
182 192***
29.0 22.7*** .26
21.5 23.2*
NS
NS NS NS NS NS NS NS NS
NS NS NS
NS NS NS
**
*
- Probabil *#•
* ***
NS NS NS NS
NS NS NS NS
NS NS NS NS
!RBC1 = randombred control line; E = subline of RBC1 developed by selecting for increased egg production; RBC2 = randombred control line; F = subline of RBC2 selected for increased 16-wk body weight; C = commercial sire line; and RBC3 = randombred control started by reciprocally crossing Lines F and C. 2 Adjusted to a common body weight by covariance analysis. *P < .05. **P < .01. ***P < .001.
(Table 4). Adjustment for BW removed line differences. The weight of intestines did not differ on an absolute or relative basis. There was no sex by RBC1 vs E interaction for any part of the gastrointestinal tract. Lengths of the intestines and ceca did not differ between lines (Table 5). Influence of Selecting Solely for Increased Body Weight Selecting only for increased BW in the F line resulted in greatly increased mature BW and, as a result, weights of BWB and total supply organs (RBC2 vs F line contrast, Table 1). Adjustment for BW differences between F and RBC2 lines resulted in nonsignificant line differences in weights of BWB and total supply organs. Nestor (1977c, 1984) previously reported that BW at maturity was greater for females of the F line than those of the RBC2 line in earlier
generations of the F line. Bacon and Nestor (1982) observed that the change in BW during the egg production period was similar in the F and RBC2 lines. During the growing period, Nestor et al. (1987, 1988) and Emmerson et al. (1991) observed that the F line had higher breast muscle weight than the RBC2 line at 16 wk of age and older on an actual and percentage BW basis. The increases in breast muscle size in the F line were associated with decreases in percentage of leg muscles. Lung weight on an absolute basis was greater in the F line than in the RBC2 control line (Table 2). The line difference was due to the large difference in BW because there was no line difference after adjustment for BW. Timmwood et al. (1987a) studied lung growth on an unidentified unselected stock of turkeys. Three birds were killed at 22 and 25 d of incubation, on hatch day, and at 1,4,
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Line RBC1 E RBC2 F C RBC3 Sex Male Female SEM Contrasts RBC1 vs E RBC2 vs F F vs C RBC1 vs RBC3 Sex by RBC1 vs E Sex by RBC2 vs F Sex by F vs C Sex by RBC1 vs RBC3
608
NESTOR ET AL.
The weights of the ECP, intestines, and ceca were larger in the F line than in the RBC2 line (Table 4). These line differences were due to differences in BW. Actual gizzard weights were similar in the two lines, but when adjustments were made for BW differences, gizzard weight was smaller in the F line. Sex interacted with the line comparisons for adjusted gizzard weights. In the 11th generation of the F line, Nestor et al. (1981) found that the actual weights of the crop plus thoracic esophagus, proventriculus, small intestines, large intestines plus ceca, and total digestive tract were larger in the F than the RBC2 line at the beginning of lay. In addition, when weights of the digestive tract were expressed as a percentage of BW, the values were lowered in the F line. In the study of Nestor et al. (1981), the actual and relative weights of the gizzard were smaller in the F line. The differences in results obtained in the present study and in the earlier study (Nestor et al, 1981) may have been the result of genetic changes occurring in the F line since the 11th generation and the different method of adjusting for BW differences. Based on actual weights, the ceca were heavier in F than in RBC2, but this line difference was removed by adjustment for BW. The line comparison of the length of the intestine was similar to that observed with the weight data. The length of the intestines was greater in the F line than in the RBC2 line before adjustment for weight differences (Table 5). After adjustment, there was no line difference. There was no line difference in length of the ceca. Effect of Differences in Body Conformation in Large-Bodied Turkeys The contrast of the F and C lines compares two large-bodied lines varying in body conformation. Although the BW of the F and C lines differed by 1.8 kg (Table 1), the BW of these two lines were much greater than the BW of the RBC1, RBC2, and E lines. The weight of the BWB was larger in C than in F (5.96 vs 5.27 kg), but the difference between lines was not significant. After adjustment for BW differences, there was a large line difference (1.26 kg) in weight of breast with bone. The F line was selected
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7, 10,14, 21, 28, 112, and 420 d of age. The growth of the lung was divided into three stages: 1) tissue proliferation, in which explosive growth occurred in lung volume relative to BW and in the gas-exchange compartment within the lung (22 d of incubation to hatch); 2) equilibrated growth, in which most lung compartments grew evenly with lung volume (hatch day to 28 d of age); and 3) regulated growth, in which all lung compartments except large vessels and the exchange compartment grew evenly and at a slower rate than BW (from 28 d of age to adult). In another paper, Timmwood et al. (1987b) compared the growth of the lungs of the unimproved stock and a commercial line selected for increased growth and conformation. No qualitative histological differences were observed between the lungs of the two lines but there were morphometric differences in lung growth relative to BW. During equilibrated lung growth, there was less rapid growth of air and blood capillary volumes and surfaces relative to BW in the selected than in the unselected turkey. The gas exchange compartment did not enlarge concomitant with the large increase in muscle mass of the selected turkeys, whereas large-vessel volume and small-airway volume grew similarly to BW in both turkey lines. Trachea weight was greater in the F line than in the RBC2 line but there was an interaction between sex and the F vs RBC2 contrast (Table 2). The magnitude of the sex difference in trachea weight was greater in the F line than in the RBC2 line. The trachea was longer in the F line than in the RBC2 line on an absolute basis but not relative to BW. The interaction of sex and the F vs RBC2 contrast was significant in both the actual and adjusted lengths. The size of the sex difference was greater for the F line in both comparisons. The weights of the heart, liver, and spleen were greater in the F than RBC2 line (Table 3). Adjustment for BW differences removed the line differences for heart weight and changed the direction of the difference for liver weight. There were no line differences in pancreas weight. The interaction of sex and the F vs RBC2 contrast was significant only for actual heart weight. The sex difference was larger in the F than in the RBC2 line.
GENETIC CHANGES AND ORGAN GROWTH OF TURKEYS
the F and C lines (Table 4). Only the actual weight of ECP differed between lines. The length of the intestines was greater in the F line than in the C line but the difference was due to a difference in BW (Table 5). There was no line difference in the length of the ceca. Comparison of Two Randombred Control Lines The comparison of the RBC1 and RBC3 lines should represent a conservative estimate of the progress made in the commercial turkey over a 29-yr period (1957 to 1987) through genetic selection. The RBC1 line was formed by the crossing of four commercial strains that were popular at the time (McCartney, 1964) and the RBC3 line was formed by reciprocally crossing the C line and the F line selected only for increased BW. The two randombred control lines differed by 6.7 kg in BW (Table 1). Weight of the BWB was almost twice as large in RBC3 as in RBC1. After adjustment for the large differences in BW, the difference in the weight of the BWB between lines was reduced but remained greater in the RBC3 line. These results indicate that commercial turkey breeders have made progress in improving the relative amount of breast muscle in addition to increasing total BW. The actual weight of the supply organs was greater in RBC3 than in RBC1. After adjustment for BW differences, the line difference was not significant. Differences between the RBC1 and RBC3 lines in weights of the lungs and trachea were not significant after adjustment for BW (Table 2). Trachea length adjusted for BW was longer in RBC1 than RBC3. Heart weight and adjusted liver weight were not different between the RBC1 and RBC3 lines (Table 2). Adjusted pancreas and spleen weights were different between lines but there was an interaction of sex with the comparison. The interaction for the adjusted spleen weight was the result of the sex difference being larger in the RBC3 line than in the RBC1 line. For adjusted pancreas weight, males had larger weights than females in the RBC1 line whereas the reverse was true for the RBC3 line. The RBC1 and RBC3 lines differed in the actual weights of parts (ECP, gizzard, and
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solely for increased 16-wk BW. The selection criteria in the C line were unknown but a major emphasis was probably placed on breast size. Nestor et ah (1988) reported similar findings in that the actual weight of the breast muscles and the weight expressed as a percentage of BW were greater in C than in F at 16 wk of age. The interaction of sex with the contrast of F vs C was significant for the weight of the BWB on an actual and relative basis (Table 1). The interaction for the actual weight of the BWB was due to a larger sex difference occurring in the F line than in the C line. The interaction in the weight of the BWB after adjustment of BW was due to the lack of a sex difference in the F line (3.76 vs 3.77 kg for males and females, respectively) whereas a sex difference existed in the C line (5.20 vs 4.84 kg for males and females, respectively). The total weight of all supply organs measured differed between the F and C lines on an absolute basis but not after adjustment for BW differences. Trachea weight of the F line was greater than that of the C line but the comparison was complicated by an interaction with sex (Table 2). Actual trachea were longer in the F line than in the C line but the line differences were due to BW differences between the lines. The interaction of sex with the F vs C contrast was significant for actual and adjusted trachea length. In both cases, the sex differences were larger in F than in C. The line differences in trachea weight and length were probably the result of differences in neck length. Individuals of the F line are noticeably taller, have longer shanks (Nestor et al., 1988), and appear to have longer necks than individuals of the C line. No line differences were observed in lung weight. Spleen weight (both actual and relative) was greater in the F line than in the C line (Table 3) and the interaction with sex was significant in both cases. There was no difference between lines for the actual weights of the heart, liver, and pancreas. Adjustment for BW differences resulted in significant line differences in the heart and liver. The hearts were smaller in the C line than in the F line but the reverse was true for the liver. The weights of the parts of the gastrointestinal trait did not differ greatly between
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General Discussion All of the turkey lines were maintained using at least 36 parental pairs (Nestor, 1977b) so genetic drift should not greatly influence the results (Nestor, 1977a). The possible effects of natural selection in the selected and control lines cannot be ruled out. The lines of turkeys used in the present study were very diverse. This allowed for the comparison of the effects of selection for increased egg production, BW, and conformation on various tissues and organs in mature turkeys. The only major reallocation of resources mat could not be accounted for by differences in BW was for the comparison of the E line and its corresponding randombred control line. The weight of supply organs measured decreased and the weight of the BWB increased. There were some differences in individual supply organs in the various comparisons. Most notably, gizzard weight was relative smaller in faster growing birds (RBC2 vs F and RBC1 vs RBC3). It appeared from the results of the current study that selection for increased growth and conformation did not greatly modify the distribution of resources in mature turkeys other than changes associated with BW per se. It is possible that transient changes in resource allocations occurred during the growing period but were not evident in mature turkeys.
REFERENCES Anthony, N. B., D. A. Emmerson, and K. E. Nestor, 1991. Genetics of growth and reproduction in the
turkey. 12. Results of long-term selection for increased 180-day egg production. Poultry Sci. 70: 1314-1322. Bacon, W. L., and K. E. Nestor, 1982. Body weight changes during the reproductive period in four strains of turkey hens. Poultry Sci. 61:575-577. Burger, R. E., F. W. Lorenz, and C. E. Gates, 1962. Relationships of organ weight to body weight. Poultry Sci. 41:1762-1773. Emmerson, D. A., N. B. Anthony, K. E. Nestor, and Y. M. Saif, 1991. Genetic association of selection for increased leg muscle and increased shank diameter with body composition and walking ability. Poultry Sci. 70:739-745. Katanbaf, M. N., E. A. Dunnington, and P. B. Siegel, 1988a. Allomorphic relationships from hatching to 56 days in parental lines and Fj crosses of chickens selected 27 generations for high or low body weight. Growth Dev. Aging 52:11-22. Katanbaf, M. N., P. B. Siegel, and E. A. Dunnington, 1988b. Organ growth of selected lines of chickens and their Fj crosses to a common body weight or age. Theor. Appl. Genet. 76:540-544. Latimer, H. B., 1924. Postnatal growth of the body, systems, and organs of the Single-Comb White Leghorn. J. Agric. Res. 29:363-397. Latimer, H. B., 1925. The relative postnatal growth of the systems and organs of the chicken. Anat. Rec. 31:233-253. Latimer, H. B., 1927. Correlations of the weights and lengths of the body, systems, and organs of the turkey hen. Anat. Rec. 35:365-377. McCartney, M. G., 1964. A randombred control population of turkeys. Poultry Sci. 43:739-744. McCartney, M. G., K. E. Nestor, and W. R. Harvey, 1968. Genetics of growth and reproduction in the turkey. 2. Selection for increased body weight and egg production. Poultry Sci. 47:981-990. Naber, E. C , and S. P. Touchbum, 1970. Ohio Poultry Rations. Ohio Cooperative Extension Service Bulletin 343. The Ohio State University, Columbus, OH. Nestor, K. E., 1971. Genetics of growth and reproduction in the turkey. 3. Further selection for increased egg production. Poultry Sci. 50: 1672-1682. Nestor, K. E., 1977a. The stability of two randombred control populations of turkeys. Poultry Sci. 56: 54-57. Nestor, K. E., 1977b. The use of a paired mating system for the maintenance of experimental populations of turkeys. Poultry Sci. 56:60-65. Nestor, K. E., 1977c. Genetics of growth and reproduction in the turkey. 5. Selection for increased body weight alone and in combination with increased egg production. Poultry Sci. 56:337-347. Nestor, K. E., 1980. Genetics of growth and reproduction in the turkey. 8. Influence of a management change on response to selection for increased egg production. Poultry Sci. 59:1961-1969. Nestor, K. E., 1984. Genetics of growth and reproduction in the turkey. 9. Long-term selection for increased 16-week body weight. Poultry Sci. 63: 2114-2122. Nestor, K. E., W. L. Bacon, G. B. Havenstein, Y. M. Saif, and P. A. Renner, 1988. Carcass traits of turkeys from lines selected for increased growth rate or increased shank width. Poultry Sci. 67:1660-1667.
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intestines) of the gastrointestinal system but the line differences were removed by covariance analysis to adjust for BW differences (Table 4). Gizzard weight was larger in the RBC3 before adjustment for BW but was larger (P > .05) in RBC1 after adjustment. This result supports the data from the RBC2 vs F comparison in that gizzard weight is reduced in large birds after BW differences are taken into consideration. The length of the intestines was not different between the RBC1 and RBC3 lines after adjustment for differences in BW (Table 5). The ceca were longer in RBC3 than in RBC1 even after adjustment for differences in BW.
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Nestor, K. E., W. L. Bacon, P. D. Moorhead, Y. M. Saif, SAS Institute, 1985. SAS® User's Guide: Statistics. G. B. Havenstein, and P. A. Renner, 1987. Version 5 Edition. SAS Institute Inc., Cary, NC. Comparison of bone and muscle growth in turkey Timmwood, K. I., D. M. Hyde, and C. G. Plopper, lines selected for increased body weight and 1987a. Lung growth of the turkey, Meleagris increased shank width. Poultry Sri. 66:1421-1428. gallopavo: I. Morphologic and morphometric Nestor, K. E., A. H. Cantor, W. L. Bacon, and K. I. description. Am. J. Anat. 178:144-157. Brown, 1981. The influence of body weight restriction during the growing and holding Timmwood, K. I., D. M. Hyde, and C. G. Plopper, 1987b. Lung growth of the turkey, Meleagris periods on reproduction of turkey females from gallopavo: n. Comparison of two genetic lines. strains differing in body weight. Poultry Sci. 60: 1458-1467. Am. J. Anat. 178:158-169.
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