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Growth and Development of Broiler Breeders.
Growth and Development of Broiler Breeders. 2. Independent Effects of Dietary Formulation Versus Body Weight on Skeletal and Muscle Growth 1 M. S. LILBURN Department of Poultry Science, The Ohio State University, The Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 K. NGIAM-RILLING and D. J. MYERS-MILLER Hubbard Farms Research and Development, Walpole, New Hampshire 03608
ABSTRACT The relationship between body weight gain, nutrient intake, and skeletal and muscle growth in broiler breeder pullets was studied in two experiments. A total of 720 and 540 pullets were started in Experiments 1 and 2, respectively. In the first study, growing pullets were fed either a 15% protein, 2,885 kcal ME/kg pullet grower diet or a 23% protein, 3,133 kcal ME/kg broiler starter diet from 2 to 16 wk of age. Within each dietary treatment, there were three body weight groupings (light, control, heavy) achieved by manipulating weekly feed allowances. At 8,12, and 16 wk of age, 12 pullets from each diet and body weight grouping were killed for muscle [pectoralis major] and skeletal (shank, keel, tibia, clavicle) measurements. As body weight increased, so did skeletal growth, but there were no significant differences in skeletal measurements related to diet. At 12 and 16 wk of age, pullets fed the broiler starter diet had significantly larger p. major muscles. In Experiment 2, growing pullets were fed restricted diets: 1) the 15% protein grower diet (control), 2) the broiler starter diet adjusted weekly to the same calculated calorie intake as that obtained with the grower diet (broiler starter calorie), or 3) the broiler starter diet adjusted to the same calculated protein intake as the grower ration (broiler starter protein). At 16 wk, there were no significant differences between body weight or skeletal measurements of the control and broiler starter calorie treatments. Pullets in the broiler starter calorie treatment did have significantly larger pectoralis muscles and less abdominal fat than those fed the 15% grower diet. Pullets in the broiler starter protein treatment were significantly lighter and had shorter bones, less abdominal fat, and smaller p. major muscles than those in the control treatment. (Key words: broiler breeders, skeletal growth, dietary protein, dietary energy) 1989 Poultry Science 68:1274-1281 INTRODUCTION
TU • r i. -i l. J • ii The gain of broiler breeders is normally _ .. , , . . - . . . controlled byJ quantitative feed restriction , J l . „,. _ „„, (Anonymous, 1985-86). Excessive BW gain has a negative effect on the production of fertile,eggs; control of BW gain through feed restruition helps to overcome this negative effect (Pearson and Herron, 1981; McDaniei et a/., 1981). Rearing programs for pullets are designed such that optimally, egg production (5%) begins between 24 and 25 wk of age (Anonymous, 1985-86). Commencement of produci„ , .
.
.
.. ..
„
.
'Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University.
Manuscript number 148-88.
tion at that age helps to minimize the number of small eggs that cannot be set for chick " . °6. . ... , , , . production. Little published data exist concernf iU . _. .\ , „ . „ . „, ing the relationships between nutrient intake ^ c a r c a s s d e v e i 0 pment of the young breeder pullet
The
concept
of
skdetal
growth
or
" f r a m e s i z e - and i t s relationship to the overall rearing program has become a much discussed topic within the industry during the past few years (DeKalb XL-Link, Pullet and Layer Management Guide, 3rd ed., DeKalb Corp., Sycamore Rd., DeKalb, IL 60115). Shank length measurements have been studied as indices of skeletal development for use with growing Leghorn and broiler pullets (Leeson and Summers, 1984). Broiler breeder pullets are generally fed a ,.
. , . , , . . . ' „„ *•* falls m t 0 m e r a n 8 e of 2>800 t0 kcal M E / k g and 16 to 1 8 % C P
starter dlet
2,970
(Anonymous, 1985-86). After 2 to 3 wk of 1274
Downloaded from http://ps.oxfordjournals.org/ at Florida International University on June 10, 2015
(Received for publication May 27, 1988)
NUTRIENT INTAKE AND SKELETAL GROWTH TABLE 1. Composition of diets (Experiments 1, 2) Ingredient
Broiler starter
Pullet grower ("H
55.53
58.85
28.75 6.25
11.10
3.35 1.25 .50 1.25 .25 .90 .70 .22 .50 .05 .5 23.2 3,133 .80 .41
6.00 .20 5.00 15.00 1.75 .80 .50 .25 .50 .05 15.35 2,885 .80 .47
The methionine premix consisted of 10% DLmethionine and 90% ground com. 2 The broiler starter diet contained the following per kilogram: vitamin A, 4,840 IU; vitamin D3, 2^00 IU; vitamin E, 11 IU; menadione sodium bisulfite, .75 mg; vitamin Bj2, 15.4 u,g; riboflavin, 5.5 mg; niacin, 52.8 mg; Ca-pantothenate, 12 mg; choline chloride, 824 mg-, folic acid, 1 mg; pyridoxine, 3.3 mg; thiamine, 2.2 mg; d-biotin, 110 ug; ethoxyquin, 125 mg; selenium, 1.0 mg; Mn, 66 mg; Fe, 22 mg; Cu, 2.2 mg; Zn, 49.5 mg; 1,1.1 mg; Ca, 600 mg. 3 Chick grower diet contained the following per kilogram: vitamin A, 4,840 IU; vitamin D3,2,200 IU; vitamin E, 11 IU; menadione sodium bisulfite, .75 mg; vitamin B 1 2 , 11.2 ug; riboflavin, 5.5 mg; niacin, 26.4 mg; Ca-pantothenate, 11 mg; choline chloride, 385 mg; folic acid, .55 mg; pyridoxine, 2.7 mg; thiamine, 2.2 mg; d-biotin, 5.5 ug; ethoxyquin, 125 mg; selenium, 1.0 mg; Mn, 66 mg; Fe, 22 mg; Cu, 2.2 mg; Zn, 49.5 mg; I, 1.1 mg; Ca, 600 mg. 4 G.V.-11 = A grade name for gentian violet (Naremco Inc., Springfield, MO) containing 1.6% gentian violet. The diet contained Coban at a concentration of 90 mg/ kg6 The National Research Council (1984) published ingredient specifications were used to calculate the nutrient content of each diet.
age, the pullets are started on a quantitative feed restriction program and are switched to a grower or developer diet that is lower in protein (14 to 16% protein) and may be slighdy lower in energy (2,750 to 2,850 kcal ME/kg). It is within this range of dietary constraints in the starter and grower feeds that
the question arises, can the diet influence skeletal development independent of any changes in the pattern of BW gain? Leeson and Summers (1984) and Lilburn et al. (1987) reported that very low levels of dietary protein can significantly decrease shank length during the ad libitum starter period. Once chicks are fed a common diet or feed intake is restricted, however, these differences in shank length disappear. The objective of the experiments reported herein was to study the relationship between differences in dietary density and skeletal and muscle growth in broiler breeder pullets whose BW gain was controlled by quantitative feed restriction. MATERIALS AND METHODS
Experiment 1. This experiment was designed to study the independent effects of BW gain (as controlled by feed restriction) and nutrient intake on overall growth and development of broiler breeder pullets. A total of 720 commercial broiler breeder pullets was assigned to 12 floor pens (9.45 m 2 ). All chicks were fed ad libitum a commercial grower diet (Table 1) from 0 to 14 days of age before being assigned to restricted feeding treatments. The experiment was designed as a 3 x 2 factorial with three restricted feeding programs and two diets, with two replicate pens per treatment. The two diets fed in this experiment were a commercial broiler starter diet and a pullet grower diet (Table 1). Each diet was fed to one-half the birds in the experiment (i.e., broiler starter to 6 pens; pullet grower to 6 pens) from 14 days of age through the remainder of the experiment. A broiler starter diet and a pullet grower diet were chosen for comparison during the growing period in order to maximize differences in nutrient intake. Within each dietary treatment, two replicate pens were assigned to one of three BW groupings: light, control, or heavy. The BW gain of those pullets in the control treatment was similar to that recommended in the 1985 Hubbard Farms Broiler Breeder Management Guide (Anonymous, 1985-1986). Fifteen birds from each pen were weighed weekly, and the BW gain within each treatment was controlled by adjusting the weekly feed allowances. The heavy and light BW groupings were intended to be heavier and lighter, respectively, than the control weight birds by 30, 20, and 10% at 8, 12, and 16 wk of age, respectively. The
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Ground yellow corn Dehulled soybean meal (49% CP) Com gluten meal (60% CP) Dried brewers grains Blended fat Ground barley Wheat middlings Meat + bone meal (48% CP) Dicalcium phosphate (38.5%) Menhaden fishmeal (60% CP) Limestone Methionine premix1 Salt Vitamin-mineral premix2'3 G.V.-ll 4 Coccidiostar Composition6 CP, analyzed ME, calculated (kcal/kg) Ca, calculated Available P, calculated
1275
1276
LILBURN ET AL.
different amounts of the same diet; this was only 92 and 66%, respectively, of the control feed allotments. At 4, 8, and 16 wk of age, 15 chicks from each pen were randomly selected and killed by cervical dislocation. No attempt was made to equalize BW for carcass comparisons as in Experiment 1. Abdominal fat weight was measured. This weight included all the fat around the gizzard, but none associated with the intestine. Statistical Analysis. All data were subject to analysis of variance (least squares) using the general linear model procedure of the Statistical Analysis System, Cary, NC. In the first experiment, the effects tested were BW grouping (light, control, heavy), diet (grower, broiler starter), and their interaction. The variation due to replicate pen was not significant and was, therefore, included in the overall error term. Data were analyzed separately for each age. In Experiment 2, data were also analyzed separately for each age using a one-way analysis of variance. Dietary treatment was the main effect tested within each age; where significant differences occurred, means were separated using Duncan's new multiple range test (Steel and Torrie, 1960). RESULTS
In Experiment 1, there were no significant effects of diet on skeletal development. Feed restriction was used to manipulate BW gain (Table 2); BW grouping did significandy influence skeletal growth (Table 3). At 12 and
TABLE 2. Cumulative feed consumption of broiler breeders fed either a broiler starter or grower diet and differentially feed restricted to achieve three different body weight classes during growth BW grouping1 Light Control Heavy
Diet
8
Broiler starter Grower Broiler starter Grower Broiler starter Grower
.93 1.11 1.23 1.68 2.46 2.87
Age (wk) 12 16 (kg/bird) 2.48 4.42 2.81 4.85 3.19 5.10 4.00 6.08 4.67 6.74 5.33 7.56
In this study, 720 pullets were randomly divided among 12 pens at 1 day of age. Four pens were randomly allotted to each of the body weight groups; half the pens within each group were fed either the broiler starter or pullet grower diets.
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authors were not always successful in maintaining these exact differences between the BW groupings, but this slight deviation from the experimental design did not interfere with the overall objective of the study. In order to guarantee all birds access to relatively equal quantities of feed, all treatments were fed on an alternate day basis beginning with the onset of restriction at 14 days of age. Feeder space was initially .13 m/bird at this age, and deaths did not exceed 5% in any pen from 14 days of age through the remainder of the study. All feed allotments were adjusted for deaths as needed. At 8, 12, and 16 wk of age, 12 birds per pen that were close to the target weight for that treatment were killed by cervical dislocation and dissected for skeletal and muscle measurements. The length of four major long bones (keel, clavicle, tibia, shank) was measured to the nearest .5 cm. The right half of the pectoralis major was also isolated by dissection and weighed. Experiment 2. This experiment was designed to test the hypothesis that dietary energy intake is the first limiting nutrient controlling BW gain and skeletal growth in dietarily restricted broiler breeders. A total of 540 commercial breeder pullets was randomly assigned to nine of those pens used in Experiment 1. The same broiler starter and pullet grower diets (Table 1) as used in Experiment 1 were again fed. In the control treatment, the birds in three pens were fed the grower diet for the duration of the experiment. Fifteen birds from each of the control pens were weighed weekly beginning at 2 wk of age. The average BW from those three pens was used in adjusting their weekly feed allotments. Weekly feed allowances for the control were dependent upon how the BW for that particular week compared with the recommended BW for that age as described in the Hubbard Farms Broiler Breeder Management Guide (Anonymous, 1985-1986). In the second treatment (broiler starter calorie), pullets in three pens were fed the broiler starter diet, but were restricted to the same calculated calorie intake as that of the control treatment. In the third treatment (broiler starter protein), chicks in another three pens were also fed the broiler starter diet; they received me same calculated protein intake as the control treatment. Pullets in the broiler starter calorie and broiler starter protein treatments thus received
1277
NUTRIENT INTAKE AND SKELETAL GROWTH TABLE 3. Effect of diet and body weight groupings on carcass components in broiler breeders at 8 wk of age (Experiment 1) BW grouping1'2
Diet
BW
Broiler starter Grower Broiler starter Grower Broiler starter Grower SEM
420 472 666 692 1,011 1,044 32
Pectoralis major
Bone length Keel
Tibia
7.1 7.3 8.3 8.0 8.9 9.1 .2
7.7 8.0 8.9 8.9 11.0 10.8 .2
Shank
, ,,
(r\ \B)
Light Control Heavy
10.1 10.2 19.0 16.7 32.3 30.5 1.1 179 0001 927
.154 .0001 .499
.928 .0001 .372
5.9 5.9 7.1 7.2 8.8 8.6 .2
.822 .0001 .298
.923 .0001 .835
3.0 3.3 3.5 3.6 4.2 4.1 .1 .230 .0001 .172
'The body weight grouping was achieved by controlling the feed allotments of broiler starter and pullet grower diets, respectively. The control treatment corresponds to the body weight recommendation outlined in the Hubbard Farms Management Guide, 1985-86 (Anonymous, 1985-86). 2 In this study, 720 pullets were randomly divided among 12pensat 1 day of age. Four pens were randomly allotted to each of the body weight groups, and half the pens within each group were fed either the broiler starter or pullet grower diets.
16 wk of age, however, those pullets fed broiler starter diets did have significandy greater p. major muscle development (Tables 4 and 5). Data also showed a large variation among BW groupings in the measured lengths of individual skeletal components. At 8 wk of age, keel length in the light BW grouping was 20% shorter man in the heavy BW group, whereas the shank length was 32% shorter as calculated from the corresponding groups. At 16 wk of age, the heavy group was still 20% heavier in BW than the light BW group, but the differences in the lengm of all the bones measured was less than 10%. In Experiment 2, those pullets in die broiler starter calorie treatment were significantly heavier (15%) and lighter (12%) than those pullets in die control treatment at 4 and 8 wk, respectively (Table 6). Birds in bodi treatments were significantly heavier than mose in the broiler starter protein treatment at 8 and 16 wk. At the latter two ages, chicks in the broiler starter protein treatment had the shortest bones, whereas birds in the other two treatments were similar in skeletal measurements. At 4 and 8 wk, the size of the p. major muscle followed the same pattern as BW. At both 4 and 8 wk, abdominal fat measures were significandy lower in both the broiler starter calorie and broiler starter protein treatments than in
controls. At 16 wk, mere were no significant differences between BW or abdominal fat measures of birds in control and broiler starter calorie treatments, but p. major muscles were significandy larger in the latter treatment. Pullets in the broiler starter protein treatment had significandy less abdominal fat and smaller p. major muscles than mose in the control treatment at 8 and 16 wk of age. DISCUSSION
These data support the hypothesis mat frame size or skeletal growtfi in broiler breeders is primarily a function of BW gain. Multiple regression analysis showed tiiat BW alone accounted for most of the variation in keel (R2 = .633) and tibia length (R2 = .808) at 12 wk of age (n = 72). The model was not significandy changed by adding in die cumulative intakes of energy (kilocalories) and protein (keel, R 2 = .641; tibia, R 2 = .838, respectively). Differences in dietary protein and energy can influence the rate of gain and in this way indirecdy influence skeletal growm. In commercial practice, however, where BW gain is closely monitored, nutrient density itself will not specifically increase or decrease linear skeletal development. Data from both experiments (Tables 3 to 6) support
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Probability Source of variation, df Diet (D), 1 BW grouping (BWG), 2 D x BWG, 2
Clavicle
1278
LILBURN ET AL. TABLE 4. Effect of diet and body weight grouping on carcass composition in broiler breeders at 12 wk of age (Experiment 1)
BW grouping1,2
Diet
BW
Broiler starter Grower Broiler starter Grower Broiler starter Grower SEM
958 945 1,200 1,255 1,654 1,592 55
Pectoralis major
Bone length Keel
Tibia
8.6 8.8 9.2 9.4 10.7 10.3 .2
10.7 11.0 11.8 11.9 13.4 13.0 .2
Shank
,
(r>
Light Control Heavy
884 j0001 356
.042 .0001 .741
.793 .0001 .482
N
13.6 13.8 14.9 14.9 16.4 16.5 .2
.601 .0001 .691
.731 .0001 .861
4.3 4.5 4.8 4.8 5.1 5.2 .1
.334 .0001 .900
T h e body weight grouping was achieved by controlling the feed allotments of broiler starter and grower diets, respectively. The control treatment corresponds to the body weight recommendation outlined in the Hubbard Farms Management Guide, 1985-86 (Anonymous, 1985-86). In this study, 720 pullets were randomly divided among 12 pens at 1 day of age. Four pens were randomly allotted to each of the body weight groups, and half the pens within each group were fed either the broiler starter or pullet grower diets.
TABLE 5. Effect of diet and body weight grouping on carcass components in broiler breeders at 16 wk of age (Experiment 1) BW grouping1,2
Diet
Pectoralis major
BW
Bone length Keel
Tibia
10.7 10.6 10.7 11.2 11.7 11.5 .1
13.0 12.4 12.9 13.4 13.3 13.4 .2
fri
Light Control Heavy
Broiler starter 1,589 1,521 Grower Broiler starter 1,589 Grower 1,698 Broiler startei-1,937 Grower 1,955 SEM 59
Probability Source of variation, df Diet (D), 1 BW grouping (BWG), 2 D x BWG, 2
59.5 50.8 62.3 60.3 82.6 71.3 3.1 679 0001 332
1
.001 .002 .354
.816 .0001 .511
Shank — (cm) 16.0 15.7 15.8 16.5 16.7 16.9 .2
.604 .0001 .804
.962 .0001 .678
Clavicle 5.2 5.1 5.5 5.4 5.6 5.7 .1 .615 .0001 .121
The body weight grouping was achieved by controlling the feed allotments of broiler starter and pullet grower diets, respectively. The control treatment corresponds to the body weight recommendation outlined in the Hubbard Farms Management Guide, 1985-86 (Anonymous, 1985-86). 2 In this study, 720 pullets were randomly divided among 12 pens at 1 day of age. Four pens were randomly allotted to each of the body weight groups, and half the pens within each group were fed either the broiler starter or pullet grower diets.
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Probability Source of variation, df Diet (D), 1 BW grouping (BWG), 2 D x BWG, 2
27.3 27.1 38.8 37.9 60.9 53.8 2.2
Clavicle
Control Broiler starter calorie Broiler starter protein3
Control Broiler starter calorie Broiler starter protein
Control Broiler starter calorie Broiler starter protein
4
8
16
419 483 418 974 867 707 1,959 2,018 1,556
BW
± ± ± ± ± ± ± ± ±
llb 16" 12b 19" 18 b 19° 58" 48" 38 b ± ± ± ± ± ±
(g) — .4° .6" .5 b .8" .7 b .9C
83.1 ± 3.6b 97.6 ± 3.8" 72.3 ± 3.4C
10.1 14.8 12.5 25.9 21.8 16.4
Pectoralis major 4.8 2.7 1.9 8.2 4.3 1.6 38.2 31.6 8.5
± ± ± ± ± ± ± ± ±
.7" .4 b .2 b 1.2" .7 b .2C 4.9" 4.1" 1.6b
Abdominal fat ± .lb ± .1" ± .lb ± .1" ± .1" ± .lb ± .2" ± .2" ± .lb 7.8 8.1 7.8 10.9 10.7 10.1 15.3 15.3 14.7
Tibia ± ± ± ± ± ± ± ± ±
.1" .1" .1" .1" .1" .1" .1" .1" .1"
(cm) 10.1 ± .1" 10.6 ± .1" 10.2 ± .1" 13.9 ± .1" 13.7 ± .1" 12.9 ± .2 b 16.4 ± .1" 16.4 ± .1" 15.9 ± .1"
Shank
Bone length
3.9 3.9 3.9 4.5 4.5 4.4 6.3 6.2 5.9
± ± ± ± ± ± ± ± ±
la .1" ,lb
.1 .1 .1 .1 .1 .1
Clavicle
^Differences in body weight and carcass components in these two treatments are the result of quantitative differences in consumption of similar diets.
Treatments consisted of: the 15% protein grower diet (control); the broiler starter diet adjusted weekly to the same calculated calorie intake as that obtained with the grower diet (broiler starter calorie); and the broiler starter diet adjusted to the same calculated protein intake as the grower ration (broiler starter protein). Body weight gains were in accordance with the recommendation of the Hubbard Farms Management Guide, 1985-86.
5.9 6.4 6.1 8.4 8.4 7.9 12.0 12.3 11.6
Keel
3
_
3
a JO o
AKE AND SKELET
'Mean ± SE.
Means within column and age with no common superscripts are significantly different (P<.05).
Treatment2
Age
a_c
om http://ps.oxfordjournals.org/ at Florida International University on June 10, 2015
TABLE 6. Influence of protein versus energy intake on muscle and fat accretion in broiler breeder pullets (Experiment 2f NUTRIEN1
1280
LILBURN ET AL.
skeletal growth. The weight of the p. major muscle was a reflection of differences in BW at 4 and 8 wk of age. At 16 wk of age, however, the increased protein intake associated with the broiler starter calorie treatment did significantly increase pectoralis muscle size. This treatment also resulted in less abdominal fat at all ages; this is a function of an increased protein-to-energy ratio when caloric intake is equalized. The muscle and protein changes suggest that carcass composition in feed restricted pullets can be manipulated without any major changes in BW or skeletal growth. In the present experiment, when protein intakes were equalized, an energy deficiency effect was created in birds in the broiler starter protein treatment; this was reflected in significantly decreased BW and impaired skeletal development at 8 and 16 wk. At 8 wk, pullets in the broiler starter protein treatment weighed 82 and 73% as much as those in the broiler starter calorie and control treatments, respectively; the differences were approximately the same, 77 and 79%, respectively, at 16 wk. Although the differences in BW were substantial, differences in skeletal measurements at the latter two ages were less than 6%. These results suggest, therefore, that under commercial situations, there would need to be a very large shift in BW gain before skeletal growth would be affected significantly by energy deficiency of the magnitude used in the present experiments. ACKNOWLEDGMENTS
The authors wish to diank Laurel Newman and Wanda Acord for their help in the preparation and handling of this manuscript. REFERENCES Anonymous, 1985-1986. Hubbard Farms Broiler Breeder Management Guide, 1985-86. Hubbard Farms, Walpole, NH. Leeson, S., and J. D. Summers, 1984. Influence of nutritional modification on skeletal size of Leghorn and broiler breeder pullets. Poultry Sci. 63:1222-1228. Lilburn, M. S., K. Ngiam-Rilling, and J. H. Smith, 1987. Relationships between dietary protein, dietary energy, rearing environment, and nutrient utilization by broiler breeder pullets. Poultry Sci. 66:1111-1118. McDaniel, G. R., J. Brake, and M. K. Eckman, 1981. Factors affecting broiler breeder performance. 4. The interrelationship of some reproductive traits. Poultry Sci. 60: 1792-1797. National Research Council, 1984. Nutrient Requirements of
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the results of Wagner (1979), which showed different planes of nutrition significantly influenced BW gain and skeletal growth in similar aged chickens. Leeson and Summers (1984) fed increasing protein levels (13 to 20%) to young pullets (0 to 21 days); the present results support their data showing that dietary effects on skeletal development appear to be lost once BW is equalized via restricted feeding. Although simple control of BW gain by feed restriction did effectively restrict skeletal growth, other aspects of carcass development responded to the nutrient content of the diet. At 12 and 16 wk of age in Experiment 1 and at 16 wk of age in Experiment 2, p. major muscle growth responded to specific manipulations of calorie and protein intake even where no differences may have existed in BW or skeletal growth (Tables 4 to 6). Wagner (1979) also observed that when chickens from different nutritional treatments were grouped according to keel length, there were still significant differences in pectoral muscle weights. The relationship between energy intake and BW gain is very strong in feed restricted broiler breeder pullets (Lilburn et ah, 1987) and adult breeder hens (Spratt and Leeson, 1987). Results from Experiment 2 support the previous observations. Similar energy intakes from 2 to 16 wk resulted in similar BW and skeletal measurements at the latter age. This was not the case at 4 and 8 wk of age, however. From 2 to 4 wk, the calculated feed allotment for those pullets in the broiler starter calorie treatment was obviously in excess of the birds' requirements for the desired amount of gain. Those pullets sampled from the control and broiler starter protein treatments had similar BW and skeletal measurements at 4 wk of age, suggesting that dietary protein intake may be more important than energy in controlling growth of very young birds. At 8 wk of age, pullets in the broiler starter calorie treatment derived a greater percentage of their energy needs from dietary protein than birds in the control treatment. The less efficient utilization of protein as an energy source may have contributed to the significantly greater BW in pullets from the control treatment. The differences in BW, however, were not reflected in any significant differences in skeletal measurements. This latter observation supports the data from Experiment 1 showing that within a given range of BW, there are no differences in
NUTRIENT INTAKE AND SKELETAL GROWTH Poultry. Natl. Acad. Sci., Washington, DC. Pearson, R. A., and K. M. Herron, 1981. Effects of energy and protein allowances during lay on the reproductive performance of broiler breeder hens. Br. Poult. Sci. 22: 227-239. Spratt, R. S., and S. Leeson, 1987. Broiler breeder performance in response to diet protein and energy. Poultry
1281
Sci. 66:683-693. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., New York, NY. Wagner, J., 1979. The influence of the nutrition level of the skeletal growth in chicken. Pr. Mater. Zootech. 20: 41-53.
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ABSTRACT The relationship between body weight gain, nutrient intake, and skeletal and muscle growth in broiler breeder pullets was studied in two experiments. A total of 720 and 540 pullets were started in Experiments 1 and 2, respectively. In the first study, growing pullets were fed either a 15% protein, 2,885 kcal ME/kg pullet grower diet or a 23% protein, 3,133 kcal ME/kg broiler starter diet from 2 to 16 wk of age. Within each dietary treatment, there were three body weight groupings (light, control, heavy) achieved by manipulating weekly feed allowances. At 8,12, and 16 wk of age, 12 pullets from each diet and body weight grouping were killed for muscle [pectoralis major] and skeletal (shank, keel, tibia, clavicle) measurements. As body weight increased, so did skeletal growth, but there were no significant differences in skeletal measurements related to diet. At 12 and 16 wk of age, pullets fed the broiler starter diet had significantly larger p. major muscles. In Experiment 2, growing pullets were fed restricted diets: 1) the 15% protein grower diet (control), 2) the broiler starter diet adjusted weekly to the same calculated calorie intake as that obtained with the grower diet (broiler starter calorie), or 3) the broiler starter diet adjusted to the same calculated protein intake as the grower ration (broiler starter protein). At 16 wk, there were no significant differences between body weight or skeletal measurements of the control and broiler starter calorie treatments. Pullets in the broiler starter calorie treatment did have significantly larger pectoralis muscles and less abdominal fat than those fed the 15% grower diet. Pullets in the broiler starter protein treatment were significantly lighter and had shorter bones, less abdominal fat, and smaller p. major muscles than those in the control treatment. (Key words: broiler breeders, skeletal growth, dietary protein, dietary energy) 1989 Poultry Science 68:1274-1281 INTRODUCTION
TU • r i. -i l. J • ii The gain of broiler breeders is normally _ .. , , . . - . . . controlled byJ quantitative feed restriction , J l . „,. _ „„, (Anonymous, 1985-86). Excessive BW gain has a negative effect on the production of fertile,eggs; control of BW gain through feed restruition helps to overcome this negative effect (Pearson and Herron, 1981; McDaniei et a/., 1981). Rearing programs for pullets are designed such that optimally, egg production (5%) begins between 24 and 25 wk of age (Anonymous, 1985-86). Commencement of produci„ , .
.
.
.. ..
„
.
'Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University.
Manuscript number 148-88.
tion at that age helps to minimize the number of small eggs that cannot be set for chick " . °6. . ... , , , . production. Little published data exist concernf iU . _. .\ , „ . „ . „, ing the relationships between nutrient intake ^ c a r c a s s d e v e i 0 pment of the young breeder pullet
The
concept
of
skdetal
growth
or
" f r a m e s i z e - and i t s relationship to the overall rearing program has become a much discussed topic within the industry during the past few years (DeKalb XL-Link, Pullet and Layer Management Guide, 3rd ed., DeKalb Corp., Sycamore Rd., DeKalb, IL 60115). Shank length measurements have been studied as indices of skeletal development for use with growing Leghorn and broiler pullets (Leeson and Summers, 1984). Broiler breeder pullets are generally fed a ,.
. , . , , . . . ' „„ *•* falls m t 0 m e r a n 8 e of 2>800 t0 kcal M E / k g and 16 to 1 8 % C P
starter dlet
2,970
(Anonymous, 1985-86). After 2 to 3 wk of 1274
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(Received for publication May 27, 1988)
NUTRIENT INTAKE AND SKELETAL GROWTH TABLE 1. Composition of diets (Experiments 1, 2) Ingredient
Broiler starter
Pullet grower ("H
55.53
58.85
28.75 6.25
11.10
3.35 1.25 .50 1.25 .25 .90 .70 .22 .50 .05 .5 23.2 3,133 .80 .41
6.00 .20 5.00 15.00 1.75 .80 .50 .25 .50 .05 15.35 2,885 .80 .47
The methionine premix consisted of 10% DLmethionine and 90% ground com. 2 The broiler starter diet contained the following per kilogram: vitamin A, 4,840 IU; vitamin D3, 2^00 IU; vitamin E, 11 IU; menadione sodium bisulfite, .75 mg; vitamin Bj2, 15.4 u,g; riboflavin, 5.5 mg; niacin, 52.8 mg; Ca-pantothenate, 12 mg; choline chloride, 824 mg-, folic acid, 1 mg; pyridoxine, 3.3 mg; thiamine, 2.2 mg; d-biotin, 110 ug; ethoxyquin, 125 mg; selenium, 1.0 mg; Mn, 66 mg; Fe, 22 mg; Cu, 2.2 mg; Zn, 49.5 mg; 1,1.1 mg; Ca, 600 mg. 3 Chick grower diet contained the following per kilogram: vitamin A, 4,840 IU; vitamin D3,2,200 IU; vitamin E, 11 IU; menadione sodium bisulfite, .75 mg; vitamin B 1 2 , 11.2 ug; riboflavin, 5.5 mg; niacin, 26.4 mg; Ca-pantothenate, 11 mg; choline chloride, 385 mg; folic acid, .55 mg; pyridoxine, 2.7 mg; thiamine, 2.2 mg; d-biotin, 5.5 ug; ethoxyquin, 125 mg; selenium, 1.0 mg; Mn, 66 mg; Fe, 22 mg; Cu, 2.2 mg; Zn, 49.5 mg; I, 1.1 mg; Ca, 600 mg. 4 G.V.-11 = A grade name for gentian violet (Naremco Inc., Springfield, MO) containing 1.6% gentian violet. The diet contained Coban at a concentration of 90 mg/ kg6 The National Research Council (1984) published ingredient specifications were used to calculate the nutrient content of each diet.
age, the pullets are started on a quantitative feed restriction program and are switched to a grower or developer diet that is lower in protein (14 to 16% protein) and may be slighdy lower in energy (2,750 to 2,850 kcal ME/kg). It is within this range of dietary constraints in the starter and grower feeds that
the question arises, can the diet influence skeletal development independent of any changes in the pattern of BW gain? Leeson and Summers (1984) and Lilburn et al. (1987) reported that very low levels of dietary protein can significantly decrease shank length during the ad libitum starter period. Once chicks are fed a common diet or feed intake is restricted, however, these differences in shank length disappear. The objective of the experiments reported herein was to study the relationship between differences in dietary density and skeletal and muscle growth in broiler breeder pullets whose BW gain was controlled by quantitative feed restriction. MATERIALS AND METHODS
Experiment 1. This experiment was designed to study the independent effects of BW gain (as controlled by feed restriction) and nutrient intake on overall growth and development of broiler breeder pullets. A total of 720 commercial broiler breeder pullets was assigned to 12 floor pens (9.45 m 2 ). All chicks were fed ad libitum a commercial grower diet (Table 1) from 0 to 14 days of age before being assigned to restricted feeding treatments. The experiment was designed as a 3 x 2 factorial with three restricted feeding programs and two diets, with two replicate pens per treatment. The two diets fed in this experiment were a commercial broiler starter diet and a pullet grower diet (Table 1). Each diet was fed to one-half the birds in the experiment (i.e., broiler starter to 6 pens; pullet grower to 6 pens) from 14 days of age through the remainder of the experiment. A broiler starter diet and a pullet grower diet were chosen for comparison during the growing period in order to maximize differences in nutrient intake. Within each dietary treatment, two replicate pens were assigned to one of three BW groupings: light, control, or heavy. The BW gain of those pullets in the control treatment was similar to that recommended in the 1985 Hubbard Farms Broiler Breeder Management Guide (Anonymous, 1985-1986). Fifteen birds from each pen were weighed weekly, and the BW gain within each treatment was controlled by adjusting the weekly feed allowances. The heavy and light BW groupings were intended to be heavier and lighter, respectively, than the control weight birds by 30, 20, and 10% at 8, 12, and 16 wk of age, respectively. The
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Ground yellow corn Dehulled soybean meal (49% CP) Com gluten meal (60% CP) Dried brewers grains Blended fat Ground barley Wheat middlings Meat + bone meal (48% CP) Dicalcium phosphate (38.5%) Menhaden fishmeal (60% CP) Limestone Methionine premix1 Salt Vitamin-mineral premix2'3 G.V.-ll 4 Coccidiostar Composition6 CP, analyzed ME, calculated (kcal/kg) Ca, calculated Available P, calculated
1275
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LILBURN ET AL.
different amounts of the same diet; this was only 92 and 66%, respectively, of the control feed allotments. At 4, 8, and 16 wk of age, 15 chicks from each pen were randomly selected and killed by cervical dislocation. No attempt was made to equalize BW for carcass comparisons as in Experiment 1. Abdominal fat weight was measured. This weight included all the fat around the gizzard, but none associated with the intestine. Statistical Analysis. All data were subject to analysis of variance (least squares) using the general linear model procedure of the Statistical Analysis System, Cary, NC. In the first experiment, the effects tested were BW grouping (light, control, heavy), diet (grower, broiler starter), and their interaction. The variation due to replicate pen was not significant and was, therefore, included in the overall error term. Data were analyzed separately for each age. In Experiment 2, data were also analyzed separately for each age using a one-way analysis of variance. Dietary treatment was the main effect tested within each age; where significant differences occurred, means were separated using Duncan's new multiple range test (Steel and Torrie, 1960). RESULTS
In Experiment 1, there were no significant effects of diet on skeletal development. Feed restriction was used to manipulate BW gain (Table 2); BW grouping did significandy influence skeletal growth (Table 3). At 12 and
TABLE 2. Cumulative feed consumption of broiler breeders fed either a broiler starter or grower diet and differentially feed restricted to achieve three different body weight classes during growth BW grouping1 Light Control Heavy
Diet
8
Broiler starter Grower Broiler starter Grower Broiler starter Grower
.93 1.11 1.23 1.68 2.46 2.87
Age (wk) 12 16 (kg/bird) 2.48 4.42 2.81 4.85 3.19 5.10 4.00 6.08 4.67 6.74 5.33 7.56
In this study, 720 pullets were randomly divided among 12 pens at 1 day of age. Four pens were randomly allotted to each of the body weight groups; half the pens within each group were fed either the broiler starter or pullet grower diets.
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authors were not always successful in maintaining these exact differences between the BW groupings, but this slight deviation from the experimental design did not interfere with the overall objective of the study. In order to guarantee all birds access to relatively equal quantities of feed, all treatments were fed on an alternate day basis beginning with the onset of restriction at 14 days of age. Feeder space was initially .13 m/bird at this age, and deaths did not exceed 5% in any pen from 14 days of age through the remainder of the study. All feed allotments were adjusted for deaths as needed. At 8, 12, and 16 wk of age, 12 birds per pen that were close to the target weight for that treatment were killed by cervical dislocation and dissected for skeletal and muscle measurements. The length of four major long bones (keel, clavicle, tibia, shank) was measured to the nearest .5 cm. The right half of the pectoralis major was also isolated by dissection and weighed. Experiment 2. This experiment was designed to test the hypothesis that dietary energy intake is the first limiting nutrient controlling BW gain and skeletal growth in dietarily restricted broiler breeders. A total of 540 commercial breeder pullets was randomly assigned to nine of those pens used in Experiment 1. The same broiler starter and pullet grower diets (Table 1) as used in Experiment 1 were again fed. In the control treatment, the birds in three pens were fed the grower diet for the duration of the experiment. Fifteen birds from each of the control pens were weighed weekly beginning at 2 wk of age. The average BW from those three pens was used in adjusting their weekly feed allotments. Weekly feed allowances for the control were dependent upon how the BW for that particular week compared with the recommended BW for that age as described in the Hubbard Farms Broiler Breeder Management Guide (Anonymous, 1985-1986). In the second treatment (broiler starter calorie), pullets in three pens were fed the broiler starter diet, but were restricted to the same calculated calorie intake as that of the control treatment. In the third treatment (broiler starter protein), chicks in another three pens were also fed the broiler starter diet; they received me same calculated protein intake as the control treatment. Pullets in the broiler starter calorie and broiler starter protein treatments thus received
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NUTRIENT INTAKE AND SKELETAL GROWTH TABLE 3. Effect of diet and body weight groupings on carcass components in broiler breeders at 8 wk of age (Experiment 1) BW grouping1'2
Diet
BW
Broiler starter Grower Broiler starter Grower Broiler starter Grower SEM
420 472 666 692 1,011 1,044 32
Pectoralis major
Bone length Keel
Tibia
7.1 7.3 8.3 8.0 8.9 9.1 .2
7.7 8.0 8.9 8.9 11.0 10.8 .2
Shank
, ,,
(r\ \B)
Light Control Heavy
10.1 10.2 19.0 16.7 32.3 30.5 1.1 179 0001 927
.154 .0001 .499
.928 .0001 .372
5.9 5.9 7.1 7.2 8.8 8.6 .2
.822 .0001 .298
.923 .0001 .835
3.0 3.3 3.5 3.6 4.2 4.1 .1 .230 .0001 .172
'The body weight grouping was achieved by controlling the feed allotments of broiler starter and pullet grower diets, respectively. The control treatment corresponds to the body weight recommendation outlined in the Hubbard Farms Management Guide, 1985-86 (Anonymous, 1985-86). 2 In this study, 720 pullets were randomly divided among 12pensat 1 day of age. Four pens were randomly allotted to each of the body weight groups, and half the pens within each group were fed either the broiler starter or pullet grower diets.
16 wk of age, however, those pullets fed broiler starter diets did have significandy greater p. major muscle development (Tables 4 and 5). Data also showed a large variation among BW groupings in the measured lengths of individual skeletal components. At 8 wk of age, keel length in the light BW grouping was 20% shorter man in the heavy BW group, whereas the shank length was 32% shorter as calculated from the corresponding groups. At 16 wk of age, the heavy group was still 20% heavier in BW than the light BW group, but the differences in the lengm of all the bones measured was less than 10%. In Experiment 2, those pullets in die broiler starter calorie treatment were significantly heavier (15%) and lighter (12%) than those pullets in die control treatment at 4 and 8 wk, respectively (Table 6). Birds in bodi treatments were significantly heavier than mose in the broiler starter protein treatment at 8 and 16 wk. At the latter two ages, chicks in the broiler starter protein treatment had the shortest bones, whereas birds in the other two treatments were similar in skeletal measurements. At 4 and 8 wk, the size of the p. major muscle followed the same pattern as BW. At both 4 and 8 wk, abdominal fat measures were significandy lower in both the broiler starter calorie and broiler starter protein treatments than in
controls. At 16 wk, mere were no significant differences between BW or abdominal fat measures of birds in control and broiler starter calorie treatments, but p. major muscles were significandy larger in the latter treatment. Pullets in the broiler starter protein treatment had significandy less abdominal fat and smaller p. major muscles than mose in the control treatment at 8 and 16 wk of age. DISCUSSION
These data support the hypothesis mat frame size or skeletal growtfi in broiler breeders is primarily a function of BW gain. Multiple regression analysis showed tiiat BW alone accounted for most of the variation in keel (R2 = .633) and tibia length (R2 = .808) at 12 wk of age (n = 72). The model was not significandy changed by adding in die cumulative intakes of energy (kilocalories) and protein (keel, R 2 = .641; tibia, R 2 = .838, respectively). Differences in dietary protein and energy can influence the rate of gain and in this way indirecdy influence skeletal growm. In commercial practice, however, where BW gain is closely monitored, nutrient density itself will not specifically increase or decrease linear skeletal development. Data from both experiments (Tables 3 to 6) support
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Probability Source of variation, df Diet (D), 1 BW grouping (BWG), 2 D x BWG, 2
Clavicle
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LILBURN ET AL. TABLE 4. Effect of diet and body weight grouping on carcass composition in broiler breeders at 12 wk of age (Experiment 1)
BW grouping1,2
Diet
BW
Broiler starter Grower Broiler starter Grower Broiler starter Grower SEM
958 945 1,200 1,255 1,654 1,592 55
Pectoralis major
Bone length Keel
Tibia
8.6 8.8 9.2 9.4 10.7 10.3 .2
10.7 11.0 11.8 11.9 13.4 13.0 .2
Shank
,
(r>
Light Control Heavy
884 j0001 356
.042 .0001 .741
.793 .0001 .482
N
13.6 13.8 14.9 14.9 16.4 16.5 .2
.601 .0001 .691
.731 .0001 .861
4.3 4.5 4.8 4.8 5.1 5.2 .1
.334 .0001 .900
T h e body weight grouping was achieved by controlling the feed allotments of broiler starter and grower diets, respectively. The control treatment corresponds to the body weight recommendation outlined in the Hubbard Farms Management Guide, 1985-86 (Anonymous, 1985-86). In this study, 720 pullets were randomly divided among 12 pens at 1 day of age. Four pens were randomly allotted to each of the body weight groups, and half the pens within each group were fed either the broiler starter or pullet grower diets.
TABLE 5. Effect of diet and body weight grouping on carcass components in broiler breeders at 16 wk of age (Experiment 1) BW grouping1,2
Diet
Pectoralis major
BW
Bone length Keel
Tibia
10.7 10.6 10.7 11.2 11.7 11.5 .1
13.0 12.4 12.9 13.4 13.3 13.4 .2
fri
Light Control Heavy
Broiler starter 1,589 1,521 Grower Broiler starter 1,589 Grower 1,698 Broiler startei-1,937 Grower 1,955 SEM 59
Probability Source of variation, df Diet (D), 1 BW grouping (BWG), 2 D x BWG, 2
59.5 50.8 62.3 60.3 82.6 71.3 3.1 679 0001 332
1
.001 .002 .354
.816 .0001 .511
Shank — (cm) 16.0 15.7 15.8 16.5 16.7 16.9 .2
.604 .0001 .804
.962 .0001 .678
Clavicle 5.2 5.1 5.5 5.4 5.6 5.7 .1 .615 .0001 .121
The body weight grouping was achieved by controlling the feed allotments of broiler starter and pullet grower diets, respectively. The control treatment corresponds to the body weight recommendation outlined in the Hubbard Farms Management Guide, 1985-86 (Anonymous, 1985-86). 2 In this study, 720 pullets were randomly divided among 12 pens at 1 day of age. Four pens were randomly allotted to each of the body weight groups, and half the pens within each group were fed either the broiler starter or pullet grower diets.
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Probability Source of variation, df Diet (D), 1 BW grouping (BWG), 2 D x BWG, 2
27.3 27.1 38.8 37.9 60.9 53.8 2.2
Clavicle
Control Broiler starter calorie Broiler starter protein3
Control Broiler starter calorie Broiler starter protein
Control Broiler starter calorie Broiler starter protein
4
8
16
419 483 418 974 867 707 1,959 2,018 1,556
BW
± ± ± ± ± ± ± ± ±
llb 16" 12b 19" 18 b 19° 58" 48" 38 b ± ± ± ± ± ±
(g) — .4° .6" .5 b .8" .7 b .9C
83.1 ± 3.6b 97.6 ± 3.8" 72.3 ± 3.4C
10.1 14.8 12.5 25.9 21.8 16.4
Pectoralis major 4.8 2.7 1.9 8.2 4.3 1.6 38.2 31.6 8.5
± ± ± ± ± ± ± ± ±
.7" .4 b .2 b 1.2" .7 b .2C 4.9" 4.1" 1.6b
Abdominal fat ± .lb ± .1" ± .lb ± .1" ± .1" ± .lb ± .2" ± .2" ± .lb 7.8 8.1 7.8 10.9 10.7 10.1 15.3 15.3 14.7
Tibia ± ± ± ± ± ± ± ± ±
.1" .1" .1" .1" .1" .1" .1" .1" .1"
(cm) 10.1 ± .1" 10.6 ± .1" 10.2 ± .1" 13.9 ± .1" 13.7 ± .1" 12.9 ± .2 b 16.4 ± .1" 16.4 ± .1" 15.9 ± .1"
Shank
Bone length
3.9 3.9 3.9 4.5 4.5 4.4 6.3 6.2 5.9
± ± ± ± ± ± ± ± ±
la .1" ,lb
.1 .1 .1 .1 .1 .1
Clavicle
^Differences in body weight and carcass components in these two treatments are the result of quantitative differences in consumption of similar diets.
Treatments consisted of: the 15% protein grower diet (control); the broiler starter diet adjusted weekly to the same calculated calorie intake as that obtained with the grower diet (broiler starter calorie); and the broiler starter diet adjusted to the same calculated protein intake as the grower ration (broiler starter protein). Body weight gains were in accordance with the recommendation of the Hubbard Farms Management Guide, 1985-86.
5.9 6.4 6.1 8.4 8.4 7.9 12.0 12.3 11.6
Keel
3
_
3
a JO o
AKE AND SKELET
'Mean ± SE.
Means within column and age with no common superscripts are significantly different (P<.05).
Treatment2
Age
a_c
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TABLE 6. Influence of protein versus energy intake on muscle and fat accretion in broiler breeder pullets (Experiment 2f NUTRIEN1
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LILBURN ET AL.
skeletal growth. The weight of the p. major muscle was a reflection of differences in BW at 4 and 8 wk of age. At 16 wk of age, however, the increased protein intake associated with the broiler starter calorie treatment did significantly increase pectoralis muscle size. This treatment also resulted in less abdominal fat at all ages; this is a function of an increased protein-to-energy ratio when caloric intake is equalized. The muscle and protein changes suggest that carcass composition in feed restricted pullets can be manipulated without any major changes in BW or skeletal growth. In the present experiment, when protein intakes were equalized, an energy deficiency effect was created in birds in the broiler starter protein treatment; this was reflected in significantly decreased BW and impaired skeletal development at 8 and 16 wk. At 8 wk, pullets in the broiler starter protein treatment weighed 82 and 73% as much as those in the broiler starter calorie and control treatments, respectively; the differences were approximately the same, 77 and 79%, respectively, at 16 wk. Although the differences in BW were substantial, differences in skeletal measurements at the latter two ages were less than 6%. These results suggest, therefore, that under commercial situations, there would need to be a very large shift in BW gain before skeletal growth would be affected significantly by energy deficiency of the magnitude used in the present experiments. ACKNOWLEDGMENTS
The authors wish to diank Laurel Newman and Wanda Acord for their help in the preparation and handling of this manuscript. REFERENCES Anonymous, 1985-1986. Hubbard Farms Broiler Breeder Management Guide, 1985-86. Hubbard Farms, Walpole, NH. Leeson, S., and J. D. Summers, 1984. Influence of nutritional modification on skeletal size of Leghorn and broiler breeder pullets. Poultry Sci. 63:1222-1228. Lilburn, M. S., K. Ngiam-Rilling, and J. H. Smith, 1987. Relationships between dietary protein, dietary energy, rearing environment, and nutrient utilization by broiler breeder pullets. Poultry Sci. 66:1111-1118. McDaniel, G. R., J. Brake, and M. K. Eckman, 1981. Factors affecting broiler breeder performance. 4. The interrelationship of some reproductive traits. Poultry Sci. 60: 1792-1797. National Research Council, 1984. Nutrient Requirements of
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the results of Wagner (1979), which showed different planes of nutrition significantly influenced BW gain and skeletal growth in similar aged chickens. Leeson and Summers (1984) fed increasing protein levels (13 to 20%) to young pullets (0 to 21 days); the present results support their data showing that dietary effects on skeletal development appear to be lost once BW is equalized via restricted feeding. Although simple control of BW gain by feed restriction did effectively restrict skeletal growth, other aspects of carcass development responded to the nutrient content of the diet. At 12 and 16 wk of age in Experiment 1 and at 16 wk of age in Experiment 2, p. major muscle growth responded to specific manipulations of calorie and protein intake even where no differences may have existed in BW or skeletal growth (Tables 4 to 6). Wagner (1979) also observed that when chickens from different nutritional treatments were grouped according to keel length, there were still significant differences in pectoral muscle weights. The relationship between energy intake and BW gain is very strong in feed restricted broiler breeder pullets (Lilburn et ah, 1987) and adult breeder hens (Spratt and Leeson, 1987). Results from Experiment 2 support the previous observations. Similar energy intakes from 2 to 16 wk resulted in similar BW and skeletal measurements at the latter age. This was not the case at 4 and 8 wk of age, however. From 2 to 4 wk, the calculated feed allotment for those pullets in the broiler starter calorie treatment was obviously in excess of the birds' requirements for the desired amount of gain. Those pullets sampled from the control and broiler starter protein treatments had similar BW and skeletal measurements at 4 wk of age, suggesting that dietary protein intake may be more important than energy in controlling growth of very young birds. At 8 wk of age, pullets in the broiler starter calorie treatment derived a greater percentage of their energy needs from dietary protein than birds in the control treatment. The less efficient utilization of protein as an energy source may have contributed to the significantly greater BW in pullets from the control treatment. The differences in BW, however, were not reflected in any significant differences in skeletal measurements. This latter observation supports the data from Experiment 1 showing that within a given range of BW, there are no differences in
NUTRIENT INTAKE AND SKELETAL GROWTH Poultry. Natl. Acad. Sci., Washington, DC. Pearson, R. A., and K. M. Herron, 1981. Effects of energy and protein allowances during lay on the reproductive performance of broiler breeder hens. Br. Poult. Sci. 22: 227-239. Spratt, R. S., and S. Leeson, 1987. Broiler breeder performance in response to diet protein and energy. Poultry
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Sci. 66:683-693. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., New York, NY. Wagner, J., 1979. The influence of the nutrition level of the skeletal growth in chicken. Pr. Mater. Zootech. 20: 41-53.
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