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Effect of Feed Restriction on Growth, Body Composition, and Egg Production of Broiler Females Through 68 Weeks of Age
Effect of Feed Restriction on Growth, Body Composition, and Egg Production of Broiler Females Through 68 Weeks of Age KELLY R. ROBBINS,1 GEORGE C. McGHEE,1 PETER OSEI,1 and ROY E. BEAUCHENE2 University of Tennessee, Knoxville, Tennessee 37901-1071 (Received for publication February 20, 1986)
1986 Poultry Science 65:2226-2231 INTRODUCTION
Restriction of feed intake by broiler breeder females during both the rearing and laying periods is a common industry practice. Such restriction programs can reduce body weight and mortality, improve feed efficiency, and improve egg fertility, shell quality, and production (Pym and Dillon, 1974; Brake and McDaniel, 1981; McDaniel et al, 1981a,b). Most commercial restricted feeding programs consist of severe to moderate restriction during rearing, a period of stepwise increases in feed allotment during the pullet-layer transition, and modest feed restriction during the laying period. The age at onset of sexual maturity and subsequent egg production are affected by both degree and length of feed restriction during rearing, although the response does vary among strains (Pym and Dillon, 1974; Brody et al, 1980, 1984). Restriction to 50% of ad libitum feed consumption during rearing is not uncommon. However, heavy, rapid growing strains appear to respond favorably to even more severe restriction.
'Department of Animal Science. Department of Nutrition and Food Science.
2
Many breeder management guides recommend a stepwise increase in feed allotment during the pullet-layer transition period. However, Bornstein and Lev (1982) demonstrated that an abrupt increase in daily energy allowance 2 or 3 weeks prior to onset of egg production resulted in better performance than a regimen of slow, gradual increases in feed allotment based on flock production rate. There appears to exist both age and body weight limits below which broiler breeder hens will not become sexually mature (Brody et al, 1980,1984; Bornstein et al, 1984; Soller et al, 1984). Because of the degree of restriction imposed during rearing, the lower age limit is usually exceeded; age at sexual maturity is primarily a function of body weight, and, more specifically, lean body mass (Soller et al., 1984). For example, sexual maturity of breeders switched from a restricted to an ad libitum feeding program at either 22 or 35 weeks of age occurred only after a period of compensatory growth (Brody et al, 1980). Hence, it appears that an abrupt rather than a gradual increase in feeding level during the pullet-layer transition may hasten sexual development and promote flock uniformity. The effect of feed restriction during the laying period has been less well studied. In a study in which laying feeding regimen was not confounded with rearing treatment (Pym and Dillon,
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ABSTRACT Effects of ad libitum and restricted (50% of ad libitum) feeding on performance of female broilers were assessed in a 68-week experiment. The treatments imposed were AA, fed ad libitum throughout; RR, fed restricted amounts of feed throughout; RA, restricted through 24 weeks of age and ad libitum thereafter; and AR, fed ad libitum through 24 weeks and restricted thereafter. Average age at first egg was delayed by 17 days in RA hens compared with AA hens. Average body weight at first egg was 3.9 kg for RA birds and 4.5 kg for AA birds. Peak production was higher for RA birds (71 vs. 59%), but age at peak production was similar for both AA and RA hens. Through 68 weeks, AR birds produced 50% more eggs than AA birds (159 vs. 106). Cumulative number of eggs produced for RR and AR birds were 37 and 47, respectively. Mortality was similar for RR, RA, and AR birds but was approximately fourfold greater in AA birds. At 68 weeks of age, live body, carcass, abdominal fat pad, and estimated fat-free carcass weights were similar for AA and RA birds. Although abdominal fat as a percent of carcass weight was similar for AR and RR birds, average live weight, carcass weight, and fat-free carcass weight were higher for AR than RR birds at 68 weeks. (Key words: broiler breeders, feed restriction, sexual maturity, production)
DIETARY RESTRICTION OF BROILER FEMALES
age; and RA, restricted (50% ad libitum) feed consumption through 24 weeks of age and ad libitum consumption from 24 to 68 weeks of age. All birds were allowed unlimited access to feed during the first 3 days of the experiment. Thereafter, a randomly selected pen assigned to treatment AA was used to calculate daily feed allotments for all other pens through Week 24 and for all pens except those assigned to treatment RA from 24 to 68 weeks of age. A randomly selected RA pen was used to calculate daily feed allotment for this treatment after 24 weeks of age. Feed consumed during a 24-hr period by the randomly selected reference pen was measured every 3rd day with daily feed allotments for the subsequent 3 days for the other pens calculated from this measure. The compositions of the diets fed are presented in Table 1. Average daily feed consumptions for each treatment are presented in Table 2. Chicks were hatched in May. Birds were subjected to natural day length through 13 weeks of age. During the period 14 through 17 weeks of age, 13 hr of daily light were provided; during 18 through 25 weeks of age, 14 hr of daily light were provided; and beginning at 26 weeks of age, 15 hr of daily light were provided. All birds were administered Newcastle-bronchitis vaccine at 7 days, 8 weeks, and 14 weeks of age. Fowl
MATERIALS AND METHODS
Fifty 1-day-old female broiler chicks (Hubbard x Hubbard) were individually wingbanded and randomly distributed to each of 12 floor pens (11.2 centares each) in a conventional-type broiler house. Three randomly selected pens were assigned to each of four treatments: AA, ad libitum feed consumption through 68 weeks of age; RR, restricted (50% of ad libitum) feed consumption through 68 weeks of age; AR, ad libitum feed consumption through 24 weeks of age and restricted (50% ad libitum) consumption from 24 to 68 weeks of
TABLE 1. Percentage composition of diets
Ingredient Yellow corn Soybean meal Alfalfa meal (17% CP) Menhaden fish meal Rock phosphate Limestone Vitamin mix A 1 Vitamin mix B 2 Salt Coccidiostat premix Manganous sulfate Calculated analysis Crude protein, % Metabolizable energy, kcal/kg Calcium, % Available phosphorus %
International feed number 4-02-935 5-04-612 1-00-023 5-02-009 6-01-780 6-02-632
Period fed (weeks of age) 0-3 72.8 13.9 5.64 5.0 1.2 .5 .6 O .25 .10 .03 17.2 3,000 .96 .48
3-16 73.95 14.0 6.5 2.5 1.57 .4 .6 0 .35 .10 .025 16.0 2,980 .95 .48
17-21 73.96 14.1 6.5 2.5 1.57 .4 .6 0 .35 0 .025 16.0 2,980 .95 .48
22-68 64.15 18.0 6.5 2.5 1.62 6.2 0 .65 .35 0 .025 17.0 2,740 3.16 .48
'Contained per kilogram: vitamin D 3 , 125,000 ICU; vitamin A, 700,000 IU; riboflavin, 790 mg; vitamin B ] 2 , 1.83 mg; niacin, 6.94 g; D-Ca panthothenate, 1.22 g; choline, 78 g. 'Contained per kilogram: vitamin D 3 , 600,000 ICU; vitamin A, 500,000 IU; riboflavin, 910 mg; vitamin B 1 2 , 1.31 mg; niacin, 5.00 g; D-Ca-pantothenate, 875 mg; choline, 76.5 g.
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1974), ad libitum feed consumption during laying resulted in higher production of hatchable eggs but also higher hen mortality when compared with birds restricted during laying. The present study was conducted to evaluate further the effects of restricted versus ad libitum feeding during both the rearing and laying phases on growth, body composition, mortality, and egg production. More specifically, our objective was to define better the relationship of body weight and composition with mortality and hen performance. In an attempt to maximize treatment differences, a heavy, rapid growing commercial broiler strain was used in lieu of a breeder strain.
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ROBBINS ET AL. TABLE 2. Average feed
consumption
Treatment Age
1
AR
RR
RA
58 125 159 176 193 227 224 211 228 202 192 196 188 174 167 140 168
58 125 159 176 193 227 110 107 116 102 96 95 94 87 83 69 84
29 62 80 88 96 111 110 107 116 102 96 95 94 87 83 69 84
29 62 80 88 96 111 210 278 218 216 210 208 202 197 174 155 158
(months) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1
AA = Fed ad libitum throughout; RR = fed onehalf ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum thereafter; AR = fed ad libitum through 24 weeks of age, and one-half ad libitum thereafter.
pox vaccine was administered at 12 weeks of age. Access to water was unlimited. Trapnests were installed in each pen when birds were 16 weeks of age, and individual egg production was recorded throughout the experiment. Birds were weighed individually every 2 weeks through 24 weeks of age and approximately monthly thereafter. During 20 to 52 weeks of age, 16 randomly selected birds from each pen were permanently removed for physiological assays (not reported). As a result of removal of these birds, and removal of missexed, morbid, and dead birds, 45 birds on Treatment AA, 80 birds on RR, 78 birds on AR, and 85 birds on RA completed the experiment. Upon conclusion of the experiment, all birds were weighed, killed, and processed. Abdominal fat pad was excised from the dressed carcass. For each bird, weights were obtained for the abdominal fat pad and the dressed carcass in both air and water (at ambient temperature). A sample of 25 carcasses (minus fat pad), which varied considerably in weight, was saved for subsequent analysis. These carcasses were individually ground through a meat grinder, dried to greater than 95% dry matter in a forced-air
RESULTS AND DISCUSSION
Mean body weights through 68 weeks of age are presented in Figure 1. The RA birds responded to ad libitum feeding with a rapid increase in body weight from Week 24 to approximately Week 30. After Week 30, they continued to grow, but at a slower rate, and achieved an average body weight equal to that of AA birds at 68 weeks of age (Fig. 1, Table 4). Pym and Dillon (1974) imposed four levels of feed restriction (100%, 80%, 60%, and 40% of ad libitum) and also observed that ad libitum feeding during the laying period resulted in equivalent 67-week body weights regardless of rearing treatment. Average age and body weight at first egg were 174 days and 4.5 kg, respectively, for A A birds and 191 days and 3.9 kg, respectively, for RA birds (Table 4; Fig. 1). Soller et al. (1984) found that, regardless of the degree of feed restriction during rearing, birds entered lay at the same lean body weight, ash, and protein content but at different age, carcass weight, dry matter, and fat content. Based on their results, it is likely that the .6 kg difference in body weight of A A and RA birds at first egg was primarily due to a difference in body fat content. The data further suggest that the rapid growth of RA birds between 24 and 27 weeks of age was largely due to an increase in lean body mass; average lean carcass weight of RR birds was 78% that of RA birds at 68 weeks of age (Table 4), and average live weight of RR birds was approximately 75% that of RA birds at 27 weeks of age (Fig. 1). The slower rate of growth of RA birds from 30 to 68 weeks of age was likely due to body fat accumulation. Peak egg production of AA birds was 59% at 30 weeks of age and for RA birds was 71% at 31 weeks of age (Fig. 2). The RA birds produced an average of 50% more eggs than AA
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AA
drying oven (60 C for 72 hr), and subsampled for fat analysis. Samples were analyzed for ether extract per methodology of the Association of Official Analytical Chemists (AOAC, 1970). Percent carcass fat was expressed on a fresh tissue basis. Using data obtained from this 25 bird sample, a regression equation was derived (Table 3) from which carcass fat of all other birds was estimated. Analysis of variance with single degree of freedom comparisons was used to assess treatment effects (Steel and Torrie, 1960); pens were considered the experimental units.
DIETARY RESTRICTION OF BROILER FEMALES
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TABLE 3. Prediction equation for estimating dressed carcass fat content1
Variable
n
Mean
SD
Min
Max
Live body wt, g Carcass wt, g Abdominal fat, g Abdominal fat, % of carcass wt Carcass wt in air/carcass wt in water Carcass fat, %
25 25 25
4,108 2,817 153
1,120 726 137
2,420 1,620 ND
5,880 4,000 482
R' a b, b2
4
4.6
3.8
25 25
10.85 19.5
1.62 10.0
13.7
ND 8.10 3.8
13.65 42.3
.874 .871 .906 .910 .891 1.000
Estimate
SE3
Significance
.911 -18.22 2.869 1.427
5.978 .6316 .2656
P<.01 P<.001 P<.001
*n = Number of samples; SD = standard deviation; Min = minimum value (ND = not detectable); Max maximum value. Correlations were all significant (P<.001). 2
Equation: % Carcass fat = a + b, X (carcass wt in air/wt in water) + b 2 X (% abdominal fat)
3
SE = Standard error of estimate.
4
Inclusion of live body weight, carcass weight, and abdominal fat weight increased R 2 by only .003.
birds through 68 weeks (Table 4). We used a heavy, rapid growing broiler strain under the assumption that effects of body composition (particularly fatness) on hen performance would be maximized. Indeed, egg production was substantially lower for A A than for RA birds. This was apparently the result of accumulation of excessive body fat prior to or during the early weeks of lay, because mean body weight and composition of RA and AA birds were similar by 68 weeks of age (Table 4). Contrary to results of Pym and Dillon (1974), mortality of RA birds did not differ significantly from mortality of birds fed restricted amounts of feed during the laying period (Table 4), thus clearly demonstrating that ad libitum feeding of RA birds during lay did not increase mortality rate. However, a very high rate of mortality occurred in A A birds after 24 weeks of age. The highest frequencies of death on treatment AA were associated with the stress of monthly weighing of birds and involved mostly very heavy birds (average weight, 4950 ± 760 g). Eighty percent of the hens on treatment RR reached sexual maturity. Of those that did produce eggs, the average age and weight at first egg were 226 days and 3.2 kg (Table 4, Fig. 1),
:
respectively. Peak production of RR birds was 45% at 37 weeks of age (Fig. 2). The fat-free carcass weight of RR birds at 68 weeks of age was 21% less than AA and RA birds and 12% less than AR birds (Table 4), thus indicating that maximum fat free body mass was not achieved under conditions of continual feed restriction.
AGE (WEEKS)
FIG. 1. Mean body weights through 68 weeks of age. AA = Fed ad libitum throughout; RR = fed one-half ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum thereafter; AR = fed ad libitum through 24 weeks of age and one-half ad libitum thereafter.
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Parameter 2
25
Correlation with carcass fat
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ROBBINS ET AL. TABLE 4. Summary of production characteristics through 68 weeks of age Treatment 1
Item
RR
AA
RA
AR
pSEM2
Mortality, %3 Total eggs per hen 3 Age at first egg, days 3 Live weight at 68 weeks, g3 Carcass weight, g3 Abdominal fat, % of carcass weight s Carcass weight in air/carcass wt. in water, g/g s Fat-free carcass weight, g 3,6
8 37 226" 2,675 1,891
38 106 174 4,842 3,377
10 159 191 4,860 3,300
10 47 176 3,045 2,253
2.5 4.8 3.9 58.8 60.3
1.12
7.75
8.20
1.48
.453
9.87 1,717
14.79 2,169
13.88 2,192
10.04 1,958
.565 43.5
2
pSEM = Pooled standard error of the mean; 8 degrees of freedom.
3
The main effect of 0 to 24 week feeding regimen; the main effect of 24 to 68 week feeding regimen; and their interaction were significant (P<.05). 4
20.5% of the birds on this treatment produced 0 eggs and are not included in this figure.
5
The main effect of 24 to 68 week feeding regimen was significant (P<.001).
6
Estimated from carcass weight using the prediction equation described in Table 3.
Between 24 and 68 weeks of age, AR birds lost an average of 1.5 kg body weight (33% of 24 week body weight). Given that the average fat-free carcass weight of AR birds was 90% that of AA birds at 68 weeks, most or all of the weight loss probably consisted of fat. This response demonstrates that excessive fat deposited
FIG. 2. Mean percent hen-day production through 68 weeks of age. AA = Fed ad libitum throughout; RR = fed one-half ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum therafter; AR = fed ad libitum through 24 weeks of age and one-half ad libitum thereafter.
during the rearing phase is not refractory to dietary restriction. The response of RR birds was particularly surprising. Bornstein et al. (1984) concluded that a high degree of fatness is associated with the onset of ovulation. Brody et al. (1980) found that hens maintained at a low mean body weight by continued restriction did not mature sexually. In our study, However, 80% of RR birds did become sexually mature. Although body fat content of RR birds was not determined until 68 weeks of age, they likely were very lean throughout the experiment. Birds assigned to treatment RA produced an average of 159 eggs in 68 weeks, which is a level similar to that achieved by two broiler dam lines in 67 weeks (Pym and Dillon, 1974). Restriction of these birds through 24 weeks of age followed by an abrupt switch to ad libitum feeding resulted in a rapid and uniform onset of lay (Fig. 2). The RA birds continued to gain weight between 30 and 68 weeks of age as egg production rate declined. It is likely that this weight gain consisted primarily of fat and was due to decreased demand for productive energy. If so, diet restriction could have controlled body weight and reduced the amount of feed per egg. However, based on our results, mortality would not have been reduced.
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' A A = Fed ad libitum throughout; RR = fed one-half ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum thereafter; AR = fed ad libitum through 24 weeks of age, and one-half ad libitum thereafter.
DIETARY RESTRICTION OF BROILER FEMALES ACKNOWLEDGMENT
The authors sincerely thank Adesina Adekunmisi for his expert technical assistance. REFERENCES
of hatching. Br. Poult. Sci. 21:437^*46. Brody, T. B., P. B. Siegel, and J. A. Cherry, 1984. Age, body weight and body composition requirements for the onset of sexual maturity of dwarf and normal chickens. Br. Poult. Sci. 25:245-252. McDaniel, G. R., J. Brake, and R. D. Bushong, 1981a. Factors affecting broiler breeder performance. 1. Relationship of daily feed intake level to reproductive performance of pullets. Poultry Sci. 60:307-312. McDaniel, G. R., J. Brake, and M. K. Eckman, 1981b. Factors affecting broiler breeder performance. 4. The interrelationship of some reproductive traits. Poultry Sci. 60:1792-1797. Pym, R.A.E., and J. F. Dillon, 1974. Restricted food intake and reproductive performance of broiler breeder pullets. Br. Poult. Sci. 15:245-259. Soller, M., Y Eitan, andT. Brody, 1984. Effect of diet and early quantitative feed restriction on the minimum weight requirement for onset of sexual maturity in White Rock broiler breeders. Poultry Sci. 63:12551261. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Procedures of Statistics. McGraw-Hill Book Co., Inc., New York, NY.
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 24, 2015
Association of Official Agricultural Chemists, 1970. Official methods of analysis. 11th ed. Washington, DC. Bornstein, S., and Y. Lev, 1982. The energy requirements of broiler breeders during the pullet-layer transition period. Poultry Sci. 61:755-765. Bornstein, S., I. Plavnik, and Y Lev, 1984. Body weight and/or fatness as potential determinants of the onset of egg production in broiler breeder hens. Br. Poul. Sci. 25:323-341. Brake, J., and G. R. McDaniel, 1981. Factors affecting broiler breeder performance. 2. Relationship of daily feed intake to performance of force molted broiler breeder hens. Poultry Sci. 60:313-316. Brody, T , Y Eitan, M. Soller, I. Nir, and Z. Nitsan, 1980. Compensatory growth and sexual maturity in broiler females reared under severe food restriction from day
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1986 Poultry Science 65:2226-2231 INTRODUCTION
Restriction of feed intake by broiler breeder females during both the rearing and laying periods is a common industry practice. Such restriction programs can reduce body weight and mortality, improve feed efficiency, and improve egg fertility, shell quality, and production (Pym and Dillon, 1974; Brake and McDaniel, 1981; McDaniel et al, 1981a,b). Most commercial restricted feeding programs consist of severe to moderate restriction during rearing, a period of stepwise increases in feed allotment during the pullet-layer transition, and modest feed restriction during the laying period. The age at onset of sexual maturity and subsequent egg production are affected by both degree and length of feed restriction during rearing, although the response does vary among strains (Pym and Dillon, 1974; Brody et al, 1980, 1984). Restriction to 50% of ad libitum feed consumption during rearing is not uncommon. However, heavy, rapid growing strains appear to respond favorably to even more severe restriction.
'Department of Animal Science. Department of Nutrition and Food Science.
2
Many breeder management guides recommend a stepwise increase in feed allotment during the pullet-layer transition period. However, Bornstein and Lev (1982) demonstrated that an abrupt increase in daily energy allowance 2 or 3 weeks prior to onset of egg production resulted in better performance than a regimen of slow, gradual increases in feed allotment based on flock production rate. There appears to exist both age and body weight limits below which broiler breeder hens will not become sexually mature (Brody et al, 1980,1984; Bornstein et al, 1984; Soller et al, 1984). Because of the degree of restriction imposed during rearing, the lower age limit is usually exceeded; age at sexual maturity is primarily a function of body weight, and, more specifically, lean body mass (Soller et al., 1984). For example, sexual maturity of breeders switched from a restricted to an ad libitum feeding program at either 22 or 35 weeks of age occurred only after a period of compensatory growth (Brody et al, 1980). Hence, it appears that an abrupt rather than a gradual increase in feeding level during the pullet-layer transition may hasten sexual development and promote flock uniformity. The effect of feed restriction during the laying period has been less well studied. In a study in which laying feeding regimen was not confounded with rearing treatment (Pym and Dillon,
2226
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ABSTRACT Effects of ad libitum and restricted (50% of ad libitum) feeding on performance of female broilers were assessed in a 68-week experiment. The treatments imposed were AA, fed ad libitum throughout; RR, fed restricted amounts of feed throughout; RA, restricted through 24 weeks of age and ad libitum thereafter; and AR, fed ad libitum through 24 weeks and restricted thereafter. Average age at first egg was delayed by 17 days in RA hens compared with AA hens. Average body weight at first egg was 3.9 kg for RA birds and 4.5 kg for AA birds. Peak production was higher for RA birds (71 vs. 59%), but age at peak production was similar for both AA and RA hens. Through 68 weeks, AR birds produced 50% more eggs than AA birds (159 vs. 106). Cumulative number of eggs produced for RR and AR birds were 37 and 47, respectively. Mortality was similar for RR, RA, and AR birds but was approximately fourfold greater in AA birds. At 68 weeks of age, live body, carcass, abdominal fat pad, and estimated fat-free carcass weights were similar for AA and RA birds. Although abdominal fat as a percent of carcass weight was similar for AR and RR birds, average live weight, carcass weight, and fat-free carcass weight were higher for AR than RR birds at 68 weeks. (Key words: broiler breeders, feed restriction, sexual maturity, production)
DIETARY RESTRICTION OF BROILER FEMALES
age; and RA, restricted (50% ad libitum) feed consumption through 24 weeks of age and ad libitum consumption from 24 to 68 weeks of age. All birds were allowed unlimited access to feed during the first 3 days of the experiment. Thereafter, a randomly selected pen assigned to treatment AA was used to calculate daily feed allotments for all other pens through Week 24 and for all pens except those assigned to treatment RA from 24 to 68 weeks of age. A randomly selected RA pen was used to calculate daily feed allotment for this treatment after 24 weeks of age. Feed consumed during a 24-hr period by the randomly selected reference pen was measured every 3rd day with daily feed allotments for the subsequent 3 days for the other pens calculated from this measure. The compositions of the diets fed are presented in Table 1. Average daily feed consumptions for each treatment are presented in Table 2. Chicks were hatched in May. Birds were subjected to natural day length through 13 weeks of age. During the period 14 through 17 weeks of age, 13 hr of daily light were provided; during 18 through 25 weeks of age, 14 hr of daily light were provided; and beginning at 26 weeks of age, 15 hr of daily light were provided. All birds were administered Newcastle-bronchitis vaccine at 7 days, 8 weeks, and 14 weeks of age. Fowl
MATERIALS AND METHODS
Fifty 1-day-old female broiler chicks (Hubbard x Hubbard) were individually wingbanded and randomly distributed to each of 12 floor pens (11.2 centares each) in a conventional-type broiler house. Three randomly selected pens were assigned to each of four treatments: AA, ad libitum feed consumption through 68 weeks of age; RR, restricted (50% of ad libitum) feed consumption through 68 weeks of age; AR, ad libitum feed consumption through 24 weeks of age and restricted (50% ad libitum) consumption from 24 to 68 weeks of
TABLE 1. Percentage composition of diets
Ingredient Yellow corn Soybean meal Alfalfa meal (17% CP) Menhaden fish meal Rock phosphate Limestone Vitamin mix A 1 Vitamin mix B 2 Salt Coccidiostat premix Manganous sulfate Calculated analysis Crude protein, % Metabolizable energy, kcal/kg Calcium, % Available phosphorus %
International feed number 4-02-935 5-04-612 1-00-023 5-02-009 6-01-780 6-02-632
Period fed (weeks of age) 0-3 72.8 13.9 5.64 5.0 1.2 .5 .6 O .25 .10 .03 17.2 3,000 .96 .48
3-16 73.95 14.0 6.5 2.5 1.57 .4 .6 0 .35 .10 .025 16.0 2,980 .95 .48
17-21 73.96 14.1 6.5 2.5 1.57 .4 .6 0 .35 0 .025 16.0 2,980 .95 .48
22-68 64.15 18.0 6.5 2.5 1.62 6.2 0 .65 .35 0 .025 17.0 2,740 3.16 .48
'Contained per kilogram: vitamin D 3 , 125,000 ICU; vitamin A, 700,000 IU; riboflavin, 790 mg; vitamin B ] 2 , 1.83 mg; niacin, 6.94 g; D-Ca panthothenate, 1.22 g; choline, 78 g. 'Contained per kilogram: vitamin D 3 , 600,000 ICU; vitamin A, 500,000 IU; riboflavin, 910 mg; vitamin B 1 2 , 1.31 mg; niacin, 5.00 g; D-Ca-pantothenate, 875 mg; choline, 76.5 g.
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 24, 2015
1974), ad libitum feed consumption during laying resulted in higher production of hatchable eggs but also higher hen mortality when compared with birds restricted during laying. The present study was conducted to evaluate further the effects of restricted versus ad libitum feeding during both the rearing and laying phases on growth, body composition, mortality, and egg production. More specifically, our objective was to define better the relationship of body weight and composition with mortality and hen performance. In an attempt to maximize treatment differences, a heavy, rapid growing commercial broiler strain was used in lieu of a breeder strain.
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ROBBINS ET AL. TABLE 2. Average feed
consumption
Treatment Age
1
AR
RR
RA
58 125 159 176 193 227 224 211 228 202 192 196 188 174 167 140 168
58 125 159 176 193 227 110 107 116 102 96 95 94 87 83 69 84
29 62 80 88 96 111 110 107 116 102 96 95 94 87 83 69 84
29 62 80 88 96 111 210 278 218 216 210 208 202 197 174 155 158
(months) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1
AA = Fed ad libitum throughout; RR = fed onehalf ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum thereafter; AR = fed ad libitum through 24 weeks of age, and one-half ad libitum thereafter.
pox vaccine was administered at 12 weeks of age. Access to water was unlimited. Trapnests were installed in each pen when birds were 16 weeks of age, and individual egg production was recorded throughout the experiment. Birds were weighed individually every 2 weeks through 24 weeks of age and approximately monthly thereafter. During 20 to 52 weeks of age, 16 randomly selected birds from each pen were permanently removed for physiological assays (not reported). As a result of removal of these birds, and removal of missexed, morbid, and dead birds, 45 birds on Treatment AA, 80 birds on RR, 78 birds on AR, and 85 birds on RA completed the experiment. Upon conclusion of the experiment, all birds were weighed, killed, and processed. Abdominal fat pad was excised from the dressed carcass. For each bird, weights were obtained for the abdominal fat pad and the dressed carcass in both air and water (at ambient temperature). A sample of 25 carcasses (minus fat pad), which varied considerably in weight, was saved for subsequent analysis. These carcasses were individually ground through a meat grinder, dried to greater than 95% dry matter in a forced-air
RESULTS AND DISCUSSION
Mean body weights through 68 weeks of age are presented in Figure 1. The RA birds responded to ad libitum feeding with a rapid increase in body weight from Week 24 to approximately Week 30. After Week 30, they continued to grow, but at a slower rate, and achieved an average body weight equal to that of AA birds at 68 weeks of age (Fig. 1, Table 4). Pym and Dillon (1974) imposed four levels of feed restriction (100%, 80%, 60%, and 40% of ad libitum) and also observed that ad libitum feeding during the laying period resulted in equivalent 67-week body weights regardless of rearing treatment. Average age and body weight at first egg were 174 days and 4.5 kg, respectively, for A A birds and 191 days and 3.9 kg, respectively, for RA birds (Table 4; Fig. 1). Soller et al. (1984) found that, regardless of the degree of feed restriction during rearing, birds entered lay at the same lean body weight, ash, and protein content but at different age, carcass weight, dry matter, and fat content. Based on their results, it is likely that the .6 kg difference in body weight of A A and RA birds at first egg was primarily due to a difference in body fat content. The data further suggest that the rapid growth of RA birds between 24 and 27 weeks of age was largely due to an increase in lean body mass; average lean carcass weight of RR birds was 78% that of RA birds at 68 weeks of age (Table 4), and average live weight of RR birds was approximately 75% that of RA birds at 27 weeks of age (Fig. 1). The slower rate of growth of RA birds from 30 to 68 weeks of age was likely due to body fat accumulation. Peak egg production of AA birds was 59% at 30 weeks of age and for RA birds was 71% at 31 weeks of age (Fig. 2). The RA birds produced an average of 50% more eggs than AA
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 24, 2015
AA
drying oven (60 C for 72 hr), and subsampled for fat analysis. Samples were analyzed for ether extract per methodology of the Association of Official Analytical Chemists (AOAC, 1970). Percent carcass fat was expressed on a fresh tissue basis. Using data obtained from this 25 bird sample, a regression equation was derived (Table 3) from which carcass fat of all other birds was estimated. Analysis of variance with single degree of freedom comparisons was used to assess treatment effects (Steel and Torrie, 1960); pens were considered the experimental units.
DIETARY RESTRICTION OF BROILER FEMALES
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TABLE 3. Prediction equation for estimating dressed carcass fat content1
Variable
n
Mean
SD
Min
Max
Live body wt, g Carcass wt, g Abdominal fat, g Abdominal fat, % of carcass wt Carcass wt in air/carcass wt in water Carcass fat, %
25 25 25
4,108 2,817 153
1,120 726 137
2,420 1,620 ND
5,880 4,000 482
R' a b, b2
4
4.6
3.8
25 25
10.85 19.5
1.62 10.0
13.7
ND 8.10 3.8
13.65 42.3
.874 .871 .906 .910 .891 1.000
Estimate
SE3
Significance
.911 -18.22 2.869 1.427
5.978 .6316 .2656
P<.01 P<.001 P<.001
*n = Number of samples; SD = standard deviation; Min = minimum value (ND = not detectable); Max maximum value. Correlations were all significant (P<.001). 2
Equation: % Carcass fat = a + b, X (carcass wt in air/wt in water) + b 2 X (% abdominal fat)
3
SE = Standard error of estimate.
4
Inclusion of live body weight, carcass weight, and abdominal fat weight increased R 2 by only .003.
birds through 68 weeks (Table 4). We used a heavy, rapid growing broiler strain under the assumption that effects of body composition (particularly fatness) on hen performance would be maximized. Indeed, egg production was substantially lower for A A than for RA birds. This was apparently the result of accumulation of excessive body fat prior to or during the early weeks of lay, because mean body weight and composition of RA and AA birds were similar by 68 weeks of age (Table 4). Contrary to results of Pym and Dillon (1974), mortality of RA birds did not differ significantly from mortality of birds fed restricted amounts of feed during the laying period (Table 4), thus clearly demonstrating that ad libitum feeding of RA birds during lay did not increase mortality rate. However, a very high rate of mortality occurred in A A birds after 24 weeks of age. The highest frequencies of death on treatment AA were associated with the stress of monthly weighing of birds and involved mostly very heavy birds (average weight, 4950 ± 760 g). Eighty percent of the hens on treatment RR reached sexual maturity. Of those that did produce eggs, the average age and weight at first egg were 226 days and 3.2 kg (Table 4, Fig. 1),
:
respectively. Peak production of RR birds was 45% at 37 weeks of age (Fig. 2). The fat-free carcass weight of RR birds at 68 weeks of age was 21% less than AA and RA birds and 12% less than AR birds (Table 4), thus indicating that maximum fat free body mass was not achieved under conditions of continual feed restriction.
AGE (WEEKS)
FIG. 1. Mean body weights through 68 weeks of age. AA = Fed ad libitum throughout; RR = fed one-half ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum thereafter; AR = fed ad libitum through 24 weeks of age and one-half ad libitum thereafter.
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Parameter 2
25
Correlation with carcass fat
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ROBBINS ET AL. TABLE 4. Summary of production characteristics through 68 weeks of age Treatment 1
Item
RR
AA
RA
AR
pSEM2
Mortality, %3 Total eggs per hen 3 Age at first egg, days 3 Live weight at 68 weeks, g3 Carcass weight, g3 Abdominal fat, % of carcass weight s Carcass weight in air/carcass wt. in water, g/g s Fat-free carcass weight, g 3,6
8 37 226" 2,675 1,891
38 106 174 4,842 3,377
10 159 191 4,860 3,300
10 47 176 3,045 2,253
2.5 4.8 3.9 58.8 60.3
1.12
7.75
8.20
1.48
.453
9.87 1,717
14.79 2,169
13.88 2,192
10.04 1,958
.565 43.5
2
pSEM = Pooled standard error of the mean; 8 degrees of freedom.
3
The main effect of 0 to 24 week feeding regimen; the main effect of 24 to 68 week feeding regimen; and their interaction were significant (P<.05). 4
20.5% of the birds on this treatment produced 0 eggs and are not included in this figure.
5
The main effect of 24 to 68 week feeding regimen was significant (P<.001).
6
Estimated from carcass weight using the prediction equation described in Table 3.
Between 24 and 68 weeks of age, AR birds lost an average of 1.5 kg body weight (33% of 24 week body weight). Given that the average fat-free carcass weight of AR birds was 90% that of AA birds at 68 weeks, most or all of the weight loss probably consisted of fat. This response demonstrates that excessive fat deposited
FIG. 2. Mean percent hen-day production through 68 weeks of age. AA = Fed ad libitum throughout; RR = fed one-half ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum therafter; AR = fed ad libitum through 24 weeks of age and one-half ad libitum thereafter.
during the rearing phase is not refractory to dietary restriction. The response of RR birds was particularly surprising. Bornstein et al. (1984) concluded that a high degree of fatness is associated with the onset of ovulation. Brody et al. (1980) found that hens maintained at a low mean body weight by continued restriction did not mature sexually. In our study, However, 80% of RR birds did become sexually mature. Although body fat content of RR birds was not determined until 68 weeks of age, they likely were very lean throughout the experiment. Birds assigned to treatment RA produced an average of 159 eggs in 68 weeks, which is a level similar to that achieved by two broiler dam lines in 67 weeks (Pym and Dillon, 1974). Restriction of these birds through 24 weeks of age followed by an abrupt switch to ad libitum feeding resulted in a rapid and uniform onset of lay (Fig. 2). The RA birds continued to gain weight between 30 and 68 weeks of age as egg production rate declined. It is likely that this weight gain consisted primarily of fat and was due to decreased demand for productive energy. If so, diet restriction could have controlled body weight and reduced the amount of feed per egg. However, based on our results, mortality would not have been reduced.
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' A A = Fed ad libitum throughout; RR = fed one-half ad libitum throughout; RA = fed one-half ad libitum through 24 weeks of age and ad libitum thereafter; AR = fed ad libitum through 24 weeks of age, and one-half ad libitum thereafter.
DIETARY RESTRICTION OF BROILER FEMALES ACKNOWLEDGMENT
The authors sincerely thank Adesina Adekunmisi for his expert technical assistance. REFERENCES
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