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J APPL POULT RES 2006. 15:312-325
© 2006 Poultry Science Association
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Field Reports

Growth, Meat Yield, and Economic Responses of Broilers Provided Three- and Four-Phase Schedules Formulated to Moderate and High Nutrient Density During a Fifty-Six-Day Production Period1

W. A. Dozier, III*,2, R. W. Gordon{dagger}, J. Anderson{ddagger}, M. T. Kidd§, A. Corzo§ and S. L. Branton*

* USDA, Agriculture Research Service, Poultry Research Unit, PO Box 5367, Mississippi State, MS 39762-5367; {dagger} Gold Kist Inc., PO Box 2210, 244 Perimeter Center Parkway NE, Atlanta, GA 30301; {ddagger} Department of Agricultural Economics, and § Department of Poultry Science, Mississippi State University, Mississippi State 39762

2 Corresponding author: bdozier{at}msa-msstate.ars.usda.gov


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
This study examined growth responses and meat yield of broilers provided a 3- or 4-phase feeding schedule formulated to moderate or high nutrient density. Four dietary treatments were implemented consisting of high or moderate nutrient density diets that were provided for the duration of 3 phases (1 to 17, 18 to 35, and 36 to 56 d) or 4 phases (1 to 17, 18 to 35, 36 to 46, and 47 to 56 d).

Provision of a 3-phase schedule did not alter growth performance, meat yield, or diet cost per final BW. Broilers receiving high nutrient diets had improved growth rate and feed conversion from 1 to 35 d. In the 3-phase schedule, birds given the high nutrient density diets had advantages in BW gain and pectoralis minor breast weight. Market changes in meat prices impact differences in gross feeding margins between diets formulated to high or moderate nutrient density more than variation in diet cost.

Key Words: broiler • feeding schedule • lysine • methionine • nutrient density


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Broiler chickens marketed at heavy weights (final BW of 3.0 to 3.4 kg) are typically provided a 3- or 4-phase feeding schedule in the United States [1]. However, a 4-phase schedule is more likely when market weights exceed 3.4 kg, because reduction of nutrient specifications in the final feed may be economically advantageous. A 3-phase feeding schedule can improve milling efficiency by requiring less downtime because of adding an additional diet. Conversely, the advantages of a 4-phase schedule include having a 3-phase medicated schedule and more flexibility in lowering diet cost, particularly for the fourth feed.

High nutrient density diets (above NRC [2] lysine and TSAA recommendations) improve growth performance and meat yield [3, 4, 5, 6, 7]. Fortifying diets with a higher proportion of amino acids from 1 to 35 d of age is advantageous with respect to meat yield when broilers are marketed at heavy BW [5]. Kidd et al. [6] reported that broilers fed diets formulated to 115 and 125% of the NRC [2] lysine recommendations from 1 to 18 and 19 to 49 d of age, respectively, had more breast meat than birds fed diets containing lysine at 115 and 105% of the NRC [2] recommendations, respectively, during the same age periods. However, feeding high nutrient dense diets throughout may not be economically advantageous for live production cost but may be warranted based on meat yield.

Feeding a 3-phase schedule formulated to high nutrient density may provide economic advantages based on breast meat accretion compared with a 4-phase schedule formulated to high nutrient density. This study evaluated growth responses and meat yield of broilers fed a 3- or 4-phase dietary schedule formulated to moderate or high nutrient density. Measurements also included economic assessments based on diet cost, final BW, carcass, and total white meat.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Bird Husbandry
Sixteen hundred sixty-four Ross x Ross 508 [8] 1-d-old male and female broiler chicks were purchased from a commercial hatchery and randomly distributed among 32 floor pens (26 males and 26 females/pen; 0.07 m2/bird) of a solid-sided facility. Vaccinations for Marek’s disease, Newcastle disease, and infectious bronchitis were administered at the hatchery. Each pen was equipped with 1 pan feeder, 1 nipple watering system with 9 nipples (flow rate = 30 mL/min from 1 to 21 d; 70 mL/min from 22 to 56 d), and fresh pine shavings. Feed and water were provided ad libitum. Starter feed was provided as crumbles, and subsequent feeds were provided as whole pellets. A step-up lighting schedule [9] and a temperature regimen [10] simulating commercial practice were used. Husbandry practices were approved by the USDA-ARS Animal Care and Use Committee (Mississippi State, MS).

Treatments
Four dietary treatments were implemented (Tables 1Go and 2Go): 1) a 3-phase schedule formulated to high nutrient density, 2) 3-phase schedule formulated to moderate nutrient density, 3) a 4-phase schedule formulated to a high nutrient density, and 4) a 4-phase schedule formulated to a moderate nutrient density. Each treatment was replicated with 8 pens. The duration of feeding of the 3-phase schedule was 1 to 17, 18 to 35, and 36 to 56 d. The 4-phase schedule consisted of 1 to 17, 18 to 35, 36 to 46, and 47 to 56 d. The CP, lysine, and TSAA concentrations of the final feed in the 3-phase schedule formulated to moderate and high nutrient densities were an average of those specifications of the third and fourth feeds in the 4-phase schedule. The nutrients of the moderate nutrient diets had typical levels of CP, lysine, and TSAA used in commercial practice for producing heavy broilers [1]. Moderate and high nutrient density refers to the actual concentration of CP, lysine, and TSAA in the diet. The concentrations of CP, lysine, and TSAA in the high nutrient density diets contained 110% of that in the diets characterized as moderate nutrient density.


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  		Table 1. Ingredient and calculated nutrient composition of diets provided to male and female broilers from placement until 35 d of age
 

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  		Table 2. Ingredient and calculated nutrient composition of diet provided to male and female broilers from 36 to 56 d of age
 
Measurements
Birds and feed were weighed by pen at 17, 35, 46, and 56 d of age. Mortality was recorded daily. Birds were weighed at 56 d, and feed was removed 12 h before processing. At 57 d, 12 birds from each pen (6 males and 6 females) were selected at random for processing and placed into transportation coops. Birds were electrically stunned and manually eviscerated. Eviscerated carcass weight and abdominal fat pad weight were determined. Carcasses were split into front and back halves and chilled on ice for 24 h. Front halves were deboned on cones to obtain weights of boneless, skinless pectoralis major and minor breast muscles.

Economics
The economic assessment included an estimated feed cost (diet cost [11] x feed consumption) relative to final BW. Diet cost [11] was based upon ingredient prices in the southeastern United States as of September 2004. The soybean meal prices in September 2004 were higher than normal. The gross feeding margin per bird was estimated by using market prices and weights of the carcass and total white meat (pectoralis major and minor breast muscles) as outputs and feed cost (diet cost [11] and feed consumption) as inputs. Gross feeding margin per bird on a carcass basis was calculated by total output (carcass price [12] x carcass weight) – total feed cost (diet cost [11] x feed consumption). The calculation to determine gross feeding margin per bird based on total white meat was total output (pectoralis major price [12] x pectoralis major weight + pectoralis minor price [12] x pectoralis minor weight) – total feed cost (diet cost [11] x feed consumption).

Sensitivity analysis was performed to determine gross feeding margin (on both carcass and white meat basis) under several different diet costs and output price scenarios. Diet costs ranged from 80 to 120% of the base cost and meat prices ranged from 70 to 130% of the base price. The base prices for carcass, pectoralis major, and pectoralis minor were $1.32, $3.32, and $3.97/kg, respectively. These base prices were selected as they reflect moderate prices in typical market fluctuations.

Statistics
Data were statistically evaluated with the GLM procedure of SAS [13] using a randomized complete block design. Pen location was used as the blocking factor. The 2 treatments during the starter (1 to 17 d) and grower periods (18 to 35 d) had 16 replications per treatment. At 47 and 56 d, each treatment was replicated with 8 pens. Three orthogonal contrasts were used to separate treatment differences. In addition, a least significant difference comparison was used to separate treatment means. Statistical significance was considered P ≤ 0.10.


   RESULTS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Broilers fed diets formulated to high nutrient density had improved growth through 35 d of age (Table 3Go). Provision of a high amino acid density diet increased (P ≤ 0.003) BW gain and decreased (P ≤ 0.001) feed conversion during 1 to 17 d of age. Feeding broilers the high amino acid density diet improved (P ≤ 0.008) BW gain, feed consumption, and feed conversion from 18 to 35 d of age. Broilers fed the high amino acid density diet had improved (P ≤ 0.003) growth through 35 d, but feed consumption and the incidence of mortality were unaffected.


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  		Table 3. Live performance responses of male and female broilers provided diets formulated to moderate and high nutrient specifications from placement to 35 d of age1
 
The feeding schedule did not alter broiler growth from 35 to 46 or 1 to 46 d (Table 4Go). Dietary amino acid density did not influence growth rate, feed consumption, feed conversion, or incidence of mortality from 36 to 46 d of age. However, differences caused by dietary amino acid density were apparent from 1 to 46 d of age. In the 4-phase feed schedule, formulation of the diet to a high nutrient density improved BW (P ≤ 0.057), BW gain (P ≤ 0.056), and feed conversion (P ≤ 0.039) over broilers fed diets formulated to moderate nutrient density.


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  		Table 4. Live performance responses of male and female broilers provided a 3- or 4-phase feed schedule formulated to moderate and high nutrient specifications from placement to 46 d of age1
 
In parallel to the previous period, the 3-phase schedule did not improve the rate and efficiency of growth compared with the 4-phase schedule from 47 to 56 or 1 to 56 d of age (Table 5Go). Increasing dietary amino acid density from moderate to high concentrations within the 3- and 4-phase feeding schedules increased (P ≤ 0.054 and P ≤ 0.063) BW gain, respectively, during 47 to 56 d of age. Diets formulated to a high nutrient density in the 3-phase schedule increased BW (P ≤ 0.054) and BW gain (P ≤ 0.054) and in the 4-phase schedule increased BW (P ≤ 0.065) and BW gain (P ≤ 0.063) from 1 to 56 d of age. The response of BW and BW gain was more acute in the 3-phase schedule formulated to high nutrient density than within the 4-phase schedule. Feed consumption, feed conversion, and the incidence of mortality were not influenced by nutrient density. A high incidence of mortality occurred (no treatment differences) during the final phase of growth (47 to 56 d), which could have been due to high environmental temperatures (26.5 and 27°C) on d 52 and 53, respectively.


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  		Table 5. Live performance responses of male and female broilers provided a 3- or 4-phase feed schedule formulated to moderate and high nutrient specifications from placement to 56 d of age1
 
Feeding schedule did not influence carcass weight or its relative yield as measured at processing (Table 6Go). The proportion of abdominal fat was decreased (P ≤ 0.065) by increasing nutrient density in the 4-phase schedule but not in the 3-phase schedule. Breast meat yield was similar between the 3- and 4-phase schedules (Table 7Go). Increasing nutrient density in the 3-phase schedule led to greater pectoralis major (P ≤ 0.063) and minor (P ≤ 0.044) weights.


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  		Table 6. Carcass yield of male and female broilers provided a 3- or 4-phase schedule formulated to moderate and high nutrient specifications from placement to 56 d of age1
 

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  		Table 7. Boneless, skinless breast meat yield of male and female broilers provided a 3- or 4-phase regimen formulated to moderate and high nutrient specifications from placement to 56 d of age1
 
Feed cost per kilogram of 56-d BW or gross feeding margin per bird was not affected by feeding schedule (Table 8Go). Diets formulated to high nutrient density, regardless of feed schedule, increased feed cost by $0.012/kg of BW but did not influence the feeding margin per bird. Sensitivity analysis revealed the effect of changes in dietary costs and meat prices on gross feeding margin per bird under each of the feeding schedules (Tables 9Go and 10Go). In general, these results show changes in diet cost have virtually no effect on differences in gross feeding margins between 3- and 4-phase schedules. The impact of dietary costs on differences in gross feeding margin between high or moderate nutrient densities was very low. Changes in meat prices had little effect on differences in gross feeding margin per bird between 3- and 4-phase schedules. The impact of change in meat prices on differences in gross feeding margin between high or moderate nutrient densities appeared to be relatively large in the 3-phase schedule, particularly on a white meat basis. For example, at pectoralis major and minor prices of $2.32 and $2.78/kg, respectively (i.e., 70% of the base price used in Table 8Go), the gross feeding margins under the 3-phase schedule formulated to the high nutrient density were $0.235 and $0.231/bird for the 3-phase schedule formulated to moderate nutrient density translating to a difference of $0.004/bird. Conversely, at pectoralis major and minor prices of $4.30 and $5.16/kg, respectively (i.e., 130% of the base price used in Table 8Go), the difference in gross feeding margin was $0.076/bird.


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  		Table 8. Cost estimates per unit of BW, carcass, and total white meat of male and female broilers provided a 3-or 4-phase schedule formulated to moderate and high nutrient specifications from placement to 56 d of age1
 

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  		Table 9. Sensitivity analysis of gross feeding margin per bird based on total feed cost and meat yield of male and female broilers provided a 3-phase program formulated to moderate and high nutrient specifications from placement to 56 d of age
 

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  		Table 10. Sensitivity analysis of gross feeding margin per bird based on total feed cost and meat yield of male and female broilers provided a 4-phase program formulated to moderate and high nutrient specifications from placement to 56 d of age
 

   DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
In the experimental diets, the analyzed composition of CP was in close agreement with the calculated values (Tables 1Go and 2Go). The lysine content of the starter diets was in close agreement with the calculated values. The actual lysine concentrations in the diets of grower, withdrawal (WD), WD1, and WD2 were from 3 to 7% higher than the calculated concentrations, but this trend was consistent across all treatments. The analyzed values for TSAA were closer to their calculated values than lysine in the grower, WD, WD1, and WD2 diets; however, the actual values of TSAA in all diets ranged from 0 to 4% higher than the calculated concentrations. Conversely, actual threonine concentrations were lower than calculated values; however, minimums were not set for threonine in diet formulations.

The 3- and 4-phase schedules used in the present research were unique compared with other feeding regimens used in previous research. In the present research, the WD diets in the 3-phase schedule contained an average calculated nutrient composition of the WD1 and WD2 diets used in the 4-phase schedule. To our knowledge, this type of feeding schedule has not been used with previous research. It is a common practice in the industry when developing 3- or 4-phase schedules for a particular feed mill, but research is sparse on the effects on broiler growth and meat yield. Conversely, other research evaluating feeding regimens has been based on amino acid density and duration [4, 14, 15, 16, 17] or solely on duration [18, 19, 20, 21]. With previous research, amino acid and energy concentrations of the final diet of a 3-phase schedule have not been an average of the last 2 diets with a 4-phase schedule as in the present research. These results reported herein indicate that a 3- or 4-phase schedule will provide adequate performance with heavy broilers.

In the present research, broilers fed higher nutrient density diets had improved growth performance in each phase of growth with the exception of 36 to 47 d of age. From 1 to 35 d, provision of broilers diets formulated to contain higher nutrient density resulted in a 2.5% increase in BW gain. No treatment differences occurred in growth from 36 to 47 d of age. Conversely, increased dietary nutrient density in the 3- and 4-phase schedules from 47 to 56 d of age led to 12 and 8% increases in BW gain, respectively. Diets formulated to moderate nutrient density might have met or exceeded broiler nutrient needs in the 3- or 4-phase schedule from 36 to 47 d of age. From 47 to 56 d of age, reduction of the dietary nutrient density to moderate concentrations limited growth rate, which indicated that at these dietary concentrations growth was not optimized in the 3- or 4-phase schedules.

Kidd et al. [5] reported an 11% increase in 49-d BW with Ross x Ross 508 [8] broilers provided diets formulated to a high amino acid density vs. moderate amino acid density. In the current study, formulating diets to a high amino acid density increased (P = 0.054 and P = 0.065) 56-d BW by 3% over moderate amino acid density with 3- and 4-phase schedules, respectively. The 35-d BW of broilers provided diets formulated to a high nutrient density exceeded the primary breeder management guide [22] but not at 46 and 56 d of age. The reduced response to nutrient density at 46 and 56 d of age might have been due to high ambient temperatures during the later periods of growth (25.3 and 25.0°C from 35 to 46 and 47 to 56 d of age, respectively). Research has shown that the response to dietary threonine may be less pronounced when broilers are exposed to high ambient temperatures than to favorable environmental conditions [23, 24].

Increased dietary amino acid density has been shown to decrease abdominal fat percentage of broiler chickens [3, 4, 5, 7, 25]. In the current research, abdominal fat percentage was not significantly affected as dietary nutrient density increased within the 3- and 4-phase schedule. Broilers fed moderate nutrient density diet in the 3-phase schedule had less abdominal fat percentage than birds provided diets formulated to moderate density in the 4-phase schedule.

The ratio of dietary calories to CP influences abdominal fat percentage [26, 27]. Broilers fed diets containing moderate nutrient density in the 3-phase schedule had a calorie:CP ratio of 176, whereas diets formulated to moderate nutrient density in the 4-phase schedule from 36 to 46 d and from 47 to 56 d had calorie:CP ratios of 166 and 184, respectively. The increase in calorie:CP ratio of the diet formulated to moderate nutrient density with the 4-phase schedule during 47 to 56 d could have increased abdominal fat.

In the present research, increased nutrient density in the 3-phase schedule led to higher breast meat weights translating to a 5% increase in total white meat (629 vs. 596 g). Increased dietary lysine in the starter period affects breast meat yield [3, 6]. Kidd et al. [5] reported a 5% relative increase (20.5 vs. 19.4%) in total breast meat (pectoralis major and minor breast muscles) when broilers are fed diets formulated to a high nutrient density vs. diets consisting of moderate nutrient density. The nutrient specifications for CP, lysine, and TSAA with the moderate schedule diet fed from 36 to 49 d by Kidd et al. [5] was much lower than the CP, lysine, and TSAA used in the moderate feeds from 36 to 56 d in the study reported herein. The differences between the specifications for CP, lysine, and TSAA used in the moderate schedule and the amount needed by the birds were probably greater in the study by Kidd et al. [5] than in the current study. Therefore, responses to growth rate and breast meat yield were more acute in the study reported by Kidd et al. [5].

Improvements in gross feeding margin associated with dietary amino acid density were more pronounced as chicken meat prices increased than was variation in diet cost. Increased amino acid density from moderate to high concentrations (100% base cost) in the 3-phase schedule increased gross feeding margin from $0.004 to $0.076 of the base price (Table 9Go). For a complex processing 1 million broilers per week, this cost translates to increases of $4,000 to $76,000 in gross feeding margin. Conversely, increased dietary amino acid density from moderate to high concentrations (100% base price) in the 4-phase schedule decreased gross feeding margin from –$0.040 to –$0.013 per bird as breast meat prices increased from 70 to 130% of the base price (Table 10Go). Increasing nutrient density in the 3-phase schedule is dependent on chicken meat prices. A broiler company may need several formulations differing in amino acid density, and the decision to determine the appropriate formulation should be based on diet cost and meat prices. The moderate dietary amino acid density appeared to be more appropriate with the 4-phase schedule with varying breast meat prices than the amino acid-dense diet. The 3-phase schedule formulated to high amino acid density (100% base price) increased gross feeding margin by $0.008 to $0.033 per bird as breast meat prices were increased from 100 to 130% of the base price compared with the moderate amino acid density diet of the 4-phase schedule.


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. Feeding a 3-phase schedule did not alter growth performance, processing yields, or gross feeding margin per bird compared with the 4-phase program.
  2. Increased nutrient density in the 3-phase schedule led to increased 56-d BW and breast tender weight, whereas formulating to a high nutrient density with the 4-phase schedule increased 56-d BW.
  3. Diet cost had minimal effect on differences in gross feeding returns between high and moderate nutrient densities and between 3- and 4-phase schedules.
  4. Meat prices (carcass from $0.92 to $1.72/kg, pectoralis major from $2.32 to $4.30, and pectoralis minor from $2.78 to $5.16/kg) could have substantial effect on differences in gross feeding margins between high and moderate nutrient densities, particularly in the case of the 3-phase schedule.


   FOOTNOTES
 
1 Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. Back


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

  1. Gordon, R. 2005. Gold Kist Inc., Atlanta, GA. Personal communication.
  2. National Research Council. 1994. 9th ed. Natl. Acad. Press, Washington, DC.
  3. Holsheimer, J. P., and E. W. Ruesink. 1993. Effect on performance, carcass composition, yield, and financial return of dietary energy and lysine levels in starter and finisher diets fed to broilers. Poult. Sci. 72:806–815.
  4. Dozier, W. A., III, and E. T. Moran Jr. 2001. Response of early- and late-developing broilers to nutritionally adequate and restrictive feeding schedules during the summer. J. Appl. Poult. Res. 10:92–98.[Abstract/Free Full Text]
  5. Kidd, M. T., C. D. Mcdaniel, S. L. Branton, E. R. Miller, B. B. Boren, and B. I. Fancher. 2004. Increasing amino acid density improves live performance and carcass yields of commercial broilers. J. Appl. Poult. Res. 13:593–604.[Abstract/Free Full Text]
  6. Kidd, M. T., B. J. Kerr, K. M. Halpin, G. W. McWard, and C. L. Quarles. 1998. Lysine interactions in broilers in starter and grower-finisher diets. J. Appl. Poult. Res. 7:351–358.[Abstract/Free Full Text]
  7. Corzo, A., M. T. Kidd, D. J. Burnham, E. R. Miller, S. L. Branton, and R. Gonzalez-Esquerra. 2005. Dietary amino acid density effects on growth and carcass of broilers differing in strain cross and sex. J. Appl. Poult. Res. 14:1–9.[Abstract/Free Full Text]
  8. Aviagen Inc., Huntsville, AL.
  9. A continuous lighting schedule consisting of 23 h of light with an intensity of 20 lx was implemented from placement until 7 d of age, 16 h of light with an intensity of 5 lx from 8 to 28 d, and 24 h of light with an intensity of 5 lx from 29 to 56 d of age.
  10. Temperature set points consisted of 34°C from placement to 4 d, 32°C from 5 to 9 d, 29°C from 10 to 14 d, 28°C from 15 to 19 d, 27°C from 20 to 24 d, 26°C from 25 to 29 d, 24°C from 30 to 34 d, 22°C from 35 to 39 d, 21°C from 40 to 43 d, and 19°C from 44 to 56 d.
  11. Diet costs during the starter period formulated to a moderate and high nutrient density were $0.218 and $0.227/kg, respectively, and $0.203 and $0.213/kg for the moderate and high nutrient density diets, respectively, during the grower period. The costs of the withdrawal (WD) diets (36 to 56 d) of the 3-phase schedule formulated to moderate and high nutrient density were $0.187 and $0.195/kg, respectively. Costs of the WD1 diets (36 to 47 d) formulated to moderate and high nutrient density were $0.192 and $0.199/kg, respectively; and WD2 diets (47 to 56 d) formulated to moderate and high nutrient density for the 4-phase schedule were $0.182 and $0.189/kg, respectively.
  12. The carcass price was $1.32/kg, and prices used for pectoralis major and pectoralis minor were $3.31 and $3.97/kg, respectively.
  13. SAS Institute. 2004. SAS User’s Guide. Statistics. Version 9.1 ed. SAS Institute Inc., Cary, NC.
  14. Warren, W. A., and J. L. Emmert. 2000. Efficacy of phase-feeding in supporting growth performance of broiler chicks during the starter and finisher phases. Poult. Sci. 79:764–770.[Abstract/Free Full Text]
  15. Pope, T., and J. L. Emmert. 2001. Phase-feeding supports maximum growth performance of broiler chicks from forty-three to seventy-one days of age. Poult. Sci. 80:345–352.[Abstract/Free Full Text]
  16. Pope, T., L. N. Loupe, J. A. Townsend, and J. L. Emmert. 2002. Growth performance of broilers using a phase-feeding approach with diets switched every other day from forty-two to sixty-three days of age. Poult. Sci. 81:466–471.[Abstract/Free Full Text]
  17. Roush, W. B. 1983. An investigation of protein levels for broiler response and the time of diet change by response surface methodology. Poult. Sci. 62:110–116.
  18. Saleh, E. A., S. E. Watkins, and P. W. Waldroup. 1996. Changing time of feeding starter, grower, and finisher diets for broilers. 1. Birds grown to 1 kg. J. Appl. Poult. Res. 5:269–275.[Abstract/Free Full Text]
  19. Saleh, E. A., S. E. Watkins, and P. W. Waldroup. 1997. Changing time of feeding starter, grower, and finisher diets for broilers. 2. Birds grown to 2.2 kg. J. Appl. Poult. Res. 6:64–73.[Abstract/Free Full Text]
  20. Saleh, E. A., S. E. Watkins, and P. W. Waldroup. 1997. Changing time of feeding starter, grower, and finisher diets for broilers. 3. Birds grown to 3.3 kg. J. Appl. Poult. Res. 6:290–297.[Abstract/Free Full Text]
  21. Roush, W. B., D. Boykin, and S. L. Branton. 2004. Optimization of phase starter, grower, and finisher diets for male broilers by mixture experimental design: Forty-eight-day production period. Poult. Sci. 83:1264–1275.[Abstract/Free Full Text]
  22. Ross x Ross 508 North American Broiler Performance Objectives. Aviagen North America, Huntsville, AL.
  23. Dozier, W. A., III, E. T. Moran, Jr., and M. T. Kidd. 2000. Threonine requirement of broiler males from 42 to 56 days of age in a summer environment. J. Appl. Poult. Res. 9:496–500.[Abstract/Free Full Text]
  24. Dozier, W. A., III, E. T. Moran, Jr., and M. T. Kidd. 2000. Threonine requirement of the broiler male from 42 to 56 days of age. J. Appl. Poult. Res. 9:214–222.[Abstract/Free Full Text]
  25. Kidd, M. T., A. Corzo, D. Hoehler, E. R. Miller, and W. A. Dozier III. 2005. Broiler responsiveness (Ross x 708) to diets varying in amino acid density. Poult. Sci. 84:1389–1396.[Abstract/Free Full Text]
  26. Bartov, I., S. Bornstein, and B. Lipstein. 1974. Effects of calorie to protein ratio on the degree of fatness in broilers fed on practical diets. Br. Poult. Sci. 15:107–117.
  27. Mabray, C. J., and P. W. Waldroup. 1981. The influence of dietary energy and amino levels on abdominal fat pad development of the broiler chicken. Poult. Sci. 60:151–159.



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