The use of step-down and modi®ed constant
protein feeding systems in developing
pullets reared in hot climates
Ahmed S. Hussein
*Department of Animal Production, Faculty of Agricultural Sciences, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates
Received 20 October 1999; received in revised form 16 February 2000; accepted 13 April 2000
Abstract
The effect of using varied levels of dietary protein with high energy levels in rearing diets on pullet development and on subsequent layer performance in hot climates, was studied using 160 Lohmann White Leghorn pullets. Five replicate groups of 16 pullets, 1 day of age were randomly assigned to each of two series of rearing diets. Pullets in both treatments were fed a 190 g crude protein (CP)/kg starter diet in the ®rst week. Dietary protein level series used during Weeks 2±6, 7± 14, and 15±18 were 190, 160, and 135 g CP/kg, respectively, for the decreasing protein series treatments and 160, 160, and 135 g CP/kg, respectively, for the semi-constant series. Energy level used during the rearing period in all diets was 12.55 MJ AME/kg. Pullets were reared under a natural cyclic hot temperature ranging as low as 278C measured at 07:00 hours and as high as 348C measured at 13:00 hours. At the beginning of Week 19, pullets were transferred to laying cages and fed two isocaloric layer diets for 20 weeks. Diet 1 used 190 g CP/kg and 4 g methionine/kg and Diet 2 used 160 g CP/kg and 3.4 g methionine/kg. Each diet was fed to half of the pullets within each rearing treatment program. During the rearing period, body weight of pullets in both treatment programs was similar, as was feed intake during Weeks 7±14 and 15±18. However, pullets fed diets with 160 g CP/kg had signi®cantly (p<0.05) higher feed intake than those fed the 190 g CP/kg diet during Weeks 2±6. Hen-day egg production, days to 50% egg production, egg weight and Haugh unit values were not affected by dietary protein treatments during the rearing period. Reducing protein levels from 190 to 160 g CP/kg in laying hen diets signi®cantly increased egg production during Weeks 27±30 and 35±38, but reduced egg weight during Weeks 23±30 period of egg production. In addition, the results of this study showed that when birds were given adequate pullet development, very few differences in egg production parameters resulted due to feeding 160 or
85 (2000) 171±181
*Tel.:971-3-7051442; fax:971-3-7632384. E-mail address: [email protected] (A.S. Hussein)
190 g CP/kg during the early production period under this climatic condition. #2000 Elsevier Science B.V. All rights reserved.
Keywords:Protein; Rearing diets; Pullet; Hot climates; Egg performance
1. Introduction
Dietary protein requirements for Leghorn-type chicken strains have been de®ned or established by many researchers as reported earlier in the NRC (1994). However, with continued development and improvement of new commercial strains, many researchers have been studying the effect of protein levels in layer diets on egg production performance, and pullet development in general. Earlier literature indicated some parameters regarding dietary protein requirements for growing pullets, including Berg and Bearse (1958), who reported that the protein requirements decreased rapidly after 8 weeks of age. Furthermore, Sunde and Bird (1959) reported that growing pullets need about 200 g CP/kg from 0 to 6 weeks of age, 150 g CP/kg from 6 to 12 weeks and 120 g CP/kg from 12 to 20 weeks. In addition, it was reported that different commercial strains of laying hen require a different range of body weight (BW) at the onset of egg production in order to reach maximum egg production performance (Creger, 1974).
Stockland and Blaylock (1974) found that pullets reared under constant temperature of 29.48C from 6 to 20 weeks of age ate less feed, were more ef®cient in the utilization of feed, and needed more days to achieve 50% egg production than pullets raised under 18.38C or ambient temperature. On the other hand, McNaughton et al. (1977) reported that neither dietary protein nor energy affected pullets BW at high cyclic temperature (24 to 35 to 248C) and feed consumption of birds was directly related to the energy levels in these diets. However, dietary protein had no signi®cant effect on feed intake.
layer diet from 160 to 190 g CP/kg. Furthermore, they concluded that BW and feed intake of pullets given the constant protein (160 g CP/kg) diets were intermediate between and not signi®cantly different from those of step-down or step-up protein feeding systems.
Recent concerns in the Arabian Gulf region deal with nutrient requirements of newly developed replacement pullets reared under hot climatic conditions which are imported (1-day old) from Europe or the US, although produced for and under temperate climates in the US or Europe. Furthermore, these new strains were developed mainly for proper BW at the onset of egg production in order to achieve maximum laying production. Most studies determining the protein requirement of the new strains have been undertaken under temperate climates (Cantor and Johnson, 1985; Hussein et al., 1996), or constant hot temperature (Stockland and Blaylock, 1974), yet very little has been done with hot cyclic temperature (Leeson and Summers, 1989). One reason for conducting the current research was to re-evaluate the use of the conventional step-down protein and a modi®ed constant protein feeding system under hot climatic conditions using cyclic temperatures.
2. Materials and methods
Five replicate groups of 16 Lohmann White Leghorn pullets, 1 day of age were randomly assigned to each of two dietary treatments for raising pullets: decreasing protein and semi-constant protein series. Each group of the 16 pullets was housed in Petersime battery brooders from Weeks 1 to 6. At Week 7, pullets were transferred to pullet brooder cages (100 cm long55 cm wide40 cm high) at a density of eight pullets per cage (two cages per replicate). They were then reared and fed the respective experimental diets until 18 weeks of age. All pullets were fed a 190 g CP/kg starter diet during Week 1. Then there were two dietary protein sequences treatments (Table 1); a decreasing protein sequence of 190, 160 and 130 g CP/kg, and a semi-constant protein sequence of 160, 160 and 130 g CP/kg. In a previous study (Hussein et al., 1996) pullets were given a constant protein diet of 160 g CP/kg from 2 to 18 weeks of age. However, several studies recommended feeding protein levels less than 160 g CP/kg during the end of the rearing period (Berg and Bearse, 1958; Sunde and Bird, 1959; Stockland and Blaylock, 1974). Therefore, the constant protein treatment was modi®ed to a semi-constant protein feeding system in the present study. Each sequence was fed to ®ve replicate groups of 16 pullets per replicate during Weeks 2±6, 7±14 and 15±18, respectively. Since the pullets in the current study were hatched in the spring, they
Table 1
Experimental treatments (dietary CP levels, g CP/kg) during the rearing period of replacement pulletsa
Protein treatments Weeks 2±6 Weeks 7±14 Weeks 15±18 Step-down (conventional) 190 160 130
Semi-constant 160 160 130
aAll replacement pullets in step-down and semi-constant protein treatments fed the 190 g CP/kg during the
developed in the summer (the hottest season of the year, April±August). It was decided to increase dietary energy during the rearing period up to 12.55 MJ/kg in order to overcome any reduction in energy intake associated with low feed intake in this hot climatic region. Starting at Week 19, birds were moved to laying cages. Each replicate was divided into two eight-bird groups and housed two birds per cage (50 cm long45 cm wide45 cm high) until 38 weeks of age. Dietary treatments during the laying period were as outlined previously (Hussein et al., 1996). Each of two layer diets was fed to half of the pullets (®ve replicate groups of eight birds) within each rearing treatment sequence. Diet 1 contained 190 g CP/kg with 4.0 met, 7.2 metcys, 10.3 lys, 36.2 Ca, 4.5 g available P/kg and 11.80 MJ ME/kg, while Diet 2 contained 160 g CP/kg with 3.4 met, 6.2 metcys, 8.0 lys, 36.2 Ca, 4.5 g available P/kg and 11.80 MJ ME/kg. Pullets were reared under a natural cyclic hot temperature ranging as low as 278C measured at 07:00 hours and as high as 348C measured at 13:00 hours. During the laying period, the temperature ranged from 22 to 298C, measured at 07:00 and 13:00 hours, respectively.
Feed and water were provided on an ad libitum basis. The composition of the pullet diets is shown in Table 2. The nutrient composition of the diets were calculated based on information found in the ingredient tables of Scott et al. (1982). During Week 1 pullets were given 22 h of light per day. During Weeks 2±18 light was provided for 9 h per day.
Table 2
Composition of experimental pullet diets
Variable Diet (g CP/kg)
190a 160b 130c
Ingredient
Maize 66.33 75.04 78.89
Wheat bran 2.64
Soybean meal (480 g CP/kg) 27.62 20.02 13.40
Corn oil 1.44 0.24 0.40
Salt 0.40 0.40 0.37
Limestone (380 g Ca/kg) 1.17 1.20 1.25 Dicalcium phosphate 2.01 2.09 2.04 Vitamin±mineral mixd 1.00 1.00 1.00
DL-methionine 0.03 0.01 0.01
Chemical analysis
Crude protein (g CP/kg) 193 164 137
aCalculated nutrient composition is: protein, 190 g; ME, 12.55 MJ/kg; Met, 3.4 g/kg; MetCys, 6.7 g/kg;
Lys, 9.9 g/kg; calcium, 10 g/kg and available phosphorus, 5.0 g/kg.
bCalculated nutrient composition is: protein, 160 g; ME, 12.55 MJ/kg; Met, 2.9 g/kg; Met
Cys, 5.7 g/kg; Lys, 7.7 g/kg; calcium, 10 g/kg and available phosphorus, 5.0 g/kg.
cCalculated nutrient composition is: protein, 135 g; ME, 12.55 MJ/kg; Met, 2.5 g/kg; MetCys, 4.9 g/kg;
Lys, 5.9 g/kg; calcium, 10 g/kg and available phosphorus, 5.0 g/kg.
dProvided the following per kilogram of diet: Vitamin A, 6000 IU; Vitamin D
3, 1000 ICU; Vitamin E,
15 IU, menadione dimethylpyrimidinol bisul®te, 2.0 mg; thiamin, 5.94 mg; ribo¯avin, 5.4 mg; pantothenic acid, 15 mg; niacin, 41 mg; pyridoxine, 4.5 mg; biotin, 0.23 mg; choline, 1450 mg; folacin, 0.83 mg; Vitamin B12,
Birds were then photostimulated by raising the daily light to 13 h at the start of the laying period and increasing by 0.5 h per week until reaching 17 h of light per day.
Feed intake, mortality, and BW of pullets were measured during the rearing period at 6, 14 and 18 weeks of age. Records of daily egg production and egg weight, weekly feed intake and monthly BW were maintained during the layer period. Eggs collected within each replicate during the last three consecutive days of every period were kept for egg and eggshell quality measurements (Haugh unit scores and eggshell weight). Haugh unit scores were determined using Ames Haugh unit gauge similar to the method reported by Bish et al. (1984). Haugh unit scores were obtained directly from the instrument based on each individual egg weight. Data collected from the 3-day egg collection were pooled within replicate groups. Crude protein analysis for the experimental pullets diets (Table 2) was determined according to the methods of AOAC (1984).
Data from the growing period were analyzed using the t-tests for two samples (Snedecor and Cochran, 1980) using a statistical analysis program for microcomputers (Statistix, v.4.0, Analytical Software, Tallahassee, FL). Data collected during the laying period were subjected to an ANOVA based on a 22 factorial arrangement, using the same statistical software. A probability level of <0.05 was required for signi®cance.
3. Results
The effect of feeding different levels of dietary protein on BW and feed intake of replacement pullets is shown in Table 3. Dietary protein levels administered throughout the rearing period did not signi®cantly affect BW. Feed intake of pullets fed the decreasing protein series was signi®cantly lower than those birds fed the semi-constant protein series during Weeks 2±6. However, there were no signi®cant differences for feed consumed during Weeks 7±14 or 15±18.
There were no signi®cant interactive effects of dietary protein in the rearing diets with protein levels in the layer diets on any performance parameters during the laying period.
Table 3
Effect of dietary protein levels on body weight and feed intake of replacement pulletsa
Period Dietary protein Weeks 2±6 Conventional 190 299.4 12.2 b 3.8
Semi-constant 160 307.2 19.4 a 5.0
Thus, only the main effect of dietary protein in the pullet and layer diets are presented. Dietary protein levels did not affect hen-day egg production, days to 50% egg production nor egg weight of the laying hens in both treatments during the laying period (Table 4). A similar effect was observed regarding the in¯uence of dietary protein on feed intake
Table 4
Main effect of dietary protein level treatment used for pullet rearing on laying hen performance during Weeks 19±38a
Variable Protein sequence (g CP/kg) Pooled S.E.M. 190±160±130 160±160±130
Days to 50% egg production 144.2 144.4 1.4
Hen-day production(%)
Weeks 19±22 29.5 27.5 2.0
Weeks 23±26 88.0 88.7 1.7
Weeks 27±30 94.0 95.5 1.3
Weeks 31±34 91.1 91.7 1.6
Weeks 35±38 93.9 93.9 1.5
Feed intake(g per hen per day)
Weeks 19±22 91.9 89.1 2.6
Weeks 23±26 103.0 105.0 1.9
Weeks 27±30 105.5 107.6 1.1
Weeks 31±34 108.5 110.2 1.9
Weeks 35±38 112.8 b 116.3 a 1.4
Body weight(g)
Weeks 19±22 1492 a 1432 b 15.0
Weeks 23±26 1575 1544 20.0
Weeks 27±30 1599 1563 18.7
Weeks 31±34 1639 1610 17.4
Weeks 35±38 1670 1645 18.8
Egg weight(g)
Weeks 19±22 47.3 46.2 0.9
Weeks 23±26 55.4 55.1 0.3
Weeks 27±30 59.4 58.9 0.4
Weeks 31±34 61.1 61.1 0.4
Weeks 35±38 61.0 61.6 0.5
Haugh unit scores
Weeks 19±22 89.4 91.5 1.1
Weeks 23±26 77.1 78.7 1.3
Weeks 27±30 76.4 77.9 1.1
Weeks 31±34 79.2 79.0 1.5
Weeks 35±38 76.2 76.2 1.2
Eggshell weight(g)
Weeks 19±22 5.0 5.0 0.1
Weeks 23±26 5.5 a 5.0 b 0.1
Weeks 27±30 5.3 a 4.9 b 0.1
Weeks 31±34 5.3 5.1 0.1
Weeks 35±38 5.1 5.1 0.1
during the ®rst 16 weeks of egg production. However, birds fed the semi-constant protein levels ate more than those hens fed the decreasing protein levels during Weeks 35±38. Body weight of hens fed the decreasing protein sequence during rearing was signi®cantly (p<0.05) higher than that of birds fed the other protein series after 4 weeks of production,
Table 5
Main effect of dietary protein level of layer diets on laying hen performance during Weeks 19±38a
Variable Dietary protein level (g CP/kg) Pooled S.E.M.
190 160
Days to 50% egg production 143.6 145.0 1.4
Hen-day production(%)
Weeks 19±22 29.2 27.7 2.0
Weeks 23±26 86.9 89.8 1.7
Weeks 27±30 92.7 b 96.8 a 1.3
Weeks 31±34 89.2 93.6 1.6
Weeks 35±38 91.5 b 96.3 a 1.5
Feed intake(g per hen per day)
Weeks 19±22 90.0 91.0 2.6
Weeks 23±26 102.4 105.6 1.9
Weeks 27±30 106.1 107.0 1.1
Weeks 31±34 108.0 110.7 1.9
Weeks 35±38 112.5 b 116.6 a 1.4
Body weight(g)
Weeks 19±22 1483 1441 15.0
Weeks 23±26 1563 1555 20.0
Weeks 27±30 1604 1558 18.7
Weeks 31±34 1648 1600 17.4
Weeks 35±38 1670 1645 18.8
Egg weight(g)
Weeks 19±22 47.3 46.2 0.9
Weeks 23±26 56.2 a 54.2 b 0.3
Weeks 27±30 59.7 a 58.2 b 0.4
Weeks 31±34 61.7 60.5 0.4
Weeks 35±38 61.7 60.9 0.5
Haugh unit scores
Weeks 19±22 90.8 90.1 1.1
Weeks 23±26 77.2 78.6 1.3
Weeks 27±30 76.6 77.7 1.1
Weeks 31±34 78.9 79.3 1.5
Weeks 35±38 75.7 76.7 1.2
Eggshell weight(g)
Weeks 19±22 5.0 5.1 0.1
Weeks 23±26 5.3 5.3 0.1
Weeks 27±30 5.1 5.1 0.1
Weeks 31±34 5.1 5.2 0.1
Weeks 35±38 5.1 5.1 0.1
but not thereafter. Also, eggshell weight of birds fed the decreasing protein series was signi®cantly higher than that of birds fed the semi-constant protein levels at the end of the 8th and 12th weeks of egg production (Weeks 23±26 and 27±30, respectively). Egg weight and Haugh unit values were not signi®cantly affected by dietary treatments during the rearing period.
The main effect of feeding different dietary protein levels during the laying period on layer performance is shown in Table 5. Feeding 160 g CP/kg in the diet (versus 190 g CP/ kg) increased egg production during Weeks 27±30 and 35±38 and feed intake during Weeks 35±38. There was no signi®cant effect of laying hen dietary protein levels on bird BW and eggshell weight throughout the study. However, increasing layer diet protein levels from 160 to 190 g CP/kg signi®cantly increased egg weight during the second and third periods, Weeks 23±26 and 27±30, respectively. There was no signi®cant effect of dietary protein on interior egg quality as measured by Haugh units.
4. Discussion
The results of feeding replacement pullets step-down (190, 160 and 130 g CP/kg) and semi-constant (160, 160 and 130 g CP/kg) diets upon BW during the rearing period (Table 3) showed that both systems resulted in similar BWs at 6, 14 and 18 weeks of age. In contrast, Cantor and Johnson (1985) observed that BW of pullets fed a constant protein diet of 160 g CP/kg was signi®cantly less than for those birds fed step-down protein diets at 6 and 14 weeks of age, although BW at 20 weeks of age were comparable for both treatments. Also, Hussein et al. (1996) reported that BW of replacement pullets signi®cantly increased as the level of dietary protein increased from 160 to 190 g CP/kg at 6 weeks of age, which disagreed with the ®ndings of the current study. However, at 14 and 18 weeks of age there was no signi®cant difference in BW between rearing treatments, which agreed with the results of the current study. The discrepancy between the current data and those previously obtained by Cantor and Johnson (1985) and Hussein et al. (1996) could be due to different environmental conditions, or in using different egg-type strains. Doran et al. (1983) found that the step-down protein feeding system produced signi®cantly larger pullets at 20 weeks of age compared to the step-up protein (130, 160 and 190 g CP/kg) regime. They also reported that BW of pullets fed the diets were 290, 942 and 1153 g at Weeks 6, 16 and 20, respectively. These results were similar to those obtained in the present study with the step-down treatment, in which pullets weighed about 299, 924 and 1185 g at 6, 14 and 18 weeks of age. Leeson and Summers (1989) found that increasing dietary protein levels had an initial signi®cant effect on BW of pullets reared under hot-cyclic temperatures (22±328C). However, at the end of the rearing period (20 weeks of age) dietary protein levels ranging from 150 to 200 g CP/kg had no effect on this parameter, and this result agreed with the current study. McNaughton et al. (1977) found that dietary protein did not signi®cantly affect BW of replacement pullets at 20 weeks of age under high-cyclic temperature conditions of 24 to 35 to 248C, which agrees with the results of the current study using similar hot cyclic temperatures.
of age. In this case, it could be stated that the differences in feed intake and its response effect on pullets BW at 6 weeks of age (where they have similar BW),would probably not be explained on the basis of feeding two different concentrations of protein in their respective diets, but rather is attributed to intake of protein as well as some other nutrients. Also, the signi®cant differences in feed intake in this case could be due to birds fed a diet containing 160 g CP/kg needing extra protein and other nutrients compared to birds fed a diet containing 190 g CP/kg protein to reach a similar BW. However, a signi®cant difference was not observed at 14 and 18 weeks between the two protein feeding systems (Table 3). In the present study, feed intake was decreased under hot cyclic temperatures (27±348C) during the rearing period, compared with birds reared under similar dietary conditions and normal temperature conditions (Hussein et al., 1996). Stockland and Blaylock (1974) found that pullets reared under a hot constant temperature of 298C from 6 to 20 weeks of age consumed less feed than pullets reared at 18.38C. Leeson (1986) reported that rearing pullets under hot environmental conditions required an increase in dietary energy in order to reach optimum growth performance.
Hussein et al. (1996) found that pullets reared on a step-down protein system signi®cantly consumed more feed than the other two treatments (step-up and constant protein systems) during Weeks 2±6, in contrast with the results of the current study where pullets fed the step-down protein system signi®cantly consumed less feed than the semi-constant protein system during the same period. However, there were no signi®cant differences in feed intake among the three- and two-protein sequences in Hussein et al. (1996) and the current study, respectively, during Weeks 7±14 and 15±18. Also, Cantor and Johnson (1985) reported similar results regarding feed intake during 2±6 weeks of age when the step-down protein system was used to rear pullets, compared with constant and step-up protein feeding systems. McNaughton et al. (1977) found that rearing small or large strain pullets under hot-cyclic temperatures produced no signi®cant differences in feed intake at 20 weeks of age when fed varying levels of dietary energy. This ®nding agreed with the current results at 18 weeks of age.
produce similar weights of pullets at 18 weeks of age, which are adequate according to the commercial breeder guidelines. The recent recommendation published by NRC (1994) regarding dietary protein requirements for replacement pullets is 180 g for 0±6 weeks, 160 g for 6±12 weeks and 150 g CP/kg for 12±18 weeks of age. This agrees with the use of the step-down protein feeding system in the current study, and also explains the signi®cant increase in feed intake in pullets fed the semi-constant versus the step-down regimen during Weeks 2±6. Also, Stockland and Blaylock (1974) indicated that laying hens reared under high temperatures produced smaller and fewer eggs, and ate more feed to produce a dozen eggs than birds reared under lower temperatures. However, high temperature had no signi®cant effect on egg quality, which agreed with the results of this present study.
Results of the current study show that protein levels had no effect on days to 50% egg production, BW, Haugh units and eggshell weight throughout the laying period. However, the dietary protein level of 160 g CP/kg increased egg production during Weeks 27±30 and 35±38 of the production period. Feed intake for birds fed 160 g CP/kg was higher only during the last 4 weeks of the study. The data showed that feeding a diet containing 190 g CP/kg signi®cantly increased egg weight after 8 and 12 weeks of production, with the results in agreement with those obtained by Keshavarz (1984) and Hussein et al. (1996). Also, as observed in the current study Leeson and Summers (1979) found no signi®cant interaction between rearing diets and layer dietary protein levels on pullets development and subsequent egg performance.
5. Conclusion
The results of this study show that substitution of a pullet feeding program using protein levels of 160 g during Weeks 2±14, followed by a level of 130 g CP/kg during Weeks 15±18 is satisfactory, in comparison with a conventional protein step-down program, with respect to pullet development under hot temperatures and subsequent production. In comparison, there is very little difference in feed cost between these two programs. Moreover, given adequate pullet development, very few differences in egg production parameters resulted due to feeding 160 or 190 g CP/kg during the early production period.
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