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Poult Sci 2007. 86:1140-1148
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METABOLISM AND NUTRITION

Threonine Requirement of Slow-Growing Male Chickens Depends on Age and Dietary Efficiency of Threonine Utilization

Samadi1 and F. Liebert2

Institute for Animal Physiology and Animal Nutrition, Georg-August-University, 37077 Goettingen, Germany

2 Corresponding author: flieber{at}gwdg.de


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Nitrogen-balance experiments were conducted with a total of 288 male chickens to assess Thr requirement data on 2 commercial slow-growing genotypes (I 657 and Red JA from Hubbard ISA) by use of a modeling procedure described previously. Six graded levels of dietary protein supply from high-protein soybeanmeal were used within 4 age periods (period I: 10 to 25 d; period II: 30 to 45 d; period III: 5 to 65 d; and period IV: 70 to 85 d). The provided dietary amino acid ratio (Lys:Met + Cys:Thr = 1:0.85:0.54), with 3.87% Thr in the feed protein, identified Thr as the first limiting dietary amino acid. The nitrogen maintenance requirement (NMR) was established by exponential approximation of N excretion depending on N intake (on average, NMR = 173 mg of N/BWkg0.67 per d). The theoretical maximum for daily N deposition was estimated by the Levenberg-Marquardt algorithm (SPSS program, version 11.5) and by exponential fitting of N balance data depending on N intake. The observed dietary Thr efficiency was used to model Thr requirements for a given protein deposition depending on age. The optimal dietary Thr concentration (percentage of feed) was established by different predictions for daily feed intake. Daily CP deposition of approximately 60% of the potential required 0.83 and 0.87% (10 to 25 d), 0.73 and 0.75% (30 to 45 d), 0.66 and 0.69% (50 to 65 d), and 0.51 and 0.53% (70 to 85 d) of Thr in feed for genotype I 657 and genotype Red JA, respectively (average daily feed intakes of 30, 75, 100, and 100 g in age periods I to IV). Results of model calculations need verification in comparative growth studies with assessment of nutrient deposition and varying dietary Thr efficiencies.

Key Words: threonine • requirement • modeling • slow-growing genotypes • age


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The efficacy of amino acid utilization in growing animals depends on the adequacy of the dietary amino acid supply. Quantitative amino acid requirements are influenced by genotype, age, and sex (Leclercq, 1983; Renden et al., 1992; Zuprizal et al., 1992; Smith et al., 1998; Rosa et al., 2001; Chamruspollert et al., 2002). Following Met and Lys, Thr is considered the third limiting amino acid in chicken diets based on soybean meal (Fernandez et al., 1994; Kidd, 2000).

Currently, Thr requirement studies are focused on fast-growing chickens (Kidd et al., 1997; Rosa et al., 2001; Samadi and Liebert, 2006b), but different results have been observed depending on genotype, age, sex, and response criteria (Sasse and Baker, 1973; Woodham and Deans, 1975; Sibbald, 1987; NRC, 1994; Rosa et al., 2001; Kidd et al., 2004; Samadi and Liebert, 2006b). Additionally, dietary factors such as amino acid efficiency and the procedure for assessing the requirement itself are of importance (Sibbald, 1987; Samadi and Liebert, 2006b, 2007). Conclusive Thr requirement data for defined slow-growing chicken genotypes are currently unavailable. Application of our modeling procedure (Samadi and Liebert, 2006a,b, 2007) requires genotype- and age-dependent information for nitrogen maintenance requirements (NMR) and the genetic potential for daily nitrogen deposition (NDmaxT), which are currently unavailable. Furthermore, the present experiments used Thr as the amino acid under study because corn-soybean meal diets provide Thr as the third limiting amino acid following Met and Lys (Kidd, 2000). Experiments were conducted to establish reliable model parameters for 2 commercial slow-growing chicken genotypes and to draw first conclusions about Thr requirements depending on age and efficiency of dietary Thr utilization, respectively.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Animals and Housing
Day-old male chickens from Hubbard ISA genotypes (genotype A: I 657; genotype B: Red JA) were obtained from a commercial hatchery and fed a starter diet up to the beginning of the experiments. A total of 144 chickens from each genotype were used in 4 N-balance studies, according to age periods I, II, III, and IV (period I: 10 to 25 d; period II: 30 to 45 d; period III: 50 to 65 d, and period IV: 70 to 85 d). For each age period, 72 chickens (36 each from genotype A and B) were randomly allocated to 6 diets with a graded protein supply (Table 1Go). Birds were individually housed in metabolism cages with wire floors equipped with individual feeding and self-drinking systems.


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  		Table 1. Ingredient composition of the experimental diets (% as fed)
 
Initial average BW within the age periods were 234 ± 18 and 230 ± 18 g (period I), 844 ± 30 and 893 ± 37 g (period II), 1,736 ± 37 and 1,891 ± 47 g (period III), and 2,569 ± 37 and 2,877 ± 31 g (period IV) for genotype A and B, respectively. Room temperature was maintained at 32°C (day-old chickens) and was continuously decreased to 24°C up to the end of the experimental period (70 to 85 d). Warm red light was provided for 24 h/d throughout the experiment.

The experiments were carried out at the facilities of the Institute for Animal Physiology and Animal Nutrition in accordance with animal welfare legislations and were approved by the ethics committee of the Agricultural Faculty of Goettingen University.

Diets, Feeding, and Sampling
The experimental diets (Tables 1Go and 2Go) provided 6 graded levels of dietary CP (N1 = 6.6%, N2 = 13.0%, N3 = 19.6%, N4 = 25.1%, N5 = 31.8%, and N6 = 37.6% CP in DM) from high-protein soybean meal as the protein source. The basics of this procedure were also applied in earlier studies with fast-growing chicken genoytpes (Samadi and Liebert, 2006a,b, 2007). To maintain Thr as the first limiting amino acid in all diets, crystalline amino acids (L-Lys·HCl, DL-Met) were supplemented (Samadi and Liebert, 2006b). A graded dietary protein supply and equal amino acid ratios were provided by diluting the protein source using wheat starch (Table 1Go), according to principles of the diet dilution technique (Fisher and Morris, 1970). Within the physiological limitations for fat addition, the calculated dietary energy content (WPSA, 1984) was kept similar.


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  		Table 2. Analyzed nutrient content (DM basis) of the experimental diets
 
Each N-balance experiment within the age periods used 6 chickens per diet and genotype. The experimental period was divided into 5-d adaptation and 2 consecutive excreta collection periods (5 d each), providing a total of 6 N-balance data per diet, genotype, and age period. To predict the proper level of individual feed supply, at the beginning of the adaptation period, the pelleted diets were fed at a free-choice level. The individual feed supply was kept constant, beginning on the third day of the adaptation period, slightly adapted during the first 2 d of the collection period, and kept constant again up to the end of each collection period. In this way, the age effect on feed intake was mostly compensated. Quantitative excreta collection was conducted 3 times a day to minimize ammonia losses from nonacidified excreta. Collected excreta samples were immediately frozen and stored at –20°C until further analysis.

Chemical Analyses
Chemical analyses were done according to the German standards of Verband Deutscher Landwirtschaftlicher Untersuchungs- und Forschungsanstalten (Naumann and Bassler, 1976–1997). An automatic N analyzer (Leco LP-2000, Leco Instruments GmbH, Kirchheim, Germany) was applied for N detection in diets and excreta samples according to the Dumas procedure. Crude protein contents were calculated (N x 6.25). Amino acids in the diets were analyzed in duplicate by ion-exchange chromatography (LC 3000; Biotronik, Eppendorf-Netheler-Hinz GmbH, Hamburg, Germany) following acid hydrolysis with and without an oxidation step for quantitative determination of sulfur-containing and other amino acids, respectively. Ether extracts in feed samples were analyzed following HCl hydrolysis.

Statistical Analyses
Experimental data are presented as mean values ± standard errors of the means. Statistical analyses were carried out by use of the SPSS statistical software package (version 12.0 for Windows, SPSS, Inc., Chicago, IL). The statistical procedure for estimating the threshold value (NRmaxT) of the exponential function used the Levenberg-Marquardt algorithm within the SPSS package. The applied N utilization model for growing monogastric animals, based on Gebhardt (1966), was adapted as reported earlier (Thong and Liebert, 2004a,b,c; Samadi and Liebert, 2006a,b, 2007):


Formula 1([1])

where NR is daily N retention (ND + NMR, mg/BWkg0.67), NI is daily N intake (mg/BWkg0.67); NRmaxT is the theoretical maximum for daily N retention (mg/BWkg0.67); NDmaxT = NRmaxT – NMR is the theoretical maximum for daily N deposition (mg/BWkg0.67); NMR is the daily N maintenance requirement (mg/BWkg0.67); b is the slope of the N retention curve (indicating the feed protein quality independent of N intake); and e is the basic number of natural logarithm (ln).

For modeling the requirements of the limiting amino acid (LAA), equation [2] was applied (Samadi and Liebert, 2006b, 2007):


Formula 2([2])

where LAAI is the daily intake of the LAA depending on performance and LAA efficiency (mg/BWkg0.67), and bc–1 is the slope between the LAA concentration (c) and feed protein quality (b).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
NMR and NDmaxT
Nitrogen-balance data (Tables 3Go and 4Go) from the graded protein supply were used for assessing NMR and NDmaxT as reported for fast-growing chicken genotypes (Samadi and Liebert, 2006a,b, 2007). The established model parameters, NMR and NDmaxT (Table 5Go), were used for further calculation of amino acid requirements depending on age, performance, and dietary amino acid efficiency (Thong and Liebert, 2004a,b,c; Samadi and Liebert, 2006b, 2007). According to Samadi and Liebert (2006a, 2007), the NMR estimation by breakpoint analysis with the y-axis, as demonstrated for genotype A (Figure 1Go), yielded very similar results for the age periods under study (Table 5Go). Thus, the averages of NMR = 173 mg/BWkg0.67 per d were used as approaches for the daily N maintenance requirement of slow-growing chickens of both genotypes within the examined age periods. In comparison with the NMR (264 mg/BWkg0.67 per d) proposed by the Committee for Requirement Standards of the German Society of Nutrition Physiology (GRRS, 1999), the observed NMR was lower. However, the current results are in close agreement with Leeson and Summers (2001), who summarized data from protein-free feeding of adult birds. Generally, actual NMR data are scarce because present investigations are more focused on amino acid requirements for maintenance (Edwards and Baker, 1999; Edwards et al. 1999; Sklan and Noy, 2005) using factorial approaches for assessing amino acid requirements.


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  		Table 3. Summarized results of N-balance experiments (n = 6) with genotypes A (I 657) and B (Red JA) in age periods I and II,1 used for determination of model parameters
 

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  		Table 4. Summarized results of N balance experiments (n = 6) with genotypes A (I 657) and B (Red JA) in age periods III and IV,1 used for determination of model parameters
 

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  		Table 5. Estimated daily N maintenance requirement (NMR) and theoretical potential for daily N deposition (NDmaxT) of slow-growing chickens depending on age and genotype
 

Figure 1
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  		Figure 1. Assessment of N maintenance requirement by fitting an exponential function between daily nitrogen intake (NI) and nitrogen excretion (NEX) following a graded protein supply in growing male chickens (example: genotype I 657).

 
The estimation of threshold values for protein deposition of genotype B is demonstrated in Figure 2Go. The summarized results of male slow-growing chickens (Table 5Go) showed decreasing NDmaxT data with increasing age, from 2,807 mg/BWkg0.67 per d (age period I) to 1,191 mg/BWkg0.67 per d (age period IV) for genotype A and from 2,789 mg/BWkg0.67 per d (age period I) to 1,043 mg/BWkg0.67 per d (age period IV) for genotype B.


Figure 2
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  		Figure 2. Assessment of the theoretical potential for daily N deposition (NDmaxT) in different age periods of the growing male chicken (example: genotype Red JA), based on estimation of the threshold value of the function between daily nitrogen intake and nitrogen balance by the Levenberg-Marquardt algorithm. ND = nitrogen deposition; NRmaxT = theoretical maximum for daily N retention; NMR = N maintenance requirement.

 
Thus, the observed genetic potential for protein deposition of both genotypes was very similar. According to previous studies with chickens (Rimbach and Liebert, 1999; Samadi and Liebert, 2006a) and pigs (Wecke and Liebert, 2005), the threshold values decrease with increasing age. The decreasing potential for nitrogen deposition might be due to morphological changes in the gut (Nitsan et al., 1991; Uni et al., 1999), a changing fractional rate of protein synthesis (Kang et al., 1985), and impaired efficiency of amino acid deposition in the carcass (Sklan and Noy, 2004). Compared with fast-growing genotypes (Rimbach and Liebert, 1999; Samadi and Liebert, 2006a), the established threshold values (NDmaxT) of slow-growing chickens were lower. This result is generally in line with the higher absorption rates observed in fast-growing chickens (Shelton et al., 2003).

Modeling of Thr Requirements
Model calculation of Thr requirements depending on age period, protein deposition, and observed average dietary Thr efficiency (Tables 6Go to 9GoGoGo) used different standards for comparison (mg/BWkg0.67 per d; mg/d; percentage of the diet). To calculate Thr requirements according to growth performance as expected under more practical feeding conditions, 50, 60, and 70% of the threshold value (NDmaxT) were applied as levels of growth performance. To calculate the optimal Thr concentration in the diets, predictions for daily feed intake in line with the observed free-choice feed intake were used.


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  		Table 6. Model calculation of the Thr requirement for slow-growing chickens in age period I (10 to 25 d), depending on genotype, daily CP deposition, dietary Thr efficiency, and feed intake1
 

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  		Table 7. Model calculation of the Thr requirement of slow-growing chickens in age period II (30 to 45 d), depending on genotype, daily CP deposition, dietary Thr efficiency, and feed intake1
 

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  		Table 8. Model calculation of the Thr requirement of slow-growing chickens in age period III (50 to 65 d), depending on genotype, daily CP deposition, dietary Thr efficiency, and feed intake1
 

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  		Table 9. Model calculation of the Thr requirement of slow-growing chickens in age period IV (70 to 85 d), depending on genotype, daily CP deposition, dietary Thr efficiency, and feed intake1
 
Literature data for optimal dietary Thr concentration showed remarkable variation. Additionally, to our knowledge quantitative Thr requirements for slow-growing genotypes as used in the current study are not available. Using diets with 16.2% CP, Hewitt and Lewis (1972) concluded that the optimal dietary concentration was 0.48% Thr. Woodham and Deans (1975) reported 0.50 to 0.52% Thr. The NRC (1994) recommendation is 0.80% Thr in diets for chickens (0 to 3 wk of age). Based on a broken-line regression analysis, Rangel-Lugo et al. (1994) concluded that the optimal concentrations were 0.77% Thr (20% CP diet) and 0.86% Thr (25% CP diet) for chickens (0 to 14 d). The scope of suggestions corresponds to our observations, in particular at age period I (10 to 25 d) and according to approximately 60% of NDmaxT and 30 g of daily feed intake (Table 6Go). However, considerable variation was observed when making different assumptions for the daily feed intake. In commercial chicken genotypes, Webel et al. (1996) observed 0.61% (3 to 6 wk) and 0.52% (6 to 8 wk) digestible Thr as optimal amounts to maximize feed efficiency, assuming 87% Thr digestibility in corn-soybean meal diets, corresponding to 0.70% (3 to 6 wk) and 0.60% (6 to 8 wk) total Thr. These conclusions ranked below those of the NRC (1994), which recommends 0.74% (3 to 6 wk) and 0.68% (6 to 8 wk) Thr. Our results for age periods II and III (Tables 7Go and 8Go) and 60% of NDmaxT with 75 g (period II) and 100 g (period III) of daily feed intake are in agreement with those of the NRC (1994). Generally, it is difficult to compare requirement data from different experiments because of variations in genotype, age, feed intake, dietary factors, and the procedure applied for requirement determination.

Alleman et al. (1999) reported Thr requirements of 0.84 and 0.61% within the same age period (28 to 49 d) using lean-line and fat-line chickens, respectively. However, in terms of the digestible Thr requirement per gram of gain, the Thr requirements for both lines were very similar (13.9 vs. 12.4 mg for lean- and fat-line chickens, respectively).

The current results also showed (Tables 6Go to 9GoGoGo) that both genotypes of slow-growing chickens needed quite similar Thr concentrations in the diet. Rosa et al. (2001) observed no significant difference in optimal dietary Thr concentrations (0.68 to 0.69%) between high-yield and classic broiler strains (0 to 18 d), although the growth and feed conversion ratio were superior in the high-yield strain. This optimal dietary Thr concentration is considerably below the NRC (1994) recommendations (0.80%) for a similar age. Rosa et al. (2001) used corn, peanut meal, poultry by-products, and crystalline Thr as dietary amino acid sources. In our study, the dietary Thr efficiency was only from high-protein soybean meal. This dietary factor cannot be generalized without detailed results about the variation of Thr efficiency in the main feed ingredients. In pig studies (Thong and Liebert, 2004a,b), dietary Thr efficiency provided significant effects on derived Thr requirements. Additionally, the predicted feed intake is of great importance for the derived optimal dietary amino acid concentration. Environmental conditions have also led to different growth responses of chickens depending on the Thr supply (Kidd et al., 2003a). Furthermore, an increased need for Thr under suboptimal environmental conditions can be attributed to the increased maintenance requirements associated with intestinal functions (Corzo et al., 2003) and immune system activation (Bhargava et al. 1971). Interactions between dietary protein supply and optimal Thr concentration in the feed were also established (Cifti and Ceylan, 2004) and different response criteria may influence the conclusions regarding the optimal dietary Thr content. However, for 95% of the maximum response, the established total Thr requirements derived from BW gain and breast meat yield in the age period of 21 to 42 d were 0.74 and 0.71%, respectively (Kidd et al., 2004). This observation was near the NRC (1994) recommendations and was very similar to our modeling for approximately 60% of NDmaxT and average feed intake (Table 7Go).

In the finishing period (42 to 56 d), Kidd et al. (2003a, b) concluded that the optimal concentration was 0.60 to 0.67% Thr for female chickens and 0.63 to 0.68% Thr for male chickens, respectively. For 30 to 42 d, Corzo et al. (2003) observed that the optimal concentrations were 0.69 and 0.71% Thr for growth and feed conversion, respectively. Birds reared in a clean environment responded to Thr in a quadratic manner, whereas under suboptimal environmental conditions, chickens responded linearly for growth performance and carcass traits. In age period III (Table 8Go), we established 0.67% Thr as optimal for both genotypes, assuming 100 g of daily feed intake and 60% of NDmaxT.

In conclusion, the results of our model calculation of Thr requirements in slow-growing chicken genotypes are within the scope of data reported in the literature. Based on our present knowledge, age effects were established and the predicted feed intake was a superior factor of influence for determining optimal Thr concentrations in the feed. Additionally, the expected variation in dietary efficiency of Thr utilization from the main feed ingredients requires much more scientific attention. The reported data are derived only from observed Thr efficiency in high-protein soybean meal. Currently, no information is available corresponding to the usual variation in this dietary factor in different batches of different feed ingredients. The applied modeling procedure, which used principles of the diet dilution technique, has the potential to provide conclusive amino acid requirement data, as reported for fast-growing chicken genotypes (Samadi and Liebert, 2006a,b, 2007). Additionally, requirement data provided by this procedure are related to the effects of breeding success, age, sex, and growth performance, and they take into account the efficiency of individual dietary amino acids. Similar to other methods in requirement studies, the current results have yet to be applied and verified in long-term growth experiments with determination of nutrient deposition and several carcass traits. Ongoing experiments are focused on this application side of our modeling procedure.


   FOOTNOTES
 
1 Present address: Animal Husbandry Department, Syiah Kuala University, 23111 Darussalam-Banda Aceh, Indonesia. Back

Received for publication November 14, 2006. Accepted for publication February 15, 2007.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
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