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Unformatted text preview: Estimation of Nitrogen Maintenance Requirements and Potential for Nitrogen Deposition in Fast-Growing Chickens Depending on Age and Sex Samadi and F. Liebert 1 Institute for Animal Physiology and Animal Nutrition, Georg-August-University, 37073 Goettingen, Germany ABSTRACT Experiments were conducted to estimate daily N maintenance requirements (NMR) and the genetic potential for daily N deposition (ND max T) in fast-growing chickens depending on age and sex. In N-balance studies, 144 male and 144 female chickens (Cobb 500) were uti- lized in 4 consecutive age periods (I: 10 to 25 d; II: 30 to 45 d; III: 50 to 65 d; and IV: 70 to 85 d). The experimental diets contained high-protein soybean meal and crystalline amino acids as protein sources and 6 graded levels of protein supply (N1 = 6.6%; N2 = 13.0%; N3 = 19.6%; N4 = 25.1%; N5 = 31.8%; and N6 = 37.6% CP in DM). The connection between N intake and total N excretion was fitted for NMR determination by an exponential function. The average NMR value (252 mg of N/BW kg 0.67 per d) was applied for further calculation of ND max T as the threshold Key words : nitrogen maintenance requirement, growth potential, protein deposition, growing chicken, modeling protein metabolism 2006 Poultry Science 85:1421–1429 INTRODUCTION Accurate estimation of the amino acid requirements in growing animals is of fundamental importance for diet formulation. Physiological-based models for simulating growth have been partly used to predict these require- ments (Smith, 1978; Hurwitz et al., 1983; Alleman et al., 1999). Genetically, growing animals have a finite potential to deposit protein (Leclercq, 1983; Renden et al., 1992; Smith et al., 1998). In addition, sex (Rosa et al., 2001; Chamruspollert et al., 2002) and age (Zuprizal et al., 1992; Rimbach and Liebert, 1999) are important factors of in- fluence, and it has been demonstrated that, related to the metabolic body mass, the potential of the growing chicken to deposit protein decreases with increased age (Liebert et al., 2000). In addition, the ongoing improvement of the genetic potential for protein deposition ( PD max T ) by breeding success has to be taken into account for qualified and physiologically based amino acid requirement data, ac- 2006 Poultry Science Association Inc. Received January 4, 2006. Accepted March 27, 2006. 1 Corresponding author: [email protected] 1421 value of the function between N intake and daily N bal- ance. For estimating the threshold value, the principle of the Levenberg-Marquardt algorithm within the SPSS program (Version 11.5) was applied. As a theoretical max- imum for ND max T, 3,592, 2,723, 1,702, and 1,386 mg of N/BW kg 0.67 per d for male and 3,452, 2,604, 1,501, and 1,286 mg of N/BW kg 0.67 per d for female fast-growing chickens (corresponding to age periods I to IV) were ob- tained. The determined model parameters were the pre- condition for modeling of the amino acid requirement based on an exponential N-utilization model and de-...
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