[Methodical investigations on evaluation of lysine utilization in pigs after extreme changes of protein quantity and quality]

Effects of dietary levels of glycine, threonine and protein on threonine efficiency and threonine dehydrogenase activity in hepatic mitochondria of chicks

This study was carried out to evaluate the relationship between threonine (Thr) efficiency and Thr dehydrogenase (TDG) activity as an indicator of Thr oxidation on chicks fed with levels of diets (CP [17.5% and 21.5%] and Thr [3.8 and 4.7 g/100 g CP]; glycine [Gly][0.64% and 0.98%] and true digestible Thr [dThr] [0.45% and 0.60%]). Calculation of the Thr efficiency was based on N-balance data and an exponential N-utilization model, and TDG activity was determined as accumulation of aminoacetone and Gly during incubation of hepatic mitochondria. This study found that in the liver of chicks who received a diet containing up to 0.79% Thr (4.7 g Thr/100 g of CP) in the 17.5% CP diet, no significant (p>0.05) effect on TDG activity was observed. However, significantly (p = 0.014) increased TDG activity was observed with a diet containing 21.5% CP (4.7 g Thr/100 g of CP) and the efficiency of Thr utilization showed a significant (p = 0.001) decrease, indicating the end of the Thr limiting range. No significant (p>0.05) effect on the total TDG activity and accumulation of Gly was observed with addition of Gly to a diet containing 0.45% dThr. In addition, addition of Gly to a diet containing 0.60% dThr also did not result in a change in accumulation of Gly. Due to an increase in accumulation of aminoacetone, an elevated effect on total TDG activity was also observed. No significant (p>0.05) reduction in the efficiency of Thr utilization was observed after addition of Gly at the level of 0.45% dThr. However, significantly (p<0.001) reduced efficiency of Thr utilization was observed after addition of Gly at the level of 0.60% dThr. Collectively, we found that TDG was stimulated not only by addition of Thr and protein to the diet, but also by addition of Gly, and efficiency of Thr utilization was favorably affected by addition of Gly at the level near to the optimal Thr concentration. In addition, no metabolic requirement of Gly through the TDG pathway was observed with almost the same accumulation of Gly and a slight increase in TDG activity by addition of Gly. Thus, our findings suggest that determination of TDG activity and parameter of efficiency of Thr utilization may be useful for evaluation of dietary Thr level.

Estimation of Nitrogen Maintenance Requirements and Potential for Nitrogen Deposition in Fast-Growing Chickens Depending on Age and Sex

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 utilized 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 value of the function between N intake and daily N balance. For estimating the threshold value, the principle of the Levenberg-Marquardt algorithm within the SPSS program (Version 11.5) was applied. As a theoretical maximum 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 obtained. The determined model parameters were the precondition for modeling of the amino acid requirement based on an exponential N-utilization model and depended on performance and dietary amino acid efficiency. This procedure will be further developed and applied in the subsequent paper.

Amino acid requirement of growing pigs depending on amino acid efficiency and level of protein deposition. 2nd communication: threonine

This study was conducted to evaluate the variability of the efficiency of threonine in different feed proteins for growing pigs. This information is of importance for actual conclusions about threonine requirement within the exponential N-utilization model (Liebert and Gebhardt, 1986) used in our investigations. Wheat (as basal protein), high-protein soybean meal, low-protein soybean meal, rapeseed meal, field bean (Vicia faba), peas (Pisum sativum), corn gluten meal and soybean protein concentrate were used as protein sources. Fifty-six growing barrows (40-65 kg BW) of the genotype Piétrain x (Duroc x Landrace) were randomly allotted to eight N-balance experiments (n = 7). Diets were formulated with two main ingredients (wheat + one feed protein) with threonine as the first limiting amino acid in the mixture which was partly supplemented with crystalline amino acids. Based on N-balance data, the efficiency of threonine was determined in protein mixtures and individual feed proteins. Threonine requirement was calculated depending on efficiency of threonine and level of daily protein deposition. The results from the present studies indicate that the efficiency of threonine in different feed proteins varied in a wide range. Consequently, this factor has to be taken into account for requirement calculations. The threonine requirement depending on daily protein deposition (130, 145 and 160 g) and the efficiency of threonine according to different reference units (g/BW(kg)(-0.67)/d, g/d and % of threonine in the diet) were calculated. The threonine requirement of growing barrows (50 kg BW) corresponding to an average threonine efficiency was 8.52, 9.92 and 11.61 g/d for a daily protein deposition of 130, 145 and 160 g, respectively. The results for a daily protein deposition of 145 or 160 g are in agreement with actual studies and recommendations for threonine supply.