Czech Journal of Animal Science (Jul 2015)

Optimum proportion of standardized ileal digestible sulfur amino acid to lysine to maximize the performance of 25-50 kg growing pigs fed reduced crude protein diets fortified with amino acids

  • G.J. Zhang,
  • P.A. Thacker,
  • J.K. Htoo,
  • S.Y. Qiao

DOI
https://doi.org/10.17221/8276-CJAS
Journal volume & issue
Vol. 60, no. 7
pp. 302 – 310

Abstract

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The study was conducted to determine the standardized ileal digestible (SID) sulfur amino acid (SAA) to lysine (Lys) ratio required to maximize the performance of 25-50 kg pigs fed reduced crude protein (CP) diets fortified with crystalline amino acids. A total of 360 crossbred (Duroc × (Landrace × Large White)) pigs, weighing 25.6 ± 2.7 kg, were blocked by gender, litter, and initial body weight (BW) and allotted to 1 of 5 dietary treatments with 6 pens per treatment and 12 pigs per pen for a 35-day performance trial. The basal diet was based on corn, soybean meal, and wheat bran and was formulated to be deficient in SAA (50% proportion of SID SAA to Lys). Graded levels of dl-methionine were added to the basal diet at the expense of wheat bran in order to provide 55.6, 60.0, 65.6, or 70.0% proportion of SID SAA to Lys, respectively. A constant SID Lys level of 0.90% was set so that Lys was the second limiting amino acid (AA) in all diets. Average daily gain (ADG) and feed conversion ratio (FCR) improved (linear and quadratic, P < 0.05) with increasing dietary proportion of SID SAA to Lys. Increasing the dietary proportion of SID SAA to Lys decreased the serum urea nitrogen (SUN) level (quadratic, P < 0.05). A two-slope broken-line model estimated the optimum proportion of SID SAA to Lys to be 62.2, 61.5, and 62.3% for maximum ADG and minimum FCR and SUN, respectively, whereas a curvilinear-plateau model yielded an optimum proportion of SID SAA to Lys level of 63.8, 62.5, and 61.5% for maximum ADG and minimum FCR and SUN, respectively. Based on an average of these estimates, we conclude that the proportion of SID SAA to Lys required for 25-50 kg pigs fed low CP diets is 62.3%. This estimate is higher than the NRC (2012) recommendation of 56.1% for 25-50 kg pigs fed normal CP diets.

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