Nitrogen Solubility and Dietary Protein Fractions of Various Feed Stuffs

Protein fractions (A+B_l, B₂, B₃ and C) and N solubility of 10 feed ingredients in 10 different solvents was determined. The amount of N extracted was maximum for pepsin followed by NaOH, sodium lauryl sulphate (SLS) and distilled water and lowest In cetyl trimethyl ammonium bromide (CTAB). Significant correlation existed between N solubility in phosphate buffer and In McDougall's buffer, NaCI, NaOH, SLS and CTAB. The N solubility was poorly correlated with CP content and fiber composition. The correlations between N solubility in phosphate buffer, McDougall's buffer, NaCI and Triton X-100 and ED as well as rate of N degradation were significant. The ED and rate can foe predicted from solubility by the equations ED = 18.455+0.760* McDougall's buffer solubility (r= 0.72, P<0.02) and Rate = G.09372 + 0.00248* NaCI solubility (r = 0.8S, P<0.01). The partitioning of dietary protein into fractions (A+B₁, B₂, B₃ and C) indicated lower ruminal degradability and higher intestinal digestibility of proteins in soyflakes followed by sunflower cake and maize and higher ruminal degradahility and lower intestinal digestibility of proteins in mustard seed cake followed by neein seed kernel cake and wheat. The correlation of fraction A+B₁ was significant with 1,2, 4 hr in sacco N disappearance, rate of N degradation (P<0.01), and EI.) (P<0.01). Fraction B, was significantly but negatively correlated with ED (P<0.01) and 48 hr in sacco N disappearance (P<0.05). Fraction B₂.+ B₃ was significantly (P<0.01) but negatively correlated with rate of N degradation and ED. The 48 hr in sacco N disappearance, rate of N degradation and ED may be predicted from these fractions with the equations 48 hr disappearance = 55.4+0.595* B₂+B₃+0.815* A+B - 0.730*B2 (r=0.73), Rate = 0.167 + 0.000383* 6,+B, + 0.00213* A+B₁ -0.000732 * B₂ (r = 0.81) and ED = 189.7 - 1.17 *B₂+B₃ - 0.554 *A+B₁-0.948 * B₂ (r=0.84). Feedstuffs having lower content of A and B₁ and higher content of B₂ and B₃ dietary protein fractions are preferred sources of digestible undegradable nitrogen (DUP).