DEGRADATION CHARACTERISTICS OF STRAW FROM DIFFERENT WHEAT GENOTYPES AND THEIR RESPONSE TO UREA-AMMONIATION TREATMENT

Two experiments were conducted to evaluate straw from 15 wheat genotyp es for rumen degradability and to investigate response to ammoniation in straw varying in quality. All the straw varieties were grown in 3 r eplicates under the same agronomic conditions. Results of the first ex periment demonstrated that degradability characteristics of straw were strongly influenced by wheat genotypes. All the straw genotypes showe d an average degradation lag time of 1.67 h in the rumen. Relatively s mall fraction of the straw varying from 10.29% to 16.02% (P < 0.001) w as found instantly soluble in the rumen. The potentially degradable pa rt of the straw also varied due to genotypes (P < 0.001). The effect o f genotype on degradation rate (% h(-1)) was apparently confounded by large variations due to animals (P < 0.001) and replicates (P <: 0.001 ) and were therefore, not different (P = 0.11). However, effective deg radability at different rumen outflow rates showed significant variati on(P < 0.001) due to genotypes. Comparison among the 15 wheat genotype s revealed that the effective degradability at 4% and 6% rumen outflow rates, was maximum for the straw from C-518 and Sarhad-83 and lowest in case of Dirk and Pak-81. The in sacco degradability parameters show ed close relationship with in vitro digestibility in wheat straw. Pred icted straw intake for a steer (250 kg BW) calculated on the basis of degradability parameters, varied from 4.57 to 5.76 kg/day (P < 0.01) a mong the genotypes. Results of the second experiment revealed that amm oniation, irrespective of genotypes, increased (P < 0.001) the average crude protein (CP) contents from 4.12 In untreated straw to 9.83% in treated straw. Ammoniation also caused changes (P < 0.001) in the fibe r fractions of straw but these were not related to increase in the dig estibility of ammoniated straw. Increase in the in vitro dry matter di gestibility (IVDMD) of straw due to ammoniation was influenced by geno types (P < 0.001) and quality of untreated straw (P < 0.001). A negati ve linear correlation (r = -0.79, P < 0.001) between the quality of un treated straw and increase in IVDMD after ammoniation was found which suggested that response to ammoniation was maximum in poor quality str aw. (C) 1998 Published by Elsevier Science B.V. All rights reserved.