Degradation characteristics of straw from different wheat genotypes and their response to urea-ammoniation treatment

Abstract

Two experiments were conducted to evaluate straw from 15 wheat genotypes for rumen degradability and to investigate response to ammoniation in straw varying in quality. All the straw varieties were grown in 3 replicates under the same agronomic conditions. Results of the first experiment demonstrated that degradability characteristics of straw were strongly influenced by wheat genotypes. All the straw genotypes showed an average degradation lag time of 1.67 h in the rumen. Relatively small fraction of the straw varying from 10.29% to 16.02% ( P<0.001) was found instantly soluble in the rumen. The potentially degradable part of the straw also varied due to genotypes ( P<0.001). The effect of 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 degradability at different rumen outflow rates showed significant variation ( P<0.001) due to genotypes. Comparison among the 15 wheat genotypes 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 showed close relationship with in vitro digestibility in wheat straw. Predicted 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) among the genotypes. Results of the second experiment revealed that ammoniation, 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 fiber fractions of straw but these were not related to increase in the digestibility of ammoniated straw. Increase in the in vitro dry matter digestibility (IVDMD) of straw due to ammoniation was influenced by genotypes ( P<0.001) and quality of untreated straw ( P<0.001). A negative linear correlation ( r=−0.79, P<0.001) between the quality of untreated straw and increase in IVDMD after ammoniation was found which suggested that response to ammoniation was maximum in poor quality straw.