Genetic Variation in the Morphological Characteristics, Chemical Composition and Rumen Digestibility of Wheat Straw Cultivars Grown in NWFP

Abstract

In continuation of the previous studies, two experiments were conducted in the period under report 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 previously grown in 3 replicates (3X0.9 meter plot/replicates) under the same agronomic conditions. In the first experiment, ruminal degradability of straw from 15 genotypes was determined with the standard in Sacco technique in two rumen fistulated buffalo steers at 4, 8, 12, 24, 48, and 72 hours. The results were used to calculate potentially degradable fraction, rate of degradation and effective degradability of the straw varieties at different rumen outflow rates. Dry matter intake in animal was predicted from the degradability parameters. In the second experiment, straw from 9 wheat genotypes each varying in quality (dry matter digestibility), were selected for ammoniation. These were grouped as good, medium, and poor, each group consisting three genotypes. The straw, in batches of 1 kg, were treated with urea solution which provided final concentrations of urea 4% and moisture 40%. The treated straw was stored in sealed polytene bags at room temperature for a period of 7 weeks. Both untreated and ammoniated straw samples were processed for chemical analysis and in vitro dry matter digestibility. Results of the first experiment demonstrated that degradability characteristics of straw were strongly influenced by wheat genotypes. All the straw genotype showed and average lag time of 1.67 hours before initiation of degradation in the rumen. Relatively small fraction of the straw varying from 10.29 to 16.02% and affected by genotypes (P<0.001) were found instantly soluble in the rumen. The potentially degradable part of the straw also varied due to genotypes (P0.001). Results of degradation rate (percent/hour) were confounded by large variation (P<0.01) due to animals and replicates and were therefore not different (P=0.11) among the different genotypes. Based on these results, effective degradability at different rumen outflow rates was estimated which 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 SArha-83 and lowest in case of Dirk and Pak-81. Straw from the remaining genotypes were ranked as intermediate. Predicted straw intake by a steer or a cow weighing 250 kg varied from 4.57 to 5.76 kg/day due to genotypes. The results suggested that straw consumption could be increased to an extent of 26% through selection of wheat genotypes for better quality straw. Dry matter digestibility of straw samples determined with the in vitro and in Sacco techniques were highly correlated, suggesting the validity of both techniques for assessment of straw quality. However, the use of in Sacco techniques was considered more appropriate because of its high relevancy to practical situation. Results of the second experiment revealed that ammoniation, irrespective of genotypes, increased (P<0.001) the average crude protein contents from 4.12 in untreated straw to 9.83% in treated straw. Such an increase due to ammoniation which brought the protein value of wheat straw close to that of local non-legume fodders was considered favourable in efficient utilization of the straw. The need for appropriate supplementation to further increase utilization of straw in ruminants was discussed. Ammoniation also affected (P<0.001) the fibre fractions of straw but the changes were not related to increase in the digestibility of ammoniated straw. Increase in the vitro dry matter digestibility (IVDMD) of straw due to ammoniation was influenced by the 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. Economic comparison of response to ammoniation in wheat straw revealed that the technology should be applied strategically only for upgrading the feeding value of poor quality straw even after ammoniation, remained below that of untreated good quality straw. This emphasize selection of genotypes for good quality straw as an economically and managemental viable approach for sustainable improvement in utilization of cereal straws in ruminant feeding. Better quality of straw can be obtained without scarifying for the grain yield. Results of the previous studies conducted this laboratory revealed that it is possible to select genotypes which combine both high grain yield and superior quality straw.