The present. study, which is first of its type in Pakistan, was conducted to identify wheat. straw variety which has inheritedly better feeding value and to investigate the effect of breeding on the quality of wheat. straw and hopefully, it will serve as a base line for further researches in this direction.

During the present study, two adult rumen fistulated buffalo steers, of almost the same age and weights maintained at the animal nutrition section of Veterinary Research Institute Feshawar, were used. Five different varieties of wheat straw namely Firsahak-85, Firsahak-91 , C-518, Blue silver and Khushai grown on the same soil under the same agronomical conditions , were collected each in three replicates from the Agricultural Developrnent. Farm of NWFP. Agricultural University, Peshawar during their harvesting season In May, 1992.

Representative samples of these five test varieties were analysed in triplicate, for nutrient, composition viz; dry matter, ash, crude protein (CP) , crude fibre (CF) , crude fat (EE), neutral detergent fibre (NDF), acid detergent fibre (ADF), .Lignin and silica, according to the standard procedures of AOAC (1980) and Goering and Van Soest (1979).

The results of chemical analyses revealed that. there was no difference among the straw varieties in ash, CP, CF, NDF, lignin and silica contents. However, the %age of AUF' and EF in the wheat straw significantly varied (P<0. 05) due to cultivars.
The variety C-518 was apparently higher in CF and EE contents (4. 99% and 0.85% in DM respectively), comparatively lower in CF and ADF (40. 1% and 48. 95% in PM respectively) than the other varieties.

Mean in Sacco matter digestibility of the five wheat straw cultivars were determined at different incubation times of 6, 12 24, 48 and 72 hours by using the nylon bag technique described by Orskov et al (1980). The analysis of variance for the. individual. incubation time indicated that the dry matter digestibility at all the hours except 24 hours significantly varied (P<0. 05) due to cultivars.

Based on the results of in sacco measurements at different hours, the rate of digestibility and other digestibility characteristics were calculated by least squares. The rate of digestibility (C; % per hour) was also significantly different (P<0. 05) among the cultivars. C-518 resulted in more "C' value of 4.4% per hour (F< 0. 05) as compared to the. other four wheat straw cuitlvars. Similarly the effective dry matter digestibility calculated at. a rumen out-flow rate of 0.02 was also significantly affected (P<0. 001) by the straw cultivars and significantly higher (F<0. 05) in C-518 and Khushai. than the other three varieties.

The regression correlation between rate of digestibility and nutrient composition of all the five wheat straw cuitivars were interpreted in accordance to the procedures of steel and Tone (1980) which indicated that the rate of digestibility was postiveiy correlated with CF contents in wheat straw and negatively correlated with CF, ADF, NDF, ash and silica contents in the wheat. straw. However, lignin and EE did not. show any relationship with the rate of digestion of wheat straw.

Dry matter intakes and Energy values were predicted for all the wheat straw cultivars, on the basis of their measurements, using the multiple regression equation developed by Orskov et al (1988) which showed that under practical feeding situations, C-518 cultivar of wheat straw will be consumed by cattle in higher quantities and the same variety will supply 38% more metabolizable energy to the animal.