[The effect of straw in ground and pelleted form on the rumen fermentation and protozoa]

Cows possessing a large ruminal fistula were fed straw meal and pelleted wheat straw to investigate its effect on ruminal fermentation (concentration of NH3 and volatile fatty acids (FFS), pH, molar proportions of FFS, rates of FFS production) and on the protozoa population. The straw-concentrate mixture used in the present trial contained 40% of straw. The feeding of pelleted straw produced a significant rise in FFS concentrations (from 8.8. to 12.3 mMole/100 ml) and a corresponding decline of pH (from 6.7 to 6.1). With high molar proportions of acetate (72 mole%) the influence of the straw diet on molar FFS proportions was low. The NH3 peak observed 1 hr after feeding was higher with the pelleted straw than with the straw meal. The feeding of finely gound straw produced a higher level of FFS production (by 10%) than that of straw pellets. (3.88 and 4.29 mMole per gm DM). The number of protozoa (per ml of ruminal fluid) was 335,000 (straw meal) and 121,833 (pellets). The number of large infusorial cells (Isotricha, Diplodinium, Ophryoscolex) decreased correspondingly from 70,000 (straw meal) to 18,870 per ml (pellets). These results suggest that the feeding of pelleted straw-concentrate mixtures to cows as sole feed will not bring about optimum conditions for ruminal fermentation (FFS formation, protein synthesis) and for the layering of ruminal contents.