COLONIZATION OF RICE STRAW BY WHITE-ROT FUNGI (CYATHUS-STERCOREUS) - EFFECT ON RUMINAL FERMENTATION PATTERN, NITROGEN-METABOLISM, AND FIBERUTILIZATION DURING CONTINUOUS-CULTURE

Experimental diets consisted of fungal treated or untreated lice straw : concentrate 75:25 on a DM basis and ground through a 1 mm sieve. Fun gal treated rice straw (FRS) and untreated rice straw (C) diets were f ormulated to be isonitrogenous (11% crude protein; CP), but varied in total nonstructural carbohydrates, neutral detergent fiber and acid de tergent fiber (18.3 vs, 11.4%; 49.7 vs. 61.0%; 45.0 vs. 47.5%), respec tively. Four fermenters were inoculated with ruminal fluid from a rumi nally cannulated lactating Holstein cow fed a total mixed ration consi sting of 50% silage: 50% grain (DM basis). A randomized complete block design was used with diets replicated within each experimental period and four times across periods, Each period was 10 days in length, 7 d ays for adaptation followed by 3 days for sample collection. Digesta s olid and liquid dilution rates were 0.055 h(-1). Apparent and true dig estion of DM and OM of the FRS-diet was higher (P < 0.05) compared wit h the C-diet. Fungal treatment increased (P < 0.05) the digestibility of the major fiber component, cellulose, compared to the C-diet (61.1 vs, 48.8%). Actual quantities of nutrients digested per unit rime indi cated that fungal treatment increased cellulose digestion by 27% but d ecreased hemicellulose digestion by 37%, when compared with the C-diet . Arabinose and xylose from FRS-diet were less digestible, however glu cose digestion was increased by 38% compared with the C-diet, Increase d digestion of carbohydrates from FRS-diet resulted in an increase (P < 0.05) on production of total volatile fatty acids (VFA) compared wit h the C-diet. Increased VFA production of FRS-diet was due to increase d molar proportion (moles 100 moles(-1)) of propionate and butyrate (2 8.8 vs. 24.2; 13.1 vs. 7.9), respectively. Branched chain VFA producti on was not detectable with the FRS-diet when compared with an average of 2.6 moles 100 moles(-1) for the C-diet. A similar pattern of inhibi tion was found with ammonia-N production with FRS-diet compared with t he C-diet (0.77 vs. 22.3 mg dl(-1)). Nitrogen metabolism of FRS-diet r esulted in lower true digestion of CP and microbial protein synthesis compared with the C-diet, resulting in increased dietary-N flow. This study demonstrated that fungal treatment increased fiber digestibility by increasing the availability of cellulose but decreasing CP availab ility for rumen microbial digestion.