THE POTENTIAL OF YEAST AND NATURAL FUNGI FOR ENHANCING FIBER DIGESTIBILITY OF FORAGES AND ROUGHAGES

The potential of yeast (Saccharomyces cerevisiae) and white rot fungi (Armillaria heimii) to improve forage digestibility was tested in vitr o on four roughage based diets and in vivo on veld hay. Four rumen fis tulated steers were fed the four diets (veld hay, mainly Hyparrhenia f ilipendula; katambora hav, Chloris gayana; pea bean hay, Fasciolas vul garis; veld hay supplemented with soya-bean meal) in a 4 X 4 Latin squ are design. Rumen liquor sampled from each donor animal was incubated in vitro with the corresponding diet subjected to the following treatm ents in a 4 X 4 factorial arrangement within the Latin square: (i) bas al diet without microbial supplements; (ii) basal diet plus 20 mg yeas t granules, (iii) basal diet plus 20 mg white rot fermentation extract ; (iv) basal diet plus 10 mg yeast granules plus 10 mg white rot ferme ntation extract. The in vitro digestibility of neutral detergent fibre (NDFD) was increased (P<0.05) by all the microbial treatments, with t he yeast plus fungi combination showing the highest values of 59.6% fo r veld hay, 78.2% for supplemented veld hay, 70.3% for katambora hay a nd 72.2% for pea bean hay, versus control values of 30.5%, 69.2%, 43.8 % and 47.9%, respectively. The fungal treatment resulted in higher (P< 0.05) NDFD than treatment with yeast, i.e. 50.9% vs. 45.8% for veld ha y, 75.2% vs. 73.7% for supplemented veld, 63.6% vs. 57.5% for katambor a hay and 64.4% vs. 58.0% for pea bean hay. In the in vivo study, 16 m ature wethers were allocated to four treatments: (i) veld hay; (ii) ve ld hay plus yeast granules; (iii) veld hay plus white rot fermentation extract; (iv) veld hay plus a combination of yeast granules and white rot fermentation extract. The microbial treatments increased (P<0.05) the intake of dry matter, metabolisable energy and NDFD of veld hay ( respective values of 0.786 kg day-1, 4.47 MJ day-1 and 43.8% for yeast , 0.748 kg day-1, 4.64 MJ day-1 and 49.2% for fungi, 0.889 kg day-1, 6 .69 MJ day-1 and 58.0% for the combination compared with control value s of 0.742 kg day-1 3.55 MJ day-1 and 37.4%). No signs of ill-health w ere detected in any of the animal's. It was concluded that a combinati on of S. cerevisiae and A. heimii had the best potential for increasin g forage digestibility.