Fungal enzymes as animal feed additives

[摘要] ENGLISH ABSTRACT: The use of fungal enzymes as ruminant feed digestibility enhancers was investigated. Currently,ruminants may not digest 38 to 80 % of fibrous forages' content. A renewed interest in the potentialof feed enzymes for ruminants was prompted by the high costs of livestock production, togetherwith the availability of newer enzyme preparations. Direct application of enzyme preparations canimprove in vitro dry matter (DM) and neutral detergent fibre (NDF) degradation, indicating thatdirect-fed fibrolytic enzymes may be effective in enhancing in vivo digestion of forages.Two commercial enzyme products, Fibrozyme and Celluclast, and fungal extracellularenzyme extracts from Aureobasidium pullulans, Trichoderma reesei, Aspergillus aculeatus, andThermomyces lanuginosus were evaluated for enhancing in vitro feed digestibility. Fibrozymeaddition to both wheat straw and lucerne hay did not improve their in vitro digestibilities, even aftera two hour pre-incubation period. The four fungal enzyme extracts did not enhance wheat straw'sdigestibility, but marginal increases were evident for lucerne hay. Celluclast addition resulted inmarginal increases in the digestibility of both oat hay and oat silage, with no enhanced effect onlucerne hay and NaOH-treated wheat straw. No relationship could be found between the level ofenzyme activity and the degree of feed digestion in the in vitro assay.Enzyme hydrolysis with Celluclast, in the absence of rumen fluid, gave more conclusiveresults. All the feed samples tested showed a positive response to Celluclast addition, even the lessdigestible feeds, namely sugarcane bagasse and wheat straw.In vitro results show that the assays were unsuccessful, because almost all of theexperiments conducted showed inconclusive results. Alternative feed evaluation assays, whichinclude the in vivo, in sacco and in situ methods of analysis, as well as gas production measurementand in vitro analysis with the DAISyII system, should be evaluated. A more detailed study of feeddigestibility should be motivated by determining which feeds are hydrolysable, their chemicalcomposition, i.e. how accessible the feeds are, and also evaluation of feed mixtures. The enzymesupplements also need to be evaluated for optimum temperature and pH, as well as the compilationof enzyme cocktails.

[发布机构] Stellenbosch University