Digesta markers for evaluating the effect of exogenous enzymes on nutrient digestibility in beef feedlot cattle
Year: 2017
Type: dissertation
Abstract: The Food and Agriculture Organization (FAO) stated that it is vital to intensify animal \nand feed production in a sustainable manner. Producers are therefore increasing focus \non methods to improve production efficiency. The use of exogenous enzymes in \nruminant diets can improve production efficiency while also reducing waste products, \nthereby contributing to more sustainable food production. There are many \ncombinations of enzymes that first have to be screened through in vitro methods, \nthereby selecting a number of enzyme combinations with the highest potential \neffectiveness. Ultimately, however, the best combinations need to be validated using in \nvivo digestibility studies. Ruminants, in general, have variable responses to \nsupplementation with exogenous enzymes and the animal response to different \nenzymes can be influenced by the type of enzyme or combinations used as well as the \nexperimental conditions. The in vivo validation of prototype enzymes by means of \ndigestibility studies is therefore of utmost importance before commercialisation of a \nproduct. \nTo measure total tract digestibility the total faecal collection method is normally used. \nTotal faecal collection is, however, labour intensive because all the faeces produced in a period of time must be collected and the animals must be confined to individual housing \nwhich may disturb the animals. Marker-based methods are less labour intensive are an \nattractive alternative to the total faecal collection technique. Before any marker can be \nused in digestibility studies, it should be validated to confirm the suitability of the \nspecific marker in a specific diet. \nThe aim of this study was first to evaluate the effect of different enzyme prototypes on \nfeedlot diet digestibility and secondly to validate different markers as an alternative to \ntotal faecal collection in digestibility studies using high maize feedlot diets. \nSix ruminally cannulated steers were used to evaluate the apparent total tract nutrient \ndigestibility using two different enzyme prototypes against a control diet. The steers \nwere fed twice daily and received either the control diet or a control diet supplemented \nwith either enzyme A or enzyme B. Three different markers, chromic (III) oxide (Cr2O3), \nacid insoluble ash (AIA) and acid detergent lignin (ADL) were validated against total \nfaecal collection to determine which marker is most suitable in digestibility studies for \nfeedlot diets containing high levels of maize (60%) and low levels of roughage (20%). \nThe mean apparent total tract digestibility (TTD) for dry matter (DM), starch and crude \nprotein (CP) showed no difference (P>0.05) between the control diet and diets \nsupplemented with enzyme A or enzyme B. The neutral detergent fibre (NDF) \ndigestibility did show a difference (P<0.05) between the control diet and the diet \nsupplemented with enzyme B. However there were no differences (P>0.05) between \nthe control diet and the diet supplemented with enzyme A or between the two diets \nsupplemented with the enzymes A and B. Acid insoluble ash and Cr2O3 showed no \ndifference (P>0.05) between treatments in its ability to predict digestibility when \ncompared to total faecal collection. Acid detergent lignin predictions differed (P<0.05) from total collection and is probably unsuitable to be used as a marker in high maize \nfeedlot diets. \nThe use of enzymes containing xylanase, amylase and protease had no effect on \nnutrient total tract digestibility in our study; however, the enzyme-containing xylanase \nand β-glucanase had an effect on apparent total tract NDF digestibility. Both AIA and \nCr2O3 can be used as markers to determine apparent total tract nutrient digestibilities in \nfeedlot diets with a high maize content based on a comparison with the total faecal \ncollection. Acid detergent lignin appears to be a poor marker in high concentrate \nfeedlot diets due to the low ADL content of the diet.
Authors: Van Wyk, Anna María
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2770118741