The Food and Agriculture Organization (FAO) stated that it is vital to intensify animal
and feed production in a sustainable manner. Producers are therefore increasing focus
on methods to improve production efficiency. The use of exogenous enzymes in
ruminant diets can improve production efficiency while also reducing waste products,
thereby contributing to more sustainable food production. There are many
combinations of enzymes that first have to be screened through in vitro methods,
thereby selecting a number of enzyme combinations with the highest potential
effectiveness. Ultimately, however, the best combinations need to be validated using in
vivo digestibility studies. Ruminants, in general, have variable responses to
supplementation with exogenous enzymes and the animal response to different
enzymes can be influenced by the type of enzyme or combinations used as well as the
experimental conditions. The in vivo validation of prototype enzymes by means of
digestibility studies is therefore of utmost importance before commercialisation of a
To measure total tract digestibility the total faecal collection method is normally used.
Total 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
which may disturb the animals. Marker-based methods are less labour intensive are an
attractive alternative to the total faecal collection technique. Before any marker can be
used in digestibility studies, it should be validated to confirm the suitability of the
specific marker in a specific diet.
The aim of this study was first to evaluate the effect of different enzyme prototypes on
feedlot diet digestibility and secondly to validate different markers as an alternative to
total faecal collection in digestibility studies using high maize feedlot diets.
Six ruminally cannulated steers were used to evaluate the apparent total tract nutrient
digestibility using two different enzyme prototypes against a control diet. The steers
were fed twice daily and received either the control diet or a control diet supplemented
with either enzyme A or enzyme B. Three different markers, chromic (III) oxide (Cr2O3),
acid insoluble ash (AIA) and acid detergent lignin (ADL) were validated against total
faecal collection to determine which marker is most suitable in digestibility studies for
feedlot diets containing high levels of maize (60%) and low levels of roughage (20%).
The mean apparent total tract digestibility (TTD) for dry matter (DM), starch and crude
protein (CP) showed no difference (P>0.05) between the control diet and diets
supplemented with enzyme A or enzyme B. The neutral detergent fibre (NDF)
digestibility did show a difference (P<0.05) between the control diet and the diet
supplemented with enzyme B. However there were no differences (P>0.05) between
the control diet and the diet supplemented with enzyme A or between the two diets
supplemented with the enzymes A and B. Acid insoluble ash and Cr2O3 showed no
difference (P>0.05) between treatments in its ability to predict digestibility when
compared 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
The use of enzymes containing xylanase, amylase and protease had no effect on
nutrient total tract digestibility in our study; however, the enzyme-containing xylanase
and β-glucanase had an effect on apparent total tract NDF digestibility. Both AIA and
Cr2O3 can be used as markers to determine apparent total tract nutrient digestibilities in
feedlot diets with a high maize content based on a comparison with the total faecal
collection. Acid detergent lignin appears to be a poor marker in high concentrate
feedlot diets due to the low ADL content of the diet.
Dissertation (MSc Agric)--University of Pretoria, 2017.