Effect of exogenous fibrolytic enzyme supplementation on rumen fermentation in sacco NDF disappearance and total tract nutrient digestibility of feedlot steers fed hominy chop - maize based diets

Abstract

The focus of this study was to determine the effect of exogenous enzyme supplementation on rumen fermentation parameters, since a healthy or improved rumen environment favors more efficient growth performance and contributes to higher total tract digestibility, the focus being on the South African feedlot industry. The effects on total tract digestibility, in sacco digestion and dry matter disappearance of Neutral detergent fibre (NDF) as well as rumen fermentation patterns were studied using three differing levels of formulated fibre. The primary energy component were different combinations of maize and hominy chop, leading to differing dietary fibre levels. Hominy chop is a by-product of the South African maize milling industry and often a raw material used extensively in feedlots around the country due to the ease of supply and possible cheaper acquisition price than maize. The experimental trial was designed as a 6x6 latin square, repeated in time, within a factorial arrangement of treatments (3x2). The treatments included non-enzyme and enzyme treatment of three diets differing in starch and fibre content, the primary constituents being maize and hominy chop. During each feeding cycle, enough time for adaption to the new diet was allowed as well as enough time for enzyme washout to avoid carry-over effects from the previous treatment. Digestibility was measured using an internal marker, in sacco incubation was performed on the different experimental diets as well as hominy chop on its own, and lastly, rumen fluid samples were analysed for pH, volatile fatty acid (VFA) and ammonia-nitrogen levels. Total tract crude protein and starch digestibility did not differ significantly between treatments (P<0.05), but fibre digestibility was affected by enzyme treatment. For both the 75HC:25M and 25HC:75M diets, the enzyme supplementation increased ADF digestibility (P<0.05) from 43.79% to 54.12% and 46.11% to 54.49% respectively. No significant effects were seen between the same the diets on the different treatments for NDF digestibility, while there were significant effects across all the diets for both ADF and NDF digestibility (P<0.05). The mean NDF digestibility (P<0.05) improved from 54.73% to 60.10%, while the mean ADF digestibility (P<0.05) improved from 46.11% to 54.49% for the non-enzyme vs enzyme treatment respectively. The enzyme supplementation did not affect the in sacco DM and NDF disappearance for either the hominy chop or the TMR when comparing results within experimental treatments. There were also no overall effects of enzyme vs non-enzyme supplementation on in sacco hominy chop and TMR DM and NDFom ruminal digestibility (P < 0.05). Within experimental diets as well as overall, enzyme supplementation did not affect any of the rumen fermentation parameters measured. Results suggest that enzyme supplementation can play an important role in improving apparent total tract fibre digestion when feeding diets where part of the maize component is replaced with hominy chop, as is many times the case in Southern African feedlots.