The influence of urea supplementation or treatment of rice straw and fish meal supplementation on rumen environment and activity in sheep

Abstract

The rate and extent of degradation of dry matter (DM) of untreated rice straw (URS) was studied in four rumen environments created by feeding urea-supplemented rice straw (USRS) or urea-treated rice straw (UTRS) as basal diets with or without fish meal (FM) supplement. In addition the animals were given rice bran (RB) to form a straw to RB ratio of 70:30 and adequately supplemented with a mineral and vitamin premix. Four rumencannulated adult sheep in a 4 × 4 Latin square were used. Rumen pH, NH 3-N and volatile fatty acids (VFA) were measured in the same experiment. An incomplete but balanced 4 × 4 Latin square was used to measure the rate and extent of degradation of USRS and UTRS in the rumen of sheep where the same feeds were fed as basal diets. The results showed that the extent and rate of degradation of URS were more or less similar when incubated in the rumen of sheep fed the four treatment diets. Similarly, there was little difference in degradation between USRS and UTRS incubated in the rumen of sheep given these feeds as basal diets with or without FM supplementation. The UTRS was degraded to a higher degree than URS and USRS and this was reflected in a significantly ( P < 0.001) lower concentration of rumen NH 3-N in the two UTRS diets compared with USRS diets. The rumen pH and VFA concentrations did not show any differences between the four rumen environments. Although urea treatment and FM supplementation had been expected to show a stimulatory effect on microbial density and colonisation of cellulolytic bacteria it was not possible to detect any difference in the URS degradation between the four treatment diets. The reason may be that USRS together with 30% RB created an optimal rumen environment for rice straw degradation which was not improved by FM supplementation or by feeding the more degradable UTRS.