An assessment of the microbial colonization of forage in the rumen of dairy cows and camels

An in situ study was conducted to investigate the extent and kinetics of microbial colonization of forage particles exposed to the rumen environment of lactating cows and dry camels, not previously reported. Two Holstein cows and three camels, fitted with ruminal cannulas were used at the University of Arizona and United Arab Emirates University, respectively. Besides dairy concentrate, cows received alfalfa hay and camels Rhodes grass hay. The cows received two diets differing in the concentrate by including either dry-rolled (DDR) or steam-flaked (DSF) sorghum grain making up 35% of the diet DM. The concentrate for the camels included 25% barely grain. Corn plants were labeled with N-15 as an internal N marker. Amounts of N-15 in excess of 0.366 atom% were considered as enrichment. Dilution of enrichment estimated percentage of microbial nitrogen (MN). Labeled whole corn cobs (WCC) were placed in nylon bags and incubated in the rumen of cows for up to 48 h and in camels for up to 72 h. Labeled corn stalks (CS) were also incubated in camels. Contamination was expressed as the percentage of microbial-N (MN) in the residual N, while colonization was microbial crude protein (MCP) percentile in the residual DM of the WCC or CS exposed to ruminal fermentation. During the initial 2 h of rumen incubation in cows, MN was 39% of the residual N in WCC (contamination) and 73% at 48 h of incubation. Also at 48 h, MCP was 6.0% and 7.5% of DM is WCC residues (colonization) in cows fed DDR and DSF respectively. In camels, during the first 2 h of rumen exposure, MN was 7% of residual N (contamination) and 57% at 72 h, while MCP was 5.5% of DM in WCC and 9.8% of DM in CS residues (colonization). In both cows and camels, microbial colonization and microbial contamination increased with incubation time. Microbial contamination greatly affected estimates of in situ ruminal protein degradation of these forges of low N content in both cows and camels. Undegraded feed protein would have been estimated close to or greater than 100% if not corrected for MN contamination, while more consistent values are shown when corrected. (C) 1999 Published by Elsevier Science B.V.