Investigations on the influence of roughage/concentrate ratio and linseed oil supplementation on rumen fermentation and microbial protein yield in dairy cows

Abstract

The objective of the study was to investigate the influence of the roughage/concentrate ratio and linseed oil supplementation on rumen fermentation and microbial protein yield in late lactating dairy cows. Seven late lactating double fistulated cows were randomly assigned to four experimental periods applying an incomplete 2 x 2 Latin square design. The rations consisted of meadow hay and a concentrate mixture given in a ratio of 70 : 30 (H 70) or 30 : 70 (H 30) on a dry matter basis. The basal mixtures fed were either supplemented with 200 g linseed oil daily (HLO 70 and HLO 30) or nonsupplemented. After about three weeks of adaptation to the experimental rations, samples from the rumen and the duodenal chyme were taken to study parameters of rumen fermentation and the nutrient flow to the duodenum. The pH-value, the NH3 -N concentration, and the content of short-chain fatty acids in the rumen as well as the apparent ruminal digestibility of organic matter (OM) and neutral detergent fibre (NDF) were not significantly affected by linseed oil supplements. However, low portions of hay in the ration significantly reduced the pH-value and increased the NH3 -N concentration. An increased hay portion in the ration resulted in an increased NDF-degradation in the rumen as compared to the rations high in concentrate. Due to an increased flow of microbial OM after high concentrate feeding, the “apparent ruminal digestibility” of OM was calculated to decrease although the quantity of FOM (fermented organic matter) increased. Feeding the rations poor in hay increased the flow of non ammonia nitrogen (NAN) and utilisable crude protein (uCP) significantly due to the significantly increased microbial protein synthesis (g MP/d) and a improved efficiency of microbial protein synthesis (g MP/kg FOM) as well.