The relationships of dairy ruminal odd- and branched- chain fatty acids to the duodenal bacterial nitrogen flow and volatile fatty acids

Abstract

The objectives of the present research were to investigate the changes in duodenal bacterial nitrogen flow and volatile fatty acids (VFAs) with the different dietary ratios of forage and concentrate (F:C) and to determine the relationship of duodenal bacterial nitrogen flow and volatile fatty acids with ruminal odd- and branched-chain fatty acids (OBCFAs). The experimental design was a 3 × 3 Latin square. Three rumen- and duodenal-fistulated dry Holstein cows were fed three rations with different dietary ratios of forage and concentrate (F:C; 30:70, 50:50 and 70:30). The rumen and duodenal samples were collected every two hours over 3 consecutive days of each sampling period. The determined parameters included OBCFA profiles in the rumen, duodenal bacterial nitrogen flow, VFAs, ammonia nitrogen (NH3-N) content and pH. The results showed that ruminal OBCFA contents, duodenal bacterial nitrogen flow, VFAs, ammonia nitrogen (NH3-N) and pH were significantly influenced by the different dietary F:C ratios and sampling times (P < 0.01). The ruminal contents of C15:0 and C15:0 + C17:0 were positively related to the molar proportions of duodenal acetate but negatively correlated with the propionate, butyrate and NH3-N contents (P < 0.05). The ruminal C15:0/C17:0 ratio was positively correlated with the proportions of acetate and pH (P < 0.05) but negatively correlated with VFA contents in the duodenum (P < 0.05). The duodenal bacterial nitrogen flow was positively correlated with ruminal C11:0 and isoC17:0 contents (P < 0.05) but negatively correlated with C15:0/C17:0 and isoC15:0/isoC17:0 (P < 0.05). These findings suggested that some ruminal OBCFAs are closely related to the microbial nitrogen and volatile fatty acids in duodenal flow and significantly changed with the proportion of forage in diets. Ruminal OBCFA have the potential to predict microbial nitrogen flow, and the predicted equations for duodenal microbial nitrogen flow were established with OBCFAs in the rumen.