Influence of β 1-4 galacto-oligosaccharides supplementation on nitrogen utilization, rumen fermentation, and microbial nitrogen supply in dairy cows fed silage

Abstract

In a balanced incomplete block design, two dry Holstein cows were used to investigate the effect of β 1-4 galactooligosaccharides (GOS) supplementation on nitrogen (N) utilization, rumen fermentation and microbial N supply in the rumen. During the experiment, cows were fed four diets: orchardgrass (Dactylis glomerata L.) silage (OS), OS with GOS supplementation (OSG), OS mixed with alfalfa (Medicago sativa L.) silage (MS) and MS with GOS supplementation (MSG). GOS was supplemented at 2% of dry matter intake. Diets were fed at maintenance level of protein and energy. Results showed that N digestion was affected by silage and interaction of silage and GOS supplementation. Cows fed OSG had the highest N digested (p<0.05) followed by MS, OS and MSG Supplementation of GOS to OS or MS diets tended to improve N utilization through reducing the N losses on dairy cows. There was no effect of GOS supplementation on rumen fermentation parameters (i.e. pH, NH3-N and total VFA) at 1 h and 6 h after feeding. Compared to cows fed MS, cows fed OS silage had higher (p<0.05) allantoin excretion (80.8 vs. 67.1 mmol/d) and higher (p<0.05) total purine derivatives excretion (92.9 vs. 78.5 mmol/d). The microbial N supply in cows fed OSG was higher (p<0.05) than those fed OS, MS and MSG.