Effects of substituting dietary corn with beet pulp on growth performance and microbial profiles in the rumen of Korean cattle steers

Abstract This experiment evaluated the effects of substituting corn with beet pulp (BP) on growth performance and ruminal fermentation characteristics and microbiomes in fattening steers. Twelve Korean cattle steers (body weight, 485 ± 19 kg; age, 18.0 ± 0.17 months) were divided into corn and BP groups. Both groups were fed the basal concentrate to meet 80% of the nutrient requirements. For the corn group, corn (dry matter) was supplemented for the remaining 20% of requirement by top dressing; the BP group was supplemented with 14.88% BP plus 1.92% fat to provide the iso-energy content as the corn group. Steers were fed oat grass (2 kg as-fed basis) daily. Body weight was measured, and rumen fluid was collected after 3 h of feeding using oral stomach tube methods: at the start of the experiment then at 4-week intervals. Feed intake, average daily gain, and gain-to-feed ratio were not (P > 0.05) affected by BP substitution; nor were acetate, propionate, butyrate, or total volatile fatty acid concentrations in the rumen fluid (P > 0.05). BP substitution increased (P < 0.05) the acetate to propionate ratio at 4, 8, and 12 weeks. Genomic DNA was extracted from pellets of rumen contents, and microbial populations were measured using real-time PCR at 8 and 12 weeks. BP substitution increased relative abundances of cellulolytic bacteria including Fibrobacter succinogenes (P = 0.01) and Ruminococcus albus (P = 0.04) at 12 weeks, whereas it did not affect amylolytic bacteria, including Succinimonas amylolytica, Ruminobacter amylophilus, and Streptococcus bovis. At 8 weeks, none of the microbial populations were altered by BP substitution. In conclusion, BP could provide a good energy source substitute for corn without affecting growth performance in the fattening period of beef cattle. Increased relative abundances of several cellulolytic bacteria supported the increased ruminal acetate to propionate ratio.