Partial Substitution of Corn Grain in the Diet with Beet Pulp Reveals Increased Ruminal Acetate Proportion and Circulating Insulin Levels in Korean Cattle Steers

SIMPLE SUMMARY: Intramuscular fat content is one of the important beef quality traits due to its contribution to beef palatability, including flavor, tenderness, and juiciness. Intramuscular fat content is determined by fat synthesis using substrates such as acetate and glucose in ruminants. Beet pulp is a byproduct of sugar beet processing and contains abundant neutral detergent fiber and pectin, with these two components readily fermentable in the rumen. Beet pulp may be a useful energy source in cattle to produce acetate during ruminal fermentation, thereby aiding in lipogenesis (fatty acid synthesis). In this study, partial substitution of corn grain in the diet with beet pulp increased ruminal acetate proportion and circulating insulin levels in beef cattle. Beet pulp could be used as a lipogenic energy source without affecting growth performance in cattle. ABSTRACT: We investigated the effects of the partial substitution of corn grain in the diet with beet pulp on growth performance, ruminal fermentation characteristics, microbial profiles, and blood lipogenic parameters in fattening steers. Twelve Korean cattle steers (body weight, 485 ± 19.32 kg; age, 18.0 ± 0.17 months) were equally divided into corn grain (CG) and beet pulp (BP) groups. Approximately 75% of dry matter of the requirement was offered as a concentrate portion, and the remaining 25% was offered as oat straw. Eighty percent of the concentrate portion was provided by a pelleted basal concentrate, and the remaining 20% with corn grain for the CG group, or 18% beet pulp plus 2.0% rumen-protected fat for the BP group, respectively, by top dressing. The experiment was conducted for 14 weeks, including a 2-week acclimation period. Growth rate was not affected by beet pulp feeding (p = 0.55). The molar proportions of ruminal acetate (p < 0.05) on wk 4, the relative abundances of ruminal cellulolytic bacteria, including Fibrobacter succinogenes (p = 0.01) and Ruminococcus albus (p = 0.04) on wk 12, and serum insulin concentrations (p < 0.05) on wk 12 were higher in the BP group than in the CG group, whereas the molar proportions of propionate (p < 0.05) on wks 8 and 12 and serum nonesterified fatty acids (p < 0.05) on wk 12 were lower in the BP group. Beet pulp could be used as a lipogenic energy source without affecting growth performance during the fattening period of cattle.