Effects of the Use of Rice Grain on Growth Performances, Blood Metabolites, Rumen Fermentation, and Rumen Microbial Community in Fattening Hanwoo Steers

SIMPLE SUMMARY: As the price of imported corn rises due to environmental issues and the growing demand for bio-ethanol production, animal nutritionists are actively seeking alternative energy sources to corn. While previous research has shown that rice grain provides a comparable nutritional value to corn, it is noted that most of the studies on rice grain as a starch source for ruminants have been conducted on dairy cattle. The objective of this study is to assess the effects of total mixed ration (TMR) containing rice grains on the growth performance, blood metabolites, rumen fermentation, and rumen microbial community in fattening Hanwoo steers. Our results demonstrated that rice grain had no adverse effects on the growth performance of Hanwoo steers, rumen fermentation characteristics, and blood metabolites. In conclusion, this study suggests that utilizing rice grains as the primary starch source in TMR may serve as an alternative option for fattening Hanwoo steers. ABSTRACT: This study aimed to assess the influence of rice grain in the total mixed ration (TMR) on the growth performance, blood metabolites, rumen fermentation, and rumen microbial community of fattening Hanwoo steers. Two experimental diets were prepared: (i) a TMR containing 33% dry matter (DM) corn grains (Corn TMR) and (ii) a TMR containing 33% DM rice grains (Rice TMR). Twenty-two Hanwoo steers (body weight [BW], 498 ± 32 kg; months, 17 ± 0.5) were distributed into two treatment groups in a completely randomized block design according to BW. The Rice TMR group had a higher final BW and DM intake (DMI) compared to those in the Corn TMR group (p < 0.01). However, no difference was observed in the average daily gain (ADG) and feed conversion ratio (FCR) between the two treatments. For the rumen fermentation parameters, the molar portion of butyrate in the Rice TMR was higher than in the Corn TMR (p < 0.01). Streptococcus bovis tended to be higher in the Rice TMR (p = 0.09). The results of this study suggest that using rice grain as the primary starch source in TMRs may be an alternative option for fattening Hanwoo steers.