Understanding Beef Cattle Efficiency: I) Understanding Physiological and Digestive Factors Affecting Residual Feed Intake and II) Tannin Supplementation: Effects on Animal Performance, Fermentation, and Carcass Traits



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Objectives of this study were 1) to characterize the relationship between beef cattle efficiency, namely residual feed intake (RFI), and digestive, microbial, and fermentation parameters in growing beef calves and 2) to examine the effects of added dietary hydrolysable or condensed tannin on animal performance and efficiency, fermentation and carcass and non-carcass traits. To accomplish the first objective, multiple RFI studies were conducted and in all studies RFI was calculated as the difference between actual and expected dry matter intake (DMI) based on average gaily gain (ADG) and body weight0.75(BW). A total of 187 head selected out of a population of 600 head of growing beef calves were evaluated for diet and nutrient digestibility, ruminal and fecal volatile fatty acids (VFA) concentrations and methane producing activity (MPA). Low RFI calves consumed less DMI and had lower feed conversion ratios (FCR) as compared to high RFI calves. Low RFI calves also had higher diet and nutrient digestibilities compared to high RFI calves. Residual feed intake was negatively correlated with diet and nutrient digestibilities such that more efficient animals had higher digestibilities. Low RFI calves tended to have lower ruminal propionate and higher acetate:propionate ratios when fed a high-forage diet. Calves with divergent RFI did not have different gross microbial populations as evidenced by the Firmicute:Bacteriodetes ratio, but low RFI calves tended to have higher fecal Prevotella spp. and lower fecal Spirochaetes and ruminal Cyanobacteria. The importance of these subtle shifts in microbial ecology is not evident at this time and more research is needed to fully elucidate the interaction of host and microbes to fully grasp the importance of minor microbial deviations. No differences in 3 h MPA were detected in low vs. high RFI calves but low RFI calves had higher fecal MPA when sampled at 24 h; however, calculated methane emissions were lower for low RFI calves. Tannin supplementation had no effect on animal performance and efficiency, ruminal fermentation VFA concentrations, MPA, or ammonia concentrations in finishing beef steers. There was also no detrimental effect of tannins on carcass traits; however, hydrolysable tannin supplementation resulted in increased empty rumen mass. Results from these studies indicate that diet and nutrient digestibility are affected by RFI such that more efficient calves had higher DMD, microbial ecology is responsive to RFI such that minor microbial shifts were observed, and tannin supplementation, at the current inclusion rate, had no effect on animal and carcass performance.