The gastrointestinal microbiota of cattle is important for feedstuff degradation and feed efficiency determination. This study evaluated the fecal microbiome of Angus steers with distinct feed efficiencies during the feedlot-finishing phase. Angus steers (n = 65), fed a feedlot-finishing diet for 82 days, had growth performance metrics evaluated. Steers were ranked based upon residual feed intake (RFI), and the 5 lowest RFI (most efficient) and 5 highest RFI (least efficient) steers were selected for evaluation. Fecal samples were collected on 0-d and 82-d of the finishing period and microbial DNA was extracted and evaluated by 16S rRNA gene sequencing. During the feedlot trial, inefficient steers had decreased (p = 0.02) Ruminococcaceae populations and increased (p = 0.01) Clostridiaceae populations. Conversely, efficient steers had increased Peptostreptococcaceae (p = 0.03) and Turicibacteraceae (p = 0.01), and a trend for decreased Proteobacteria abundance (p = 0.096). Efficient steers had increased microbial richness and diversity during the feedlot period, which likely resulted in increased fiber-degrading enzymes in their hindgut, allowing them to extract more energy from the feed. Results suggest that cattle with better feed efficiency have greater diversity of hindgut microorganisms, resulting in more enzymes available for digestion, and improving energy harvest in the gut of efficient cattle.

Mud increases net energy requirements for cattle because mud and precipitation compromise the ability of the hair coat to insulate and maintain core body temperature of the cow. The increase in energy required for a gestating cow to compensate for a muddy environment is unknown. The objective of this study was to evaluate effects of muddy conditions on cow body weight (BW) and fetal growth during late gestation. Sixteen multiparous Angus cows (n = 8/treatment) were paired based on initial BW and one cow from each pair was randomly allocated to either the mud (MUD) or control (CON) treatment on day 213 of gestation. Pens in the CON group were bedded with wood chips, while pens in the MUD group were designed to create a muddy lot (average depth of 23.6 ± 5.8 cm). Cows were housed outdoors individually and fed the same diet that consisted of a limit-fed total mixed ration. Each pair was fed to meet energy and protein requirements for maintenance and gestation. From day 213 to 269 of gestation, cows were weighed and sampled for blood metabolites weekly. Data were analyzed as a randomized complete block design with repeated measurements (SAS 9.4). Though cows consumed the same amount of dry matter, cows in the MUD treatment weighed 37.4 kg less than cows in the CON treatment (P < 0.01) by day 269 of gestation. Cows in the MUD treatment decreased approximately half a body condition score (BCS), while cows in the CON treatment gained approximately 1 BCS during the treatment period (P < 0.01). There was no evidence of a treatment × day of gestation effect for 12th rib back fat (P = 0.85), rump fat (P = 0.48), total plasma protein concentrations (P = 0.85), or plasma 3-methylhistidine (P = 0.84); however, there was a marginally significant treatment × day of gestation effect for plasma non-esterified fatty acid concentration (P = 0.09). Despite differences in cow BW at the end of the treatment period, calf birth weight (P = 0.66) and calf total plasma protein (P = 0.27) were not different; however, the divergence in cow BW remained marginally significant at parturition (P = 0.06). These results indicate that mud increased net energy requirements for cows in the MUD treatment, as calf birth weight was not different but maternal BW was decreased compared with cows in the CON treatment. Winter and spring precipitation are expected to increase 20% to 30% by the end of the century in the Midwest, United States. As a result of this environmental change, beef cattle in this region of the United States are increasingly becoming exposed to muddy conditions in pastures and lots. These muddy conditions cause a cow to increase her metabolic heat production to maintain her internal body temperature, thus increasing her net energy requirements. The increase in net energy required during late gestation for a beef cow is unknown; therefore, we completed a study to estimate the increase in net energy requirements. Based on the present results, cows housed in muddy conditions that were consuming the same amount of dry matter as cows housed in wood chips lost body weight and needed an additional 3.9 Mcal/d in order to maintain their body weight. While cows housed in muddy conditions lost body weight and body condition, we do not believe fetal growth was affected as calf birth weight was similar between the cows housed in pens with the muddy conditions and the cows housed in pens with wood chips.

The catabolic activity of the ruminal microbial community of cattle enables the conversion of low-quality feedstuffs into meat and milk. The rate at which this conversion occurs is termed feed efficiency, which is of crucial importance given that feed expenses account for up to 70% of the cost of animal production. The present study assessed the relationship between cattle feed efficiency and the composition of their ruminal microbial communities during the feedlot finishing period. Angus steers (n = 65) were fed a feedlot finishing diet for 82 days and their growth performance metrics were evaluated. These included the dry matter intake (DMI), average daily gain (ADG), and residual feed intake (RFI). Steers were rank-ordered based upon their RFI, and the five lowest RFI (most efficient) and five highest RFI (least efficient) steers were selected for evaluations. Ruminal fluid samples were collected on days 0 and 82 of the finishing period. Volatile fatty acids (VFA) were quantified, and microbial DNA was extracted and the 16S rRNA gene was sequenced. The results showed that the ADG was not different (p = 0.82) between efficiency groups during the 82-day feedlot period; however, the efficient steers had lower (p = 0.03) DMI and RFI (p = 0.003). Less-efficient (high RFI) steers developed higher (p = 0.01) ruminal Methanobrevibacter relative abundances (p = 0.01) and tended (p = 0.09) to have more Methanosphaera. In high-efficiency steers (low RFI), the relative abundances of Ruminococcaceae increased (p = 0.04) over the 82-day period. The molar proportions of VFA were not different between the two efficiency groups, but some changes in the concentration of specific VFA were observed over time. The results indicated that the ruminal microbial populations of the less-efficient steers contained a greater relative abundance of methanogens compared to the high-efficiency steers during the feedlot phase, likely resulting in more energetic waste in the form or methane and less dietary energy being harvested by the less-efficient animals.

Winter and spring precipitation are expected to increase 20-30% by the end of the century in the Midwest, U.S. As a result, cows in this region are exposed to muddy conditions in pastures during late gestation. Two experiments were completed with multiparous cows and primiparous heifers to determine the energetic cost of mud during late gestation. In the first experiment, multiparous Angus cows (n = 8/treatment) were paired based on initial body weight (BW). One cow from each pair was randomly assigned to either the mud (MUD) or control (CON) treatment. Cows were housed and fed individually from d 213 to 269 of gestation. Each pair was fed to meet requirements for maintenance and gestation. In the second experiment, primiparous Angus heifers (n = 9/treatment) were paired based on initial BW. One heifer from each pair was randomly assigned to either the MUD or CON treatment. Heifers were housed and fed individually from d 196 to 266 of gestation. Each pair was fed to meet requirements for maintenance, growth, and gestation. Data in both experiments were analyzed as randomized complete block designs with repeated measurements (SAS 9.4). Although cows consumed the same amount of dry matter, cows in the MUD treatment weighed 37.4 kg less than the CON treatment (P < 0.01) and were 1.5 body condition score (BCS) units less (P < 0.01) by d 269 of gestation. Similarly, heifers in the MUD treatment weighed 43.5 kg less than the CON treatment (P < 0.01) and were 1.8 BCS units less (P < 0.01) by d 266 of gestation. In both experiments, however, calf birth weight was similar (P = 0.34). Although cows and heifers housed in mud were in a negative energy balance, they prioritized fetal growth and mobilized body tissues to meet the energetic demands of gestation.

Growing Angus steers (n = 20) were blocked by weight and randomly assigned to one of two treatment groups: Control group (CON, n = 10) fed a feedlot ration ad libitum, or a ruminally protected hydrogenated fat-embedded calcium gluconate (HFCG) treatment group (HFCG, n = 10), which was fed the control ration top-dressed at 16 g/head/day for 55 days. During the slaughter process, digesta samples were collected from the cecum, colon, and rectum. Acetate concentrations were greater in the cecal and rectal digesta of steers (p ≤ 0.05) in the HFCG treatment group. Propionate concentrations were greater in the cecal, colonic, and rectal (p ≤ 0.05) digesta of steers in the HFCG treatment group. Butyrate concentrations were greater (p = 0.098) in the colon digesta of steers in the HFCG treatment group; however, they were not different in the cecal and rectal digesta. To determine the microbial composition within each section of the hindgut, DNA was extracted, and 16S rRNA gene sequencing was performed. Data were analyzed using a General Linear Model with dietary treatment as the main effect. Species richness in the cecum, colon, and rectum was not different between treatments. Erysipelotrichaceae, Peptostreptococcaceae, and Atopobiaceae abundances were increased (p ≤ 0.05) in the cecal bacterial community of steers in the HFCG group, while a significant decrease (p ≤ 0.05) in Rikenellaceae and Muribaculaceae abundances was recorded within the same bacterial community. In the colon bacterial community of steers in the HFCG group, Ruminococcaceae and Muribaculaceae abundances were elevated (p ≤ 0.05), while there was a reduction (p ≤ 0.05) in Lachnospiraceae, Erysipelotrichaceae, Atopobiaceae, and Peptostreptococcaceae abundances. Paeniclostridium, Romboutsia, and Turicibacter abundances were increased (p ≤ 0.05) in the cecal bacterial community of steers in the HFCG group, while there was a decrease (p ≤ 0.05) in Rikenellaceae_RC9 _gut_group abundance within the same bacterial community. In the colon microbiota of steers in the HFCG group, Turicibacter abundance was decreased (p ≤ 0.05). Supplementing growing steers with HFCG impacted some members of the bacterial populations, which have important roles in gut homeostasis and health, along with the formation of beneficial end-products in the gastrointestinal tract.