The effects of feeding increasing concentrations of corn oil on energy metabolism and nutrient balance in finishing beef steers

The use of added fat source is common in high-concentrate finishing diets. The objective of our experiment was to determine if feeding increasing concentrations of added dietary corn oil would decrease enteric methane production, increase the ME:DE ratio, and improve recovered energy (RE) in finishing beef steers. Four treatments were used in a replicated 4 × 4 Latin square (n = 8; initial BW = 397 kg ± 3.8). Data were analyzed using a Mixed model with the fixed effects of period and dietary treatment and random effects of square and steer within square. Treatments consisted of: (1) 0% added corn oil (Fat-0); (2) 2% added corn oil (Fat-2); (3) 4% added corn oil (Fat-4); (4) 6% added corn oil (Fat-6). Dry matter intake or GE intake did not differ across diets (P > 0.39). As a proportion of GE intake, fecal energy loss, DE, and urinary energy loss did not differ by treatment (P > 0.27). Additionally, methane energy respired decreased linearly as corn oil increased in the diet (P < 0.01). No differences were detected in ME loss as a proportion of GE intake (P > 0.98); however, the ME:DE ratio increased linearly as corn oil increased in the diet (P < 0.01). No differences in RE or heat production as a proportion of GE intake were noted (P > 0.59). Dry matter digestibility did not differ across diets (P > 0.36). Digestibility of NDF as a proportion of intake responded quadratically increasing from 0% corn to 4% corn oil and decreasing thereafter (P = 0.02). Furthermore, ether extract digestibility as a proportion of intake increased quadratically, increasing from 0 to 4% corn oil inclusion before reaching a plateau (P < 0.01). No differences were detected in OM digestibility across treatments (P > 0.35). From these data, we interpret that adding dietary fat decreases enteric methane production and increases the ME:DE ratio, in addition to increasing the amount of energy retained as fat and carbohydrate.