PS5-12. Evaluating the Effects of Dietary Fat Source on Growth Performance, Carcass Characteristics, and Gas Flux in Finishing Steers.

Abstract The objective of this study was to evaluate the influence of supplemental dietary fat source on growth performance, carcass characteristics, and gas flux in finishing steers. Steers (N = 177) arrived at the CSU research feedlot and were stratified by arrival body weight (334 kg ± 13.73) then randomly assigned to one of four treatments: 1) palm oil (PALM; 4% inclusion; DM basis), 2) beef tallow (TAL; 4%), 3) soybean oil (SOY; 4%), or 4) no supplemental fat (CON). The experiment was a completely randomized design and animal was the experimental unit. Following a 17-day covariate period on a common finishing diet, a 7-day step-up phase was initiated (2% fat source inclusion; DM basis) before cattle were transitioned to their respective experimental diets for 115 days. Pens were equipped with 5 SmartFeed intake systems and a GreenFeed emission monitoring system (C-Lock Inc., Rapid City, SD) used to measure individual dry matter intake (DMI) and enteric methane emissions (CH4). Individual body weight was collected every 28 days. Weekly diet samples were collected from each treatment and composited for wet chemistry analysis at Dairy One Laboratory (Ithaca, NY). Weekly samples of each fat source were also collected and sent to Michigan State University (Lock Lab, East Lansing, MI) for fatty acid composition analysis. Upon completion of the trial, cattle were harvested at a commercial abattoir and carcass data were collected. Estimated beginning hot carcass weight, carcass gain, and carcass feed conversion were calculated using initial body weight, hot carcass weight, and predictive equations. Data were analyzed using LSMeans comparisons with Tukey adjustment, with the fixed effects of treatment and appropriate covariates using JMP Student Edition 19 (SAS Institute Inc., Cary, NC). Significance was declared at P < 0.05. Inclusion of SOY resulted in greater average daily gain (ADG; P = 0.03), hot carcass weight (P = 0.02), carcass gain (P = 0.02), and calculated yield grade (P = 0.01) compared to CON. Supplemental PALM and TAL reduced CH4 emissions (P < 0.01) compared to CON and SOY, and reduced CH4 yield (g CH4/kg of DMI; P < 0.01) relative to CON. The addition of SOY and TAL to the diet reduced CH4 intensity (g CH4/kg of ADG; P < 0.01) compared to CON. All fat sources reduced carcass gain intensity (g CH4/kg of carcass gain; P < 0.01) compared to CON. These results indicate that dietary fat source can influence both growth performance and methane emissions in finishing cattle. Supplemental SOY improved ADG, whereas PALM and TAL reduced CH4 emissions relative to CON. Strategic selection of supplemental fat source may provide feedlot producers with a nutritional management approach to influence performance and enteric methane emissions in finishing systems.