PS2-20. Effects of Supplementation with Distillers Grains or Total Mixed Ration on Performance and Carcass Quality of Grass-finished Beef.

Abstract The objective of the study was to determine the impact of distillers grains and a feedlot total mixed ration on animal performance and carcass measurements of steers and heifers finished on pasture. Fall-born Red Angus and Red Angus x Akaushi (n = 60) were allocated by sex, weight, and breed composition to four treatments with three replicates each; biodiverse pasture (GRASS; n = 15), biodiverse pasture + distillers grains (GRASS + DDG; n = 15), biodiverse pasture + TMR (GRASS + TMR; n = 15), and feedlot (TMR; n = 15). The GRASS, GRASS + DDG, and GRASS +TMR cattle were managed under rotational grazing moved 3 to 5 times per week based on forage availability. TMR cattle were housed indoors in concrete pens and fed an 80% grain diet once daily with ad libitum access to fresh water and free-choice mineral. TMR, DDG, and forage samples were collected throughout the trial and composited monthly for proximate analysis, and pasture botanical composition was monitored during the grazing season. Cattle were transported 24 h prior to slaughter and harvested at a commercial abattoir. Carcass measurements, including hot carcass weight (HCW), dressing percentage, ribeye area, 12th-rib backfat, USDA calculated yield grade, and marbling score were collected 72 h postmortem. Performance metrics included total and average daily gain (ADG) over 129 d on trial. Data were analyzed using one-way ANOVA in R (RStudio) with significance declared at p ≤ 0.05. Initial body weight did not differ among treatments (p = 0.136). Cattle assigned to the TMR treatment had greater final body weight (708.9 kg) and average daily gain (1.69 kg/d) than GRASS (581.9 kg; 0.95 kg/d), GRASS + DDG (634.2 kg; 1.33 kg/d), and GRASS + TMR (645.5 kg; 1.29 kg/d) treatments (p < 0.001). Hot carcass weight followed a similar pattern, with TMR cattle having greater HCW than grazing treatments (p < 0.001). Marbling score was greater for TMR cattle compared with GRASS and GRASS + DDG treatments (p = 0.001). GRASS cattle had lower USDA yield grade than TMR cattle (p = 0.008). For most performance and carcass parameters, GRASS + DDG and GRASS + TMR treatments did not differ. Results indicate that TMR-fed cattle had greater growth performance and carcass weight compared with grass-finished cattle. Supplementing grazing cattle with distillers grains or a total mixed ration improved average daily gain relative to a grass-only system but resulted in limited differences in carcass characteristics among grazing treatments. These results represent Year 1 of an ongoing two-year study. For image description, please refer to the figure legend and surrounding text.