Effects of growing system and silage type on feedlot growth performance, carcass characteristics, and nutrient digestibility of beef steers

The effects of beef cattle growing systems (grazing vs. bunk) and silage type (corn vs. sorghum) on finishing phase growth performance, carcass characteristics, and nutrient digestibilities were evaluated. Steers (n = 128; BW = 394 ± 21 kg) were backgrounded by either grazing (forage sorghum AF7401, 104 d) or bunk fed (65% concentrate diet, 85 d). Following the backgrouding period, animals were blocked by BW, and randomly allocated to one of the two dietary treatments, corn (BH8895) or sorghum (AF7401) silage at 20%, DM basis, in a randomized complete block design. During the finishing phase, steers were fed once daily at approximately 0800 h. A 5-d spot fecal collection (twice daily) and acid insoluble ash were used to estimate total tract apparent digestibility. Slaughter was performed on 132, 146, or 174 d on feed. Data were analyzed using the Glimmix procedure of SAS, using pen as the experimental unit. No interaction (growing system x silage type) was observed (P > 0.16), except for a tendency (P = 0.06) of bunk backgrounded steers to consume more sorghum than corn silage diet, compared with grazing backgrounded steers. Steers that grazed forage sorghum had greater ADG (25%), DMI (23%), and greater gain:feed (5%) during the finishing phase, compared with bunk backgrounded steers (P < 0.01). A greater HCW (7.8%), lower dressing percent (0.8% unit), and lower fat thickness (18%) were observed for steers grown under sorghum grazing conditions compared to backgrounded bunk fed steers (P < 0.01). Steers fed the corn silage diet had lower DMI (7%), greater ADG (5%), and consequently greater gain:feed (10%) compared with steers fed sorghum silage diet (P < 0.01). A 0.5% unit greater (P = 0.03) dressing percent and 0.1% unit greater (P = 0.04) KPH were observed for steers fed corn silage compared to those fed sorghum silage. Steers fed the corn silage diet also had greater (P < 0.01) DM (11%), CP (9%), EE (1.9%), and starch (8%) digestibilities compared to steers fed sorghum silage diet. Digestibility of fiber components were not affected (P = 0.12) by silage type or growing system. Sorghum grazing backgrounded steers positively affected finishing phase, but such strategies must be further be evaluated considering economical aspects and water use. Replacing corn silage with sorghum silage in beef finishing diets even at low roughage inclusion requires adjustments to balance dietary energy.