The use of bmr-6 sorghum as forage source in beef cattle growing and feedlot systems on growth performance and nutrient utilization

The effects of silage type (corn vs. sorghum) in beef cattle finishing diets and backgrounding system on growth performance, carcass characteristics, nutrient digestibility, ruminal kinetics, and feeding behavior were evaluated. In study 1, steers (n = 128; BW = 394 ± 21 kg) were fed corn (BH8895) or sorghum (AF7401) silage (20 %, DM basis), backgrounded by either grazing (forage sorghum) or bunk fed (65 % concentrate diet) in a completely randomized block design. In study 2, a 4 × 6 unbalanced Latin square design with six steers (BW = 363 ± 23 kg) and four diets (corn or sorghum silage, either at 10 or 20% inclusion, DM basis) was used. In study 3, intact sorghum grain was manually separated from sorghum silage (AF7401) from 10 experimental silos (18.9-L units from 2 sites). Intact grains were ruminally incubated (3 steers; BW = 544 ± 36 kg) using in situ technique, following a complete randomized design. Regardless of backgrounding system, steers fed corn silage diet had lower (P < 0.01) intake (7%), greater (P < 0.01) efficiency (10%), greater (P < 0.01) DM and fiber digestibility (10%), and lower (P < 0.01) acetate:propionate ratio compared with steers fed diets containing sorghum silage. Moreover, steers fed diets with 20% corn silage had 15% greater (P < 0.01) total VFA molar proportion compared with the average of other treatments. Independent of silage type, steers that grazed forage sorghum before feedlot entry had greater (P < 0.01) gain (25%), intake (23%), and efficiency (5%) during finishing phase, compared with bunk backgrounded steers; backgrounding system did not affect (P ≥ 0.25) digestibility of nutrients. Chewing activity increased (P = 0.02) for steers fed 20% silage inclusion, compared to those fed 10% silage; and tended (P = 0.07) to be greater for steers fed sorghum silage than those fed corn silage. Corn silage DM and fiber were more extensively degraded in the rumen (P < 0.01) compared with sorghum silage. After 96 h inside the rumen, ensiled grain degradability of DM reached only 51.7%, showing that material presents potential for improvement on starch availability. Replacing corn silage with sorghum silage in beef finishing diets (low roughage inclusion) requires adjustments to balance dietary energy. Sorghum material induced desirable roughage effect in feeding behavior, but also offered potential to be improved regarding fiber digestibility and intact grain ruminal degradability. Sorghum grazing backgrounded steers positively affected finishing phase, but such strategies must be further evaluated considering economical aspects and water use.