196. Backgrounding Cattle Fed Diets Containing Direct-cut or Wilted Grass Silage: Effects on Intake, Feed Sorting, and Performance in a Commercial Feedlot.

Abstract Grass silage is an important fiber source for growing cattle, but grasses are often harvested at low dry matter (20–25%), impairing fermentation and intake. Wilting before ensiling may alleviate this limitation. Thus, this study evaluated diets with direct-cut (DC) or wilted (WS) grass silage for backgrounding cattle. The trial was carried out at a commercial feedlot. A 160-ha field of Miyagi grass (Panicum maximum) was established under center-pivot irrigation. After three months, half the area was harvested as DC silage and half as WS. The DC and WS silages were stored for 53 d in separate side-by-side pile silos until the feeding trial was initiated. A total of 1,995 Nellore young bulls (IBW = 283 ± 31 kg) were randomly assigned to one of two treatments (100 bulls per pen; 10 replicates per treatment). Treatments consisted of diets with either DC or WS. The diets (DM basis) consisted of grass silage (DC or WS; 43.4%), DDGS (34.6%), ground corn (19.0%), urea (0.8%), and supplement (2.2%). Diets were delivered at 0800 and 1500 h as a TMR for 67 d. Dry matter intake fluctuation was defined as the difference in intake between consecutive days. Diets and orts were sampled daily to evaluate feed sorting using the Penn State Particle Separator. Silage samples were collected weekly for analysis. Data were analyzed as a completely block design using the SAS MIXED procedure, with pen as the experimental unit and treatment as a fixed effect; pen nested within treatment was included as a random effect (α = 0.05). Dry matter concentrations of silages were 22 ± 2% and 60 ± 7% for DC and WS, respectively. Direct-cut silage and DC diets contained 1,938 ± 388 and 961 ± 147 mg/kg DM of putrescine and 1,427 ± 272 and 677 ± 161 mg/kg DM of cadaverine, respectively, whereas WS silage and WS diets contained 157 ± 47 and 315 ± 108 mg/kg DM of putrescine and 38 ± 18 and 81 ± 16 mg/kg DM of cadaverine. Dry matter intake was not affected by treatment (P ≥ 0.05). The DC diet resulted in greater intake fluctuation and a higher amount of orts (P < 0.01). Regarding feed sorting, bulls fed the WS diet sorted against long particles (>19 mm; P < 0.01), whereas those fed the DC diet showed no sorting behavior. Final BW and ADG did not differ between treatments, but cattle fed the DC diet had a greater gain:feed ratio (P < 0.01). Overall, as expected, WS was better preserved, as indicated by the lower concentrations of biogenic amines. Nevertheless, this improved fermentation profile did not translate into differences in intake or performance.