Ensiling Characteristics of Sunn Hemp and Tall Fescue Affect Nutritive Value and Animal Performance.

In fescue-based forage-livestock systems, tall fescue (TF; Lolium arundinaceum (Schreb.) S.J. Darbyshire) is commonly harvested for stored forage at later stages of maturity, when its nutritive value is less than optimum. A high yielding and high nutritive value warm-season legume, like sunn hemp (SH; Crotalaria juncea L.) may be used as a suitable alternative stored forage. Our objectives were to compare ensiling characteristics and nutritive values of SH and TF, as well as animal performance when fed over winter. SH and TF baleage were analyzed for ph, ammonia, and total VFA, as well as nutritive value (CP, NDF, ADF, IVTD) in each bale during feedout. Stored forage was allocated to weaned steers at 3.5% of body weight to ensure no limit-feeding occurred. Forage refusals were weighed and removed daily. Cattle were weighed every 20 days for an 80-d period to determine ADG. Total VFA and ammonia concentrations for SH were 51.5, and 27.1 g/kg DM, respectively; those of TF were 19.8, and 11.3 g/kg DM. We observed a species x period interaction for CP and IVTD. Crude protein was greater in SH than TF through all periods except for period 1(P=.0431). IVTD was greater in TF than SH through all periods except for period 2 (P<.0001). A species x period interaction (P=0.0114) was observed such that ADG was greatest for TF during period 2 (0.83 kg/d) and least for SH in period 3 and 4 (0.12 and -0.03 kg/d, respectively). Our results suggest ensiling of SH resulted in lower amounts of fermentable substrates, indicated by greater VFA’s and lower digestibility. Greater concentrations of ammonia may have increased metabolic load, and increased degradation of feed source protein. Significantly lower ADG in SH indicate greater ammonia and VFA’s concentrations negatively influenced rumen function and net energy required for gain.