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Selection of hybrid bromegrass for increased NDF digestibility
The objective of this study was to determine whether selecting hybrid bromegrass for improved NDF digestibility would improve NDF digestibility and the performance of growing lambs. In 2010, 128-hybrid bromegrass (Bromus riparius Rehm. × Bromus inermis Leyss.; cv. AC Knowles) plants were clipped (5-cm stubble height) and used to determine 24-h in situ NDF digestibility (NDFd). Individual plants with the greatest (HNDFd; n=20) and least (LNDFd; n=20) digestibility values were selected (34.5 and 23.5%, respectively; P < 0.001) and polycrossed in isolation to produce seed. Seedlings were established in a field nursery June 8, 2011 and harvested July 23, 2012 and July 11, 2013 for in situ NDF digestibility determination. The DM yield tended to be greater for the LNDFd population (350 vs. 380 g/plant; P = 0.072) than HNDFd, while the degradable DM (37.2 vs. 33.6%; P = 0.098) and OM (39.8 vs. 35.7%; P = 0.092) fractions tended to be greater for HNDFd than LNDFd. Degradation rates for DM, OM, CP, NDF and ADF were not affected by treatment (P ≥ 0.398). Additional plots of the HNDFd and LNDFd hybrid bromegrass populations were swathed on July 11, 2013, dried, and baled for an in vivo digestibility experiment. Twelve Suffolk × Canadian Arcott wether lambs were randomly assigned to the HNDFd or LNDFd treatments. The bromegrass hay was fed ad libitum and all lambs were supplemented with a pellet fed at 0.88% of initial BW. Total DMI and forage intake were not affected by treatment (P = 0.219). Nutrient intake (OM, CP, NDF, ADF, and ether extract; P ≥ 0.143) was also not different between lambs fed LNDFd or HNDFd. However, NFC intake tended to be greater for HNDFd than LNDFD (0.34 vs. 0.29 kg/d; P = 0.070). Feeding the HNDFd or LNDFd bromegrass for 21 d did not affect final body weight or ADG (P ≥ 0.189), but cumulative weight gain was greater for lambs fed HNDFd (P = 0.013). Total tract digestibility of DM, OM, NDF, ADF and NFC were not affected by treatment (P ≥ 0.328), but CP and ether extract digestibility values tended to be greater for LNDFd than HNDFd (P≤ 0.068). These data suggest that although there were improvements in the degradable fractions of DM and OM and cumulative weight gain of the lambs fed HNDFd, the hybrid bromegrasses did not differ in NDF digestibility.
Keywords: Digestibility, forage intake, hybrid bromegrass