174 The effect of forage quality and protein supplementation source on digestibility of Kentucky 31 Tall Fescue

An in vitro experiment was performed to evaluate the effect of forage quality and supplementation (CON-control, no supplement, DDG-dried distillers grains, 29.32% CP; LFD-liquid feed, 56.45% CP) on IVDMD, NDF disappearance (NDFD) and ruminal fermentation parameters of Kentuck 31 Tall fescue (Festuca arundinacea). Forage was harvested at 2 wk, 4 wk, boot, soft dough, and hard dough stages over three years to simulate various forage management practices. Samples were analyzed by Near-infrared spectroscopy and stratified by relative forage quality (RFQ). Samples were selected to represent high (120), medium (100), and low (80) RFQ. The LFD was added at 5.4% of DMI, equivalent to 0.91 kg (as fed) per head per day. The DDG was included at equivalent of 16.99%, 14.36%, and 12.23% of total DM for the high, medium, and low low RFQ forages, respectively, to make the treatments isonitrogenous to the LFD treatments. Fermentations were carried out for 48 h on 3 d. The experiment was analyzed as a 3 x 3 factorial arrangement with RFQ and type of supplement as factors. Both IVDMD (55.0, 60.3, and 65.4%) and NDFD (41.7, 53.8, and 56.1%) increased (P < 0.001) as RFQ increased. Supplementation with LFD or DDG improved (P < 0.001) NDFD compared to CON. However, IVDMD was only improved (P < 0.001) by the LDF treatment. Interaction RFQ x supplement was not observed for IVDMD and NDFD. The highest values of IVDMD were observed for LFD supplementation, regardless of forage quality; whereas the effect of supplementation with LFD or DDG on NDFD was observed only for low RFQ forage. There was no effect of supplementation on total gas production, pH, or total VFA concentrations. These results indicate that supplementation with LFD improved DMD, and both LDF or DDG can enhance NDFD in low RFQ forage.