In situ disappearance of dry matter and fiber from fall-grown cereal-grain forages from the north-central United States1

Abstract

Recent research has demonstrated that fall-grown wheat (Triticum aestivum L.), triticale (X Triticosecale Wittmack), and oat (Avena sativa L.) forages contain limited lignin and exhibit relatively stable estimates of in vitro true DM disappearance, as well as TDN, across a wide fall-harvest window. These traits suggest that ruminal availability of forage fiber is extensive. Our objectives were to evaluate this premise by assessing in situ DM and NDF disappearance for Kaskaskia wheat, Trical 2700 triticale, Ogle oat (grain-type, mid-maturity rating), and ForagePlus oat (forage-type, late maturity rating) grown and harvested during fall in Wisconsin. During 2006, ruminal disappearance rate (K(d)) of DM declined linearly (P ≤ 0.002) across fall harvest dates for all cultivars; K(d) ranged narrowly (0.091 to 0.100/h) on the initial September 15 harvest date, but by October 30, K(d) generally was slower for oat (0.042 to 0.053/h) than for triticale (0.069/h) or wheat (0.072/h). Estimates of effective ruminal disappearance of DM (RDDM) were large for all cultivars (72.0 to 82.8% of DM), and generally exhibited polynomial trends over harvest dates that displayed both linear (P ≤ 0.003) and quadratic (P ≤ 0.004) character. For 2007, RDDM was extensive across all forages (70.5 to 83.1%), except for Ogle oat harvested on October 10 (61.5% of DM) or November 7 (57.0% of DM), at which time tillers had reached the boot- and fully headed stages of growth, respectively. For ruminal disappearance of NDF, K(d) declined linearly (P ≤ 0.002) across harvest dates for all cultivars during 2006 and 2007; a quadratic (P ≤ 0.033) effect also was detected for ForagePlus oat, but not for other cultivars (P ≥ 0.072). During both years, effective ruminal disappearance of NDF (RDNDF) declined linearly (P ≤ 0.008) over harvest dates for all cultivars, but detection of additional quadratic responses was dependent on cultivar and year. Concentrations of RDNDF for all cultivars ranged from 60.5 to 68.8% of NDF on mid-September harvest dates. Generally, these estimates declined to 51.4 to 60.0% of NDF by the final harvest date for all cultivars except Ogle oat, which reached numerical minimums of 46.8 and 37.2% of NDF on the final harvest dates of 2006 and 2007, respectively. Cereal-grain cultivars that elongate during fall will exhibit relatively stable RDDM and RDNDF through stem elongation; however, these estimates may decline substantially after tillers exhibit visible seedheads.