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Title: In-situ disappearance of dry matter and fiber from fall-grown cereal-grain forages from North Central US

item Coblentz, Wayne
item Walgenbach, Richard

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2010
Publication Date: 11/22/2010
Citation: Coblentz, W.K., Walgenbach, R.P. 2010. In-situ disappearance of dry matter and fiber from fall-grown cereal-grain forages from North Central US. Journal of Animal Science. 88:3992-4005.

Interpretive Summary: Recent research has shown that cereal-grain forages that joint and exhibit stem elongation following late summer seeding (oat or triticale) will outyield forages that remain vegetative (wheat) by an approximate 2:1 ratio by late-fall. In addition, these forages display some unique nutritional characteristics, including low concentrations of fiber and lignin, as well as higher concentrations of plant sugars. In a previous study, we demonstrated that these forages also display relatively stable estimates of energy across a wide fall-harvest window that coincided with stem elongation for both oat and triticale tillers, and emergence of seedheads for oat tillers. In this study we assessed the digestibility of fiber from these fall-grown cereal-grain forages. Based on our results, elongating varieties will retain relatively stable concentrations of fiber and dry matter digestibility throughout stem elongation, but these nutritional characteristics may decline with further tiller development. However, the natural accumulation of sugars as a mechanism against freeze damage (winter hardening) may offer some potential to offset associated depressions in fiber digestibility, thereby partially maintaining estimates of available energy from these forages. The overall nutritive value and fiber digestibility of fall-grown cereal grains likely will be superior to identical varieties harvested during late-spring or summer, and livestock producers can use this characteristic to their considerable advantage under specific production scenarios.

Technical 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 disappearance of DM, 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 (Kd) of DM declined linearly (P = 0.002) across fall harvest dates for all cultivars; Kd ranged narrowly (0.091 to 0.100/h) on the initial 15 September harvest date, but by 30 October, Kd was numerically 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 high 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 10 October (61.5% of DM) or 7 November (57.0% of DM), at which time tillers had reached the boot- and fully-headed stages of growth, respectively. For ruminal disappearance of NDF, Kd 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. 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.