Effects of growth stage and growing degree day accumulations on triticale forages: 2) In-vitro disappearance of neutral detergent fiber

Authors: Coblentz, Wayne; AKINS, MATTHEW - University Of Wisconsin; Kalscheur, Kenneth; Brink, Geoffrey; CAVADINI, JASON - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2018
Publication Date: 9/18/2018
Citation: Coblentz, W.K., Akins, M.S., Kalscheur, K., Brink, G.E., Cavadini, J.S. 2018. Effects of growth stage and growing degree day accumulations on triticale forages: 2) In-vitro disappearance of neutral detergent fiber. Journal of Dairy Science. 101(10):8986-9003. https://doi.org/10.3168/jds.2018-14867.
DOI: https://doi.org/10.3168/jds.2018-14867

Interpretive Summary: The use of winter triticale in dairy-cropping systems has expanded greatly in recent years, partly because of its value as a forage crop, but also to provide winter ground cover and improve environmental stewardship. Our objectives were to describe the relationship between in-vitro NDF disappearance (NDFD) and plant growth stage or growing degree days > 5oC for winter triticale forages. Despite substantial differences in precipitation across years, single-endpoint estimates of NDFD after 24-, 30-, or 48-h of incubation were closely related (R2 > 0.906) to growth stage and GDD by linear or quadratic regression models that were generally similar across production years. Current recommendations for harvesting triticale at boot stage to facilitate the planting of a subsequent double-crop were strongly supported by the extensive fiber digestion at that growth stage, which is desirable for lactating dairy cows. Unfortunately, placing a priority on these two management criteria, will require acceptance of a substantial yield liability relative to harvesting at the soft-dough stage of growth.

Technical Abstract: The use of winter triticale (X Triticosecale Wittmack) in dairy-cropping systems has expanded greatly in recent years, partly because of its value as a forage crop, but also to improve land stewardship by providing winter ground cover. Our objectives were to use 2-pool and 3-pool nonlinear models to characterize in-vitro disappearance of NDF, and then describe the relationship between estimated parameters from those models with plant growth stage or growing degree days (GDD) > 5oC for winter triticale forages harvested during 2016 and 2017 in Marshfield, WI. Forages were harvested from replicated field plots each year at growth stages ranging from stem elongation to soft-dough. All NDF analyses included use of sodium sulfite and heat-stable '-amylase with residual fiber corrected for contaminant ash (asNDFom). Non-linear 3-pool models for in-vitro disappearance of asNDFom that included fast (Bfast) and slow (Bslow) disappearance pools, as well as an associated disappearance rate for each (Kdfast and Kdslow, respectively) were easily fitted, provided a single discrete lag time was applied to both Bfast and Bslow pools to reduce the number of parameters to be estimated. An unresolved issue related to fitting 3-pool decay models was the incomplete recovery of asNDFom from immature triticale forages at 0 h, which was partially resolved with 2 approaches that produced similar estimates of Kdfast and Kdslow. Most parameters obtained from 2- and 3-pool decay models for asNDFom could be related to growth stage or GDD using polynomial regression techniques, often with high coefficients of determination (R2). For 3-pool models of asNDFom disappearance, Bslow pools increased with plant maturity, but the associated Kdslow ranged narrowly from 0.011 to 0.015/h, and could not be related to growth stage or GDD by quartic, cubic, quadratic, or linear regression models. Despite different cultivars coupled with substantial differences in precipitation across years, single endpoint estimates of NDFD after 24-, 30-, or 48-h of incubation were closely related (R2 = 0.906) to growth stage and GDD by linear or quadratic regression models that were generally similar across production years. Typical recommendations for harvesting triticale at boot stage to facilitate the planting of a double-crop are strongly supported by the extensive 30-h in-vitro disappearance of asNDFom at that growth stage, which was 63.1 and 64.8% of asNDFom for 2016 and 2017, respectively.