|OTTMAN, MICHAEL - University Of Arizona|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2021
Publication Date: 3/4/2022
Citation: Coblentz, W.K., Ottman, M.J. 2022. Effects of harvest date and growth stage on triticale forages in the southwest USA: Kinetics of in-vitro disappearance of fiber and dry matter. Journal of Animal Science. 100(3):1-18. https://doi.org/10.1093/jas/skac020.
Interpretive Summary: Recently, there has been increased interest in including triticale (X Triticosecale Wittmack) within forage programs throughout the southwest USA. Unless there is an urgency for removing the triticale crop, such as those created by a feed shortage or need to establish a secondary crop, harvest management decisions should be based on plant growth stage, and not calendar date. Assuming a common growth stage, this work suggests that most triticale cultivars will differ only modestly with respect to digestibility before the onset of grain fill. However, producers should carefully consider cultivars with unique or atypical phenotypic traits, such as exceptional canopy height, which may cause an exception to the previous generalization. If yield is a critical management objective, harvest should most likely be delayed until after the onset of grain fill, but cultivar selection becomes more complicated at that time because varying contributions from the filling grain head can radically affect overall digestibility of DM. In this respect, producers should carefully evaluate their nutritional and production goals to assess whether their needs prioritize digestible fiber or overall DM digestibility, the latter of which may have limited contributions from digestible fiber.
Technical Abstract: Recently, there has been increased interest in including triticale (X Triticosecale Wittmack) within forage programs throughout the southwest USA. Our objectives for this study were to evaluate in-vitro disappearance kinetics of NDF and DM for cultivars identified during 2019 as positively or negatively deviant from typical cultivars, based on regressions of 48-h in-vitro disappearance of NDF on growth stage (GRST). All NDF analyses included the use of heat-stable, a-amylase and sodium sulfite, as well as correction for residual ash (asNDFom). Seven triticale cultivars were established on 18 December 2019 at the University of Arizona Maricopa Agricultural Center, located near Maricopa, AZ. Forage plots were arranged in a randomized complete block design with 3 complete blocks (replications), and then harvested on 7 dates the following late-winter and spring (26 February, 17 March, 1 April, 14 April, 28 April, 12 May, and 26 May). Based on a linear model, GRST was highly variable among cultivars on 17 March (44 ± 10.6), 1 April (57 ± 12.1), 14 April (67 ± 8.9), and 28 April (79 ± 7.2) compared to other harvest dates (SD = 1.7). For concentrations of asNDFom, all cultivars exhibited linear (P = 0.042) and quadratic (P < 0.001) polynomial contrasts in response to harvest date, and all cultivars except Merlin Max (P = 0.063) exhibited at least one additional cubic or quartic effect (P = 0.015). A contributing factor to the unique response by Merlin Max was the numerically greater maximum canopy height (145 ± 9.8 cm) compared to the mean of all cultivars (107 ± 17.7 cm), which also was associated with greater percentages of stem, as well as reduced percentages of DM partitioned within the grain head. Regressions of asNDFom disappearance after 30- or 48-h incubations on GRST indicated that GRST was an effective independent variable (R2 = 0.927), and responses were most often linear in nature. Generally, relationships for DM disappearance were quadratic, ostensibly due to the complicating effect of grain fill, but GRST was again an effective predictor variable with R2 statistics = 0.852 for 12 of 14 combinations of cultivar and incubation interval. Predicted percentages of digestible DM attributed to asNDFom disappearance were = 50.3% through the fully-flowered stage of growth, but highly digestible contributions from non-fiber components following the onset of grain fill profoundly affected overall DM digestibility among cultivars harvested at later GRST.