Evaluation of warm season annual forages for forage yield and quality in the north-central United States

Authors: Bleier, Jonathan; Coblentz, Wayne; Kalscheur, Kenneth; Panke-Buisse, Kevin; Brink, Geoffrey

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2020
Publication Date: 9/14/2020
Citation: Bleier, J.S., Coblentz, W.K., Kalscheur, K., Panke-Buisse, K., Brink, G.E. 2020. Evaluation of warm season annual forages for forage yield and quality in the north-central United States. Translational Animal Science. 4(3). Article txaa145. https://doi.org/10.1093/tas/txaa145.
DOI: https://doi.org/10.1093/tas/txaa145

Interpretive Summary: Grazing-based dairy operations require productive, high-quality forages capable of supporting the nutritional needs of mid-lactation dairy cows. Our objectives were to evaluate weekly harvests of 2 cultivars of sudangrass (SU), sorghum-sudangrass (S×SU), and pearl millet (PM) forages for growth and nutritive characteristics for grazing by dairy cows. For the cultivars evaluated in this trial, DM yields were less consistent across at the more northern location (Marshfield), which also is known for heavy, poorly drained soils. Despite locational differences, taller-growing cultivars within each forage type frequently exhibited yield advantages over dwarf or shorter-growing cultivars, but shorter cultivars often exhibited greater percentages of leaf across harvest dates, which is especially relevant within a grazing application. Consistent with these generalizations, PM cultivars exhibited shorter canopy heights and greater percentages of leaf than other cultivars, but these responses were generally associated with a yield drag. However, the greater leaf percentages for PM cultivars did not result in reduced percentages of structural plant fiber (asNDFom) on a wholeplant basis. Despite this observation, fiber digestibility was often significantly greater for PM compared to other cultivars. A direct comparison of brown midrib (bmr) and non-bmr PM cultivars indicated greater fiber digestibility for wholeplant tissues of the bmr cultivar in 5 of 6 harvest cycles evaluated, which is consistent with expectations for cultivars possessing a bmr mutation. Within the conditions established for this trial, PM cultivars generally exhibited more suitable characteristics for grazing livestock than SU or S×SU cultivars, but this management choice will likely come at a cost with respect to yield.

Technical Abstract: Grazing-based dairy operations require productive, high-quality forages capable of supporting the nutritional needs of mid-lactation dairy cows. Our objectives were to evaluate weekly harvests of 2 cultivars of sudangrass (SU), sorghum-sudangrass (S×SU), and pearl millet (PM) forages for growth and nutritive characteristics within the specific context of suitability for grazing by dairy cows. Three harvest cycles, including primary and regrowth cycles in 2016, and a single harvest cycle of primary growth in 2017, were evaluated at 2 locations (Prairie du Sac and Marshfield, WI). Within each cycle, sampling was initiated when canopy height was about 41 cm, but varied somewhat within location and harvest cycle. Thereafter, sampling was conducted on weekly intervals for 5 weeks, resulting in 6 equally-spaced sampling dates per harvest cycle. Data were analyzed as a spilt-plot design with cultivars (6) as wholeplots arranged in randomized complete blocks, and weekly harvest dates (6) as subplots. Yields of DM were less consistent at the more northern location (Marshfield), which is known for its heavier, poorly drained soils. Despite locational differences, the taller-growing cultivar within each forage type frequently exhibited yield advantages over dwarf or shorter-growing cultivars; this occurred for 7 of 9 intra-forage-type comparisons (P = 0.021) across 3 harvest cycles at Prairie du Sac, and for 6 of 9 similar comparisons (P = 0.032) at Marshfield. In 2016, shorter-growing cultivars had greater percentages of leaf in 4 of 6 intra-forage-type comparisons across both locations (P = 0.004), which is especially relevant for grazing. Similarly, PM cultivars exhibited shorter canopy heights (P = 0.002), but greater percentages of leaf (P < 0.001), than all other cultivars during all harvest cycles at both locations. However, the greater leaf percentages exhibited by PM cultivars did not translate into reduced percentages of structural plant fiber (asNDFom) on a wholeplant basis during any harvest cycle at either location; furthermore, asNDFom concentrations for PM cultivars were greater (P = 0.001) than observed for other cultivars within 2 of 6 harvest cycles across locations. Ruminal in-situ degradation of asNDFom for wholeplant forages based on a 48-h incubation was significantly greater (P = 0.006) for PM compared to other cultivars in 4 of 6 harvest cycles. Pearl millet cultivars generally exhibited more suitable characteristics for grazing livestock than SU or S×SU cultivars.