Ruminal nitrogen disappearance from sod-seeded cereal grain forages in Northern Arkansas

Abstract

Wheat (Triticum aestivum L.), oat (Avena sativa L.) and rye (Secale cereale L.) were overseeded into a dormant bermudagrass (Cynodon dactylon (L.) Pers.) sod and harvested on six dates throughout the spring. Plant growth stage was documented for each forage on each harvest date, and harvested forages were subsequently evaluated for forage quality characteristics. Four ruminally cannulated steers were used to evaluate disappearance kinetics of nitrogen (N) by an in situ method. All forages had high concentrations of N (≥31.1gkg−1DM) throughout harvest dates in March. By 15 April, rye had reached a substantially more advanced growth stage than either wheat or oat. This trait, coupled with the concurrent taller growth habit, caused concentrations of N in rye to decline (P<0.05) rapidly between the 24 March and 4 May harvest dates. The effective ruminal disappearance of N remained high (≥790gkg−1N) for all forages harvested through mid-April, thereby indicating that these cereal-grain forages exhibit the same characteristics of high N disappearance and low potential ruminal escape that are commonly observed in other high-quality cool season grasses harvested at similar growth stages. The effective disappearance of N reached a minimum (P<0.05) for all forages immediately before grain fill. Generally, substantial increases (P<0.05) in effective ruminal disappearance of N were observed as these forages partitioned N into the filling grain head. Fractional rates of N disappearance for wheat and rye were extremely rapid (≥0.383h−1) during grain fill. However, rye also exhibited an extremely rapid disappearance rate (0.548h−1) immediately prior to the onset of grain fill that was not observed for wheat (0.085h−1) at an identical growth stage. Parameters associated with disappearance kinetics can be related to growth stage at harvest by linear and polynomial regression techniques, although the best fit model was dependent on forage type.