Influence of harvest date on the nutritive value and ensiling characteristics of maize stover

Abstract

In Experiment 1, for three years, triplicate samples of maize plants were collected at varying intervals from 3 weeks pre- to 5 weeks post-physiological maturity and were analyzed as the whole stover or its stalk, leaf, husk and cob fractions. The concentration of digestible dry matter in vitro (IVDDM) in stover was negatively correlated with grain yield ( r=−0.62) and the grain-to-stover ratio ( r=−0.77), which varied with year and harvest date. The concentrations of IVDDM and crude protein (CP) decreased ( P<0.01) linearly with later harvest. The concentration of total non-structural carbohydrates (TNC) decreased linearly with later harvest in years 1 and 3, but increased in year 2 (day × year, P<0.01). Changes in the concentrations of neutral detergent fibre (NDF), acid detergent fibre (ADF) and cellulose (CE) were inversely related to those of TNC. Although the concentration of acid detergent lignin (ADL) increased linearly ( P<0.05) with later harvest, there was no change in the ADL:NDF ratio. Changes in the concentrations of TNC, NDF, ADF, ADL and IVDDM of the silages produced in polyethylene bags from the stover harvested in years 2 and 3 were similar to those observed in their respective forages before ensiling. The concentrations of lactic acid and total volatile fatty acids in the stover silages decreased ( P<0.01) with later harvest. Although the concentrations of IVDDM decreased ( P<0.05) in all the morphological fractions of the stover, significant rates of loss in the amount of IVDDM were only observed from the leaves and cobs. In Experiment 2, stover silage which was produced 17 days post-physiological maturity had a higher ( P<0.05) concentration of CP and lower ( P<0.05) concentrations of DM, ADF, ADL and CE than did stover silage harvested 14 days later. Heifers fed on the early-harvested stover silage tended to have greater daily gains and required less feed per kg gain ( P<0.05) than did heifers fed on the late-harvested stover silage.