The development of plant components in isogenic sterile and fertile forage maize and their effects on carbohydrate composition, nutritive value, in vivo digestibility values and animal performance with fresh and ensiled crops

Abstract

SummaryIsogenic fertile and sterile forage maize (cv. LG 11) grown in separate fields were harvested at regular intervals during growth between mid-July and early October 1979. Leaf, stem and ear components and whole plant (before and after ensiling) were examined for changes in the concentration of dry matter (D.M.), soluble sugars, starch, hemicellulose, cellulose, neutral detergent fibre (NDF) and acid detergent fibre (ADF). In vitro digestibility values for D.M., organic matter (OM) and OM in the D.M. were also determined in fresh and ensiled whole crops.Prior to ensiling the concentration of non-structural carbohydrates in the two crops was markedly different. Fresh fertile plants contained (as g/kg D.M.) 369 and 101 of starch and soluble sugars respectively. Corresponding values for sterile plants were 54 and 343 respectively. Sucrose was the most abundant soluble sugar present and contributed 64 and 74% of the totals in fertile and sterile plants respectively, prior to ensiling. Increases in plant D.M. during growth were significantly affected by the deposition of starch and are described by the following equation:y = 13·6 + 0·49 (±0·073) x(r = 0·93)where y = whole-crop D.M. concentration and x = starch concentration in D.M. The concentrations of hemicellulose and cellulose of both types of fresh plants were similar but those of ADF and NDF were lower in sterile plants. Xylose was the major constituent neutral sugar in the hemicellulose fraction and formed 68 and 76% of the total hemicellulose in the fertile and sterile plants, respectively. In vitro digestibility values of sterile plants tended to be higher than their fertile counterparts.After ensiling, the concentration of soluble sugar in the sterile and fertile crops decreased from 343 to 8 g/kg D.M. and 101 to 5 g/kg D.M. respectively. The in vitro DOMD values of the sterile and fertile crops decreased by 16 and 11 percentage units respectively; both final values were recorded as 61.In vivo digestibility values determined in 18-month-old wether sheep fed at maintenance, for NDF, ADF, cellulose, hemicellulose, nitrogen, OM, D.M. and OM in D.M. were 60·2, 58·0, 65·8, 64·1, 32·9, 66·6, 65·4 and 63·7 respectively for fertile plant silage. These were all markedly lower than the corresponding values for the sterile plant silage which were 68·3, 70·3, 74·8, 73·3, 60·3, 71·3, 69·6 and 67·7 respectively. Within the hemicellulose fraction the digestibility values for xylose in both sterile and fertile plant silage were considerably lower than the values recorded for either arabinose or galactose. In vitro digestibility values for D.M., OM and OM in the D.M. were similar to in vivo values for fertile plant silage but were lower than in vivo values for sterile plant silage.Dairy herd replacement heifers (aged 3–6 months) had higher D.M. intakes when given fertile plant silage ad libitum than with sterile plant silage. However, the liveweight gains of the heifers on sterile and fertile plant silage differed little.