Cell wall chemical characteristics of whole-crop cereal silages harvested at three maturity stages

Authors: WALLSTEN, JOHANNA - Swedish University Of Agricultural Sciences; Hatfield, Ronald

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2016
Publication Date: 5/10/2016
Publication URL: http://handle.nal.usda.gov/10113/62674
Citation: Wallsten, J., Hatfield, R.D. 2016. Cell wall chemical characteristics of whole-crop cereal silages harvested at three maturity stages. Journal of the Science of Food and Agriculture. 96(10):3604-3612.

Interpretive Summary: In many of the Scandinavian countries such as Sweden, the growing season is too short to grow crops such as corn. Cereals grow better in the cooler, shorter seasons and are often harvested as silages for use in dairy rations. Barley, wheat, and oat are typically harvested as whole-crop silages. Animal performance varies with the type of silage and its stage of development at ensiling. In this study, three different whole-crop cereals were ensiled at three different stages of development known as heading, milk stage, and dough stage. These materials were analyzed using the traditional detergent system for nutrient value estimates and by more detailed chemical analyses of the cell wall fraction (fiber). The detailed analyses allowed us to look at the individual carbohydrates, lignin, and other materials that make up the cell walls. There were differences in the fractions making up the cell walls that changed with the stage of development and the type of cereal. These differences were not consistent across stages of development when comparing cereal types. For example, at the heading stage, wheat had the lowest lignin content, but at the dough stage (most mature), barley had the lowest lignin content. For ether-linked ferulates (an indication of how well the cell wall components are tied together), barley was lower than oat or wheat at heading, but the highest at the dough stage. These differences in cell wall components and their changes during development likely alter how well a given cereal silage is utilized by dairy cows. Such detailed characterization may allow optimization of ensiling to produce the most digestible silage for a given cereal if harvested at the proper developmental stage. This could provide economic benefits to the farmer by harvesting and ensiling at times for optimal cow performance.

Technical Abstract: Ensiling is a convenient method of preserving nutritional quality of harvested forage materials. Whole-crop cereal silages (WCCS) are an important nutrient source for ruminant animals, especially in cooler climates such as those found in Scandinavian countries. Animal performance varies with the type of cereal forage and stage of cereal development being ensiled. Wheat, barley, and oats were harvested at the heading, early milk, and early dough stages of maturity and were ensiled in plastic-wrapped big bales. Previous work indicated that barley generally have higher fiber digestibility than other WCCS. Based on the detergent fiber analysis system, it appeared these differences were mainly due to differences in the cell wall hemicellulosic fraction calculated by acid detergent fiber (ADF) subtracted from neutral detergent fiber (NDF). A set of 27 WCCS samples of barley, wheat, and oats harvested at 3 different maturity stages were analyzed for cell wall (CW) composition. Total CW concentrations of the WCCS were higher than the NDF concentration. The correlation between the two fiber fractions across all WCCS samples was low (R=0.63), possibly due to soluble fiber fractions that were included in forage CW, but not in the forage NDF. The lignin concentration in the silages was higher (P<0.001) in oats (111 g/kg DM) than in barley (88 g/kg DM) and wheat (91 g/kg DM). Hydroxycinnamate concentrations varied among the WCCS samples. Ferulates (ester- and ether-linked) ranged from 12.2 to 14.9 g kg-1 across forage types and maturity stages. Concentrations of p-coumarates (pCA) ranged from 3.8 to 11.6 g kg-1. However, all oat samples were nearly twice that of barley or wheat. The correlation between total cell wall xylose and hemicellulosic polysaccharides (NDF-ADF) was lower than expected in all forages (R= 0.63). This may be due to the solubility of arabinoxylans in the neutral detergent system.