Research update - NIRS equations for grass/clover silages

Published 25 April 14

University of Reading’s Centre for Dairy Research

DairyCo: NIRS for Grass and Clover Silages update

The overall aim of the research project (now at the midway point) is to develop new prediction equations and to investigate if variations in the composition of grass-clover silages throughout the UK impact on the reliability of Near Infra Red Spectrometry (NIRS) analysis for nutritional composition and feeding value.

If needed, the trial will provide an opportunity to update the current equations used for the NIRS analysis of silages to account for clover content.

The expected outcomes can be used to quickly determine energy and protein content and degradability in the rumen. This will allow more precise rationing, which is expected to lead to improved production efficiency and reduced losses of nutrients to the environment.

From the initial goal of collecting 90 different silages, from as widespread an area as possible, the University of Reading has now collected 52 varieties from all over Great Britain.

Bale Processing Described

For each silage sample collected and returned to the research centre, a complex processing operation begins. Professor Chris Reynolds from Reading’s Centre for Dairy Research explains, “The amount  needed to feed one sheep for 9 weeks is calculated (usually 300-500kg depending on dry matter), and then our dedicated team of technicians chop the bale and handfill and vacuum pack small 3kg bags with the chopped silage. This allows us to store the silage for as long as is needed without risking spoilage. Several samples are taken from the silage both before and after chopping, for further analysis.

Before chopping, a representative sample of about 1kg, taken from several different parts of the bale or clamp, is aspeciated (a process which involves carefully picking apart the clover from the grass and other components to determine the exact clover percentage).

Further Analysis

A key aspect of the trial is the determination of the true values of nutrient content for each silage sample used. This involves employing a combination of traditional ‘wet chemistry’ lab techniques and measurements of digestion in sheep and cows.

Professor Chris Reynolds continued, “The analytical techniques used in the laboratory, such as the Kjeldahl method for nitrogen analysis, will give highly accurate figures for protein, fibre and other nutritional components.

“In addition, to determine digestibility of organic matter (DOM), we keep 18 sheep which are used to measure silage DOM ‘in vivo’ in order to estimate ME value. Each silage sample is fed to three different sheep for three weeks each to provide replication. On the third week, the faeces and urine of the sheep are collected and analysed further to determine an accurate digestibility for each silage sample. When not on trial, the remainder of the sheep flock graze outside on pasture.”

Progress and Findings to date

Table 1 shows a summary of the nutritional analyses received for the 45 silages analysed so far.

The variation in these figures demonstrates the effect different swards and silage-making conditions can have on the nutritional value of the silage conserved. This variation is important to the trial as it ensures the NIRS equations are robust enough to analyse ‘unusual’ silages as well as more ‘average’ ones. As an example, some of the silages containing large quantities of wild species, such as buttercups, have proved to be an interesting challenge.

 Reading results

Looking to the future

With the remaining 38 silages still to collect over the 2014 season, we are continuing our search for silages across the range of clover content, with a particular need for silages containing 20 to 30% clover.

The ongoing support of farmers in the industry is very important, if you wish to get involved in this research project, please email Dr Debbie McConnell, DairyCo research and development manager

For more information on planning and managing your silage making, see chapter 8 and 9 of Grass+.