Characterisation of feedstuffs for ruminants.

Abstract

A wide variety of feed ingredients are used in the manufacture of compound feeds in Ireland. Unprocessed feedstuffs vary from batch to batch due to differences caused by variety, soils, weather, etc. By -product feeds may also vary due to the processes from which they were produced. Accurate information on the nutritive value of feeds is essential for accurate ration formulation. A series of experiments was carried out to determine various nutritional characteristics of concentrate ingredients either locally produced or imported into Ireland. From these experiments it was concluded that : * The digestibility values of concentrate ingredients derived in maintenance-fed sheep are applicable to maintenance-fed cattle. * Feed is not utilised as efficiently when the level of feeding is increased from maintenance to 2 x maintenance. * The improved feed conversion efficiency in steers offered a restricted allowance of concentrates cannot be attributed to a difference in digestibility but can be attributed in part to a lower rate of fat deposition compared to steers offered ad libitum concentrates. * The residue after oil extraction from Camelina sativa could replace some imported protein-rich feedstuffs in ruminant rations but to fully achieve this potential, the residual oil content must be decreased. * For measurement of ruminal degradability of concentrate ingredients a wide range of forage to concentrate ratios and feeding levels can be used. * It is important to consider the actual outflow rate of nutrients from the rumen when measuring the feed value of individual concentrate ingredients as this can have an impact on the effective degradability and the relative nutritive values assigned to such ingredients. * Large variations in ruminal degradation occur within and among feeds. The ruminal degradability of different samples of any one feed should be measured to determine their true nutritive value for feeding ruminants. * Within most concentrate ingredients examined, the variation in small intestinal digestibility (SID) due to source indicates a range in the quantity of amino acids supplied to the animal for productive purposes. The more rapid and cost effective in vitro technique can be used to screen the SID of concentrate ingredients. * Target volatile fatty acid (VFA) concentrations and proportions may be produced by varying the proportions of the individual ingredients in a concentrate ration. * An in vitro procedure allowed VFA production to be measured across a large range of feeds under standardised conditions. * On average, 75% of gas produced during ruminal fermentation consists of carbon dioxide. The variation in methane production among individual concentrate ingredients provides an opportunity to formulate rations to minimize environmental pollution with methane.