Feeds and forages are variable in composition. Feed analysis provides information for farmers to optimize nutrient utilization in animal feeds; for feed compounders to prepare feed mixtures suitable for different animal production systems; for researchers to relate animal performance to feed characteristics; and for plant breeders to optimize the nutritive value of new varieties. Also of concern are the undesirable contaminants of animal feeds which may have a direct bearing on the safety of foods of animal origin. This book brings together six reviews on these subjects from the FAO Electronic Journal AGRIPPA in printed form.
The keynote article by Irene Mueller-Harvey describes current procedures for feed analysis and procedures to improve standards. She describes how to achieve quality control, quality assurance, laboratory accreditation and proficiency testing. Standard and widely accepted methods are described together with recent developments in feed analysis. Topics covered include: sample preparation, analysis of major components (dry matter, ash and minerals, crude protein, fat, fibres and starch) and of secondary plant products (tannins, mycotoxins and other contaminants). Developments in the analysis of whole samples by near infrared reflectance spectroscopy are mentioned and the potential of this technique to by-pass traditional feed analysis by directly predicting animal responses.
Feedstuffs vary because of genetic differences and as a consequence of feed processing. The paper by Gizzi and Givens considers the importance of these factors for the compound feed manufacturer, the farmer and the policy maker. Data variability also results from differences in the methodologies used to obtain the information. Chemical analysis procedures and animal study protocols may vary according to the laboratory or institute involved. Understanding the variation in chemical and nutritional characteristics of feedstuffs is vital to the effective use of feed information in livestock production.
The paper by Harinder Makkar describes the potential of the in vitro gas production method for evaluating nutritional quality of feed resources for ruminants. This technique enables selection of a feed or feed constituent for high efficiency of microbial protein synthesis in the rumen along with high dry matter digestibility, and provides a basis for development of feeding strategies to maximize efficiency. In addition, this technique provides an experimental tool to study the effects of various natural and synthetic compounds and their adverse or beneficial effects on rumen fermentation.
Felix DMello covers the microbiology of animal feeds, including forages, cereal grains, oilseed by-products and compound feeds. He notes the beneficial effects of lactic acid bacteria in the fermentation of forages during the process of ensilage. Lactic acid bacteria and yeast cultures have also been attributed with beneficial properties as feed probiotics for reducing scouring and increasing growth performance in farm animals. Animal feeds may become contaminated with harmful bacteria such as Salmonella, Listeria and E. coli. Cereal grains and oilseed by-products are regularly contaminated with fungi occurring as plant pathogens or developing during storage. Major adverse effects arise in farm animals due to the production of mycotoxins by certain species and strains of these fungi. He discusses potential methods for reducing the prevalence of deleterious fungi and regulations to control these feed contaminants, particularly mycotoxins.
In a second article, Dr DMello reviews the range of contaminants and toxins arising from anthropogenic and natural sources. He considers the distribution of heavy metals, radionuclides, mycotoxins, plant toxins, antibiotics and microbial pathogens in cereals, complete feeds and forages, together with the impact on farm livestock productivity and on the safety of resulting products. He considers methods of avoiding contamination and the regional significance of controls and legislation.
The final paper by Peter Hughes and John Heritage explores the developing controversy surrounding the use of antibiotics as growth promoters for food animals. These drugs are used at low doses in animal feeds and are considered to improve the quality of the product, with a lower percentage of fat and higher protein content in the meat. They may also help to control zoonotic pathogens such as Salmonella, Campylobacter, Escherichia coli and enterococci. Use of antibiotics, particularly at low doses, is associated with selection for resistance in pathogenic bacteria and it has been argued that the use of antibiotic growth-promoters may result in bacteria resistant to antibiotics used in clinical or veterinary practice, thus compromising the continued use of antimicrobial chemotherapy. The paper reviews the use of antibiotics as growth promoters and examines some of the alternative methods for achieving meat of high quality.
This publication intends to provide most recent information on the impact of animal feeds on food quality, food safety and the environment and to thus improve the basis for managing such risks which are increasingly at the centre of public and individual consumer attention.
Further articles will be published from time to time and can be read on-line at: http://www.fao.org/agrippa/. Peer reviewed and edited documents are published in the AGRIPPA system and immediately available to readers. Subjects covered include livestock production, animal nutrition and feeding, and farming systems.
FAO Animal Production and Health Division