While the rest of the world rejoiced in millennium–induced fervor, the feed industry took a more serious view of the challenges that lay ahead. This industry—specifically the livestock production and feed milling sectors— has been battered by successive food scares. Consequently, consumers have lost confidence in the animal food industry’s ability to provide products that are free of contaminants, pathogenic microorganisms, residues, toxins, and other harmful compounds. Even in countries such as the US that have well-established industry and regulatory agencies, people have become skeptical of food companies. They are being perceived less as benevolent providers of sustenance and more as faceless multinational conglomerates. Therefore, the primary focus of the industry in the new millennium is twofold: restore consumer confidence and stem media hostilities while positioning itself firmly in the food chain. The good news is that it has the tools to accomplish these important objectives.
The year in review: a continuous challenge
For the past several years, the livestock rearing and feed manufacturing sectors of the food chain have faced major challenges. Many have involved food safety crises in Europe that have reverberated throughout the rest of the world. Many of the problems that occurred in the past are still being addressed today (Table 1). For example, the discovery of bovine spongiform encephalopathy (BSE) in beef cattle during the late 1980s resulted in a ban on the export of beef from the United Kingdom. Now, more than a decade later, Germany and France are maintaining their embargo on UK beef in defiance of the European Union, which lifted its ban on UK beef exports in August of last year. Both countries defended their stance, claiming that UK beef continued to pose a threat to consumer health. In the US, a growing number of cases of antibiotic-resistant pathogens have prompted the Food and Drug Administration to establish a task force to investigate the contribution of the growth-enhancing antibiotics in animal agriculture to the problem.
Table 1. A review of 1999.
• FDA demands human health impact study for antimicrobials.
• Australia and New Zealand announce strict GMO labeling.
• Switzerland bans antimicrobial growth promoters.
• High concentrations of mycotoxins found in grain in seven southern US states.
• Pollen from Bt corn kills Monarch butterfly larva.
• Pfizer files suit to reverse EU virginiamycin ban.
• Canada rejects BST for dairy cows for animal health reasons.
• EU calls for livestock extensification and GMO certification.
• The Netherlands finds Salmonella enteriditis in 12% of layer units.
• EU abandons plan to ban use of fish meal in animal feed.
• US proposes labeling for beef exports to EU.
• WVA, IFAP and COMISA: prudent antibiotic use principles.
• Swiss expand BSE monitoring with Prionics BSE test.
• US swine integrators Smithfield and Carroll’s combine to become the world’s largest pork
• UK sets out date-based scheme for EU beef exports.
• Virulent Newcastle disease hits NSW, Australia.
• Vietnam stiffens meat inspection.
• Korean cooperatives market selenium-enriched pork.
• France opens food safety agency, AFSSA.
• Belgium starts new epidemiological surveillance of cattle.
• EP calls for feed ingredient labeling to aid BSE control.
• Stefane André reports hormones in 12% of hormone-free US beef.
• Substantial DNA differences found in resistant Enterococcus faecium from chickens and
• Dioxins in Belgium – bans on EU animal produce.
• EU signs up for battery cage ban for 2013.
• EU antimicrobial growth promoter ban in force.
• France calls for ban on animal meal in feed.
• US feed giants Cargill and Continental Grain merge,
• AAFCO in US forms a ‘nutraceutical/functional foods’ task force
• Germany extends pig hygiene law to all producers.
• US and EU recognize equivalence in sanitary measures.
• EU lifts ban on UK beef exports.
• Swiss find hormones in hormone-free US beef.
• US FDA proposes Veterinary Feed Directive.
• FDA amends new animal drug regulations.
• Germany sets up centralized cattle database for 2000.
• Malaysia levies heavy fines for use of banned antibiotics.
• China regulates feed ingredients.
• EU issues regulation on organic livestock production.
• UK’s main poultry producer rejects antibiotic growth promoters.
• EU’s FVO notes deficiencies in Brazil’s residue controls.
• Swiss animal movement databank opens for cattle.
• FDA finds detectable levels of dioxin in a majority of clay samples.
• Citizens’ group ask US Congress to enact GM foods labeling law.
• FDA issues draft medicated feeds policy for minor species.
• EU postpones beef labeling and proposes food safety agency.
• France and Germany maintain beef ban.
• Three US cooperatives merge into mega-feed company.
• Canadian food processor refuses GM potatoes.
• Brazil proposes establishing GM-free crop zones.
• US poultry industry commits to eliminating pathogens.
• UK lifts beef-on-the-bone ban in time for Christmas.
• EU lifts dioxin testing for Belgian pork and poultry.
Adapted from Animal Pharm, December, 1999.
Food safety problems have done considerable damage to the international feed industry. In most cases, perception overrode reality. The absence of evidence did not necessarily constitute evidence of absence. In another interesting shift, food retailers in some countries have taken a proactive role. Supermarkets in the UK and a few other markets have assumed the role of custodians of food safety. They believe that they are in the best position to guarantee the wholesomeness of food. These companies also have a global influence, dictating to meat producers as far away as Brazil and Thailand how animal products they purchase must be fed and reared. Others urge adoption of the organic approach as a marketing strategy. Successful retailers have always achieved their success based on placing the consumer at the heart of their marketing strategies; and agribusiness can be no different.
“If a butterfly dies in Iowa, does Wallstreet mourn?
Welcome to the new era of bioagriculture”
Kiplingers Investing, January 2000
Even the stock market responds to consumer concerns. The death of a monarch butterfly from ingesting pollen from a genetically modified corn variety had a disastrous effect on share prices for the seed company. Farmto-folk-to-finances appears to be the order of the day.
A new food safety furor has erupted over the use of genetically-modified (GM) crops—mainly corn and soybeans—in the production of food. Europeans have been the most vocal in their opposition to GM foods (Figure 1). Several retailers in the UK have prohibited GM ingredients from being included in their own-label products—including food produced from livestock fed GM grains. This was in spite of the fact that the scientific evidence surrounding GM crop varieties is sound. However, consumers in many parts of the world are expressing their own concerns about the impact that GM foods might have on human health and the environment. For example, in the US, consumer activists petitioned the FDA to create a labeling program for foods that contain GM products. As recently as March of 2000 President Clinton announced that meat from animals fed on GM crops would not be considered organic. Brazil has enacted a moratorium on the approval of GM crops. Japan has approved the importation of a small number of varieties of several GM crops. However, government regulators promised Japanese consumer groups that it would not approve any others.
One reason that consumers are hesitant to accept GM crops is because they do not see the benefits. Most of the traits—herbicide tolerance and insect resistance—are economic advantages to the farmer. These are ‘production genes’ with no direct advantage for the consumer. However, the consumer must assume a risk, although it may be small. The main argument then is: Why shouldn’t the food industry offer consumers a choice when deciding whether to purchase GM foods?
This past year also ushered in the ban of four antibiotic growth promoters in Europe. As the end of the year approached, European Commissioner David Byrne, on advice from the Scientific Steering Committee, announced that he was considering banning the growth promoter avilamycin. Avilamycin, among others, escaped the original ban because it did not “contribute to the development of resistance to human medicines [or] belong to the antibiotic families authorized in human medicines”. Mired in a seemingly relentless series of food crises and facing on-going erosion of consumer confidence, the Commissioner sought to err on the side of political and/or scientific caution.
Figure 1. New choices for the millennium.
The feed chain – now the food chain
Safety is the number 1 ingredient in food”
EU Commissioner for Public Health
and Consumer Protection
It is not difficult to see which way the wind is blowing in the global market for animal feed. Due to changing regulations, we as an industry are fast moving closer to the food industry in production standards. Feed mills of the future may start to resemble food production plants; biosecure facilities that can guarantee feed is free from contaminants, manufactured from raw materials that meet the highest standards of nutrition and hygiene. Further consolidation of the retail sector promises to usher in a new era of price and margin pressures for suppliers.
The implications for the agribusiness sector are clear. The feed chain is firmly affixed as part of the food chain (Figure 2). The challenge facing us is to accept that the consumer will define what products are acceptable in the food chain and that we must become proactive in our approach to these demands.
Figure 2. The food chain
Alltech in 2000: scientifically proven solutions
Since its foundation in 1980, Alltech’s product development strategy has been guided by the ACE principle, i.e. producing products that are:
• Animal-friendly: scientifically proven to respect livestock welfare and enhance physiological condition through nutrition.
• Consumer-friendly: 100% natural, traceable, non-GM products.
• Environmentally-friendly – products that actively reduce the environmental impact of intensive livestock production through the reduction of both atmospheric emissions and effluents.
For 20 years, Alltech, in partnership with the feed industry, has investigated the major issues facing our industry. Through the forum of Lecture Tours and the annual Alltech Symposium, we have collectively developed new and innovative ideas to respond to both the needs for increased health and productivity in the livestock sector and the growing expectations of the consumer . The following pages summarize progress and describe the goals for six key projects within Alltech.
Scientific projects produce natural solutions: Sel-Plex: organic selenium
Despite routine supplementation with sodium selenite, selenium-deficiency problems are common across the world. Though it is widely known that sodium selenite has limited bioavailability, the narrow margin between requirement and toxicity of the nutrient and the specific toxicity of sodium selenite have prompted strict regulation as to the amount that can be added to feed. In fact, the toxicity of sodium selenite to humans has resulted in bans against its use in certain markets, including Japan – one of many selenium-deficient regions in the world.
Bioavailability and regulatory issues have left the animal feed industry in many parts of the world with seemingly insurmountable problems in getting the necessary amount of selenium into animals. Until the advent of organic selenium, the only selenium supplements for feeds were the highly oxidized sodium selenite and sodium selenate. Selenite or selenate selenium, poorly available to begin with, often interact with compounds in water and (or) digesta to become substantially less available; yet addition of higher amounts to feeds in compensation is restricted. In addition, the highly oxidized nature of the inorganic sources is increasingly being seen as a poor method of supplying the antioxidant selenium nutrient from a biochemical perspective. The inorganic sources are pro-oxidative, which has implications for a number
of physiological processes. For example, use of selenite tends to increase post-mortem drip loss from poultry and pig meat.
Sel-Plex selenium yeast helps solve this limitation to production by providing selenium in a much more bioavailable form, i.e. the form in which it naturally occurs in plants. Yeast, like other plants, form selenoamino acids such as selenomethionine. Unlike the highly oxidized selenite, selenoamino acids are in very reduced organic selenide (-2) form, which is the form useful in physiology. Selenomethionine, differing only from methionine by substitution of the selenium for the sulfur atom, is metabolized very differently from inorganic selenium. It is absorbed as the amino acid, and instead of being largely excreted via urine, selenomethionine can be used by any tissue taking up methionine. As a result, total retention of selenium is increased, as is the selenium content of meat, milk and eggs.
In addition, selenoamino acids in muscle tissue form a reserve - supplying selenoamino acids through ongoing catabolism of muscle cells. In all animals protein turnover is constant. In the case of broilers, muscle cell turnover can be as much as 15% per week. Since selenoproteins such as GSH-Px are composed entirely of selenoamino acids, it is critical that selenoamino acids be part of the muscle amino acid profile in order that a reserve be present during stress. During stress periods, when dietary amino acids are in short supply due to low intake or digestive dysfunction, proteosomes recycle muscle protein to provide amino acids for a variety of purposes, including fermentation of selenoproteins (Figure 3).
Figure 3. Selenoamino acids are recycled to form critical selenoproteins.
While the value of selenium-rich animal food products has been used to advantage by those marketing specific nutritional or designer foods, the value of organic selenium in animal health and production is of particular note. Substitution of the inorganic selenium with Sel-Plex selenium has resulted in a wide variety of improvements in antioxidant-related response ranging from post-mortem drip loss and meat color to livability of neonates. These factors have wide-ranging impact on animal health, performance and carcass quality (Table 2).
Organic selenium offers a means of supplying sufficient quantities of selenium in metabolizable form without compromising human or animal safety and without the need to add extra-nutritional or extra-legal amounts to feed. The obvious advantages of this alternative to inorganic selenium are becoming apparent to both the livestock feeding industry and regulatory authorities. Already cleared for use in most countries around the world, Sel-Plex has recently completed the FDA food additive petition process in the US and will be marketed in the US beginning in the poultry sector.
Using the yeast cell wall: mannan oligosaccharides and modified cell wall glucan
Viable yeast have always been at the core of many Alltech projects. Products developed using particular strains of yeast include the diet-specific yeast cultures Yea-Sacc1026 and Yea-Sacc8417 and biosynthesis of organic selenium (Sel-Plex) and organic chromium (BioChrome). While the ease with which yeast can be grown industrially and the huge variety of strains available are well-suited to finding useful species without the need for genetic modification, the same characteristics have allowed us to explore use of the various fractions of the yeast cell (Figure 4). This exploration includes the variations in cell content and cell wall composition among different strains of Saccharomyces yeast. The result has been development of a number of new products; but even more importantly, it has shown us that the possibilities are limitless.
YEAST CELL WALL MANNAN OLIGOSACCHARIDES: SCIENTIFICALLY PROVEN ALTERNATIVES
Extensive experience with antibiotic growth promoters in all species has given us a general overview of what we need and expect in such an additive:
Pigs: 3-8% faster growth
Calves: lower incidence of digestive disorders, reduced medication use
Poultry: 3-8% improvement in FCR
Physical characteristics: stability during feed processing, mixability with feed ingredients, inert
Table 2. Sel-Plex, selenium status and animal performance: a summary of recent research.
Figure 4. Products of the yeast cell.
In a review of data published on effects of antimicrobial growth promoters, Rosen found that 72% of trials were successful (personal communication). When the search was on for scientific alternatives, the same criteria needed to be satisfied. Investigation of phosphorylated mannan oligosaccharides revealed that these complex carboyhydrates derived from cell walls of certain yeast strains exceeded these requirements. In a wide spectrum of trials, both in research and under commercial conditions, results have shown that subtle changes in the carbohydrate profile of the diet can often have an impact not unlike adding antibiotic growth promoters (Table 3). Bio-Mos has proved efficacious in ~80% of all animal studies; a rate that compares favorably with antibiotics. Furthermore, the product is extremely stable,
surviving autoclave temperatures. Bio-Mos is now included as a standard ingredient in many pig and poultry diets around the world; and as our information base grows, we are increasing our understanding of how to maximize its applications.
ESTERIFIED CELL WALL GLUCOMANNAN: MYCOTOXIN ADSORBENTS
Animal feed ingredients, storage bins and transfer equipment frequently present the proper conditions for mold growth; and it is recognized that mycotoxin problems exist in all parts of the world. Alltech has an ongoing commitment to finding ways to reduce animal performance losses due to mycotoxins in stored feed. This commitment is expressed both through supporting university/institute research that seeks to define the nature of mold toxins and toxicity and through projects underway in Alltech laboratories exploring ways to minimize mycotoxin impact. Mycosorb, a derivative of yeast glucan, is the result of efforts to identify natural compounds that bind mycotoxins. Modifications such as esterification enable us to take greater advantage of the natural porosity of the yeast cell wall glucomamman to adsorb toxins. In cooperation with ETH in Switzerland, adsorption capacity for zearalenone of raw glucan was increased from 2 mg/g to 80 mg/g in Mycosorb, the finished product. Now patented, Mycosorb has proven to
successfully bind aflatoxins and fusariotoxins, including T-2 toxin. Binding of T-2 toxin can be as high as 3 mg/g of glucan. Because Mycosorb binding ability is specific, inclusion rates are low in feed and the absorption of other nutrients is not blocked.
Table 3. Bio-Mos comparison with antibiotic growth promoters in poultry.
Current projects include development of increasingly specific derivations of Mycosorb, in vitro assays of binding ability, and work to define solutions to the ergot toxins that cause fescue toxicity and ryegrass staggers. In practical trials, the breakthrough in toxin binding is reflected in improved performance. The lesson appears to be that 1) we have a global problem with mycotoxins, and 2) the esterified glucomannan provides part of the solution.
Extracting new benefits from yeast cell contents
For every ton of yeast, there exists about half a ton of yeast extract, the cell contents of the yeast. Yeast extracts are concentrates of the soluble part of yeast cells following removal of the cell material. This can be accomplished by autolysis (using the enzymes present in the cell) or by hydrolysis (enzymatic or acid). Yeast extracts are used primarily in the fermentation industry as growth substrates or in the food industry as flavor enhancers. The free amino acid content is typically 35-40%; and in addition, there are substantial amounts of small molecular weight (<600 Daltons) peptides (Figure 5) and water-soluble vitamins.
Figure 5. Uses of yeast extract fractions.
The predominant amino acids are glutamic and aspartic acids, both of which lend yeast extract useful characteristics in flavoring agents. Yeast extracts are used in a wide variety of familiar applications including the flavor base of food products such as soups, gravies and sauces as well as microbial growth medium in microbiology. Yeast extracts are valued for their ability to enhance flavors and to mask sour and bitter tastes. During autolysis RNA is broken down into 3´ nucleotides. These nucleotides do not have flavor enhancing characteristics. During enzymatic hydrolysis of yeast, 5´ nucleotides of guanine, adenine, cytosine, and uracil are formed. Only the 5´GMP (guanine) and 5´IMP (inosine) have flavor enhancing ability. By adding an enzyme the 5´AMP can be converted to 5´IMP.
The 5´IMP and 5´GMP enhance flavors and suppress bitterness. By adding these two components to the amino acids, peptides and reaction products already formed, a variety of flavor enhancing properties are obtained. The possibility of developing new flavors based on yeast nucleotides in order to avoid use of MSG has interesting applications in pet food formulations, as well as human food applications.
BIOPEPTIDES FOR ANIMAL FEEDS: REDUCE NITROGEN POLLUTION, PROVIDE NON-MAMMALIAN PROTEIN
Until now, use of such extracts as sources for biopeptides for animal feeds was cost-prohibitive. Today the explosion in use of glucans and mannans has allowed Alltech to offer these extracts to the feed industry. Initially, studies with broiler chicks during the first 7-14 days have shown improvements in feed intake and reductions in mortality. Total replacement of plasma proteins in pig starter diets is possible leading to a savings of 3-5 days to slaughter. Potential uses in aquaculture are also being explored. Indeed a problem, loss of mammalian protein sources, has been transformed into an opportunity – non-GMO high quality protein.
BIOPLEX TRACE MINERALS: DIFFERENT METABOLISM ROUTES
Faster growth rates of meat chickens and pigs, higher reproductive potential in sows and higher production in general have demanded increased ability to extract nutrients from feed. In response to this, researchers went to great lengths to alter energy and protein availability while little attention was given trace element nutrition. Recommended inclusion rates have changed very little; and until recently few studies had investigated effects of mineral forms. As a result, lack of copper, manganese, iron and zinc, critical nutrients for immunity and reproduction, can render animals more susceptible to disease or reproductive dysfunction.
The Bioplex proteinates were designed to more closely simulate the forms in which trace elements naturally occur in plants. Because these nutrient forms are digested and metabolized by different routes than the inorganic oxides and sulfates, mineral retention by the body is higher. Tissue stores can accumulate against periods of peak demand; and adequate amounts can be transferred to the fetus without placing maternal health or subsequent fertility at risk.
Emphasis has been placed on exploring health and reproductive benefits that occur in response to Bioplexes. The practical impact of Bioplex trace mineral forms in dairy cattle diets has been demonstrated in a variety of studies revealing lower mastitis incidence at calving and reduced somatic cell counts in response to improved mineral status. A long term study with sows has recently shown that Bioplex mineral forms have an impact on the reproductive potential of the sow and her longevity in the herd (see chapter by Fehse and Close, this volume).
An equally important benefit of increased mineral retention is reduced trace mineral content of manure. Growing concern about trace minerals in soil profiles is leading pig and poultry researchers to explore use of Bioplexes to allow lower total diet trace mineral content, particularly where high levels of inorganics are used as growth promotants.
ENZYMES: NEW PRODUCTION TECHNOLOGIES, NEW APPLICATIONS
In response to the feed industry’s need for non-GMO enzymes, process development at Alltech has focused on appropriate technologies. The result has been the re-emergence of the ‘Koji’ system of solid state fermentation (Figure 6). Alltech’s new manufacturing plant in Serdan, Mexico is currently equipped to produce phytase, xylanases and proteases, all of similar activity to GM-derived enzymes, but with none of the negative connotations. The new plant has the capacity to produce enough enzyme to treat 95 million tons of feed – a fifth of total world animal feed production. Indeed, as we have revisited the old science and applied new technology to the process, we found that our new phytase enzyme is more stable than its GM counterpart and has a much broader range of activity.
In the area of new enzyme applications, we have also been able to sufficiently protect a fiber-digesting enzyme to allow it to be effective in the rumen. The net result has been improved productivity using the farm’s cheapest raw material, namely forage. Improvements in milk yield of 1-2 liters per day are consistently observed.
“A new scientific truth that does not triumph by convincing its
opponents, but rather because its opponents die and the new generation
grows up that is familiar with it.”
How fast can we adjust our organizations to respond to new challenges and opportunities? In the 1940s and 1950s we perhaps, as Max Planck said, could wait for the opposition to die - however not in the cyberworld where speed is of the essence. Within three years, it is expected that 15% of US households will be purchasing all food via the internet. Are we willing to accept these challenges and become proactive in our approach to meeting consumer demands? The successful feed company of the future will face the reality of today’s marketplace and view itself as a link in the food chain (Table 4). If we expect our businesses to grow, we cannot afford to wait until specific technologies such as genetic engineering of food crops become accepted in succeeding generations. We must develop effective and marketable processes and put them into practice - now. Alltech, a family of 600 people now present in 65 countries, has set itself the task of multiplying sales five-fold. An important part of this effort will bring to the table 140-180 new M.Sc and Ph.D. students, all of whom will focus on problems facing modern animal production. Through the forums of the Lecture Tour Series and the annual Symposium, information transfer is facilitated; and through a partnership approach, new solutions to the demands of the marketplace are discovered. Success, as always, awaits those with the foresight and flexibility to respond quickly and effectively to these demands.
Figure 6. Flow diagram of the Koji solid state fermentation process.
Table 4. The successful feed company of the future.
Animal Pharm. 1999. PJB Publications Ltd.
Awadeh, F.T., R.L. Kincaid and K.A. Johnson. 1998a. Effect of level and source of dietary selenium on concentrations of thyroid hormones and immunoglobulins in beef cows and calves. J. Anim. Sci. 76:1204-1215.
Awadeh, F.T., M.M. Abdelrahman, R.L. Kincaid and J.W. Finley. 1998b. Effect of selenium supplements on the distribution of selenium among serum proteins in cattle. J. Dairy Sci. 81:1089-1094.
Cantor, A.H. 1997. The role of selenium in poultry nutrition. In: Biotechnology in the Feed Industry (T.P. Lyons and K.A. Jacques, eds.), Nottingham University Press, Nottingham, UK. pp. 155-164.
de Lyons, M.S. 1998. Organic selenium as a supplement for Atlantic salmon: effects on meat quality. In: Biotechnology in the Feed Industry (T.P. Lyons and K.A. Jacques, eds) Proceedings of the 14th Annual Symposium Nottingham University Press, Nottingham, UK.
Edens, F.W., T.A. Carter and A.E. Sefton. 1996a. Influence of dietary selenium sources on post mortem drip loss from breast meat of broilers grown on different litters. Poultry Sci. 75(Suppl. 1):60.
Edens, F.W., T.A. Carter and A.E. Sefton. 1996b. Improved feathering with dietary organic Se and its modification due to litter material. 1996b. Poultry Sci. 75(Suppl. 1):114.
Edens, F.W. C.R. Parkhurst and G.B. Havenstein. 1999. Effects of conventional vs cage housing and inorganic vs organic selenium on feathering in broilers. Poultry Sci. 78(Suppl. 1):133.
Fisher, D.D., S.W. Saxton, R.D. Elliot and J.M. Beatty. 1995. Effects of selenium source and Se status of lactating cows. Veterinary Clinical Nutrition 2(2):68.
Hemken, R.W., R.J. Harmon and S. Trammell. 1998. Selenium for dairy cattle: a role for organic selenium. In: Biotechnology in the Feed Industry, Proceedings of the 14th Annual Symposium (T.P. Lyons and K.A. Jacques, eds.) Nottingham University Press, Nottingham, UK pp 497-503.
Hughes, D., S. Kenyon and K.A. Jacques. 1998. Selenium yeast improves selenium status of Welsh ewes. Poster presented at the 6th International Symposium on the Uses of Selenium and Tellurium, Selenium-Tellurium Development Association, May 10-12,1998, Scottsdale, AZ, USA
Knowles, S.O., N.D. Grace, K. Wurms and J. Lee. 1999. Significance of amount and form of dietary selenium on blood, milk and casein selenium concentrations in grazing cows. J. Dairy Sci. 82:429-437.
Mahan, D.C. 2000. Effect of organic and inorganic selenium sources and levels on sow colostrum and milk selenium content. J. Anim. Sci. 2000 78:100-105.
Mahan, D.C. and Y.Y. Kim. 1996. Effect of inorganic or organic selenium at two dietary levels on reproductive performance and tissue selenium concentrations in first parity gilts and their progeny. J. Anim. Sci 74:2711-2718.
Mahan, D.C. and N.A. Parrett. 1996. Evaluating the efficacy of Se-enriched yeast and sodium selenite on tissue Se retention and serum GSHPx activity in grower and finisher swine. J. Anim. Sci. 74:2967-974.
Mahan, D.C., T.R. Cline and B. Richert. 1999. Effects of dietary levels of selenium-enriched yeast and sodium selenite as selenium sources fed to grower-finishing pigs on performance, tissue selenium, serum glutathione peroxidase activity, carcass characteristics and loin quality. J. Anim. Sci. 77:2172-2179.
Naylor, A.J., M. Choct and K.A. Jacques. 2000. Effects of selenium source and level on performance, mortality and meat quality in male broilers. Poster presented at Southern Poultry Science, Atlanta, Georgia, Jan. 17-18.
Ortman, K. and B. Pehrsen. 1997. Selenite and selenium yeast as feed supplements for dairy cows. J. Vet. Medicine A 44:373-380.
Pagan, J.D., M.A.P. Kennedy, T. Currier and K.E. Hoekstra. 1999. Effect of selenium source on selenium digestibility and retention in exercised Thoroughbreds. Proceedings, 16th Annual Equine Nutrition and Physiology Symposium, Raleigh, NC, June 2-5, 1999. 135-140.
Paton, N.D., A.H Cantor, M.J. Ford, B.T. Slaugh, A.F. Rizvi, and T.P. Karnezos. 1998. Effect of providing organic selenium and chromium as yeast in laying hen diets on nutrient composition of eggs. Poultry Sci. 77(Suppl. 1):11.
Pehrson, B., K. Ortman, N. Madjid and U. Trafikowska. 1999. The influence of dietary selenium as selenium yeast or sodium selenite on the concentration of selenium in the milk of suckler cows and on the selenium status of their calves. J. Anim. Sci. 77:3371-3376.
Roch, G. M. Boulianne and L. de Roth. 2000. Effects of dietary vitamin E and selenium source on incidence of ascites, growth performance and blood glutathione peroxidase in cold-stressed broilers. Poster presented at Southern Poultry Science, Atlanta, Georgia, January 17-18.
Surai, P.F. and N.H.C. Sparks. 2000a. Effect of the selenium content of the maternal diet on the antioxidant system of the yolk. Proceedings, Winter Meeting, British Society of Animal Science, Scarborough, UK, March 20-22.
Surai, P.F. and N.H.C. Sparks. 2000b. Effect of the selenium content of the maternal diet on the antioxidant system of the newly-hatched chick. Proceedings, Winter Meeting, British Society of Animal Science, Scarborough, UK, March 20-22.
Vlahovic, M., Z. Pavlovski, B. Zivkovic, M. Lukic and G. Marinkov. 1998. Influence of different selenium sources on broiler performance. Yugoslav Poultry Science, Vol. 3:3-4.
Wang, C. and R.T. Lovell. 1997. Organic selenium sources, selenomethionine and selenoyeast, have higher bioavailability than an inorganic selenium source, sodium selenite, in diets for channel catfish (Ictalurus punctatus). Aquaculture 1522.
Wakebe, M. 1998. Feed for meat chickens and feed for laying hens. Japanese Patent Office, Application Heisei 8-179629. Published Jan. 27.
Wolter, B., M. Ellis, F.K. McKeith, K.D. Miller and D.C. Mahan. 1999. Influence of dietary selenium source on growth performance and carcass and meat quality characteristics in pigs. 1999. Canadian J. Anim. Sci. Vol. 79(No. 1):119-121.