Trace minerals are important nutrients in diets for swine and poultry. They are required for growth, bone development, feathering in chickens, enzyme structure and function, and appetite. Over the past 20 years, scientists in the LSU AgCenter have played an important role in understanding the need for and use of trace minerals in diets for animals. Our involvement is due in part to the potential for increased bioavailability of the organic mineral to the animal, which could result in the need to feed lower levels of the mineral to get the same or greater response. Furthermore, the increase in bioavailability could result in decreased excretion of the mineral into the waste, which will reduce environmental impact.
The majority of the mineral work we have conducted at the LSU AgCenter has been examining the use and comparison of organic and inorganic trace minerals, particularly chromium, zinc and selenium, for swine and poultry. For clarification, organic in this sense means that the trace mineral of concern is attached to or associated with a compound that contains carbon, and it is not to be confused with the term “organic meat production,” which is a system of animal production.
One of the first trace minerals that we began working on more than 15 years ago was chromium. Chromium is a trace mineral that is involved in glucose metabolism, and without chromium, insulin cannot properly remove glucose from the blood after a meal. Before our research efforts in animals began at the LSU AgCenter, most of the research conducted with chromium was with humans. Research with chromium in swine and poultry showed that organic chromium (and not inorganic chromium) improved carcass traits and quality in pigs, increased the number of pigs born alive and increased egg production in hens. Research in the AgCenter and elsewhere has led to the use of chromium in swine diets throughout the world and the allowance by the U.S. Food and Drug Administration of three organic chromium sources for use in swine diets. The beneficial effects of organic chromium include more pigs weaned per sow per year and an improvement in the amount and quality of pork produced.
We also have conducted research with broilers to assess the bioavailability of organic and inorganic sources of zinc. The results of these trials indicate that organic zinc sources consistently have increased bioavailability to broilers relative to the inorganic form, zinc sulfate. This response indicates that more zinc from organic sources was absorbed and used by the broiler than zinc from inorganic sources, which could result in decreased excretion of zinc into the litter.
Research also has been conducted to examine the effects of removing zinc from chicken diets. When zinc is completely removed from the diet, growth performance and bone strength are negatively affected. Removing zinc from chick diets after they have been fed a diet with added zinc does not always elicit this negative response, indicating that zinc has to be added in the diet from day of hatch, but it may be removed later.
It is common practice in the swine industry to include very high levels of zinc oxide in nursery diets because of the increased growth performance during this critical time period. Many people have suggested that this increased growth is due to the potential antibiotic-like effects that zinc has on the gastrointestinal tract. With this in mind, we attempted to examine the ability of sows to transfer the health effects of organic or inorganic zinc sources to their progeny during lactation – the time when they produce milk – and then determine how these same progeny performed during the nursery phase of growth when either zinc source was included in their diets.
The sows were fed diets with either zinc sulfate or an organic zinc source in addition to the zinc from their trace mineral premix from the time of breeding through weaning their piglets. There was no advantage of the organic zinc source to the sow during gestation compared with the inorganic source. Furthermore, there was little benefit to the baby pig during lactation when the sow had been fed the organic zinc source. However, there was a very large increase in total pigs born and born alive in sows fed organic zinc. The increased number of pigs did not result in a reduced pig birth weight. During the nursery period of growth, there was no advantage on growth performance or intestinal health to having additional zinc, regardless of form, above the level typically found in trace mineral premixes.
One of the most interesting trace minerals from a historical point of view is selenium. After its discovery in 1817, it was determined to be toxic and carcinogenic to animals. In 1957, however, selenium was determined to be dietary essential to animals to protect them from disorders such as liver necrosis, exudative diathesis and pancreatic fibrosis. In 1973, selenium was determined to be an essential nutrient. It is still considered to be the most toxic trace mineral that is added to diets for swine and poultry. Because of this potential toxicity, the FDA regulates the inclusion of selenium in animal feeds. The FDA recently approved the use of some organic sources of selenium. We have conducted several experiments to compare the commercially available inorganic and organic selenium sources for their use in diets for broilers and laying hens. The sources we used were sodium selenite and selenium-enriched yeast (seleno-methionine). There was no difference in selenium source on egg production, but there was an increase in the percentage of cracked eggs from hens fed organic selenium. However, selenium concentration in the eggs from hens fed selenium-enriched yeast was much greater than those from hens fed sodium selenite, which indicates an increase in availability of organic selenium to the laying hen.
In other research, the source of selenium did not affect growth performance of commercial broilers, but there was an increased tissue selenium concentration, similar to what we previously had observed in eggs from hens fed selenium-enriched yeast. Subsequent research indicated that the selenium from selenium-enriched yeast that was stored in the tissues could be used to maintain the selenium nutritional status of the broiler. These results indicate that organic selenium sources are available for use in selenium-dependent activities, even after they have been stored in body tissues such as liver or muscle. As such, the selenium-enriched yeast maintains higher levels of nutritional activity than sodium selenite over time. Therefore, depending on price, the organic selenium sources should be considered a suitable form of selenium for inclusion into poultry diets.
Organic trace mineral sources seem to have higher bioavailability than inorganic sources, and in some instances, they result in greater productivity. However, cost effectiveness must still be considered.
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