Jing, Chongqing Academy of Animal Husbandry 402460.

Abstract: Rare earth elements are composed of 17 elements, and rare earth elements and their compounds have special physical and chemical properties. In China, some rare earth salts and lanthanides (such as lanthanum and cerium) have been used as feed additives in livestock and poultry production for more than 40 years. A large number of documents show that adding trace rare earth mixture into feed can not only increase the weight of pigs, cattle, sheep and chickens, but also increase the output of milk and eggs. In recent five years, many western countries imported rare earth elements from China as feed additives for pig research. The results show that rare earth elements can improve the daily gain of pigs and the feed conversion rate, and are a new, safe and affordable growth promoter. In this paper, the application research results of rare earth elements, especially lanthanides, in agriculture, especially in pig industry at home and abroad are reviewed, and their potential mechanism is expounded in order to provide reference for future related research.

Key words: rare earth elements, lanthanides, pigs, weight gain, feed conversion rate

1. Introduction

For more than 50 years, antibiotics, as feed additives, have effectively prevented and controlled the occurrence and prevalence of livestock and poultry diseases, but at the same time, they have brought many adverse consequences, such as drug residues in meat; Environmental pollution caused by feces; Excessive use makes animals dependent on antibiotics, and even produce drug resistance. Since the end of 2005, antibiotics as feed additives have been completely banned in the European Union. At present, the global population is increasing, and the demand for animal protein is increasing. The only way is to increase meat production. However, the total ban on antibiotics will seriously affect the health and yield of weaned animals. Therefore, it is urgent to establish animal health care strategy and develop new feed. People need new auxin substitutes as feed additives, which must be effective, safe and conducive to environmental protection. Such as probiotics, probiotics, enzymes, organic acids, Chinese herbal medicine extracts and the like.

At present, people are concerned about a new type of rare earth element or rare earth element mixture additive, including scandium, yttrium and lanthanide elements from lanthanum to lutetium. Rare earth elements are not very rare in the earth's crust, but their quantities are limited. Especially lanthanum (La, element 57), cerium (Ce, element 58) and praseodymium (Pr, element 59). Lanthanum and cerium are not too rare, because they mainly exist in geological areas with similar geological concentrations to the important trace element cobalt. Since 80% of the world's rare earth elements exist in China, China has become the main supplier of these elements, which are mainly exported to other countries in the form of concentrates, oxides and alloys. Rare earth elements are mainly used in metallurgy, chemical industry, electronic industry and agriculture. Among them, about 25% lanthanum ore is used to make carbon arc lamps; 25% is used to produce lanthanum-cerium alloy, which can be used to produce flint lighters, magnesium alloys and some alloy iron; 25% is used in the glass industry: for example, neodymium praseodymium mixture, cerium salt and other lanthanide elements have important uses in the process of glass coloring and decoloration. Finally, 25% of lanthanum products are used in other industries, such as TV devices, catalysts, lasers, feed additives and so on.

2. Application of rare earth elements in domestic agriculture

2. Application of1.in planting industry

In China, rare earth elements, usually a mixture of cerium, lanthanum and praseodymium, have been used as fertilizer enhancer in agricultural planting for more than 40 years and have achieved fruitful results. The reasons for promoting growth and increasing yield are not clear, but it is speculated that the interaction between rare earth elements and calcium elements may affect the structure and function of plasma membrane, and enhance photosynthesis and enzyme activity.

These effects have been confirmed by other countries. In Australia and Britain, scientists have found that soil containing rare earth elements can increase crop yield by 15% and will not remain in agricultural products. In the study of water solubility, Tucher et al. proved that lanthanides in the culture medium have a strong influence on minerals in plants, but because the salts of rare earth elements are water-soluble, the soil concentration will not increase greatly.

2.2. Application in aquaculture

China has conducted many studies on aquaculture and reported many achievements. These reports point out that adding a small amount of rare earth elements to feed can not only increase the weight of cattle, pigs, chickens, fish and rabbits, but also increase the output of milk and eggs. In addition, the feed conversion rate of all the above varieties has improved.

Rare earth elements can enhance the growth performance of pigs. He Ruogang et al. (1998) found that the average weight of piglets fed diets supplemented with rare earth elements was 7 kg (5-9 kg), and the weight could be increased by 5%-23%[ 1]. The feed conversion rate can be increased by 4%, reaching 19%. 13- 17kg body weight group, the body weight can be increased by 1 1% to 20%, and the feed conversion rate can be increased by 5% to 9% [2]. Chen Qiao et al. (1994) found that growing-finishing pigs (30-50kg) with rare earth additives can increase their body weight by 9%- 13% and increase the feed conversion rate by 6%-8% [3]. According to the latest article published by Wang and Xu (2003), the weight can be increased by 65438 03% and the feed conversion rate can be increased by 7%.

Generally speaking, some specific rare earth elements are not added to feed, but a mixture of cerium, lanthanum, praseodymium and other lanthanides. Earlier studies mainly used nitrates and chlorides of these rare earth elements, while recent studies mainly used organic salts such as citric acid and glucose, sometimes supplemented by amino acids such as methionine, lysine and glutamine.

Different studies use different concentrations. In China, the concentration of pig feed is generally 100 -600 mg/kg. The large concentration difference leads to the lack of comparability of research data, which makes it more difficult to understand the mechanism of rare earth elements.

3. Research and application of rare earth elements in foreign breeding.

The feeding conditions in Europe and America are obviously different from those in China. They pay more attention to the breeding of livestock breeds and the optimization of feed, and the susceptibility of livestock to growth promoters and enhancers is low.

From 65438 to 0999, Lambeck and others first conducted a series of pig-raising experiments. Seventy-two German and Pitland piglets with an average weight of 7 kg were divided into two groups. The control group was fed with pure lanthanum chloride (99.7% lacl 3·6h2o), while the experimental group was fed with 38.0% Lacl3 6H2O+52.1%Cecl3 6H2O+3% CrCl3 6H2O, 75 mg/kg, 65438+. 52.7% barley, 20% wheat, 18.8% beans) for five weeks. The results show that the experimental group fed with mixed rare earth elements has the best effect. When the body weight increased by 5%, the feed conversion rate increased by 7% (P < 0.05 > [4]. In another experiment conducted by He (200 1), hybrid piglets weighing 17.5 kg were fed a formula containing 300 mg/kg of rare earth elements. After one month, the weight of the experimental group increased significantly 19%, and the feed conversion rate increased 1 1%. After continuous addition for one month, the body weight was 65438 02% higher than that of the control group, and the feed conversion rate was 3% higher. In the pig farm experiment in Switzerland, pigs were divided into two groups, one group with 97 piglets (initial weight 1 1.2 kg) and the other group with 176 piglets (initial weight 8.3 kg) (Schweizer Edelschwein, 2003). Feeding 16 days and 30 days respectively, compared with the control group, the weight of the experimental group added with 200 mg/kg rare earth element mixture increased by 3%- 10%, and the feed conversion rate increased by 2%-9%. This is the first pig farm experiment that proves that rare earth elements are effective as additives.

Because of the existence of negative ions, the bioavailability of rare earth salts will be affected, and the influence of citrate in rare earth elements should also be considered. Halle et al. (2003) found that citrate can significantly increase the weight of chickens by 7%. However, Schuller et al. (2002) found that under the same conditions, chloride could neither increase body weight nor improve feed conversion rate, so citrate was widely used in piglet feeding experiments. In addition, because citrate is less hygroscopic than chloride, it is easier to be used as feed additive. In the six-week feeding experiment, 28 piglets (7 piglets in each group, weighing 8.6 kg) were added with 50 mg, 100 mg and 200 mg citrate respectively. According to the dose ratio, the weight gain was as high as 22%, and the feed conversion rate was 19%. Kessler's research in 2004 found that citrate had a significant promoting effect on the whole fattening period. When it was added to the feed at the concentration of 250 mg/kg, it took 65,438+002 days for the control group to reach 65,438+004 kg. The experimental group only needs 93 days; The daily gain was 782g/day versus 85 1 g/day; The feed conversion rate is 2.5 VS 2.4, respectively; The difference is particularly significant.

Rare earth elements have no effect on the health of livestock and the quality and safety of meat products. The quality test data of carcass and meat show that all the meat tested is Grade E or Grade U (the two highest grades, EUROP grade system). Other meat quality parameters are not affected by rare earth elements, such as PH 1 and PH24, and the meat color and lean meat percentage are normal. From the muscle, liver and kidney samples of experimental pigs, the contents of rare earth elements in experimental group and control group are very low. Although the content of lanthanum in the experimental group is higher than that in the control group, the deposition rate of lanthanum in all experimental pigs is very low, close to the detection limit.

Some studies have also found that rare earth additives have no effect on body weight and feed conversion rate. For example, Halle(2003) and others conducted fattening experiments on pigs. Different rare earth elements were added to the feed at the concentration of 100 mg/kg, but it did not show the effect of promoting growth, probably because the concentration in this experiment was too low. In another experiment, rare earth chloride (300 mg/kg feed) had little effect on weight gain (-4.7% control group) and feed conversion rate (+1.3% control group).

4. Conclusion

At present, the mechanism of the significant effect of rare earth elements on pig performance is not very clear. It is considered that although rare earth elements absorbed by gastrointestinal tract are few, they can affect the composition of gastrointestinal microorganisms, thus promoting the digestion and utilization of nutrients in diet. High concentrations of lanthanides can usually inhibit the growth of bacteria, while low concentrations of lanthanides may promote the growth of bacteria.

Rare earth elements have the characteristics of trace elements and can be classified as nutritional additives; It can also increase the digestive rate of gastrointestinal tract, stabilize beneficial bacteria, and can be used as a probiotic additive. Judging from the application effect of pig industry at home and abroad, rare earth elements are a new feed additive with high efficiency, low cost and safety.

refer to

1. He Ruogang, Xia Zhongsheng, Effect of Rare Earth on Performance of Growing-finishing Pigs, Guangxi Agricultural Science.

1998 (5)-243-245

2. Li Defa, Yu Weimin, Effects of Rare Earth Addition on Growth Performance and Nitrogen Balance of Growing Pigs, Feed Expo.

1992 (4)-3-4

3. Chen Qiao, Gao Jiahua, Apparent digestibility of rare earth and the effect of adding rare earth on apparent digestibility of crude protein and crude fat in diet, Jiangsu Agricultural Science1994 (1)-59-61.

4. Lambeck, He, Zhang Junjie, Arnold, Henkelmann, Li. Possible role of sub-and rare earth elements as growth promoters. In: vitamin undZusatzstoffe in men and Tier. Seminar, 22-23 September, 1999, Jena/Thuringia, Germany, pp. 3117 (1999).