We are now in a new era of pig farming, characterized by high investment, advanced technology, and a focus on cost-effectiveness. Modern pig farming demands a broader perspective and strategic thinking, as well as high-quality industry professionals and managers. After years of battling diseases such as porcine circovirus, foot-and-mouth disease, and highly pathogenic blue ear disease, coupled with policy changes, small-scale pig farming in rural areas has gradually been phased out.

With increased capital investment, feed companies have developed large-scale integrated farming operations, farming cooperatives have expanded into upstream feed production, and funds from the internet, finance, energy, and mining sectors have poured into the industry, driving rapid development of farming companies. Additionally, the use of vaccines and advancements in management practices have largely eliminated the occurrence of large-scale outbreaks of infectious diseases. As a result, the focus has shifted to reducing feed conversion ratios, improving meat quality, and shortening the time to market. For pig farmers, the importance of growth promotion has become even more pronounced. This article provides a brief introduction to several growth-promoting feed additives, along with their advantages and disadvantages, for reference.

1. Antibiotics

The growth-promoting effect of antibiotics in pigs is primarily due to their bactericidal and bacteriostatic properties, which can inhibit the proliferation of harmful gastrointestinal microorganisms and toxin production, prevent disease, reduce intestinal wall thickness, and enhance nutrient absorption. This leads to improved feed utilization and promotes pig growth. However, with the emergence of antibiotic resistance and its associated risks to human health, many countries have implemented bans or restrictions on the use of certain antibiotics in feed. As a result, feed manufacturers and farming companies are increasingly seeking safer and more effective alternatives.

2. Chinese Herbal Additives and Extracts

Chinese herbal additives are primarily used for disease prevention, health maintenance, enhancing animal production performance, improving product quality, and enhancing feed quality. The use of traditional Chinese medicine has a long history, but its effectiveness varies due to the diversity of plant species, differences in origin, medicinal parts used, and preparation methods. Modern scientific research has shown that the unique medicinal components in Chinese herbs, such as polysaccharides, flavonoids, alkaloids, glycosides, volatile oils, and amino acids, can be extracted and purified to achieve optimal therapeutic effects. However, the diversity of Chinese herbs means that their efficacy is not absolute, as some components previously considered ineffective have been found to possess biological activity, while others are effective only in certain contexts.

3. Probiotics and Derivatives

Probiotics, prebiotics, and their derivatives often work synergistically, enhancing each other's effects.

• Prebiotics, such as dietary fiber and oligosaccharides, cannot be directly absorbed by animals but provide nutrition to beneficial gut bacteria, indirectly promoting their growth and proliferation.

• Probiotics, such as Bacillus species, directly participate in microbial balance by competing for nutrients and living space, improving gut health, and promoting growth.

• Probiotic Metabolites, such as acids and enzymes, have functions like improving blood pressure and boosting immunity. Many antibiotics and enzyme preparations are also produced through bacterial fermentation.

4. Nutritional Additives

These can be categorized into several types:

• Enzymes, such as proteases, cellulases, amylases, and complex enzymes.

• Organic Acids and Their Salts, including citric acid, fumaric acid, formic acid, lactic acid, and acetic acid.

• Functional Amino Acids.

• Vitamins: For example, in high-yielding sows, the demand for multivitamins increases by 10% in the diet.

• Trace Elements: With the implementation of new regulations, there are stricter limits on copper, iron, zinc, arsenic, and other elements in feed. Inorganic trace elements are gradually being replaced by organic trace elements, such as yeast selenium and amino acid-chelated metal ions, which have clear mechanisms of action and require smaller doses.

5. Modern Biotechnology and Genetic Engineering

These include steroids, beta-adrenergic agonists, adipocyte hormones, and growth hormones.

Since Szabo reported in 1981 that cysteamine can reduce the level of somatostatin (SS) and increase growth hormone (GH) levels in animals, many scholars worldwide have conducted extensive research on its mechanisms and applications.

Cysteamine (CS) is a growth-promoting additive that belongs to the hormone regulation category. It is a white crystalline compound with a basic pH, chemically known as β-mercaptoethylamine, and can be considered a decarboxylation product of cysteine. The molecular formula is (C2H6NS)2Zn, with a molecular weight of 77.15. Growth hormone (GH) is the most potent endocrine hormone promoting animal growth, regulated by growth hormone-releasing factor (GHRF) and somatostatin from the hypothalamus. Research has shown that the active thiol group in cysteamine can chemically modify the disulfide bonds in somatostatin, altering its molecular structure and physiological activity, thereby reducing somatostatin levels, increasing growth hormone levels, and promoting animal growth. Additionally, cysteamine can reduce the breakdown of dopamine in animals, enhancing the synthesis and secretion of growth hormone in the hypothalamus, which is another growth-promoting pathway.

Cysteamine is a simple chemical substance with low production costs. It can be ingested with feed and absorbed through the digestive tract, making it suitable as a feed additive. Unlike growth hormone and growth hormone-releasing factor, which are proteins and peptides requiring high production costs and must be administered via injection (as they are ineffective when ingested due to degradation in the digestive tract), cysteamine is effective across species, including poultry, pigs, and ruminants. However, cysteamine has significant drawbacks, such as a strong odor and bitter taste, making it unsuitable for direct addition to animal feed. Furthermore, cysteamine hydrochloride is highly prone to oxidation and moisture absorption, leading to oxidation during feed processing and storage, affecting its efficacy. Therefore, to apply cysteamine in feed production, the following challenges must be addressed:

• Maintaining the stability of cysteamine during storage and feed processing.
• Ensuring the stability and physiological activity of cysteamine within the body.
• Preserving physiological homeostasis, ensuring no negative feedback on growth hormone, etc.
• Addressing its hygroscopic nature and poor thermal stability, with a melting point of 66℃ to 70℃, and ensuring palatability.

The technology of functional amino acids like cysteamine, leucine, and taurine can regulate nitrogen metabolism, allowing pigs to achieve improved body shape and meat quality at lower protein levels, avoiding the use of β-agonists. The chelation of amino acids with metal ions ensures the safe utilization of trace elements without significant differences in nutritional and growth outcomes. The synthesis of stable cysteamine zinc complexes through optimized reaction conditions addresses the issues of oxidation and stability. Cysteamine zinc complexes improve the stability of cysteamine by chemically modifying its thiol group, reducing its reductive properties, and minimizing reactions with metal elements in feed. Experimental results show that pigs fed diets supplemented with cysteamine zinc had increased feed intake and weight gain, with improved feed conversion ratios, while avoiding the disadvantages associated with cysteamine and its hydrochloride salts.

The key advantages are:

1. Cysteamine zinc does not undergo oxidative decomposition at high temperatures (120℃) during feed processing.
2. In strong acidic environments, cysteamine zinc decomposes to release cysteamine, with partial decomposition as acidity decreases.
3. Biological activity studies reveal that cysteamine zinc releases more than 75% of cysteamine within half an hour in simulated gastric fluid, following the reaction (C2H6NS)2Zn + 2H+ → 2C2H7NS + Zn2+. In the acidic environment within the animal body, cysteamine zinc breaks down into two cysteamine molecules and one zinc ion.

Adding 200g of cysteamine zinc per ton of feed for finishing pigs can increase weight gain by 4.2%, reduce feed consumption per kilogram of weight gain by 6.7%, and lower diarrhea rates by 44.5% to 49.8%. Extensive trials have demonstrated that supplementing cysteamine zinc effectively enhances daily weight gain in growing-finishing pigs and increases lean meat percentage.