Now is a new era for pig farming, characterized by high investment in technology, a focus on cost-effectiveness, and efficiency. Nowadays, the pig farming industry requires a broader perspective and holistic thinking, as well as highly skilled industry professionals and managers. After enduring outbreaks of diseases such as circovirus, foot-and-mouth disease, and highly pathogenic blue ear disease, and adjusting national policies, rural family farming and small to medium-sized pig farms have gradually been phased out of the market. With increased capital investment, feed companies have developed large-scale integrated farming, while farming cooperatives are moving upstream to develop feed mills. The influx of funds from other industries like the internet, finance, and energy and mining has led to the rapid growth of farming companies. Combined with years of vaccine usage, management improvements, and evolving ideologies, large-scale outbreaks of infectious diseases have been largely eradicated. After stabilizing pig farm production, the focus has shifted to reducing feed-to-meat ratios, improving meat quality, and achieving faster growth rates. For pig farmers, the importance of growth promotion has become even more pronounced. This article briefly introduces several growth-promoting feed additives and their pros and cons for reference.

1. Antibiotics

The primary mechanism by which antibiotics promote pig growth is through their bactericidal and bacteriostatic effects. They can inhibit the reproduction of harmful microorganisms in the gastrointestinal tract, prevent toxin production, reduce intestinal wall thickness, facilitate nutrient absorption, and thereby improve feed efficiency and promote pig growth. However, with the emergence of antibiotic resistance and concerns about their impact on human health, many countries and organizations have prohibited the use of antibiotics in feed and restricted certain functions, prompting feed mills and farming companies to seek safer and more effective alternatives.

2. Traditional Chinese Medicine Additives and Extracts

Traditional Chinese medicine additives mainly function in disease prevention, health maintenance, improving animal production performance, enhancing product quality, and improving feed quality. Although the use of Chinese herbs has a long history and a variety of types, differences in origin, medicinal parts, and preparation methods result in varying efficacies. Modern scientific research shows that active ingredients in Chinese medicine, such as polysaccharides, total flavonoids, alkaloids, glycosides, volatile oils, and amino acids, can achieve optimal therapeutic effects through extraction and purification processes. However, the diverse range of Chinese medicines means that not all are effective, as some components previously considered ineffective have been found to be biologically active, while some effective components in other Chinese medicines may be ineffective.

3. Probiotics and Derivatives

Various functions can sometimes produce synergistic effects and promote each other.

Prebiotics, such as dietary fiber and oligosaccharides, are non-absorbable by animals but can provide nutrients to beneficial gut bacteria, indirectly promoting the growth and proliferation of probiotics.

Probiotics, like Bacillus, directly participate in gut microbiota balance by competitively occupying nutrients and living spaces, improving gut health and promoting growth.

Metabolites of probiotics, such as acids and enzymes, have functions like improving blood pressure and enhancing immunity. Many antibiotics and enzyme preparations are produced through bacterial fermentation.

4. Nutritional Additives

They can be categorized as follows:

• Enzyme preparations, such as proteases, cellulases, amylases, and composite enzymes.

• Organic acids and their salts, like citric acid, salicylic acid, formic acid, lactic acid, and acetic acid.

• Functional amino acids.

• Vitamin supplements. For example, the demand for multivitamins increases by 10% in the feed of high-yielding sows.

• Trace element supplements. After the introduction of new regulations, stricter limits on the content of copper, iron, zinc, and arsenic in feed have been imposed. Inorganic trace elements are gradually being replaced by organic ones, with the mechanisms of yeast selenium and amino acid chelated metal ions being clear, and the required amounts being smaller.

5. Modern Biotechnology and Genetic Engineering Applications

This includes steroids, beta-adrenergic agonists, adipokines, and growth hormones.

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

Cysteamine (CS), a hormone-regulating growth-promoting additive, chemically known as β-mercaptoethylamine, is a white crystalline substance with alkaline properties. It can be considered as the decarboxylation product of cysteine. Its molecular formula is (C2H6NS)2Zn, with a molecular weight of 77.15. Growth hormone in animals is the most potent endocrine hormone promoting growth. GH is dually regulated by the hypothalamic secretion of growth hormone-releasing hormone (GHRF) and somatostatin. Research shows that cysteamine's active mercapto groups can chemically modify somatostatin's disulfide bonds, altering its molecular structure and physiological activity, thereby reducing somatostatin levels, increasing growth hormone levels, and promoting animal growth. Additionally, cysteamine can reduce dopamine breakdown in animals, promote hypothalamic synthesis and secretion of growth hormone, and is also one of the growth-promoting pathways.

Cysteamine is a simple chemical with low production costs, can be ingested with feed, absorbed through the digestive tract, and is suitable for use as a feed additive. In contrast, growth hormones and growth hormone-releasing hormones are protein and peptide endocrine hormones with high production costs and can only be injected. Oral administration results in degradation in the digestive tract. Unlike growth hormones, cysteamine is not species-specific and is effective for poultry, pigs, and ruminants. However, cysteamine has significant drawbacks, including a strong odor and bitter taste, making it unsuitable for direct addition to animal feed. Moreover, cysteamine hydrochloride is highly oxidizable and hygroscopic, quickly oxidizing during granulation, coating processes, and product storage, affecting product efficacy. Therefore, several challenges need to be addressed to use cysteamine in feed production:

1. Maintain cysteamine stability during storage and feed processing;
2. Maintain cysteamine stability and physiological activity in the body;
3. Maintain physiological homeostasis, preventing negative feedback of growth hormones, etc.;
4. Easy deliquescence, heat-sensitive, with a melting point of 66℃ to 70℃, poor palatability, and easily oxidized in neutral and alkaline environments.

Functional amino acids like cysteamine, lysine, and taurine can regulate nitrogen metabolism (Yin Yulong), which can improve pig body shape and meat quality at low protein levels, avoiding the use of lean meat enhancers. Amino acid metal chelation technology can safely utilize trace elements without significant differences in pig nutrition and growth effects. Using cysteamine hydrochloride and heptahydrate zinc sulfate as raw materials, orthogonal experiments optimize reaction conditions to synthesize stable cysteamine zinc complexes. After chemical modification of the mercapto group in cysteamine, its stability is improved, reducing its reactivity with metal elements in feed. Experimental results show that adding cysteamine chelated zinc to pig feed increases feed intake and weight gain, reduces feed-to-weight ratios, and avoids the defects of using cysteamine and its hydrochloride salts. The main advantages are:

1. Cysteamine zinc did not undergo oxidation decomposition due to high temperatures (120℃) during feed processing;
2. In strongly acidic environments, cysteamine zinc decomposes and releases cysteamine, with partial decomposition as acidity decreases;
3. Biologically active research on cysteamine zinc shows that within half an hour in simulated gastric juice, the release rate of cysteamine exceeds 75%. In the animal body's acidic environment, cysteamine zinc decomposes into two cysteamines and one zinc ion.

In fattening pig diets, adding 200g of cysteamine zinc per ton increases weight gain by 4.2%, reduces feed consumption for each kg of weight gain by 6.7%, and reduces diarrhea rates by 44.5% and 49.8%, respectively. Numerous trials have proven that adding cysteamine zinc can effectively improve daily weight gain and lean meat percentage in growing-fattening pigs.