With the widespread and excessive use of antibiotics, their negative impacts have become increasingly evident. These include the destruction of the normal microbial population in animals, leading to an imbalance in the micro-ecological system; the promotion of resistant strains; increased sensitivity of susceptible habitats, which can lead to both exogenous and endogenous infections; interference with the immune function of animals, reducing their resistance to diseases; and the presence of antibiotic residues in animal products like meat, eggs, and milk, which pose a threat to human health. Additionally, these residues can be teratogenic or even cause poisoning and death in humans and animals. A notable example occurred in the UK in 1981, when large-scale use of "three-in-one" injections containing antibiotics and hormones led to the "mad cow disease" outbreak. In response, countries around the world—especially Europe, the U.S., and Japan—implemented strict regulations on antibiotic usage, limiting their types, dosage, and compatibility. Since 2005, EU countries have banned the addition of any antibiotics to animal feed. At the same time, there has been a growing emphasis on researching and promoting green feed additives as alternatives to antibiotics. This paper reviews the application of microbial additives, one of the most promising green feed additives.
1. Feed Microorganisms Used in Dairy Production
Microecological preparations for dairy cows mainly include bacterial and fungal cultures. The ideal strain for these preparations should be safe for both humans and animals, not easily hybridizing with pathogenic microbes, and capable of rapid growth both in vivo and in vitro. They should also have high survival rates after processing and ideally be isolated from the animal’s own gut.
1.1 Bacteria
Common bacterial strains used in dairy cow microecological preparations include *Bacillus*, *Lactobacillus*, and *Streptococcus*.
1.1.1 *Bacillus*
*Bacillus* species are spore-forming bacteria that exhibit strong resistance to stress, acid, alkali, and high temperatures. Their ability to produce various enzymes such as cellulase and glucanase helps improve digestion and nutrient absorption. These bacteria also help maintain gut microecology by supporting the growth of beneficial microbes.
1.1.2 Lactic Acid Bacteria
Lactic acid bacteria, including *Lactobacillus* and *Bifidobacterium*, play a key role in maintaining gut health. They produce lactic acid and other substances that inhibit harmful bacteria, enhance immunity, and promote overall digestive efficiency.
1.2 Fungi
Fungal-based microecological preparations, such as yeast and *Aspergillus*, are also widely used. Yeast improves rumen fermentation and enhances nutrient utilization, while *Aspergillus* produces enzymes like cellulase and phytase, aiding in fiber digestion and phosphorus absorption.
2. Mechanism of Action of Microbial Feed Additives
Microbial additives work by stimulating the growth of beneficial bacteria, regulating the gut microecological balance, and enhancing nutrient absorption. They also inhibit pathogenic bacteria and boost the immune system of dairy cows, ultimately improving milk production and overall health.
3. Application of Microbial Feed Additives in Dairy Cow Production
Studies have shown that microbial additives can significantly increase milk yield, improve feed conversion, reduce heat stress, and enhance reproductive performance. For instance, research has demonstrated that yeast cultures can increase milk production by up to 7.8%, while lactic acid bacteria help reduce the incidence of diarrhea and improve weight gain.
In conclusion, microbial feed additives offer a sustainable and effective alternative to antibiotics in dairy production, contributing to improved animal health, productivity, and food safety.
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