With the widespread and improper use of antibiotics, their negative impacts have become increasingly evident. These include the disruption of normal microbial populations in animals, leading to an imbalance in the microecological system; the promotion of resistant bacterial strains; increased sensitivity of susceptible habitats, which can lead to both exogenous and endogenous infections; and the weakening of the immune system in animals. Moreover, antibiotic residues in animal products like meat, eggs, and milk pose serious threats to human health. They may also cause teratogenic effects or even lead to poisoning and death in both humans and animals.
Since the 1981 "three-in-one" injection incident in the UK, where excessive use of antibiotics and hormones triggered mad cow disease, many countries—especially those in Europe, the US, and Japan—have implemented strict regulations on the use of feed antibiotics. The European Union, for example, banned the addition of any antibiotics to animal feed after 2005. In parallel, there has been a strong push toward developing and promoting green, safe alternatives to antibiotics in feed.
This article reviews one of the promising research areas: the application of microbiological additives in dairy cow feed, as part of the broader effort to replace traditional antibiotics with eco-friendly options.
**1. Feed Microorganisms Used in Dairy Cow Production**
Microbiological agents for dairy cows typically consist of bacterial and fungal preparations, along with their active cultures. Ideal strains should be non-pathogenic, not produce harmful hybrids, and exhibit high viability and stability after processing. Ideally, they should originate from the animal’s own gut.
**1.1 Bacteria**
Commonly used bacteria include *Bacillus*, *Lactobacillus*, and *Streptococcus*. Among them, *Bacillus* species such as *Bacillus subtilis*, *Bacillus cereus*, and *Bacillus licheniformis* are widely applied. These bacteria form spores that are highly resistant to heat, acid, and pressure, making them stable during feed processing and storage. They also produce various enzymes like cellulase and glucanase, which aid in digestion and improve feed conversion rates. As aerobic bacteria, they help maintain the balance of the gut microbiome by capturing oxygen, supporting the growth of beneficial anaerobic microbes.
**1.2 Lactic Acid Bacteria**
Lactic acid bacteria, including *Lactobacillus*, *Bifidobacterium*, and *Enterococcus*, are commonly used due to their ability to produce lactic acid, vitamins, and antimicrobial substances. However, these bacteria lack spores, making them less stable during storage. To enhance their viability, microencapsulation is often required, which increases production costs and limits their widespread use.
**1.3 Fungi**
Fungal probiotics mainly include yeast and *Aspergillus* species. Yeast improves rumen function, enhances nutrient absorption, and supports the growth of beneficial microbes. *Aspergillus* species, such as *A. niger* and *A. oryzae*, produce enzymes like cellulase and phytase, which break down plant cell walls and improve fiber digestion in ruminants.
**2. Mode of Action of Microbial Feed Additives**
These additives work by stimulating the growth of beneficial microbes, regulating the gut environment, and inhibiting pathogenic organisms. They also enhance the activity of digestive enzymes, increase nutrient absorption, and support immune function. By improving rumen fermentation, they promote better feed utilization and higher milk production.
**3. Application in Dairy Production**
Studies show that microbial additives can significantly boost milk yield, improve milk composition, and enhance feed efficiency. For instance, yeast cultures have been shown to increase milk production by up to 7.8% and improve milk fat content. They also help reduce the negative effects of heat stress, maintaining productivity during hot seasons.
In addition, microbial additives contribute to better reproductive performance, with some studies reporting increased estrus rates and conception rates in dairy cows.
Overall, microbial feed additives offer a sustainable alternative to antibiotics, supporting both animal health and the production of safe, high-quality food products.
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