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Weaning is a decisive moment in the performance of pigs throughout their lives. In general, gastrointestinal diseases are the main loss of profitability in animal production. Adam Moeser, Ph.D., DVM, Michigan State University, said that intestinal function and disease susceptibility are multifactorial, involving the interaction between pathogens, pigs and the environment.
His years of research have shown that the presence of pathogens alone is not enough to trigger the disease process. However, environmental influences, such as stressors present in the production system (see Figure 1), can exert tremendous pressure on the immune barrier and open up pathways for disease invasion.
Although every piglet suffers from some anxiety during the weaning process, minimizing stress during this period can enhance immune function and thus contribute to efficient growth. Christopher Chase, a researcher at South Dakota State University, Ph.D. DVM, said that research has shown that physical and psychological stress suppresses the animal’s immune system, ultimately leading to an increase in the incidence of infectious diseases. Although the news seems to have broken records, minimizing stress is essential to avoid weaning lag by breeding healthy pigs.
Protecting pigs starts from the intestines. The development of intestinal immunity can determine the response of pigs to future pathogens. For pig producers, there are several ways to reduce the stress load of young pigs, including starting with a better understanding of intestinal dynamics and its important role in the immune system.
Chase said, Imagine the body's digestive system as a hollow plastic tube. Food is digested in the hole of the tube and never enters the solid plastic material. Within the plastic barrier, the defense layer controls the immune response. The mucosal immune system provides the first immune defense barrier for more than 90% of potential pathogens in the gastrointestinal tract. It not only prevents harmful pathogens, but also helps to make the immune system tolerate (make the body not react) tolerant of dietary antigens and normal microbial flora, which are essential for growth and development. The mucosal immune system develops in the first six weeks after birth in newborn pigs (see Table 1).
As a major participant in the immune system, intestinal epithelial cells represent the largest part of the immune system and the largest interface between pigs and the outside world. Moeser explained that monolayer epithelial cells play an important synchronization role by absorbing effective amounts of nutrients and water and transporting electrolytes, while still providing a barrier to trillions of bacteria, antigens, and poisons.
Chase further explained that one thing that protects pigs in the respiratory and digestive tracts is an antibody called IgA. It adheres to infectious agents and prevents them from attaching to epithelial cells, thereby performing an important immune task on the mucosal surface.
Environmental factors can significantly affect the gut-associated lymphoid tissue (GALT) located in the mucosal immune layer. Chase said that when most commercial pigs are weaned at 14-24 days of age, their GALT is stunted and usually not completed. He added that the environmental impact is greater after birth and at weaning. At birth, colostrum is important for the development of the intestines. It also contains high levels of transforming growth factor, has anti-inflammatory effects and accelerates IgA antibodies. Colostrum also contributes to the development of normal microbial flora. At weaning, environmental factors also increase the risk of infection. Since pigs are no longer breast-feeding, they cannot obtain breast milk that regulates the immune response. This will disrupt the active immune balance of the weaned pig. Chase said that the severity of this "weaning" GALT crisis depends on the degree of expansion of the immune system before weaning.
Usually, the intestines of weaned pigs will overreact. Chase said: “The piglet’s intestines do many things besides absorption and secretion. To a certain extent, it is also the eye of the immune system.” Therefore, pig producers can send correct signals to epithelial cells before weaning. They shouldn’t overreact anything they did before that would make healthier pigs less susceptible to disease, Chase said.
In order for the immune system to function optimally, it must receive a proper balance of nutrients, including key vitamins and trace minerals-vitamins A, C, E and B complex vitamins, copper, zinc, magnesium, manganese, iron, and selenium. Chase said that establishing a reliable creep plan is a good starting point. Short-chain fatty acids can provide fuel for epithelial cells. Although this research on pigs is still in its infancy, the introduction of probiotics and prebiotics may bring benefits. These probiotics and prebiotics can produce metabolites that enhance the beneficial bacteria in the gut. However, Chase warned that more research on these products needs to be completed before the full nutritional potential of these products can be fully understood.
In addition, the route of vaccine administration is important for mucosal immunity, Chase said. "In order to induce secreted IgA on the mucosal surface, the vaccine preferably enters the human body through the mucosal surface. This can be achieved by feeding the vaccine to the animal, nebulizing the vaccine for inhalation or exposure in the breast," he explained.
The actual age at which pigs are weaned is indeed a personal decision of the farm. Nevertheless, it is important to recognize that Moeser’s research on how gastrointestinal dysfunction caused by early weaning is attenuated in pigs through delayed weaning and mast cell blockade shows that early weaning around 19 days of age can cause additional pain. In nature, the weaning process is more gradual than modern production practices. At weaning, piglets face sudden changes in the environment and diet, transportation pressure and increased exposure to pathogens, as well as the struggle of social hierarchy and motherhood separation.
Although the magic age and the actual procedure are very controversial, it is necessary to admit that Moeser's research confirms that premature weaning can have harmful effects on the intestinal tract and cause intestinal barrier disorders. In pigs weaned at 18 days, Moeser and his team found that intestinal permeability increased significantly or barrier function was impaired after 24 hours. In contrast, the intestinal permeability response of pigs weaned at 28 days of age was significantly different, with a slight increase in intestinal permeability after 24 hours of weaning. In addition, Moeser found that late-weaned pigs (28 days of age) had a significant increase in cortisol one day after weaning compared to early-weaned pigs.
Generally speaking, anxiety can cause the destruction of normal intestinal function in early weaned pigs, which plays an important role in intestinal diseases after weaning. Taking the research a step further, Moeser's team tracked the long-term effects of early weaning pressure on intestinal permeability. Although all piglets have decreased intestinal permeability after weaning, it is still higher than the high level of piglets after weaning. Moeser said: "This shows that only in pigs weaned at different ages, there will be continuous long-term changes in the development of the intestinal barrier."
The research team also studied the impact of the early weaning intestinal response on the infectious challenge because the barriers of these pigs are more impaired. In the experiment, both late-weaned and early-weaned pigs were introduced with subsequent enterotoxigenic E. coli. Four days after the challenge, the late-weaned pigs recovered, but the early-weaned pigs had obvious intestinal damage to this dose of enterotoxigenic E. coli. From the perspective of immune response, late weaning pigs have a strong response to E. coli, while early weaning response is suppressed.
In summary, Moeser said that early weaning pressure affects lifelong gut barrier function in the following ways:
Taking the research further, Moeser's team found that pigs less than 21 days old maintain a greater number of mast cells in the intestine, which has a major impact on the integrity of the intestinal barrier. Moeser said that mast cells are important for the immune response of pigs and other animals. Researching mast cells, scientists have found that mast cells play a key role in the intestinal permeability of early-weaned pigs. Specifically, the degranulation of mast cells in the intestinal mucosa of early-weaned piglets is stronger than that of late-weaned intestinal mucosa, which means that the intestinal inflammation will be more and more “leaky”.
Moeser said his research shows that common production stress factors are related to the intestinal barrier and gastrointestinal physiology. Stress increases intestinal permeability, affects mast cell activation and increases infection challenges. In addition, he added that this will affect feed efficiency through impaired digestion and absorption, continuous activation of the gastrointestinal immune system, or changes in the microbiome. These are all factors that can change the physiology of the gastrointestinal tract and negatively affect the way pigs handle nutrients.
The shortest time for pigs to fast and drink is very important. Certain management practices need to be adjusted. Shorter transportation times and fewer pig movements will reduce the time away from feed and water.
High-quality feed that is similar to peristaltic feed and is easy to digest will also help reduce the lag time of feed consumption. Chase said: “The higher the digestibility, the more likely the weaned pig’s intestinal absorption.”
In many cases, the importance of keeping pigs hydrated is overlooked. Clean water should always be provided. Although it may be easy to obtain clean water, this does not guarantee that newly weaned pigs will know how to find it when they arrive at the new facility. Water is necessary for immune cells to travel, absorb things, and reach the surface. IgA must be secreted. "If the animal is dehydrated and the secretions are very viscous or unable to discharge, it will not do any good for the pig," Chase explained.
Chase said that having a healthy microbiome is important. The intestine contains the most diverse bacterial community-called the microbiota-which plays an important role in preventing pathogen colonization and infection. Removing the piglet from the sow’s milk makes it extremely susceptible to intestinal diseases, partly because it disrupts the balance between the development of beneficial microorganisms and the establishment of intestinal bacterial pathogens.
Chase said that the use of oral antibiotics can change the community because antibiotics can eliminate good bacteria in the intestine, regardless of whether they are good or bad. Therefore, he recommends limiting oral antibiotics at weaning.
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