From the 2022 Kemin Intestinal Health Symposium
By Ann Hess Comparing response of early weaned female pigs versus male castrate to gut health challenges, stressors. Biological sex is a major factor that impacts disease risk and mortality, however most of the research in this area has been done on humans, not animals, according to Adam Moeser, professor and Matilda R. Wilson Endowed Chair in the Department of Large Animal Clinical Sciences at Michigan State University. “We know that many immune related diseases and diseases in general do exhibit a sex bias. For example, it's known that females are more susceptible to autoimmune inflammatory disorders, and if you're thinking about gut health disorders, irritable bowel syndrome — one of the most common GI disorders — is two to three times more prevalent in females,” Moeser said. “Whereas males on the other hand, they're more prone to exhibiting mortality, especially in infectious disease outbreaks, as well as other diseases. So, sex is playing a major role in determining disease risk, and an example of current sex biases is the recent COVID-19 pandemic. It's been pretty clear that there is a pretty significant sex bias in mortality, with males much more at risk to develop complications and mortality than females.” Whether it’s from a human or animal perspective, Moeser said studying sex differences is important and could impact disease risk and lead to a greater understanding of disease pathogenesis and targeted strategies. During the recent Kemin Intestinal Health Symposium in Palm Springs, California, Moeser detailed his latest research in this area, examining the interactions between early life adversity and biological sex in shaping disease risk across the lifespan. Previous work has demonstrated that early weaning stress in pigs can result in an early rise in intestinal permeability, with leaky gut often persisting into adulthood. Moeser said he considers this a risk factor for susceptibility to disease. To examine the sex differences, Moeser’s research team compared male castrates versus early weaned females to see which exhibited greater intestinal permeability at 60 days of age. “Early weaning in both the male castrate and the female causes an increase in intestinal permeability that persists well after weaning,” Moeser said. “But interestingly, the female pigs, these are gilts, there is a greater amount of gut leakiness in response to early weaning, that also persists.” Another critical function of the gut is driven by the nervous system, particularly the gastrointestinal nervous system because it regulates barrier properties, such as secretion, absorption and digestibility. “As the animal gets older, the early weaned animals keep the number of enteric neurons. They have a higher level of neurons that remain in their gut, whereas their later weaned pig, they have this normal decline or pruning of this enteric nervous system, so they do have more neurons,” Moeser said. Since enteric neurons are important for responding to a pathogen challenge, Moeser’s team next set out to test that functionally. “What we found was that early weaned pigs have a greater sensitivity to responding to a neuro-agonist in their gut, so they secrete more electrolytes and fluid in response to a stimulus,” Moeser said. They also showed that there is a sex effect here, with the females that are early weaned responding more sensitively to the neuro-agonists compared with the early weaned males. Stool consistency, or the percentage of days that the animals had some form of loose stools, was also examined. Moeser said this data correlated well with their functional measurements showing that the female animals early weaned exhibited greater prevalence of diarrhea. He noted this may reflect that they are more sensitive to fluids secretion. “This becomes pretty interesting when you think about exposure to enteric pathogens that are causing diarrhea and dehydration. The females, particularly females that are early weaned, may have a higher rate of clinical severity of diarrhea disease,” Moeser said. Next the team examined how early life diversity and stress, as well as sex, impact the development of the immune system. Male castrates and female gilts were lipopolysaccharide (LPS)-induced immune challenged and then immune parameters were studied to detail the response. “The females actually have a greater neutrophil lymphocyte ratio, and this is really reflective of the magnitude of that acute inflammatory response to LPS compared with male castrates. We also did additional studies where we looked at migration of immune cells into the peritoneal cavity in response to LPS and we found that also, in this case, that females, when they're responding to LPS, they also recruit more neutrophils, the higher peripheral inflammatory response compared to male castrates,” Moeser said. “Here's some more functional evidence that the immune system between a male and a female, in this case, the male castrate, are very different and very different how they're going to respond to certain pathogens and also stimuli.”
Another one of their studies examined the differences in intestines between early weaned and late leaned animals, measuring all the gene transcriptions that occurs in the gut and then looking at the number of differentiated expressed genes in the early weaned pigs relative to their late weaned counterpart. “We found that early weaned females induced a large number of differentiated expressed genes, and this is animals that are approaching six months of age, so again, these long-term effects,” Moeser said. “Also, the male castrates, they also have a lot of genes that are differentiated expressed and activated by early weaning or just differentiated expressed. Whereas you look at a male intact animal, there's a lot less. So, this is telling us that these sex differences can change the transcription activity in their gut long term.”
Looking at the different types of genes that were differentiated expressed, the research team found many genes were up regulated in the early weaned female pig versus a late weaned female pig. When they examined the male castrates, which also had a large number of differentiated express genes in response to weaning, those types of genes were totally different. “They were still responding with increased gene activity, but most of the genes that we found were down regulated. It just goes to show what a dramatic difference, that these animals are being exposed to,” Moeser said. “They may have similar clinical outputs sometimes, but the underlying genetic change is expressional, and protein changes could be vastly different, and this would be important when you're thinking about what is being targeted in diseases, in a male versus a female.”
Finally the researchers examined one of the main immune cells — the mast cells which are very sensitive to stressors, Moeser said. They are rapid responders and are strategically positioned in the body to respond to a stress event. For example, after 15 minutes of psychological stress, the mast cells become highly activated in tissue and release mediators. Mast cells are also critical to modulating intestinal permeability, Moeser said.
The team wanted to know are there also sex differences in mast cells? “When we compared between male castrates and females, the increase induced by early weaning is pretty similar. There are similar numbers of mast cells, so that didn't really explain it,” Moeser said. “However, when we activated the mast cells in the tissue and measured the release of mass mediators in the gut, the females released more mast cell mediators, despite having the same number of mast cells. What this suggested was that maybe the content of the mast cell in the female is very different.”
At the 4th annual Kemin Intestinal Health Symposium veterinarians, nutritionists and food animal producers discussed the latest research on topics related to intestinal health in the livestock space. We talk with one of the presenters at the Symposium, Dr. Amy Maschhoff, Associate Director of Health at The Maschhoffs. Dr. Maschhoff discusses how production systems should approach the topic of intestinal health and what she and her colleagues have learned from first-hand experience in their system.