From the 2022 Kemin Intestinal Health Symposium
By Ann HessEnteric pathogens have an indirect, secondary impact on heat stress, bovine respiratory disease, meat quality and more.From heat stress and bovine respiratory disease to food safety and meat quality, enteric pathogens can have an indirect or secondary impact on livestock gut health.“We’ve talked a lot about some of the basics of gut health and obviously it has an absorptive function to digest nutrients. It also houses a microbiome that's essential for function, and it also acts as a barrier,” said Rand Broadway, a USDA research microbiologist based at the Livestock Issues Research facility in Lubbock, Texas. “It also plays a neuroendocrine role, not only in satiety and appetite hormones, but also has a role of catecholamines in microbial growth, which we know can drastically alter enteric microbial populations.During the recent Kemin Intestinal Health Symposium in Palm Springs, California, Broadway detailed his latest research in this area, examining the implications of enteric pathogens in livestock through five key areas.Heat stressDuring a heat stress period, the peripheral blood flow is increased and there is a reduction in blood flow within the GI tract, which can cause several issues, such as an increased reactive oxygen species and oxidated stress, said Broadway. It can also change gut integrity disrupting releases of certain pathogens and other types of compounds from the GI tract to other tissues.“When we think about the gut and response to heat stress, we also have to couple this with feeding behaviors and how those change things, along with the health of the gut prior to heat stress — what entire pathogens were present prior to the heat stress event, and how that might relate to overall response to the heat stress event,” Broadway said.To examine this area further, Broadway’s team recently conducted a study with 700-pound heifers supplemented with a yeast product for 50 days in spring, and then brought into an indoor facility where they were subjected to a four-day heat stress event following a two-day thermoneutral period.Broadway said the improved gut health status of the cattle from the yeast supplementation may have helped mitigate some of the negative impacts of heat stress. During the heat stress event, the heifers had decreased body temperatures, increased their water consumption and visits to water, had decreased respiration rates and circulating cortisol, with variable effects on complete blood counts and minor effects on glucose and non-esterified fatty acids concentrations.Bovine respiratory diseaseAn emerging area of study regarding respiratory disease, specifically in humans, is the gut-lung axis. Broadway expects to see more of this research conducted on livestock in the near future.“If we have poor gut health, which can be caused by an interrogative infection or even antimicrobial use, because we know that antimicrobial use can change microbial populations and can even cause dysbiosis within the gut, well, that dysbiosis in the gut can lead to increased permeability, decreased barrier function, which can obviously lead to systemic changes that alters our immune response within the lung,” Broadway said. “And when we have a lung disease, we know that that can create systemic inflammation. That systemic inflammation can thereby cause more intestinal injury and we just have a perpetual cycle, that's detrimental to the animal overall.”To test how intestinal integrity might influence respiratory disease, Broadway’s team designed a respiratory disease model and collected blood analyzing serum for interferon-γ, interleukin-6 and interleukin-4 using a custom bovine 3-plex chemluminescence assay and whole blood for hematology using the ProCyte Dx Hematology Analyzer (IDEXX) with bovine-specific algorithms. When they supplemented with a prebiotic/probiotic blend, they saw a decrease in the neutrophil/lymphocyte ratio in those animals.“The way that I interpret the neutrophil/lymphocyte ratio is a lot of people will say that anything over one may be considered inflammatory, so I would suggest that this is a less inflammatory response when we fed this supplement prior to inducing a respiratory disease,” Broadway said.
Another thing they examined in the respiratory disease challenge was nasial lesion score. Those animals supplemented with a probiotic prior to the disease challenge had a decreased tendency for nasal lesion stores. They also saw a decrease in overall neutrophils and haptoglobin throughout the 72 hours of the challenge.“The overall implication is that reducing the inflammatory response by supplementing products that are known to improve gut health could have an overall impact in response to BRD,” Broadway said.Food safetyThis past August, the USDA Food Safety and Inspection declared salmonella an adulterant in frozen poultry products. While it is still unclear what the ramifications will be from that, Broadway said many people are under the assumption that this might be step one in declaring adulterants in other products, including beef.From a livestock perspective, Broadway said salmonella is a threat to calf health. It is the major cause of morbidity and mortality in dairy calves. It primarily remains enteric in calves and can migrate to peripheral tissues. A majority of these infections are limited to the gastrointestinal tract and symptoms can be asymptomatic in calves.“We don't necessarily know that they have an infection, or they don't exhibit clinical signs of the disease, but we do know that it can migrate outside of the GI tract,” Broadway said.One of the issues with salmonella is in certain environments it can survive for extremely long periods of time. It can survive in colostrum for a couple of weeks, and even refrigerated, it can survive for over a week. In manure or different soil types and moistures, researchers have seen 200 days of survivability.“It's quite possible that all these animals might not have a truly active infection,” Broadway said. “These animals can be re-inoculating themselves on a daily basis, and then they're shedding that and then re-inoculating themselves for the extent of the time they're in that particular production environment.”On the packer and processing level, Broadway notes there has been robust work done over the last 25 years to control and eliminate pathogens such as salmonella and e. coli. However, he questions with all these intervention steps post-harvest, how is salmonella still getting into the food supply today?One of the ways he thinks this is happening is by migration out of the gastrointestinal tract to the lymphatic system.“There are hundreds of lymph nodes across the body, and it could migrate into tissues that either are destined for retail cuts or are destined for trim. It's going to be ground and wind up in our food products and it will be nearly impossible to remove all of these,” Broadway said.While this theory and others may shed light on how the majority of salmonella is winding up into the food supply, the more important question is how do we control it? One of the areas Broadway’s team explored is through probiotics.The team conducted a two-by-two factorial study, where they either fed a probiotic or not and either infected the animals with salmonella or not. Two harvest points were set within 48 or 96 hours after the challenge. Calves were inoculated with 1.0 x 106 Salmonella typhimurium via milk replacer.The researchers found the control salmonella had a very elevated temperature. They saw a large reduction in the temperature response in those animals that were supplemented with the probiotic, however. They also looked at some cytokines and interference on GAMA response, across this four-day window, and they saw a huge spike that's prolonged in inter front gamma compared to the ones that received probiotic.In this particular study, they also pulled out multiple sections of the gastrointestinal tract and cultured them for salmonella. The probiotic drastically reduced salmonella level concentrations throughout the different parts of gastrointestinal tract.
Will pre-harvest interventions become more commonplace?
“The challenge there is can we find interventions that not only reduce pathogen introduction intervention pre-harvest, but can we also identify compounds that can boost performance and have a positive ROI?” Broadway said. “A question that I have great interest in exploring in the future is what is the energetic cost of nonclinical infection? We said that a lot of times these cows are asymptomatic carriers, but there's got to be an overall cost, especially in situations where these cows are being inoculated over and over.”Liver abscessesAnother area Broadway is working on is how gastrointestinal integrity overall influences liver abscesses. Are liver abscesses the result of poor gut health? How are abscesses formed and are there multiple ways? Is ruminal acidosis the only conduit for fusobacterium migration? Is fusobacterium the causative agent of abscesses and can a model be developed to study abscesses?They decided to conduct a study where they dosed animals with lipopolysaccharide, inoculated with Fusobacterium and Salmonella. Then they harvested them at three days after and 10 days after. Only one liver abscess was present and that was in the LPS group. There was a slight increase in ileum scores in the LPS group and no difference in lung or cecum scores. There was also increased rumen damage in the LPS group.This led to the questions was LPS sufficient to induce a leaky gut scenario and was 3-10 days sufficient time for abscess development?A second study was conducted with a classical model to determine if ruminal acidosis with or without the inoculation with Fusobacterium and Salmonella could induce liver abscesses in weaned Holstein calves. Treatments were a negative control, an acidotic diet, and acidotic diet plus Fusobacterium necrophorum and Salmonella Typhimurium.The timeline was seven days of acclimation to control diet, four pulses of acidotic diet, three days of acidotic diet, two days of control diet, an intraruminal bacterial infusion and 20 days of acidotic diet prior to harvest.They found ruminal acidosis alone was insufficient to induce liver abscesses, however the acidotic diet and bacterial infusion together were successful at inducing abscesses.“This was a big surprise to us because we were under the impression that just by feeding an acid diet, we would be able to induce liver abscesses because we made another assumption and that is that all cattle had Fusobacterium necrophorum in high concentrations,” Broadway said.“What we're beginning to learn is that not all the cattle possess populations of Fusobacterium necrophorum at least in very many numbers, so we found it was necessary to utilize salmonella and bacterial infusion to create those abscesses. Is Fusobacterium the causative pathogen or is it salmonella? We still don't have an answer to that and that's something that we're looking to explore since salmonella is intracellular and more invasive than infusive bacteria.”Meat qualityBeef quality is dictated by appearance (redness, amount of discoloration), palatability (tenderness, juiciness and flavor) and stability (shelf-life). It is well documented preharvest stress can impact meat quality from a color perspective, tenderness, flavor, shelf life and even quality grade.A healthy host has a balance between reactive species (ROS) and antioxidants. An imbalance of pro-oxidants to antioxidants results in oxidative stress. Contributors to ROS and oxidative stress include illness and inflammation through BRD, acidosis and mastitis or ketosis in dairy cows, and the environment and management, during times of heat stress or cold stress, poor animal handling, feed stress and transport stress.Broadway said oxidative stress is energetically expensive.Transportation-induced oxidative damage causes impaired immune function, contributing to BRD, respiratory inflammation and pulmonary adhesions. There can be reduced feed efficiency and increased protein degradation, increased proteolysis and autophagy in live tissue as well as increased ROS production in lighter muscled animals.“When we go through a stress event, whether that be a challenge event or not, the immune response is very energetically taxing and we are going to shift more towards a survival mechanism than we are lean carcass tissue deposition mechanism and thereby reduce growth,” said Broadway.To test how stress and disease impacts color and shelf life over time, Broadway’s research team went to a feed yard and identified cattle that had been treated from BRD 0, 1, 2 or 3 times, and then went to the packing plant and collected an equal number of strip warrants from those cattle that have been treated various times. While there were no major differences in color, the team decided to look at that a little bit further to see how stress could impact some of the oxidation factors.They conducted an LPS study and looked at the effect of pre-harvest stressors on TBARs values. Almost immediately following challenge, the team saw a huge spike in these lipid oxidations, however, those levels go back down to baseline very soon thereafter. More importantly, they observed a big drop in antioxidant power, persisting for almost 48 hours.Next the team decided to examine the effect transportation had on these levels. The study consisted of a negative control, a group that was LPS challenged and a group that was put on a trailer and transported for four hours. Every hour they would stop and take blood samples from those animals and then after the four-hour ride, they had a two-hour rest period. Then they were harvested.“What we found is that there was a big color difference in the muscle from these calves and we saw that the transported calves actually had a greater percentage of oxidation than those cows that were subjected to the endotoxin challenge six hours later,” Broadway said. “The other thing that we did is we aged this meat and displayed, and we looked at the percentage of the lipid observation within the state itself over time, and similarly, which was very surprising, transportation had a greater impact on meat color than an endotoxin challenge immediately prior to harvest.”
In conclusion, Broadway compares keeping good gut health to having a house that’s surrounded by toxic gas.“We want to do everything we can to seal up the house, to prevent this toxic gas from coming into the house, but inevitably we're going to have cracks and we're going to have leaks, etc. But if we can provide positive pressure within that house, we can keep things from coming in. Even if you say, you had a window break, there wouldn't be as much coming in, so I think prevention is extremely important,” Broadway said. “Establishing good gut health prior to any type of challenge is going to overall help efficiency and health.”
The fourth-annual Kemin Intestinal Health Symposium brought together respected industry experts from across the poultry, swine, dairy, beef and equine industries to discuss the key pillars of intestinal health.This article is part of the exclusive coverage that Feedstuffs provided from the event.To view all presentations and resources from the 2022 Kemin Intestinal Health Symposium, visit www.kemin.com/symposium