Liver abscesses in beef cattle have been a problem to the industry for many years. It is a major challenge for the meat-packing industry and is estimated to cost the whole beef industry more than $400 million dollars annually. These losses are due not only to liver and offal losses but carcass trim and line speed slowdowns. That doesn’t even account for the production losses at the feedlot sector which occur when a severe (A+) abscess is present.
The literature clearly indicates these cattle have poorer dry matter intake (DMI), feed conversion and average daily gain (ADG), leading to subsequently lighter animals with smaller carcasses. Frustration mounts as incidents are rising and are extremely high in the newly founded beef sector of beef-on-dairy feedlot cattle.
What causes liver abscesses?
The historical causal knowledge of liver abscesses has mainly been with feedlot animals consuming a high-grain diet and developing a ruminal upset, like acidosis. This upset then leads to damage to the rumen wall, which allows for the microbial population from the rumen to enter the portal blood flow and end up in the liver, leading to liver abscesses. The main identified/accepted culprit has historically been Fusobacterium necrophorum. Many other factors, such as diet, days on feed, weather, stress, etc., also contribute to the potential incidence rate. Currently, incidence rates are in the 20% to 30% range. However, beef-on-dairy crossbred cattle have a rate that is almost 70%.
Recently, other bacterial species have been identified in abscessed livers as well. Fusobacterium fundiliforme, Truperella pyogenes and Salmonella enterica have all been isolated in abscesses. Interestingly, salmonella is not a prevalent bacterial population in the rumen, so how does it end up in the liver abscess? Food for thought. Just as perplexing, cull cows and bulls have liver abscesses as well. We could speculate that most of that cattle population never took a bite of a high-grain diet. So how did their abscesses arise?
To make matters worse, multiple bacterial species found in these abscesses are also prevalent in the soil organic matter of feedlot pen surfaces. Unfortunately, these cattle have constant exposure to these pathogens. Because of the ruminal upset/fusobacterium connection, the industry has tried to tackle the disease with antimicrobial approaches to reduce fusobacterium concentrations, thus reducing abscesses. Antimicrobials such as chlortetracycline, oxytetracycline, virginiamycin and tylosin all have claims targeted toward reducing liver abscess. These antimicrobials have all shown efficacy and work extremely well – but, unfortunately, we still have the disease. Why? To make matters more difficult, the livestock sector faces extreme pressure from the consumer and the government to reduce antibiotic use.
Many research efforts have been focused on this disease because of its huge economic impact on the industry. Recent findings have demonstrated the Fusobacterium necrophorum is also present in the lower gastrointestinal tract (GIT), not just the rumen. Other work has demonstrated bacteroides can be present in liver abscesses. These bacteria can be found both ruminally and post-ruminally. This begs the question: Are liver abscesses caused solely from ruminal upsets, or is the whole GIT involved? Research efforts targeting “gut health” have clearly shown that psychological stress, heat stress, feed restriction and acidosis all contribute to the concept of “leaky gut.” This is basically a situation where an animal undergoes a stress challenge. Then, the intestinal cell wall lining becomes damaged, allowing for gut lumen contents to enter the portal blood and cause inflammation. This leads to nutrient loss and immune system stimulation. It is plausible that the bacteria found in abscesses can be from both ruminal and post-ruminal gut dysbiosis, suggesting that new control methods should target the whole GIT.
We have expanded our knowledge of the disease state and realize there are more things to consider. What are possible intervention options moving forward? Potential prevention/control interventions include:
- Probiotics and prebiotics
- Yeast/yeast products
- Trace minerals
- Phytotechnology/phytogenic ingredients
Realistically, combinations of some or all of these may be future interventions.
Probiotics (beneficial living microorganisms) and prebiotics (substrates that are selectively used for beneficial microorganisms) have been evaluated for many things in humans and food-producing animals. They are often associated with improvements in gut health. Unfortunately, there are very few peer-reviewed studies evaluating their use in reducing liver abscesses. Data currently available would indicate this method is not ready for liver abscess control. Yeast and yeast products fall in this same category. Very limited research is available on using yeast and yeast products, and published results are inconclusive.
Immunoglobulins are a form of artificial passive immunity. Immunoglobulin Y is not a relatively new technology. Basically, this is harvested from egg yolks from hyper-immunized hens using a predetermined antigen, thus providing targeted or customized feed antibodies. For example, there are products for dairy calves that use this technology to help reduce scours caused by rotavirus, coronavirus and E. coli. The hens are immunized against these pathogens, and the yolk is harvested and processed. Then the immunoglobulins are delivered in the feed. This approach could be customized to fusobacterium or other bacteria known to be a part of the liver abscess complex.
Bacteriophages (viruses that infect and destroy targeted bacteria) were discovered in 1915. In 1917, it became known that these viruses have the potential to kill bacteria. They are ubiquitous in the environment and are recognized as the most abundant biological agents on earth. This technology allows for the targeted killing of specific bacteria via a virus instead of using antibiotics that have the potential to also kill beneficial bacteria. Regarding liver abscesses, a “bacteriophage cocktail” can be manufactured to target fusobacterium and/or the other bacteria. This “cocktail” can then be delivered via the feed. Currently, there are groups investigating the potential of this unique approach. Bacteriophages can act like an antibiotic but allow antibiotic use reduction.
Trace minerals (copper, zinc and manganese) are known to be important for immune system function. Specifically, zinc is beneficial to hindgut integrity and reduction in “leaky gut” damage caused by stressors. There is a plethora of small-pen and large-pen feedlot studies that have evaluated different sources and levels of copper, zinc and manganese for health, growth and carcass variables. Unfortunately, there is nothing conclusive as to their effects on liver abscesses. Furthermore, the data is inconclusive on research looking into zinc sources and levels.
There is one research report that demonstrated a zinc effect when steers that had an acidotic challenge were fed supplemental zinc from zinc amino acid complex. Those steers had fewer liver abscesses than those that did not receive supplemental zinc. In that same report, in a retrospective evaluation of numerous feedlot studies (more than 10,000 head), it was concluded that feeding supplemental zinc amino acid complex reduced liver abscess rate and severity compared to cattle that did not receive the zinc amino acid complex. There may be hope in further evaluating improved zinc sources and their role in gut health and liver abscess rates.
Phytotechnology/phytogenic products (plant-based bioactive compounds) have been evaluated for years in human nutrition and have known positive effects on host health. Unfortunately, most work on these plant-based products in animal nutrition has focused solely on their role as antimicrobials and not as supporting host health in other ways. Because of the pressure on antibiotic usage, it makes sense to evaluate their antimicrobial potential, but host health also needs to be a part of the discussion. Certain plant phytophenols have been shown to have antimicrobial effects on fusobacterium, truperella and salmonella. Additionally, certain plant-based compounds like clove oil have been shown to improve intestinal structure and mucus layer in the intestine. It appears that mixtures of these compounds could be a path forward to liver abscess reduction. The limited data evaluating essential oil combinations in feedlot cattle have been mixed. However, the more we understand about each plant bioactive compound, the closer we get to a potential targeted solution relative to this disease state.
It is evident that liver abscesses are poly-microbial, with bacterial communities originating from both the rumen and lower GIT. It is also fair to say that any future interventions will likely avert absolute prevention or control, as the disease seems to be complex and multifactorial. However, the race to an effective solution is fierce, and there are some viable candidates for success. These interventions will most likely include technologies that help the host maintain gut integrity and have antimicrobial properties for bacteria both ruminally and post-ruminally.