Liver abscesses continue to be an economic concern for the beef industry, even with modern feeding practices. They are worth around 60 cents a pound if suitable for human consumption, but more important than the direct loss when abscessed livers have to be condemned is the effect on performance and carcass characteristics.
Brittany Wiese, a master’s candidate with the Western College of Veterinary Medicine at the University of Saskatchewan, recently reviewed findings from four feedlot studies involving a total of 904 steers conducted by previous graduate students at the university from 2008 to 2014. The livers in those studies were scored according to the Elanco “liver check” system used in packing plants.
A score of 0 is for normal healthy livers without abscesses.
Those with a score of A have one or two small abscesses or up to four grouped abscesses that are generally less than an inch in diameter and the remainder of the liver is healthy. The A- score for livers with one or two small abscesses or abscess scars has recently been eliminated. Livers with A- scores in the previous studies were moved into the A category for her review.
The A+ score is for livers with one or more large abscesses and inflammation of the liver tissue around the abscesses. Oftentimes, parts of the diaphragm adhere to the surface of the liver and have to be trimmed to separate the liver from the carcass.
Livers with A scores are downgraded to pet food and those with A+ scores are condemned.
It came as no surprise to Wiese to find that severe liver abscesses do hinder performance because other studies dating back to the 1980s have shown this to be true. In her review, steers with A+ livers had the lowest finished body weight overall even though all steers had similar weights at the start of each trial. As expected, the cattle with A+ livers also had the lowest average daily gain during the last 70 days on feed.
“We looked at the last 70 days because liver abscesses can heal on their own within 50 to 70 days, so most of the abscesses found at slaughter are likely occurring within the last 70 days on feed,” Wiese says.
Most interesting, although not statistically significant, was that the average daily gain on steers with A livers was better than those without abscesses. One possible reason for this is high-gaining steers eat more feed and, therefore, are more at risk for developing ruminal acidosis, which is the No. 1 predisposing cause of liver abscesses. Once an abscess gets severe enough to tip the balance, the average daily gain does drop off.
Another notable finding from her review was that steers with A livers had the lowest dressing percentage at 58.3 per cent compared to 58.8 per cent for steers with A+ livers and 58.9 for those with no abscesses. Given that increased dry-matter intake is known to increase gut mass (visceral weight), a possible reason for the lower dressing percentage could be that a higher percentage of the total carcass weight is removed as viscera during processing.
Various studies indicate that the prevalence of liver abscesses in cattle across Canada is 12 to 32 per cent. The most recent national beef quality audit by the Beef Cattle Research Council in 2010-11 found 9.9 per cent of livers from fed and non-fed cattle scored A+, compared to two per cent reported in the audit 10 years earlier. Back then, 76 per cent of livers were considered suitable for human consumption, whereas, that dropped to 69 per cent in the most recent audit.
There are no clinical signs of liver abscesses, that is, the animals are apparently healthy, Wiese says. They can lead to a fatal embolic pneumonia in feeder cattle and cows, but it’s rare.
Tylan, a therapeutic feed additive that is quite effective for preventing liver abscesses, is commonly used at feedlots for this purpose. Without its use, we could likely expect to see a rise in liver abscess rates, she adds.
Dr. Greg Penner’s lab at the university focuses on understanding gut health and exploring nutritional management strategies, not only to prevent digestive disorders but to enhance overall cattle productivity and health.
As a member of Penner’s research group, Wiese’s review of liver abscesses was just part of her master’s research on the broader subject of subacute acidosis as indicated by rumen pH levels in the 5.5 to 5.8 range.
The root cause of acidosis is a rumen pH below 5.5, most often brought on by a high level or sudden increase in highly digestible carbohydrates, such as grain. The acidic environment can damage the rumen wall, allowing bacteria that normally inhabit the rumen to travel through the bloodstream and set up in the liver.
A 2014 study led by Dr. Castillo-Lopez, also with the Penner group, involved use of special pH meters in the rumen to continuously measure pH throughout the entire feeding period. Wiese will be using data from that study to try to determine whether severity, frequency or the number of bouts of acidosis has the greatest likelihood of causing liver abscesses.
She is currently working on a new study that attempts to define the prevalence of ruminal acidosis during the step-up period in a commercial feedlot. The livers will be scored to provide insight into the relationship between rumen pH patterns and performance early on in the feeding period and development of liver abscesses later on in the feeding period.
For more on the national beef quality audit results and the video series on how management practices influence beef quality, including the incidence of liver defects, visit the Beef Cattle Research Council’s blog.