Researchers seek genetic markers for liver abscesses

Liver abscesses are associated with episodes of rumen acidosis, which are usually caused by carbohydrate overload.

Rumen acidosis damages the rumen wall and allows bacteria to pass into the bloodstream and enter the liver, where they can cause abscesses to form.

It is commonly observed in feedlot cattle and dairy cattle that are fed high level grain diets.

Risk factors include the amount of carbohydrate ingested, the timing and volume of meals, the type of grain being fed and the degree to which the grain has been processed.

Liver abscesses continue to be a significant productivity issue in the beef cattle industry.

The 2010-11 Canadian National Beef Quality Audit estimated that liver abscesses cost the beef industry $29.9 million in economic losses, or $9.36 per head.

It was also estimated that large active abscesses with inflammation of the liver (a score of A+) made up 9.9 percent of livers, which was significantly higher than the 1999 audit, when only two percent of livers had A+ scores.

Some of the economic losses result from livers no longer being suitable for human consumption. The 2010-11 audit found that 31 percent of livers weren’t suitable for human consumption.

However, economic losses are also caused by reduced feed intake, reduced weight gain, decreased feed efficiency and lower carcass dressing percentage.

Much of the research on liver abscesses has focused on nutritional management, which is obviously an important aspect of this syndrome.

Minimizing ruminal imbalance and gradually adapting cattle to high-grain diets is an important way to maintain rumen health during the feeding period.

However, a study published in the February issue of the Journal of Animal Science suggests that a genetic component may also be a potential control point for liver abscesses in feedlot cattle.

Researchers from the Meat Animal Research Center in Clay Center, Nebraska, collected 2,304 lung samples from a beef processing plant. They took samples from the lungs because they have little economic value and contain abundant DNA material.

Half the samples were collected from cattle with liver abscesses and half from cattle without. They were then pooled and DNA was extracted.

Researchers used a genotyping array method that evaluates more than 777,000 single nucleotide polymorphisms (SNPs) in the bovine genome. SNPs are single base-pair locations in the DNA molecule that have significant variation within the bovine population. Various combinations of SNPs may help code the DNA for various traits such as production factors and even disease resistance.

The researchers suggested that liver abscesses in feedlot cattle are a heritable trait and were able to identify 33 SNP locations that had a moderate effect and more than 1,000 locations that might have small effects.

This genetic variation included genes that regulate gastrointestinal pH and genes that regulate liver repair following injury and affect the function of immune cells.

Producers have traditionally selected breeding bulls based on growth potential. It could be hy-pothesized that we may have genetically selected animals that have greater appetites and feed intake, which may make them more prone to acidosis in the feedlot.

However, it is not routinely ex-pressed in the seed stock operation because we do not feed bulls and heifers in the same way we do feedlot cattle, where acidosis might be expressed.

More research is required, but these results mean it could be possible for genetic markers for liver abscesses to become a component of a control program.

Genetic testing for SNPs is becoming less expensive and will undoubtedly become a more important part of genetic selection for seed stock producers. Identifying markers for susceptibility to liver abscesses along with nutritional management may help greatly reduce the economic effects of liver abscesses.

One of the current control strategies for liver abscesses in feedlot cattle uses antimicrobials such as tetracycline or tylosin in the feed.

We could drastically reduce antimicrobial use in feedlots if the beef industry could control liver ab-scesses through genetic selection and feed management.

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