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Using blood sampling, liver biopsies to assess nutrition

Steve Blezinger for Progressive Cattle Published on 25 July 2021

As we manage and build livestock operations, especially beef cattle, producers have a need for tools that can help determine the effectiveness of management, especially with nutrition programs, against the mountain of variables that affect animals daily.

This is particularly true for the average cow-calf operation based on the grazing and consumption of forages (pasture, hay, silage) and given the variances that come with seasonal and environmental changes, stages of production and variation in feeding and supplementation programs.

Certain tools like palpation and ultrasound are common and can give us insight into the animal’s reproduction status. Nutrition is a bit more challenging. Producers commonly use tools such as body condition scoring or weight measurement (less common, since relatively few producers own animal scales), but there are few opportunities to gather meaningful data into what is going on “inside the animal” that can give us a picture of how accurate our nutrition programs are or if there is something going on that is not readily apparent.

Certain tissue samples (blood, serum, liver, rumen fluid contents, abomasal contents, feces, urine) can all provide insights into the animal’s nutritional status.

Health and nutrition issues: Blood sampling and analyses

When health or nutrition problems arise, particularly if the causes are not clear, one common analytical tool used by the veterinary community is blood sampling and analyses. In many cases when significant health issues present themselves, especially in more than one individual animal, blood analyses can give the producer and their vet a picture of what is going on in the animal. This may be of value when individual animals exhibit problems. However, when wider-range issues become obvious – for example, depressed reproductive performance across the herd – a broader approach may be necessary.

The data gathered can be extensive and potentially very useful. Common blood information is reported as levels of different cell types, immune response components, blood and liver enzyme levels, protein levels, fatty acid levels, blood chemistry (i.e., blood urea nitrogen), mineral levels and so on. These data can provide a variety of insights in the animal health (good or bad, areas of concern), metabolism and nutritional status or combinations of these since they are often interconnected.

Nutritional indicators can be provided by protein assays, blood urea nitrogen (also a protein indicator, especially soluble protein) and a wide range of mineral values. Minerals are commonly evaluated by blood assays, although these may not be the most accurate. More on this in a minute.

There are several factors that can affect blood values and the accuracy of these values – and also how truly useful this data may be.

1. Sample size – Taking blood samples from one or two animals is not an effective means of determining status in the herd. While the actual number of samples to be taken will depend on the situation, herd size, veterinary recommendations, etc., in most cases, a random sampling size of 10% of the herd is a common “rule of thumb.”

2. Taking samples and samples handling – Taking the actual samples may be something you want to leave to your vet or their team. However, blood sampling is not difficult and can be taken by jugular vein puncture at the neck or at the exposed veins at the base of the tail (coccygeal vein).

In either case, the animal needs to be well restrained, the area cleaned and the hair trimmed. Samples need to be handled carefully and injected into appropriate storage and transport tube (per vet recommendation). Samples should be kept cold but not frozen. Freezing will result in the disruption/bursting of red blood cells. This will alter the values. Blood samples should be transported to the lab as quickly as possible. Again, work closely with your veterinarian and their team to coordinate this entire process to ensure the best outcome. There is expense involved in this overall process, so you will want to collect this cost data as thoroughly as possible in advance.

3. Once the samples are taken and shipped to the lab (often the vet school at a university in your state – but could be others), it will take a little time to get the results back, possibly one to two weeks. Once the analytical report is returned, review with your vet as well as nutritionist. Collectively, you can assess the results and determine if or where changes and improvements need to be made.

A couple of things to consider when sampling blood for mineral status: First, as mentioned above, if samples are not handled carefully, the cells can break (referred to as lysing). This can significantly alter the mineral values in the sample and give erroneous readings. Again, be very careful with sample handling. Second, minerals (especially trace minerals) can be very “transient” in the body. This means the concentrations within various tissues in the body – blood, muscle, liver, etc. – can vary somewhat depending on the status of the animal, especially stress levels. It is not uncommon to see adequate trace mineral blood readings in animals that are deficient because a given mineral may have been mobilized from the liver in an effort by the body to compensate for a dietary deficiency. This is not uncommon in stressed animals either. Research has shown that in periods of stress, zinc and copper levels may show to be elevated in blood samples because the body is mobilizing these minerals to compensate for the stress.

This simply goes to illustrate that the values you find may be subject to interpretation and the values may be somewhat deceiving.

Increased accuracy – liver biopsy

In recent years, it has become more common to use liver biopsies (taking a small sample of liver tissue and performing the required analysis) to assess certain nutrient values, particularly minerals (especially copper) in the liver. Liver tissue is less transient than blood, and minerals will move more slowly in and out of the tissue. Thus, the nutrient (mineral) values indicated from liver tissue is potentially a more accurate snapshot of the animal’s current status. Plus, deficient mineral values reported in liver tissue are potentially a better representation of the animal’s actual status. In other words, if liver tissue shows a deficiency in a specific mineral, it can be assumed that a deficiency truly does exist and requires less interpretation. Liver tissue can also be used for a variety of other analyses, including liver fat concentrations as well as others.

Liver biopsy is more technical than blood sampling but is not as invasive or problematic for the animal as some tend to think. Vets and vet techs well trained and experienced in liver biopsies are fewer than those proficient in blood sampling. Nonetheless, it is not impossible to find assistance. A biopsy tool is required, which looks somewhat like a hybrid, larger-diameter, very long needle. The biopsy tool may be cleaned and used repeatedly in veterinary applications.

Sample numbers and protocols are similar to blood sampling, with samples placed in specially designed tubes that should be shipped overnight to the lab. Again, proper handling is important.

Once the results are returned, consult with your vet and nutritionist to determine where things stand and what, if anything, may need to be done. end mark

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, Texas. He can be reached at Steve Blezinger or at (903) 352-3475. Follow him on Facebook at Reveille Livestock Concepts.

Steve Blezinger
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