January 2021

Diagnosing Nutritional Issues in Beef Cattle: Part I

By Dr. Gregg Hanzlicek

This article is the first of two devoted to diagnosing the nutritional causes of down and/or dead cows.

Every year during spring calving we help investigate numerous cases involving down and/or deceased adult beef cows. These cases typically do not involve a single animal, but small to moderate numbers of animals within a herd. Commonly the history indicates that a group of adult cows were observed as normal and then several hours later (typically 12-24 hours) were found recumbent or dead.

There are several issues that may be associated with these incidences: environmental (lightning/electrocution), traumatic (gunshot), toxic (nitrate, urea, others), and nutritional (protein/energy malnutrition, calcium, magnesium).

Protein/energy malnutrition (PEM)

The clinical signs of herd PEM include: recumbent but mentally alert cows, deceased cows, cows with less than ideal body condition, udders that appear to contain low amounts of milk, and/or weak and small calves. Many times several of the clinical signs occur concurrently.

The cases we see in the Midwest almost always occur during the last pregnancy trimester in middle age to older cows in spring-calving herds. It is rare to observe this issue in fall-calving herds. As gestation proceeds, the energy demands placed on the cow from the growing fetus, placenta, and uterus are immense. For example, at 130 days of gestation the net energy maintenance (NEm) requirement for pregnancy is 0.33 Mcal/day.¹ In contrast, on gestation day 250, the requirement has increased to 3.33 Mcal/day. Similarly, protein requirements increase during the last trimester: 9.1 grams available protein are needed for pregnancy on gestation day 130, BUT 95.2 grams/day are required on day 250.¹

Unfortunately, as the late gestation bovine’s metabolic demands are increasing, her dietary dry matter intake is decreasing due to reduced rumen space (increased fetal size) and the effects of normal metabolic/hormonal processes.² If forages are laboratory analyzed and appropriate rations are subsequently formulated, fed, and consumed, the decreased feed intake is not usually an issue. Unfortunately, many of the cases we are involved with include feeding unanalyzed forages in unbalanced diets.

Analyzing the consumed diet in conjunction with clinical signs is the best method for diagnosing PEM. However, assessing energy balance can be accomplished using other methods. One is body condition scoring. Sometimes in herds dealing with PEM, body condition scoring a representative number of animals can help confirm the diagnosis. Body condition does change slowly, and depending on the size of the adult animal, one score would equate to approximately 75-150 lbs. in actual body weight. The lag time between the weight loss/gain that needs to occur before visual recognition is possible can be a major issue when using body condition to assess energy balance.

A serum test measuring non-esterified fatty acid (NEFA) can provide a current, accurate assessment of HERD pre-calving energy balance. NEFA are the natural by-products from the bovine’s utilization of lipid stores for energy. As more lipids are used to compensate for dietary energy deficiencies, NEFA will increase. Because of biological variation, some normal animals may naturally have elevated values; therefore, assessing energy balance should be from a HERD and not an individual animal perspective.

When assessing dietary energy status, 12-20 animals from any group (any group with a population of 300 or less) need to be sampled. If 10% or more of a sampled animals have elevated NEFA (≥0.4 mg/dL), this is an indication that greater than desired negative energy balance is occurring within the population.³ The ration can then be adjusted to increase diet energy or methods to increase dry matter intake can be enacted to reduce the negative energy balance.

Urea nitrogen (BUN, SUN) can be helpful in cases of suspected protein deficiency. Similarly to NEFA testing, because some normal animals will naturally have lower urea nitrogen values or individual animals may be experiencing health issues not associated with diet, the best use of urea nitrogen is from a HERD perspective. The same sample size (12-20) as discussed above is appropriate. But in this case, if 25% or more of the samples contain urea nitrogen levels <6 mg/dL, protein deficiency is likely present.⁴ As with energy issues, the diet can then be rebalanced to meet the daily protein requirements.

Part II of the series will discuss magnesium and calcium assessment in pre-calving beef cows.

References:

1. National Research Council Beef, 2000. Page 221.
2. Grummer, R.R., Mashek, D.G., et al. Dry Matter Intake and Energy Balance in the Transition Period. 2004. Veterinary Clinics of North America 20:447-470.
3. Robert J. Van Saun. Pennsylvania State University. The Difference between NEFA Values in Late Gestation Dairy and Beef Cattle. 2020. Personal Communication.
4. Hammond, A.C. Update on BUN and MUN as a Guide for Protein Supplementation in Beef Cattle. 1998. U.S. Department of Agriculture, Agricultural Research Service Publication.

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