Research Summary - 2
Answering the "why" of vitamin A deficiency
| Date/Time: |
8/28/2026
17:15
|
| Author: |
Dave Rethorst |
| Clinic: |
Beef Health Solutions |
| City, State, ZIP: |
Wamego, KS 66547 |
D.N. Rethorst, DVM
1
;
1Beef Health Solutions 13441 Anthony Dr., Wamego, KS 66547
Introduction:
Vitamin A deficiency in beef cattle is usually associated with drought conditions and more recently with confined feeding of beef cows and the use of brown rations in confined feeding. Classical signs of vitamin A deficiency include night blindness and neurological signs such as incoordination, staggering gait or convulsions. Other signs of this deficiency that may be seen earlier than the night blindness and neurological signs include immune dysfunction which results in neonatal diarrhea and/or respiratory disease, infertility, abortions, stillbirths, weak calves and retained placenta. Calves that are rough-haired, unthrifty and exhibit reduced growth may also occur. Abnormal development of the spermatozoa and reduced semen quality will occur in some cases. In recent years a number of beef cow-calf herds in the Great Plains have experienced vitamin A deficiency as diagnosed by serology. The objective of this abstract is to document vitamin A deficiency in beef cow herds, to better understand the relationship between serum and hepatic vitamin A and better understand the numerous factors that play a role in the development of vitamin A deficiency.
Materials and methods:
From 2021 to early 2026, blood samples were drawn from 280 breeding age females in 26 herds when it was determined clinically that vitamin A deficiency needed to be ruled out as a possible cause of problems in the herd. Serum harvested from these samples was submitted to the Kansas Veterinary Diagnostic Laboratory (KVDL) for analysis. Based on the KVDL results that revealed a high number of samples with results below the reference range of 0.3-0.7 ppm, it was verified that the cows were being offered mineral and that they were consuming the mineral at an appropriate rate. The vitamin A levels in the vitamin and mineral supplement were adjusted so that the cows were consuming 100,000-120,00 IU per head per day in an effort to correct the deficiency. When it was determined, in the fall of 2026, that the issues had not been resolved in several herds, liver biopsies were performed on 36 cows in 8 herds, with one of these herds being on a different source of vitamin A than the other 7 herds. One to two grams of liver was collected using a large bore liver biopsy instrument and the samples were submitted to the Iowa State Veterinary Diagnostic Laboratory (ISVDL) for analysis. Blood was drawn from these cows at the time of liver biopsy and serum harvested for submission to KVDL for analysis so that a better understanding of the correlation between liver and serum vitamin A could be had.
Results:
The range of results for the 280 serum samples was 0.028-0.41ppm with an average of 0.193 ppm and a standard deviation of 0.074. Of these samples, 23 fell within the KVDL reference range of 0.3-0.7 ppm. Other veterinary diagnostic laboratories have used a reference range of 0.225-0.5 ppm. An additional 58 samples fell within this range.
The serum vitamin A levels in the 36 samples that were collected at the time of liver biopsy ranged from 0.073 to 0.36 ppm. The average was 0.214 ppm, and the standard deviation was 0.058. The 26 sera from cows on source C vitamin A ranged from 0.073 to 0.348 ppm and averaged 0.020. The standard deviation was 0.061. The 10 sera from the source B cows averaged 0.24 ppm, ranging from 0.199 to 0.36. The standard deviation was 0.045. The difference in serum vitamin A when comparing source B to source C was not significant at the p<0.1 level (p=0.44).
The results of the 36 liver biopsies ranged from 25 to 402 ppm with an average of 114 ppm and a standard deviation of 73.8. The ISVDL reference range for liver vitamin A is 100-175 ppm (w/w). Fifteen of the 36 liver results were above the cut point of 100 ppm. The results from the 26 cows that were on source C vitamin A supplement ranged from 25-136 ppm with an average of 79.6 and a standard deviation of 32. Five of the results were above the cut point of 100 ppm. The 10 cows that were on source B supplement had results ranging from 121-402 ppm with an average of 203.8 and a standard deviation of 77. The difference in liver vitamin A when comparing source B to source C was significant at the p<0.1 level (p=0.07).
In order to evaluate correlation between the serum and liver vitamin concentration, the R squared (R2) value was calculated. For this data the marginal R2=0.01, suggesting that using serum concentration of vitamin A to predict liver concentration of vitamin A is not meaningful.
Significance:
There are a number of factors that should be considered when diagnosing and correcting vitamin A deficiency in beef cow-calf herds:
• What is the diet of the cows?
• Are the cows being fed a vitamin and trace mineral supplement?
• How is the supplement stored on the ranch and for how long?
• Are the cows consuming the supplement at an appropriate rate?
• What is the inclusion rate of vitamin A in the supplement?
• Are there vitamin A antagonists present?
• Is the NRC recommendation adequate?
• What is the source of vitamin A in the supplement?
• Is the cow body condition score adequate?
• Is colostrum intake adequate?
• Does the source of vitamin A supplement affect liver concentration of vitamin A?
• Is there a difference in sources of vitamin A?
• Does serum concentration of vitamin A correlate to liver concentration of vitamin A?
While several of these questions are husbandry questions that must be answered in the context of a veterinary-client-patient relationship and others are outside the scope of this data, the data does suggest answers to two very important questions. The data does suggest that: 1. Source of vitamin A does affect the concentration of vitamin A in the liver, and 2. Serum concentration of vitamin A does not correlate well with liver concentrations of vitamin A,
