Selenium Levels in Interlake Forages
Selenium is a very important trace mineral. Reproductive problems, retained placentas, white muscle disease and an inadequate immune system (leading to mastitis and metritis) may result when selenium is deficient in a livestock ration. Selenium was first identified in the 1930s as a toxic element. Selenium levels of 100 to over 9000 mg/kg can be found in selenium accumulator plants. Consumption of these plants leads to rapid death. Chronic toxicity can occur at 5 mg/kg.
Manitoba is generally accepted to be in a "low to deficient" selenium state. In spite of its importance, selenium analysis is not routinely done on forages due to the high cost ($58/sample). Because of this, the status of selenium in forages is not well documented. In the fall of 2001, Lori-Lynn Benn (livestock specialist in Teulon) and I decided to survey forage samples from each of the 6 ag. rep districts in the Interlake for selenium content. Due to the high cost, the number of samples per ag. rep. district was limited. The results are outlined below.
| LOCATION | FORAGE TYPE | Se (mg/kg, 100% DM) |
|---|---|---|
| Arborg | Alfalfa-grass silage Alfalfa-grass silage Alfalfa hay Alfalfa-grass hay |
0.4 0.2 0.2 0.4 |
| Ashern | Alfalfa-grass hay Alfalfa-grass hay Alfalfa-grass hay |
1.1 1.0 1.2 |
| Fisher Branch | Alfalfa-grass hay Grass hay Alfalfa silage |
0.14 0.033 0.21 |
| Lundar | Alfalfa-grass hay Alfalfa-grass hay Alfalfa-grass hay |
0.8 1.6 0.7 |
| Selkirk | Alfalfa-grass hay Alfalfa-grass hay |
0.086 0.13 |
| Stonewall | Alfalfa-grass hay | 0.39 |
| Teulon | Alfalfa Alfalfa-grass Alfalfa-grass |
0.35 0.12 0.25 |
The National Research Council (Beef, 1996; Dairy, 2001) sets the Se requirement of dairy cows at 0.3 mg/kg and at 0.1 mg/kg for beef animals. The maximum tolerable amount is set at 2 mg/kg. Selenium is routinely added to commercial feeds at levels set by Canadian Food Inspection Agency. The CFIA requires that supplemental selenium in complete feeds for poultry, swine, cattle, sheep and goats not exceed 0.3 mg/kg. This restriction is primarily due to environmental concerns. Higher levels are possible only with a veterinary prescription.
Results:
- The above results indicate a large variation can occur within a region. The results ranged from 0.033 mg/kg in a sample from Fisher Branch to 1.6 mg/kg in Lundar.
- The samples from Fisher Branch all exceeded 1mg/kg.
- The samples from Lundar all exceeded 0.5 mg/kg.
- The lowest selenium tests were found in Selkirk and Fisher Branch.
- Over 89% of the samples met the Se requirement of beef cows.
- Over 50% of the samples met the Se requirement of dairy cows.
The following table summarizes the results by analysis levels.
| SE (mg/kg) | Number of Samples |
|---|---|
| >0.1 | 2 |
| 0.1-0.19 | 3 |
| 0.2-0.29 | 4 |
| >0.3 | 10 |
The following conclusions can be made from the data:
- There is sufficient variation in the results to conclude that periodic selenium testing should be carried out, especially before adding additional Se to the feed.
- Although sample size is small, it appears that the majority of forages, in the six ag. rep. districts surveyed, meet the Se requirement of beef cows.
- When situations of white muscle disease and other Se-related problems do occur, it is important to look at vitamin E levels as well. The majority of beef rations will be low in vitamin E. This can trigger Se deficiency symptoms even when Se is adequate.
Nutrition Update
Volume 13 No.1, May 2002
