National forage survey results: trace mineral and related nutrient levels

A National Forage Survey was conducted in 18 states to determine the trace mineral and related nutrient content of forages grown in the United States. Most forages sampled were harvested hays utilized as winter feed for beef cow herds. The trace element most commonly deficient in the forages sampled was zinc. Copper and cobalt levels were adequate in 36 and 34.1% of the samples, respectively. In contrast, manganese was adequate (above 40 ppm) in 76% of the samples and was deficient (below 20 ppm) only in 4.7%. The copper antagonists, such as iron and molybdenum, were marginal to high in 28.7% and 57.8% of the samples, respectively, indicating that both of these elements are often present in levels that can cause a reduction in copper availability. Of the 352 samples collected in 18 states, the trace mineral most likely to be deficient was zinc, followed by selenium and cobalt.


Introduction
Harvested and grazed forage represents the major cost associated w ith cow-calf and stocker production.Although forage analysis is encouraged as a profitable management practice, only a limited number of producers traditionally utilize forage test ing to determine supplementation strategies.Even fewer producers utilize trace mineral analyses of their forages.
Reported below are the resu lts of a National Forage Survey conducted in 18 cooperating states to determine the nutrient and trace mineral profiles of various forages commonly used by cow-calf producers.

Experimental Procedures
To determine the health status and production practices used by producers, the USDA Animal and Plant Health Inspection Veterinary Services conducted a 48-state survey involving 2,539 cow-calf producers.This project, which took 16 months, profiled cow-calf health and production parameters and has been published in a series of five national repo rts entitled "Cow-Calf Health and Productivity Audit (CHAPA) Reports".Producers participating in the survey were offered the opportunity to have a single sample of harvested forage collected and analyzed without cost.All samples were collected by state and federal veterinary personnel and mailed to Kansas State University.All cooperating veterinary personnel were trained in proper forage sampling procedures to ensure that uniform samples were collected for analysis.Samples were collected using a standard forage probe.
Samples were dried in the Nutrition Lab at Kansas State University and then were ground and submitted to a commercial lab (Peterson Labs, Hutchinson, KS) for analysis.Samples were analyzed for crude protein (CP), acid detergent fiber (ADF), phosphorus (P), copper (Cu), cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (zn).
For analytical purposes, forages were combined into nine categories as follows.
Alfalfa/Alfalfa Mix Thirty nine samples were coded as alfalfa and 25 were classified as alfalfa mix, predominantly grass-alfalfa combinations.
Brome Eight samples were clearly designated as brome.
Bermuda Of 36 samples designated as bermuda, one was a bermuda grass/orchard grass mix.

Fescue/Fescue Mix
This category included 16 samples designated as fescue and 10 as fescue-clover combinations.

Cereal Forages
The designatio n included 17 samples of wheat, oats, and barley.

Grass
The grass category included 139 samples considered native or local for the respective state and may have included brome mixes, timothy, mixed grasses, and other grasshay combinations.

Silage
The nine samples classified as silage were coded predominantly corn silage.(Three sorghum silage samples were included in the sudan/sudan sorghum category.
Other This group included 26 forages not fitting into other categories and is not discussed in the report.

Results and Discussion
The means of nutrient and trace mineral analyses are shown in Table 1.To help interpret the trace mineral values, Table 2 indicates the amounts of the trace elements needed to meet dietary needs.In the case of antagonistic trace elements, such as iron and molybdenum, amounts that would lead to problems with copper are shown.
Copper.In the national sample s, 36% were classified as having adequate levels of copper, with 14.2% being deficient (below 4 ppm; Table 3).For most of the forage samples collected, the mean values for copper fell in the range of 5-8 ppm.This is usually adequate if high levels of antagonists, such as iron and molybdenum in the forage or sulfur in the water, are not present to cause a copper "tieup".
Of concern was the fact that 28.7% of the forage samples contained levels of iron that could be antagonistic to a copper.Of even greater concern was the fact that 57.8% of the samples contained molybdenum le vels that were high enough to tie up copper.
Zinc.This was the most commonly deficient trace element.Only 2.5% of the samples contained adequate zinc (at least 40 ppm), and 63.4% of the samples were classified as deficient (below 20 ppm zinc).
Cobalt.On a national basis, 34.1% of the samples contained adequate cobalt, whereas 48.6% were classified as deficient.However, part of this high deficiency level may reflect limitations in the laboratory procedures.The small levels of cobalt (commonly less than .2ppm) in most forage samples a re near the detection limits of practical laboratory techniques.
Manganese.Of all the trace minerals analyzed, manganese was the one most commonly present in a high enough le vel to meet the dietary requirements of cattle.Because manganese is fairly poorly digested, it's important that the forage contain an adequate level.Seventy-six percent of the samples sampled nationally had an adequate level.
Selenium.On a national basis, 19.7% of the samples collected were classified adequate in selenium and 44.3% were classified as deficient.Selenium varies widely throughout the United States, often being deficient in certain areas and in excess in others.Even more of a problem is the fact that some st ates have regions of both deficiency and toxicity.In the National Survey, 16.7% of the sam ples were classified as having excess (>.4 ppm) selenium.

Table 2 . Classification of Trace Elements Relative t o Their Ability to Meet Dietary Require- ments or Cause an Antagonistic Problem with Other Trace Elements
Above this level can cause a copper tie up.**Above 1 can cause copper tie up --ratio of copper to molybdenum should be 4:5 or above. *