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Calcium in Laying Rations: How to Sample Feed and Interpret Analysis |
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Author: Carlyle Bennett, Business Development Specialist (Manitoba Agriculture Food, & Rural Initiatives - Livestock Knowledge Centre)
The purpose of this fact sheet is to demonstrate how to sample laying hen rations and interpret the calcium levels found in the feed. The results of a study of feed from 24 Saskatchewan leghorn flocks are used to help illustrate the reliability of calcium testing.
How to Sample Feed
Because the amount of calcium can vary from one sample of feed to the next, it is important to take a good feed sample:
1. Take a small sample of feed, approximately 0.20 Kg or 0.5 lbs., each day for four days. The four samples should be taken from the feed hopper, not the troughs or pans that the birds are eating from.
2. Mix the four samples together to give one large sample. By mixing together feed from four days, you are more certain that the feed did not come from just one corner of the feed bin.
3. Send the sample to an accredited lab and tell the lab that the sample is a layer ration.
4. If the calcium level reported by the lab appears to be abnormally low or high, ask the lab to double check the results. Most labs keep samples for several weeks after analyzing them and should be able to re-analyze them if necessary.
Also check the level of ash reported for the feed. Because ash represents the total level of minerals in the feed, it should be high when the calcium is high and low when the calcium is low. If the calcium reported for the sample is abnormal but the ash appears to be normal, you may want to question the accuracy of the test. In a feed sample with a normal level of calcium, there will be 11% to 13% ash.
Can You Trust Calcium Analysis?
Analysis for calcium has a reputation for producing variable results. When the calcium tested in a feed is too high or low, it is often said, "Oh, that sample must have gotten an extra piece of limestone" or "...that sample must be missing a piece of oyster shell". If the feed is properly sampled according to the method described above, these concerns can be greatly reduced.
To determine how variable calcium testing can be, two different batches of feed were tested repeatedly for calcium. From each batch, 32 small feed samples were taken and eight large samples were then formed by mixing the small ones together in groups of four. One of the feeds was formulated to contain 3.85% calcium and all of the calcium came from ground limestone. The other feed was formulated to contain 4.0% calcium, with 75% of the calcium coming from oyster shell. One sample of each feed was submitted to the feed lab each month for eight months and the calcium levels tested.
Overall, the calcium analysis was accurate. Seven of the eight limestone feed samples was within +/- 0.35% of the formulated value while six of the eight oyster shell feed samples were within +/-0.3%. Only one sample of each type of feed tested had a calcium level low enough to be of concern. The one abnormal sample of the limestone feed initially tested at 2.95% calcium but tested at 3.85% when re-analyzed. The sample of unusual oyster shell feed tested at 2.94% calcium when first analyzed and was still 3.28% calcium when double checked. This particular sample actually was "missing" a piece of oyster shell and was lower in calcium than the other samples. While this one sample was out, it was possible to get a reasonable estimate of calcium in 15 of the 16 samples tested between the two feeds.
Producers wanting to be absolutely certain of the calcium level in the feed should test a sample taken on the farm and ask the feed company to analyze its sample of the same load of feed. By analyzing two different samples taken at different places, it is possible to rule out any errors in feed sampling or testing.
The table below will assist in interpreting your test results.
| Calcium Level |
Symptoms or Concerns |
| < 3.0% |
Poor shell thickness; cage layer fatigue; increased feed intake
and possible hemorrhagic fatty liver syndrome. |
| 3.0 to 3.5% |
Thinner shells and weaker bones if fed for a prolonged period
or feed intake is depressed. |
| 3.5 to 4.5% |
Good shell quality and bone strength. |
| 4.5 to 5.0% |
No improvement in shell quality or bone strength; higher feed
cost. |
| > 5.0% |
May dilute feed if such high levels are unplanned; possible sign
of poor feed mill calibration or quality control. |
Adapted from Saskatchewan Poultry, by C. Bennett, Animal Industry BranchPointers.
Author: Carlyle Bennett, Business Development Specialist (Manitoba Agriculture Food, & Rural Initiatives - Livestock Knowledge Centre)
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