Following up on last month’s column on the challenge of solving a feed shortage with non-conventional feeds, I would like to focus this column on identifying the issues you can face when some of the more common alternative feeds are substituted into the ration. Many of these issues are related to atypical nutrient content and thus the first step in developing an alternative feeding program is to ensure you know what you are feeding. As you will see below, in addition to the traditional feed test that provides moisture, protein, energy, calcium and phosphorus content, you may need to ask for specific tests for nitrates, sulphur, potassium, oxalates or other atypical nutrients that may cause feeding issues. The following are some common examples.
There are several byproduct/alternative feeds that producers may be forced to try this winter for the first time that are high in sulphur. The first group that comes to mind is the various byproducts arising from the ethanol industry. Dried distillers grains with solubles depending on source will have sulphur levels ranging from 0.75 to one per cent or more. Canola silage is another example of an alternative feed that is high in sulphur (i.e. 0.5 to 1.0 per cent or greater). There are two issues with high sulphur intake. The first is more long term, where high levels of dietary sulphur induce copper deficiency by tying up copper and making it unavailable to the animal. The second issue is high dietary sulphur levels are thought to be a causative factor in the development of polio in cattle. The National Research Council (2000) recommends that total dietary sulphur levels not exceed 0.4 per cent on a dry matter basis. While some nutritionists feel that this dietary guideline may be conservative, it is evident that both distillers grains and canola silage contain elevated levels of sulphur and therefore need to be blended into rations appropriately.
Nitrates can be another issue in many non-traditional feeding programs. Cereal crops such as barley or oat or canola harvested for greenfeed or silage can contain high levels of nitrate, particularly when harvested during dry growing conditions. This can be a significant issue as high nitrate levels can lead to nitrate poisoning and if severe, a significant death loss. Historically, nutritionists used a value of 0.5 per cent (total feed dry matter) to separate safe from potentially dangerous from a nitrate poisoning perspective. Again many nutritionists feel this value is too conservative as cattle seem to adapt to nitrate levels that are higher than this value as long as the exposure is not excessive or too rapid. Personally, I would not be concerned until dietary nitrate levels exceed 1.0 per cent (dry matter basis) and would take steps at this point to blend ingredients low in nitrates into the ration to ensure levels do not get excessive.
On the subject of greenfeed, another potential issue to watch for is high dietary potassium levels, particularly as you get closer to calving. Cereals, particularly when drought stressed can accumulate potassium. The situation is compounded when manure is used as a fertilizer. The issue is that high dietary potassium levels can interfere with magnesium utilization which in turn can lead to down cows with nervous symptoms similar to that seen in cows suffering from milk fever. Again, a forage analysis can indicate the potential for an issue and the need for blending into the ration.
Some of you may have had the forethought to bale fields that were infested with kochia. When baled before the plant is mature, kochia can be a good forage source. Mature kochia, however, contains relatively high levels of oxalates, which interfere with calcium metabolism in the animal leading to issues with hypocalcemia and possibly kidney function. As such, it is a good idea to restrict the amount fed to 30 to 40 per cent of the ration, depending on maturity.
One of the more common alternate feeding programs we will see this winter is the utilization of straw as a forage source. Straw can be safely fed in wintering diets at levels up to 1.25 to 1.5 per cent of body weight (dry matter basis). For a 1,300-pound cow, this means 16 to 19 pounds of straw on a dry matter basis or 19 to 22 pounds as fed. To meet energy and protein requirements, you would need to supplement with a source of energy (i.e. barley grain) and protein (i.e. canola meal) or equivalent (i.e. fortified grain screening pellets). It’s not unusual in the second trimester to feed eight to 10 pounds of barley grain when straw makes up the forage component of the ration. This will increase to 12 to 14 pounds during the third trimester. When feeding more than eight to 10 pounds of grain, it is a good idea to feed it in two separate feedings to minimize potential issues with digestive disorders.
As you can see there are many issues that need to be considered when developing alternative feeding programs. The advice of a good nutritionist can be invaluable in helping you sidestep many of these potential pitfalls.