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Grazing Cereal Pastures

Last month we discussed forages in general. As a short review, animal performance will be greater when either grazed directly or delivered daily as “green chop.” The reason is that we get all the nutrients contained in the forage. Whenever we process the forage so it can be stored, a significant portion of the nutritive value is lost.

That is, while silage and haymaking are referred to as forage “preservation,” that term is actually a misnomer. The reality is that a substantial part of the most highly digestible portion of the forage (the soluble carbohydrates and sugars) are burned up in the process. In the case of silage making, the soluble carbohydrates and sugars are converted into the organic acids that lower the pH and “preserve” the forage. In this case a significant portion of the energy is lost as CO2 and other gasses when bacteria synthesize the acids. In the case of haymaking, a larger loss occurs as the plant itself “burns up” the soluble carbohydrates during the respiration that occurs in the drying process.

For cereals, direct grazing or green chopping can result in gains of 2.0 lb./day, vs 1.25 –1.5 lb./day for silage and .5 to .75 lb./day for hay. Obviously, direct grazing is more efficient.

However, while grazing requires much less labour, machinery and effort than hay or silage, one should not be deceived. Grazing is deceptively simple. Grazing actually requires a much higher degree of management. This is particularly true for cereals. The primary reason is due to a much greater risk of death loss. Cereal grasses are high-quality feeds to the point they could almost be called “concentrates.” During the spring, when the weather is highly variable, they are subject to periods of rapid growth. This rapid growth can lead to excess amounts of nitrates, soluble proteins and/or macro minerals. The results can be nitrate toxicity, bloat or magnesium (mg) tetany.

All forages are susceptible to accumulations of nitrates, but cereals especially so. Nitrates are the precursors for protein (the source of nitrogen) and since cereals have higher protein concentrations than most grasses, they likewise usually have higher nitrate contents. I have seen nitrates in cereal grasses as high as 80,000 ppm (10,000 ppm is lethal).

Nitrates accumulate whenever good growing conditions are followed by a rapid change to overcast, cold weather. The plant absorbs nitrogen as nitrate and during rapid growth, large amounts of nitrates are absorbed. When the weather turns overcast, and photosynthesis cannot occur the plant is unable to convert the nitrates to protein, and thus nitrates pile up in the plant at toxic levels.

I should hasten to point out that nitrates can also be a problem in hay and silage. The ensiling process reduces nitrates roughly 30 per cent, but given the extreme levels cereals are capable of, a great deal of risk still exists. I once investigated a death loss in a feedlot ration with oat hay included only at a 10 per cent level. It occurred in a Third World country where we could not get laboratory analysis, but the concentration had to approach or exceed 100,000 ppm.

Bloat due to high levels of soluble protein, however, is unique to grazing (or green chopping). Again, periods of rapid weather change (such as spring) most commonly lead to bloat. These soluble proteins accumulate and create a gooey, foamy mass in the rumen (which precludes the animal from belching off fermentative gasses).

Magnesium tetany can also occur on cereal pastures, although true mg tetany only occurs in lactating cows. In upcoming columns we will discuss mg tetany, but for now I want to point out that cereal pastures are too high value a feed for cows. Certainly cows can be pastured on cereal pastures, but to do so is grossly inefficient and uneconomic.

Calves pastured on cereal pastures can and often die of what is diagnosed as mg tetany, but in reality, adequate mg will most often be present. Cereal grasses can accumulate massive amounts of potassium, which can lead to reduced mg absorption, and thus create an induced mg tetany.

Space does not permit a discussion of the preventative or remedial procedures to deal with these metabolic problems, but the point of this discussion is that grazing cereals does require that you recognize the risk. The rewards, of course, are increased gains (at a fraction of the harvesting cost). But while grazing doesn’t require all the labour, equipment and effort to harvest the forage and deliver it to the cattle, it does require a great deal of expertise and vigilance.

Cattle must be observed daily (in the early morning hours), and preferably twice daily. Remedial plans of action and/or antidotes must be on hand and capable of rapid administration. If knowledgeable veterinarians are not available locally for rapid diagnosis of unexplained death loss, highly experienced cowboys capable of detailed conversations with distant veterinarians must be employed.

Remedial action available must include having either native pasture or adequate hay available to rapidly move cattle when cereal pastures have been compromised by weather patterns and have temporary toxic levels of nitrates and/or are extraordinarily prone to cause bloat and/or magnesium tetany. When several unexplained deaths have occurred, the first response is to get the cattle moved before diagnosis is even performed.

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