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Forage Sorghum Risks

Prussic acid is a major concern in regards to feeding cattle on sorghum, whether it?۪s forage or stubble. Young growth and early regrowth have higher prussic acid levels than more mature stands of forage. Stresses on the plant will lead to an accumulation of Prussic acid, also known as Hydrocyanic Acid (HCN), within the plant. Stresses can be from:

  • Stunting,
  • Drought,
  • Wilting,
  • Frosts,
  • Cutting,
  • Crushing, and
  • Chewing.

With rainfall finally bringing an end to the drought in most areas, we are experiencing rapid vegetative growth and therefore the levels of prussic acid in forage sorghum may be higher than usual.

Some plants, including sorghums, have a greater ability to release HCN when the plant cells are disrupted. This release of HCN becomes a problem when glycosides react with specific enzymes that are found in mesophyll cells within the plant, following a stressful event.

Mesophyll cells are located within the leaves of the plant, while the cyanogenic glycoside, dhurrin, is located in the epidermal (outer) cells. Cyanogenic glycosides within the epidermal cells degrade to HCN when reacted with the enzymes that are released from the mesophyll cells when a stress, physical or environmental, is exerted upon the plant. The specific enzyme that allows the release of HCN is also found in the rumen, thus chewing will also lead to HCN production, highlighting the need for a detoxifying agent.

This fact, coupled with the knowledge that diets of various sorghum varieties are generally lead to sulphur and salt deficiencies means that a supplementation program suited to these circumstances can take your cattle a long way in terms of production. Studies show that age is a major factor in determining quality of the sorghum plant. As the plant ages past eight weeks the sulphur and salt content declines, as does the digestibility of the plant. Thus, in leaving your forage crop for longer than necessary to avoid Prussic Acid poisoning, you are losing some of the major benefits that feed crops offer.

The losses in achievable production through not supplementing, or not supplementing correctly, are recognised when compared with a well supplemented herd on forage sorghum. General appearance, comfort and weight gains are affected by a proper supplementation program. A trial conducted through one of our customers showed an increase in Average Daily Gain on Top Forage from 1kg/head/day in the non-supplemented control herd to 1.67kg/head/day in the supplemented herd. When you space this improvement out over the time you plan to feed on forage, the results speak for themselves. Over a 30 day period, that is an extra 20kg/head, thus target weight is achieved more efficiently. The gains over this time frame will roughly cost $7.80/animal, but on current industry values these additional gains are worth $107/animal (MLA Over the hooks cattle report for 20 November 2015). Multiply these calculations across a herd and for a small input, substantial benefits can be gained.

Supplementation with a lick supplying extra sulphur, sodium and other minerals likely to be deficient in green feed, such as Phosphorus, will allow you to capitalise on your forage crop at the optimum time of growth, while avoiding toxicity problems that usually affect production. Prussic acid works rapidly within the body via entering the blood system and inhibiting oxygen utilisation in the cells around the body. This process can take only 15-20 minutes to start to show clinical signs in an animal. The ease at which our seasonal conditions can trigger the change from glycosides within the plant cells to HCN means that we have to prevent the toxicity from decreasing production. One of the best ways to do this is via sulphur supplementation directly to the animal.

Animals are able to detoxify HCN within their body, given that Sulphur is readily available for this process. Sulphur generally is not deficient in a sorghum crop however a diet mainly of sorghum can lead to a deficiency in the body as Sulphur is required for the efficient conversion of Prussic Acid to non-toxic thiocyanate in the liver and the rumen. Thus an increase in prussic acid will also compromise sulphur availability in your animals. Sulphur deficiency can result in a decreased appetite which results in lower weight gains. Prussic Acid problems are presented not so much by the number of deaths, but by the losses in production to your herd.

Keeping your forage sorghum supplement fresh and protected from the weather can be difficult. Top Country manufactures quality, covered feeders that have stood the test of time and continue to provide a reliable way of storing lick for cattle in the paddock. Top Feedas are versatile, and can be adapted to also serve as a fly management tool. This season calls for a quality covered feeder that can have oil distributors and backrubbers fitted to it. Remember, Sulphur supplementation in forage sorghum helps prevent poisoning and improves your productivity. Call the office today and have a chat with one of our sales nutritionists today to discuss the best options for YOUR herd.

Tags: BEEF Supplements toxicities cattle forage sorghum prussic acid sulphur

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