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by Dr. David Porter Price Due to drought in the western states, a good deal of straw is being fed as roughage. Although book values show enormous differences between straw and conventional roughages such as silage, alfalfa hay, etc., straw can be used quite effectively in feedlot rations. It can also be used in other feeding situations with some restrictions and limitations. Straw in Feedlot Rations The principal problem straw presents for feedlots is that it is more difficult to process. The fiber is much more lignified than hay, and will be harder on equipment. Hammer mill screens and hammers will need to be replaced more often; or if a hay slicer is used, knives will need more frequent sharpening. Nutritionally, the only real problem straw presents is that an adjustment will have to be made for the lack of phosphorous, potassium, trace minerals, vitamins and of course, protein. On paper, however, computer programs or text book calculations will project substantially lower gains. The reality will be very similar gains with only slightly increased conversions. (Provided adjustments are made for reduced vitamins, minerals and protein.) The reason is that most software programs over-value roughages in finishing rations. That is, most programs function like adding machines and essentially just take the book net-energy value for roughages and add them into the ration total. The reality is that high grain rations drop the rumen pH which in turn radically reduces the population of fiber digesting bacteria and protozoa. As a result, the digestibility of roughages is greatly depressed in finishing rations. This means that properly processed and adjusted for, straw can be used quite effectively in finishing rations. All we need is fiber, and straw can fill the bill quite nicely. In Latin America where straw is often the only roughage available, many clients have found this to be the case. Corn Stover Nutritionally, corn stover is very similar to straw, but presents extra problems. Stover is much more difficult to process. Slicers simply will not work and hammer mills must be extremely heavy duty. It normally takes a tub grinder to process stover, and even then there are only a couple of commercial brands that can stand up to the daily grinding of stover. Properly processed, stover can be roughly the equivalent of straw. Properly means ground to pieces no longer than 1/2 inch. The reason processing of stover is so important is that longer pieces will usually be sorted out and not eaten. This obviously defeats the purpose for putting roughage in the ration and can lead to founder, bloat and/or acidosis. Another drawback to stover is that it is often difficult to obtain a source that has not weathered. Most commonly, stover is put up in round bales and left uncovered. The large voids in bales tend to let in moisture and mold is common. Mold and feedlot rations do not mix. A small amount of mold will make the entire ration smell bad and depress intake. Straw and Stover for Maintaining Cows When properly processed, straw and stover can be substituted for conventional roughage in feedlot rations without any real performance problem; it is much more difficult to do the same for range cows. In this case, the performance predictions of Net Energy Programs will be accurate. Cows will lose weight and unless adequately supplemented, dire consequences will be encountered at calving time; e.g. weak calf syndrome. Straw can be used, but it must be heavily supplemented with both protein and energy. In most cases the most economical supplement would be several pounds of wheat midds, distiller's grains or a combination of grain and oilseed meal such as canola, in addition to vitamins and minerals. As a nutritionist, I would not want to recommend or formulate a supplement to be used with stover. I am sure there is someone who has successfully wintered cows on stover, but it is too coarse to give consistently good results. Ammoniation In the 1980's research conducted at a number of U.S. land grant universities demonstrated that the digestibility of straw can be dramatically improved by ammoniation. Properly applied, ammonia apparently breaks down lignon and makes the fiber more digestible to rumen micro-organisms. Ammoniated straw can approach the energy value of low quality grass hay. There are other ways to treat straw (calcium hydroxide, enzymes etc.), but ammoniation is the most practical and cost-efficient. Enormous numbers of cows are maintained on ammoniated rice and wheat straw in China, and I have had clients maintain cows on ammoniated wheat straw in the U.S. Watch Out When Ammoniating Other than supplementing for the vitamins and minerals absent in straw (but present in hay), it is vitally important to realize the chemical reaction in ammoniation is temperature specific. All the published university trials have been conducted in the fall (after harvest), and reported excellent results. A client who attempted to ammoniate in August, however, ran into problems. Hot weather apparently takes the reaction further, and creates what are known as teratogenic compounds. Specifically, this client encountered birth defects that could only be traced to the straw. It is also important to realize only low quality roughages should be ammoniated. Good quality hay must not be ammoniated. Good quality hay would contain soluble sugars which combine with ammonia to form toxic compounds. Next month we will discuss the specifics on "how-to" ammoniate straw. If you need more information right away, contact Dr. Jim Males at Washington State Univ.; Dr. Bobbi Pritchard at South Dakota State Univ.; Dr. Gerry Kuhl at Kansas State Univ., or e-mail me at nutconsult@zianet.com. © |
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