David P. Price is a consulting nutritionist specializing in feedlot and range cattle
With hay supplies tight, straw is a viable substitute in feedlot rations. Indeed, in Mexico, where most feedlots have dairy sheds in the vicinity, feedlots are often forced to routinely use straw, as the dairies bid hay out of reach. Hay quality is highly important in dairy rations; not so much in feedlot rations.
With high grain feedlot rations the rumen pH falls below 5.8, and at that level of acidity the majority of the cellulolytic bacteria and protozoa (microbes that digest fibre) are dead. As a result, in feedlot rations fibre is very poorly digested and what this means as a practical matter is that hay quality is not very important. All we really need is a source of lignified fibre that will cause cattle to ruminate. Straw certainly fills that requirement.
Legume hay such as alfalfa or clover can supply a significant amount of protein, calcium and trace minerals — but very little energy. Feeding rations containing good-quality hay will have only marginally better conversions than rations with straw. (Providing we supplement extra protein and minerals to compensate for the straw.)
The big practical difference in straw versus hay is palatability. Obviously, hay is fundamentally more palatable, but there is a secondary problem common with straw. Since hay is more valuable, it is more likely to be stored properly. Straw, on the other hand, is routinely left in the field and as a result it is often difficult to find “good” quality straw.
By “good” we’re referring to free from mould. If left in the field, straw is commonly contaminated with mould. Obviously, fuzzy growth is something we don’t want in a feedlot ration, but the off-coloured “weathered” look is also a potential troublemaker.
The reality is that procuring good straw takes effort. Most often we have to contract with farmers ahead of time, and either take delivery as soon as it is cut, or otherwise see to it bales are covered or moved under a roof.
Cornstalks. While hay is more palatable than straw, good, bright straw is readily eaten by cattle when present in small quantities. Cornstalks are another story. Unless cornstalks are finely ground (and used in conjunction with a ration conditioner), cattle will sort them out and leave them. That said, I have clients who have used cornstalks long term with no problem. But it takes special equipment to grind cornstalks, and regular maintenance.
Most tub grinders and hammer mills will grind straw, but there is only one brand of tub grinder I am aware of that will handle the daily battering of grinding cornstalks. If not adequately ground, cattle will sort out and leave the large pieces. This runs the risk of acidosis and/or bloat.
If straw is not adequately ground, the same problem will occur, although what is adequate for straw is quite different for cornstalks. Pieces of straw three to four inches in length are entirely adequate; cornstalks must be shattered into pieces less than one inch.
If straw is not adequately ground, you will not find pieces left in the bunk. More commonly you will find some cattle that sort and others that become straw eaters. The end result is poor performance in the straw eaters and an otherwise higher percentage of digestive deads in the rest.
If mould is present, you will likewise not necessarily find the straw sorted out (if it is properly ground). Rather, the presence of mould will reduce overall consumption. Therefore mould carries a double whammy. Reduced gain due to reduced consumption; in addition to the detrimental (toxic) effect of the mould itself.
Corncobs. Finally, I feel compelled to mention corncobs, as eastern Canadian clients are often offering cobs as a source of roughage. On paper (a laboratory analysis) corncobs are a roughage substitute. In reality they are not. Unless ground extremely fine, cattle will not eat corncobs. If ground almost to the consistency of a meal (so cattle will eat them), cobs lose their roughage value. That is, they do not have the long fibre necessary to induce rumination. Although I have no scientific proof of this, it is my belief cobs tend to float on the top of the rumen fluid. Whether that is right or wrong, as a practical matter cobs are not protective of digestive problems to anywhere near the extent of long-stem roughages and consist of nothing but a cheap filler. This I can tell you from experience.
Final note on mould. I cannot overemphasize what a serious problem mould in straw (and cornstalks) can be. The grey “weathering” on the exterior of bales left in the open will almost always contain mould. This is bad news.
I have used bright, fresh straw (at low levels) even in receiving rations with good results. Try using weathered straw and consumption will crash. In receiving rations that will result in substantially more death loss, due to respiratory diseases. In feedlot rations we can force feed weathered straw, but performance will suffer.
The bottom line is that straw is a viable feedlot roughage substitute, but even though it is a feedstuff with very low nutritive value — quality is important. Since it is a commodity normally used only for bedding, etc., few farmers store it properly. Successful feedlot management is attention to detail, and this is an important detail to understand.