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Forage As A Feedstuff

David P. Price is a consulting nutritionist specializing in feedlot and range cattle

The more we process forage, the more we lower its value as a feedstuff

www.cattleandwildlifenutrition.com

Among the public, “natural” is supposed to be best. The reality is that there are some very nasty “natural” compounds. Preservatives are far preferable than aflatoxin or fumonisin, etc.

But with respect to forage, natural really is best. The more we process forage, the more we lower its value as a feedstuff.

A good example would be cereal crops used as forage. If we graze barley we can expect roughly a 2.0 pound daily gain. (This assumes that the barley is not overly mature and that a properly formulated mineral supplement is being provided).

If, on the other hand we cut and ensile the barley, we are looking at roughly a 1.5-pound daily gain. Certainly we can add grain or byproducts and make a silage “ration” which will increase gain similar to grazing; but if we feed straight barley silage (with only mineral supplementation) we cannot realistically expect more than about a 1.5-pound gain.

At face value that is a 25 per cent reduction in gain, but it goes deeper than that. On a per acre or per ton of green chop basis, the reduction approaches 40 per cent. Why? Because whatever we put in the pit will experience roughly a 12 to 15 per cent shrink. (Shrink can approach 25 per cent for silage mounded on the ground without walls.)

Obviously, these can include moisture runoff losses. But that moisture is not just water. The most valuable and digestible of the “soluble” carbohydrates and sugars will be contained in the “water” that leaches out. If, on the other hand we cut the barley at the exact stage of maturity where runoff is negligible, the soluble sugars and carbohydrates will also be lost; albeit not totally.

The bacteria that drive the ensiling process will attack the soluble sugars and carbohydrates converting them into organic acids. These are the acids that preserve the silage.

The problem is that the bacteria will also release some of the energy contained in the soluble carbohydrates in the form of gas (mostly CO2). This is why you should not enter the top of an upright concrete silo, as often the CO2 has replaced much of the oxygen.

The bacteria also digest a significant amount of the soluble carbohydrates for their own use. This, as well as heat produced from exothermic reactions in breaking down the carbohydrates result in the “heat” a pit of silage goes through during about the first five to seven days of being put in the silo. This heat is an energy loss and is part of the “shrink” you experience in preserving forage as silage.

The bottom line is that you get less gain on forage taken as silage; and you take less forage taken out of a pit in the form of silage than the amount of green chop that went in. Taken together, the loss approaches 40 per cent.

Losses with hay are even greater. In this case bacteria do not convert the soluble sugars and carbohydrates (into organic acids), wasting part of the energy in the process. Instead, virtually all the solubles (the most digestible portion of the forage) are lost. Not lost to bacteria, but metabolized by the plant itself.

When we cut and lay down forage, the stalk is cut off from the roots, but it continues to respire. That is, what we call the drying or curing process is actually the plant continuing to try and remain alive. The leaves attached continue to absorb the juices from the stalk and metabolize the energy contained in the juices (the soluble sugars and carbohydrates). The good news is that the moisture (and the soluble nutrients) are used up so bacteria can’t grow and spoil the hay. The bad news is that they are used up. Most of what we have left is fibre, which while digestible, is nowhere near as digestible as the juices we “dried off.”

The net result is that if we feed cattle only barley hay (and supplement only with minerals), at best we will get about a 3/4 of a pound gain. The ultimate reality is that silage and hay making do not really “preserve” the forage. Silage and hay making are processes in which we trade a portion of the value of the forage in order to convert it into a stable form for long-term storage.

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