Silage questions and answers

Written by Dr. Jim White on .

I get questions. And silage questions are among the top. I’ve gathered a few (and left off the names to protect both innocent and guilty).

Q: Is it true that high nitrates can kill cows? What dose? And why?
A: Smothering can kill cows. Excessive nitrate consumed can become nitrite in the rumen, and nitrite really holds on to oxygen. Nitrates are not always toxic to animals; most forages contain some nitrates (plants like handling nitrogen as nitrate). When feeds containing nitrates are consumed by ruminants, nitrates are changed in the rumen to ammonia that is used by rumen bacteria.

That is the good news. The bad news is that nitrite is one of the intermediate products in the breakdown of nitrate and is the cause of nitrate poisoning.

Some nitrite is absorbed, and nitrite in the bloodstream changes hemoglobin to methemoglobin. Hemoglobin carries oxygen, but methemoglobin is incapable of carrying oxygen. The toxic level depends both on the amount of nitrate in the feed, and how fast the feed that contains nitrate is consumed.

Nitrate concentration will spike up for a couple days after a drought-breaking rain. When drought-stressed plants get water, they try to make up for lost time, and nitrate levels increase.

Although nitrate levels in drought-stricken corn may be high, ensiling usually reduces more than half the nitrates. For this reason, nitrate toxicity rarely occurs when feeding ensiled drought corn. However, if drought damage was extreme and high levels of nitrogen were applied to the soil, a nitrate test on the silage should be conducted. Rate of nitrate intake is the most critical factor influencing possible toxicity. Cows grazing corn stalks are unlikely candidates for nitrate issues—they do not eat the part of the plant that has the nitrates. Nitrates accumulate in the lower base of the plant, the part cows want to leave behind if they have a choice.

Likewise if you have to get safe green chop right away, raise the chopper to take the plants just under the ear. Green chop should be fed the day it is harvested. As mentioned earlier, the nitrate breaks down to nitrite, and it is the nitrite that hogs up the oxygen in the blood as greenchop nitrite levels grow higher.

Q: What is the best moisture content to ensile drought stressed corn?
A: If you had the chance to chop corn at the best moisture content for silage, it would be 65 to 68 percent moisture. Moisture levels lower than 50 percent are low for silage. Below 50 percent is workable, but excluding air becomes a challenge.
The silage will mold if air is able to get in, so adequate sealing is important. Excluding air reduces spoilage, which saves feed (which this year saves you big money).If the corn plants did not set ears, it will tend to stay wet until it dries up, dies or a good frost comes.

Q: What is the feeding value of drought-stressed corn silage?
A: Corn silage drought stunted to less than 20 bushels per acre will have about 75 to 80 percent the total digestible nutrients of normal silage. So, if normal silage has a TDN of 72 to 75 percent on a dry matter basis, drought silage will be 54 to 60 TDN, which is adequate for many applications. It could be supplemented with energy in some cases.

Absence of ears does not imply that corn silage lacks fermentable energy. It’s actually the contrary—the kernel was not a glucose sink, and there are a high level of soluble sugars with nowhere to go. As the corn plant matures, the energy level and dry matter yield increases.

I recommend allowing corn to develop as fully as possible, even if ears and grain are lacking. There are wide variations in the nutritive content of drought-stressed corn silage. Get it tested so you know what you have to work with. If you get the forage test back that shows high potassium, expect high nitrates, which you should expect on stressed plants.

If the plants were very young, say waist high, tasselled out and dried out, you might see a protein level in the mid teens. And, in that corn, nitrates might get as high as 0.9 to 1 percent, which means that you would need to limit-feed the material. Feed at levels to keep rations below 0.25 percent nitrates for wet cows and 0.44 percent for growing animals or mature adults at maintenance.

Q: Adverse weather conditions present me with major challenges. First, I am not able to produce enough forage. Second, the forage quality is hit and miss. It is either really good (the drought-stressed alfalfa has a relative feed value over 200), or it is really bad (the corn with no grain in it). My questions are: should I buy more forage? Or, should I keep forage at a minimum, and bring in concentrates of higher fiber?
A: A common question these past two years. First, it is essential to evaluate your particular situation, including effects on cash flow. The other day I was talking to an accountant. I was whining about how they had costed out some inputs. And I asked, “Why did you do it like that?”
The accountant said, “To get the right answer.”
That seemed a good reason—the way I wanted to do it was to not consider some costs. Sure, that made for cheaper feed, but it was an inaccurate number, which would have projected more income-over-feed cost than there really was.
If you can get additional price-competitve forage, then importing forage is certainly a viable option. But consider what you’re buying. Work with a known dealer, or have an agreement for minimum quality. Also consider the forage’s availability, palatability and suitability. Drought-stressed material might also have high levels of nitrates or increased incidence of poisonous plants.
If you hold down the amount of effective fiber fed to milk cows, you will tend to want to feed lower amounts of starch-NSC to them.
When faced with a true shortage of forage, feeding lesser amounts of coarse material is a tactical approach to the inventory problem. As the pounds of NDF fiber from forage declines, the minimum diet ADF increases and the minimum diet NSC decrease.
To achieve the energy level in the diets that your cows need, you can consider supplementing MFA Dairy Heartland feed to take pressure off the shortage of forage availability.


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