Previously, on the Practicum:
“The problem, therefore, is where protein synthesis occurs, which is usually higher up in the leaves. Photosynthesis and a major portion of protein metabolism occur in the leaves, thus when environmental conditions slow or inhibit these normal plant processes, protein synthesis slows down; yet, root nitrate accumulation does not! The situation becomes akin to a dog chasing its tail, or the basic economics of supply exceeding demand, where the conversion into plant protein is unable to keep up with soil nitrate uptake.”
The information from the forage-half of the nitrate toxicity debacle is certainly a lot to take in; lots of information to process, still more questions to answer, especially when it comes to your own personal context with what animals you have, what kind of feeds you have available, and what kind of timing situation you’re faced with.
In the last instalment of this two-part series, I talked about various environmental, plant-related, and management factors that influence nitrate accumulation, as well as the juggling act of determining the best time to harvest in relation to nitrate levels.
Now, let’s leave the forage part of the nitrate-accumulation discussion behind and look at the animal side of the equation. I will revisit a part of the forage equation again later in this post, particularly with managing problematic feeds to the best ability possible.
Nitrates are a without a doubt a big concern; concentrations in the harvestable parts of a plant–primarily grasses such as annual cereals (barley or oats) or perennials (smooth brome-grass or tall fescue), as well as brassicas and weeds (pigweed, kochia, and lambs-quarters)–result in either significant death losses or more subtle productivity losses such as declining milk production and lower average daily gains. However, there are ways to manage such nitrate-rich feeds and forage stands.
In this final instalment, I talk about which animals are most susceptible to excessive nitrates, how they can be so affected–both acutely (resulting in death) or sub-clinically (resulting in production losses)– and what to look for in terms of symptoms of nitrate toxicity. I will also go over what you can do to try to save these animals. (Note: I will talk in very general terms in this area, as I am not a veterinarian.) . I will then discuss how to read nitrate feed test results and how to calculate out some of the parameters between different–and often confusing–test result values. From there, I give you some tips and tricks on how to figure out what to do if you have any nitrate-rich feed (as confirmed by a feed test), including how slow introductions can make all the difference between life and death (and how best to go about this), and what else needs to be fed or done to prevent any further issues.
Contents
What Animals are Most Likely to get Nitrate Poisoning?
The best way to show is this is with a very handy table. The asterisk (*) is for those animals that are most susceptible to nitrate poisoning.
| Ruminants | Monogastrics |
| *Cattle | Equines (horses, donkeys) |
| Sheep | Pigs |
| Goats |
How do Livestock get Poisoned? What Happens to Them?
A major difference between monogastrics and ruminants is the ability to convert nitrate to nitrite, and the inability to convert nitrite to ammonia. While ruminants have this ability (as I’ll discuss soon), horses and pigs do not, simply because they lack a rumen.
Pigs and horses usually need a direct source of nitrite (or nitrate, to some extent) to become severely ill and die. Nitrite (NO2–)is approximately 10 times more toxic than nitrate (NO3–).
Sources of nitrite are usually from high-nitrate hay that was baled up wet then heated, converting nitrate into nitrite. Other sources might include fertilizer, contaminated water, or hay grown on a fertilizer spill. Pigs are more susceptible than horses when young, and less susceptible when they’re adults. Young pigs (shoats) have the microflora in their large intestines to be able to convert nitrate into nitrite in their digestive tracts, but this capability goes away as they mature, where adult boars and sows are more nitrate-toxicity resistant. Some veterinarians reported cases, where some shoats died after feasting on some high-nitrate plants such as Redroot Pigweed and Lambsquarters, confirmed this (Wunder & Schultz, 1960; Sidhu et. al., 2014).
Horses, on the other hand, are hindgut fermenters, unlike either pigs or ruminants like cattle. The microbes in the cecum can convert nitrate into nitrite, but not nearly to the extent that it can happen in cattle or sheep. Thus horses need to have a much more direct form of nitrate (or even nitrite) to become sick, which is a rare occurrence.
The key thing is that nitrate has to be converted to nitrite in order to cause ill effects in animals. Because monogastrics don’t have nearly the capacity that ruminants have to be able to do this, this explains why nitrate poisoning is quite uncommon for them. It’s a different story for ruminants, however.
So, Why (and How) are Ruminants More Sensitive to Nitrate Toxicity?
Normally in the rumen, plant compounds such as nitrate (among other types of proteins and non-protein nitrogen) are quickly broken down into nitrite then to ammonia (NH3). The microbes make use of ammonia for their protein needs, or into urea to be expelled in the urine, or recycled back to the rumen where it’s converted back to nitrate, then nitrite, then ammonia again.
However, when rumen microbes are faced with a sudden influx of forage containing high amounts of nitrate, that nitrate gets quickly reduced into nitrite, but the microbes cannot keep up with the conversion of nitrite to ammonia.
We can almost draw a parallel between the nitrate accumulation in forages and nitrite accumulation in ruminants; where the plant’s system is too damaged to keep up with converting nitrate into usable forms of amino acids for protein synthesis, the rumen microbes are too overwhelmed with the conversion of nitrate into nitrite that they cannot break down nitrite into ammonia fast enough. The parallel between plant and ruminant ends is when nitrite, instead of remaining in the rumen (as with the accumulated excessive nitrate remaining in the plant cells’ cytoplasm), moves through the rumen wall into the animal’s bloodstream. This is where things take a turn for the worst.
Once in the bloodstream, nitrite ions come into contact with red blood cells and oxidize iron within hemoglobin, turning hemoglobin into methemoglobin. Unlike hemoglobin, methemoglobin is unable to carry oxygen to body tissues. When enough methemoglobin is converted from hemoglobin, the animal starts to suffer from oxygen starvation; basically, “internal suffocation.” This can lead to death, but not always. The rate of hemoglobin changing to methemoglobin is influenced by four main factors:
- Rate of nitrate intake (or, how quickly and how much nitrate-rich feed is consumed)
- Rate of nitrite-to-ammonia conversion (or the speed to which nitrite is being converted into ammonia in the rumen)
- Rate of digestion which corresponds with the subsequent release of nitrate in the rumen (or how rapidly feed is being digested in the rumen which influences the rate that nitrates are released into the rumen)
- Rate of nitrite movement out of the rumen (as determined by feed passage rate and rate of intake as indicated by 1 & 3)
Methemoglobin can be converted back to hemoglobin, but it takes time (Merck Veterinary Manual states it takes approximately two (2) hours to do so). However, keeping in mind the four points above, nitrate toxicity can be exacerbated by the ability of the animal to recycle nitrate back into the rumen.
One thing I failed to mention above is that while nitrate certainly does quickly get converted to nitrite, however not all of it does. Thus, nitrate will also accumulate in the rumen and get released into the bloodstream right along with nitrite.
We must keep in mind as long as the animal is consuming the feed high in nitrates, nitrate gets continually released into the rumen by the rumen microbes that are doing their due diligence of digesting the feed. Thus the addition of new nitrate also compounds the nitrate poisoning issue.
We have two primary issues that will intensify the toxification of nitrates:
- A continued supply of “fresh nitrate” into the rumen from the feed the animal is eating, and
- Nitrate being continually recycled back into the rumen.
We must also realize that it’s still not the nitrate itself that creates the initial problem. It’s the ability of the nitrate to be both converted into nitrite in the rumen, and the excess blood nitrate being recycled back into the rumen (via saliva or secretions from the intestines) to be caught and thus reduced into nitrite, which gets sent out to the bloodstream before microbes can further reduce it to ammonia. You could call it a vicious cycle, or a negative feedback loop; you’d be right on both accounts.
Ultimately, the toxicity level of nitrate is largely influenced by how much nitrate gets recycled back to the rumen as well as the rate that nitrite is broken down. This is particularly true on an individual animal basis. It is, therefore, safe to state that the level of tolerance to nitrite differs for each animal; some can take higher levels than others. In other words, there is marked variability between each individual animal in the amount of methemoglobin that gets created in the body, and consequently prior to where such amounts will affect production or reproduction, or worse, kill the animal.
At this point, it’s important to note that cattle are more sensitive to nitrate poisoning than sheep or goats; Sheep are notably somewhat more tolerant than cattle because some sources state that they are more efficient at turning nitrite into ammonia than cattle are. I could assume goats may have similar attributes as sheep, however, I don’t have sufficient evidence to be able to support such an assumption, let alone comment on those species of small ruminants any further. If you are concerned about this, however, I would advise consulting with a large-animal veterinarian about this.
What Symptoms of Nitrate Poisoning should I look for?
There are two primary types of nitrate poisoning: acute or clinical and chronic or sub-clinical toxicities. Each has its own set of symptoms.
Acute or Clinical Nitrate Poisoning
(Kansas State Veterinary Diagnostic Laboratory) Cows were found dead the morning after being fed sorghum-sudan the evening prior.
Animals that are experiencing acute poisoning are undergoing serious effects of rapid ruminal nitrate-to-nitrite conversion and immediate nitrite absorption into the bloodstream. Potential for death within a few hours is imminent. In fact, this is the most common discovery of nitrate toxicity cases; well before any symptoms of poisoning are noticed. According to Merck Veterinary Manual, some animals will die without showing any symptoms, some may undergo anoxic (lack of oxygen) convulsions within an hour after ingestion, and still, others may not succumb to the acute effects of poisoning until 12 to 24 hrs later.
Other symptoms of acute poisoning include rapid and weak heart rate, lower body temperature, muscle tremors, vomiting, blue-grey mucous membranes, excessive salivation and tearing, weakness, depression, shortened or laboured breathing, frequent urination, staggered gait, disorientation, and lack of ability to get up. Animals will usually lie back down after a short struggle to stand or walk a short distance.
Chronic or Sub-Clinical Nitrate Poisoning
Cases of chronic nitrate toxicity do not display the same signs as those of acute poisonings. There is a greater chance to notice a drop in weight gain of growing calves, lower milk production, depressed appetite, and increased susceptibility to other illnesses.
Other signs are more reproduction-related. Cows can experience abortions within the first 100 days of pregnancy due to nitrates (more likely nitrites) interfering with embryo implantation in the uterus. An embryo that doesn’t attach itself to the uterine wall dies and gets reabsorbed by the cow; no obvious abortion signs are seen during the first trimester. Instead, a cow is much more likely to come up open (not bred) with a pregnancy exam or go into heat sometime during or after what was supposed to be her first trimester, whichever comes first.
Reproductive difficulties may also occur due to a hormonal imbalance caused by nitrate or nitrite, such as reduced conception rates and more services required per conception (Davison et. al., 1964). However, such problems often do not get recognized as a feed-related issue.
Premature births are another reproduction-related problem. Calves are born a week to four weeks premature when they are affected by nitrate poisoning during the last trimester (or at least three months of pregnancy), and maybe stillborn or live until they die 18 to 24 hours after birth. Still, others that survive past that time period may undergo convulsions and seizures. A study by Ozmen et. al., (2005) mentions blindness in calves being also a result of chronic nitrate poisoning.
I cannot comment on whether these calves will eventually get over these disturbing signs of chronic nitrate poisoning, as that is something I highly recommend discussing with your large animal veterinarian. It may be in the calves’ best interest to euthanize them especially if the prognosis is poor. However, calves have been known to survive to adulthood after being born with nitrate toxicity effects, with nitrates eventually being evacuated in the urine and sweat. However, as Blum et. al. (2001) notes, such survivors may be more sensitive to nitrate poisoning should they become affected again, albeit later in life.
Is there a Way to Treat Animals with Nitrate Poisoning?
Nitrate poisoning is treatable. However, this is something your large animal veterinarian will know how to deal with if you contact them; preferably as soon as possible!!
Since I am not a veterinarian, I am not qualified to give out recommendations for such situations, except for three big tips that will help in your situation:
- Remove the animals from the suspect feed immediately. This will deny their microbes access to nitrates that they never got a chance to become accustomed to, and getting access to feed with low nitrates and high energy to quickly get the nitrates converted to a non-toxic form, and moved out of the system. As mentioned above, sudden and constant access to nitrates creates a situation that could be fatal.
- Contact your veterinarian immediately. You will only have minutes or hours (not days) to try to save those animals that are suffering from acute poisoning.
- Handle animals as quietly and as little as possible to minimize their oxygen needs.
A veterinarian will recommend a 1% solution of Methylene blue given via slow IV injection. Dosages in amounts and how often they need to be administered depends on how badly poisoned the animal is. Treatment may need to be repeated every 6 to 8 hours, particularly if the rumen is still full of nitrate-rich feed and nitrates and nitrites are still moving from the rumen to the bloodstream.
After dealing with that scare, the next steps will need to be testing the feed (as discussed in my previous post), interpreting the results, then figuring out how to best manage the feed so that your animals become adjusted and can be fed safely without going through something like this again. I talk about these next.
The Nitrate Feed Test Results: How to Read Them
Back on Nitrates in Forages: It’s All In the Timing I discussed how to gather a suitable sample of feed to send to a laboratory to get tested. You’ve waited long enough and finally get the feed test back.
The problem is, there’s a whole lot of numbers, a bunch of different types of data reporting before you finally find somewhere on the page–it could be at the bottom or lumped with the protein analysis–something that looks like the nitrate analysis.
Except that, it’s reported as some variable you’re not too sure about. So you get on the phone or hop on the computer to get in touch with someone who may know better… such as yours truly!
And there’s a very good reason for the confusion: Nitrate levels are actually reported not in just one way (it would make life much simpler, wouldn’t it) but three ways. To make matters worse, these values can be reported as a percentage, or as ppm (parts per million).
I think the best way to help you out with this arithmetic is to provide some examples that may come across your kitchen table should you have to dig out a pencil and calculator to figure out whether the numbers provided in the test report are in fact safe, or not.
What is the Highest Number for Nitrates Before Animals get Sick?
However, one major thing I must discuss with you first is the discrepancy in reporting on some of the numbers provided in the table below, particularly with the percent nitrate that has been historically deemed not safe but is now considered a generally-safe to have-caution number. Let me begin by providing you with a very handy table, courtesy of Alberta Agriculture & Forestry’s Nitrate Poisoning fact sheet (see Sources below):
| Nitrate Analysis Methodology & Data Reporting |
| Level | %NO3 (Nitrate) | %NO3-N (Nitrate-nitrogen) | %KNO3 (Potassium nitrate) | Comments |
| 1 | 0.5 | 0.12 | 0.81 | Generally safe |
| 2 | 0.5 – 1.0 | 0.12 – 0.23 | 0.81 – 1.63 | Caution |
| 3 | 1.0 | 0.23 | 1.63 | High nitrate problems |
In the past–and I have received plenty of questions regarding this–nitrate levels were believed to have been toxic to livestock if fed past 0.5% NO3. This is no longer the case, primarily because of recent studies done to find out the correct level to feed cattle.
An old study tested the tolerable nitrate levels (for all accounts it could have been sodium nitrite but I cannot find the study to confirm this) in cattle by intravenously (IV) injecting sodium nitrate into the bloodstream. The researchers concluded that the safest level of nitrate for cattle was 0.5%. A large number of agricultural extension articles published announced to farmers all over the world these findings. I still see some articles that report such values even today (primarily in the United States)!
However, other researchers certainly noticed the big elephant in the room in that this was nitrate that was not being fed to animals in the form of forage. Thus, a new paper came out (again, I wish I could find it to plug it into the Sources below) that tested nitrate levels by feeding animals feeds of different levels of nitrates, and discovered that the average maximum limit for nitrates before any noticeable acute toxicity was seen was 1.0% NO3.
The big difference between the two studies links back to what I discussed earlier: the first study completely ignored, or rather bypassed, the crucial role that rumen microbes have on nitrates in the feed. These microbes are the ones who are busy trying to convert nitrate to nitrite then to ammonia before any potential negative effects occur; especially in a feed with normal, minimal amounts of nitrate. Ignoring these very important life forms that feed the cow doesn’t do justice to the cow herself.
Therefore, what these studies indicate is that, without any effort in getting animals adjusted, nitrate levels that are lower than 0.5% of the total ration (in dry matter) are generally safe. Chronic toxicity can occur when nitrates get between 0.5% and 1%. Acute toxicity is more likely at around 1% nitrate or higher.
Now, about those calculations…
How do I Calculate this Value on my Feed Test Report?
Let’s say that you received a feed test report back on some barley greenfeed. The nitrate level on the report is coming back as Nitrate-N, and the number they gave you is 4,500 ppm. So you dig out the calculator and jot down the following calculations:
4,500 ppm Nitrate-N x 4.43 = 19,935 ÷ 10,000 = 1.99% Nitrates.
This tells you that this feed will need to be strictly managed as much as possible, lest it causes toxicity effects in your animals. I will discuss this more below.
In a second scenario, you have some standing corn you want to graze and had a nitrate test done on it, only this time the lab sent back the results as 2,500 ppm KNO3. You do the following calculations:
2,500 ppm KNO3 x 0.61 = 1,525 ÷ 10,000 = 0.15% Nitrates.
That result shows that the feed is pretty safe to feed without any noticeable repercussions.
A third example is a report you received back from getting some slightly caramelizing, heated grass hay that was baled up wet and came off a field that was heavily fertilized earlier that spring. You’ve been advised to get a nitrite test done along with a nitrate test. You missed seeing the nitrate result, and instead focus on the % nitrite number: 0.45%. You figure that’s not too bad, but dig out the calculator anyway and make the following calculations:
0.45% Nitrite x 1.3 = 0.59% Nitrates.
This tells you that you will need to make some plan of action to get your cows adjusted to the hay, and even think about feeding something else, suspecting that the heated hay isn’t going to be as good quality as you had initially hoped.
To give you a better one-stop-shop to calculate the different reported values, I’ve created the following table to better assist you.
| Method expressed: | Multiplication factors to get values on the lefthand column: | |||
| N03 [or 2]-N | NO2 | NO3 | KNO3 | |
| NO3-N (Nitrate-nitrogen) | 1.0 | 0.30 | 0.23 | 0.14 |
| NO2-N (Nitrite-nitrogen) | 1.0 | 0.30 | 0.23 | 0.14 |
| NO2 (Nitrite) | 3.3 | 1.00 | 0.74 | 0.46 |
| NO3 (Nitrate) | 4.4 | 1.34 | 1.00 | 0.61 |
| NaNO3 (Sodium Nitrate) | 6.1 | 1.85 | 1.37 | 0.84 |
| KNO3 (Potassium nitrate) | 7.2 | 2.20 | 1.63 | 1.00 |
Remember: 10,000 ppm = 1%. Or, for example: 10,000 ppm NO3 = 1% NO3.
Or, moving the decimal 4 places to the left shifts ppm into %; moving the decimal 4 places to the right shifts % to ppm.
If a value is expressed as mg/kg instead, note that 1 mg/kg = 1 ppm.
From here, we can shift focus into some tips and tricks on how to feed nitrate-rich (or “high nitrate”) feeds to your livestock safely and properly. I will not use these values in the guidelines below, as there are far too many unknown variables that may or may not help you ascertain what best suits you in your situation.
What Are Some Guidelines for Feeding/Grazing Forages with Nitrates?
There are some differences in grazing high-nitrate forages versus feeding stored forage high in nitrates. However, the key similarity between them all is getting livestock (their rumen microbes, actually) as acclimatized to the nitrates as possible, and maintaining such status until the feed or forage of concern is gone. There may be some exceptions, as I will discuss soon.
Grazing Nitrate-High Forages
Often the best course of action for grazing forages that are suspected of–or have been tested and confirmed for–nitrates is to just leave the area alone for a couple of weeks to let the nitrates settle back down to normal. This is especially true with standing forage, such as pasture or an annual crop that is set to be grazed; not so much with forage that has already been swathed.
However, if that’s not an option, then two major points need to be kept in mind with grazing standing forage: don’t overgraze and observe, observe, observe!
Here are some more tips to share with you:
- Do not allow animals that are in poor condition to graze on suspected high-nitrate areas. Death losses and poisonings are a greater risk with thin animals than those that are in good condition, and well-fed.
- Fill your animals up with low-nitrate feed before moving them onto a forage stand suspected of high nitrate loads. Hungry livestock will over-indulge themselves on the forage, which will lead to acute poisoning. When they’re moved onto pasture or a crop containing high levels of nitrates while not hungry, they have two good things going for them: they already have their rumens full of feed, which dilutes the nitrates entering the system when they start to graze, and they are much less likely to gorge themselves because they already feel full and satisfied from the feed you had them to consume first.
- Graze cattle on the high-nitrate pasture incrementally at a time, then remove them. For instance, after making sure they’re filled up on the low-nitrate feed, put them on the high-nitrate pasture or field for the first half-hour to hour (in the afternoon, never in the morning), then pull them off. Repeat the next day for a half-hour to an hour longer, and the same for the day after that. The purpose of this is to get them adjusted over time until they can be on the area full time. It takes 5 to 7 days for them to get adjusted.
- Do not strip-graze or manage pastures in such a way where cattle are most likely to go back and eat the lower-half of plant material which contains the highest amount of nitrate. In other words, avoid overgrazing by not over-stocking pastures, and by moving as frequently as possible, ideally so that animals are only eating the tops of the plants (the leaves; as their first bite), and not being forced to eat down to the stems (return to take a second bite). The leaves will have less of a nitrate load than the rest of the plant, thus allowing them to just consume the leaves and leave behind the rest is a most recommended and safe practice to avoid nitrate poisoning, as well as to help animals get used to a gradual increase of tolerable nitrates in their system.
- Avoid grazing pastures a week after a killing frost. This is especially recommended for warm-season forages that pose an additional risk of prussic acid poisoning, such as Johnsongrass, sorghum, sorghum-sudangrass, and occasionally corn. Unlike nitrates, prussic acid in these plants spike immediately after a frost and take 5 to 7 days to go back down to normal. Cool-season grasses like barley, oats, smooth brome, timothy, and orchard grass do not carry such a risk, thus these plants can be grazed much sooner, provided other management suggestions mentioned here are followed.
- Provide supplements of low- or non-nitrate feeds such as grain, hay, or greenfeed to reduce the effects of nitrate as animals are being grazed. Feeding high-energy feeds encourages the conversion of nitrates into non-toxic compounds and thereby reduces the potential for toxicity. If the animals are not quite adapted to feeding grain, start off with 2 to 3 pounds of grain per head then work your way up to the amounts you’re comfortable with over a period of a week. For instance, if you want to be feeding 6 pounds of grain per head per day, start with 2 pounds then add another two pounds every couple days, on a daily feeding regime. It would also be ideal, if possible, that grain could be fed in split feedings, such as half in the morning and half in the evening so that they have a more consistent amount throughout the day compared with feeding just once daily. It’s also a great excuse to observe your animals as often as you can.
- Observe your animals as often as possible, especially when they’re being introduced to a new pasture that is suspected to have high nitrate levels. Keep an eye out for any abnormal signs and symptoms that I mentioned above.
If you are doing swath grazing, your management will depend on when the crop was swathed, and the nitrate test results you received.
A crop that was swathed prior to frost (or hail) will not accumulate nitrates. The plants have already been killed mechanically via the swather header, so any frost that occurs after will do nothing to these plants. Also, swathing a day or two after a frost does not result in a high nitrate load in the plants. It’s a different story, though, if the crop was swathed a week later, and the crop was cut at a lower height than what I would recommend when taking nitrates into account; i.e., cutting at 8 to 10 inches (20 to 25 cm) to avoid grabbing that notorious bottom-third, instead of 4 to 6 inches (10 to 15 cm) which do grab the bottom-third of the plant.
Test results will determine what needs to be done in such a worst-case scenario. At this point, it’s worth noting that nitrate toxicity with swath grazing is rare, however that doesn’t mean it’s never going to happen. If the worst-case scenario does (or has) happen[ed] to you, you will need to manage your animals in a similar fashion to what was mentioned above.
In other words:
- Introduce them incrementally: for the first day, fill them up and put them on for a half-hour or hour in the afternoon, then remove them. Repeat the following days, each day being a little longer than the last until they’re ready be on the field full-time.
- Don’t force your animals to clean everything up; instead, allow for a bit of waste of the stemmy material.
- Have low-nitrate feed available for them on a regular basis (important for the first week of adjustment)
- Don’t strip-graze; allow enough that all your animals are going to have a fair share as possible and leave a bit of stem-material waste. Being too strict by giving them too small an area gives more reason for your more dominant animals to get premium access to the good stuff, and the “bad” material (the stemmy stuff) for your subordinate animals, which leaves them to be at greater risk for nitrate poisoning. Avoid allowing animals free access back to the previously-grazed areas.
- Do not allow poor-conditioned animals to graze. And, never put hungry animals out on the swaths, particularly during that first week.
- Observe as often as possible.
It is very rare indeed for a crop intended for swath grazing to have very high nitrate levels. However, there’s a bit of good news with this: a swathed crop can be left out for a long period of time (i.e., at least a month), where nitrates have a chance to be leached out of the plants as they lay in the swath. There has to be sufficient moisture for this to be successful (i.e., the swaths need to be rained on). Even rarer still, a crop may be so bad that it will have to be harvested as feed (silage or greenfeed) so that you can have greater control over how much your animals receive versus out on the field.
Feeding Management for High-Nitrate Feeds
Unlike with pastures or standing grazable crops, feed that has been swathed and put into bales or chopped into silage will not decrease in nitrate load after a couple of weeks. Most often such feeds have a permanently high nitrate level that will need to be managed accordingly. This faces you with two possible scenarios to deal with: the feed may have moderate levels of nitrates that are categorized as “cautionary” because the lab report you received noted that levels were between 0.5 and 1.0% NO3, or the feed has a high nitrate load that exceeds 1% NO3.
Remember two key targets with managing high-nitrate feeds:
- The rumen microbes MUST get fully adjusted to the feed, and
- Animals must be fed up to where they are able to MAINTAIN a constant “optimal” amount of nitrate to eliminate the risk of poisoning.
It is the microbes themselves that need to get adjusted to the feed, not the animal herself. It usually takes three to five days for rumen microbes to adjust, where there is a die-off in the microbe population before a re-population comes back of more acclimatized microbiota. This temporarily affects digestion rates. Once they have fully adjusted, the nitrate conversion increases in efficiency, so long as there’s a consistent and constant amount of nitrate being supplied. It’s for these reasons that an animal can tolerate higher levels of nitrates in the diet, yet it’s still difficult to determine what is specifically a safe level!
Death losses have occurred with animals consuming feed at less than 1% NO3, yet there have also been reports of successfully feeding rations that contain significantly greater than 1% nitrate with no harm (applicable only to non-pregnant animals). The crucial factor to this was a period of slow adaptation and feeding the right animals.
I would highly recommend working with a beef, dairy, or sheep nutritionist if you have to manage feeds and develop rations that are more specific to your cattle herd. However, here are some general management guidelines to follow.
- Ideally, high-nitrate feeds should be mixed with low-nitrate feeds in a mixed ration, using a mixer wagon, to a level where nitrates in the total mixed ration are less than 0.5%.
- If the physical mixing of forages is not possible, the best course of action is to start off with low-nitrate fodder first, then follow up with the high-nitrate feed. Each animal should be given a chance to fill themselves up before any one of them makes a bee-line for the high-nitrate feed.
- DO NOT put out the high-nitrate feed at the same time as the low-nitrate feed, because there’s a very likely chance that some animals will only eat from the bale with high-nitrate and not the other low-nitrate feeds. This is particularly important when getting animals introduced to nitrates!
- Split feedings into more frequent, smaller sessions. Instead of giving the animals only enough for one day, divide this up to where you’re supplying half in the morning, then half in the late afternoon. This reduces the quantity of fodder being fed throughout the day, as well as the amount of nitrate released from the rumen. Animals are able to withstand greater amounts of methemoglobin with twice-daily (or more) feedings than daily (or less) feedings.
- Maximum levels of methemoglobin reach peak levels 8 hours after feeding in daily feedings; peak levels occur 4 to 5 hours after feeding with twice-daily feeding. The latter gives higher methemoglobin total levels, which increases the risk of poisoning.
- Allow for one to two weeks for animals to adjust, and as the time required to gradually increase the amount of nitrate-rich feed in the diet.
- Include grain in the ration. This can be easily done when creating a mixed ration is impractical for your operation.
- Make sure animals are receiving a balanced ration of adequate energy, vitamins A and E, and trace minerals to reduce the effects of toxicity. Nitrate poisoning can cause a deficiency in Vitamin A as one of the chronic effects. Talk more with a nutritionist about a specific feed ration program tailored for your herd.
- Make sure animals have access to clean water that contains low amounts of nitrate at all times.
- Avoid feeding damp, heated, spoiled feed to livestock as much as possible. Such feed creates a much greater risk for poisoning as nitrates will have converted to nitrites which are much more toxic to animals. In some scenarios, it may be best to use this feed as manure to spread on the field. Do not use for bedding, as animals will still consider this a feed.
- Do not use any high-nitrate feed as bedding. Animals will still consider this as fodder, putting them at risk for poisoning.
- Pregnant animals are more sensitive to high nitrates than non-pregnant animals (i.e., steers, replacement heifers, bulls, cull cows). They should not be fed more than 0.5% (preferably even less than this) nitrate in the total ration on a dry-matter basis. Consult with your nutritionist for more guidance and information.
There has been a bit of research done in the United States that notes how ensiling forages reduces the amount of nitrate by between 40 to 60%. However, this has been at the sacrifice of quality: by means of improper packing, covering, or harvesting at too late in maturity.
The consequences for feeding low-quality silage (or any other feed for that matter) are greater than managing nitrates in a manner that is safe for the animals. It is better to feed high-quality feed, such as silage with high soluble sugar content (therefore high energy content) than having animals decline in health due to feeding poor-quality forages.
Silaged cereal crops have a high soluble sugar content, which enables them to rapidly ferment, and rapidly drop in pH (become acidic). However, this rapid drop in pH during the ensiling process does nothing to promote rapid degradation of nitrate, making good quality silage just as much of a risk for nitrate poisoning as other forages, and as much as a need for managing to get animals adjusted.
In Closing
There are many variables at play with every operation in determining what is the best way to go about feeding high-nitrate feeds, based on equipment, time, and labour available, the type of animals that need to be fed, and how high of nitrate levels you are forced to deal with.
Overall, good management is the clincher, above all, in ensuring that your animals remain alive, healthy, productive, and happy throughout this nitrate-challenging adventure you may be faced with.
I leave you with a couple of tips: gather as much information as you can, and talk to the professionals if you’re unsure of what to do, from the veterinarian to the nutritionist to the forage-beef agriculture specialist. They will guide you in what you need to do to prevent any potential train-wrecks from finding a place to happen.
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Merck & Co, Ltd. 2020. Overview of Nitrate and Nitrite Poisoning. Merck Veterinary Manual. https://www.merckvetmanual.com/toxicology/nitrate-and-nitrite-poisoning/overview-of-nitrate-and-nitrite-poisoning
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