When it comes to the what, when and how of nitrates and prussic acid in your forages, there are differences and similarities. This basic information can help you distinguish these sources of poisoning in livestock.
A significant risk of grazing forages that are damaged by frost or growing after a drought-ending rain is hydrocyanic acid poisoning, more commonly known as prussic acid or cyanide poisoning. Plants in the sorghum family are susceptible to prussic acid formation. These include johnsongrass, sudangrass, sorghum and sorghum-sudan hybrids. Pearl millet does not produce prussic acid (but does accumulate nitrates) and can be safely grazed following a frost. Under normal growing conditions, these plants produce a nontoxic substance called dhurrin. When plants are injured by frost or wilting, enzymes come into contact with dhurrin and release toxic prussic acid or cyanide. Prussic acid is lethal to animals because the cyanide prevents oxygen transfer from the blood, and animals suffocate at the cellular level.
Prussic acid poisoning often occurs very rapidly. The time from ingestion of toxic forages to death can be as brief as 10 to 15 minutes. Typical animal symptoms include excessive salivation, rapid breathing and muscle spasms. Animals are occasionally observed staggering through the pasture before collapse and death. The only reliable method to avoid animal losses is preventative management. Successful treatment is almost impossible because of the rapid progression, so animals must be removed from toxic pastures immediately.
Managing for prussic acid
High levels of prussic acid form when sorghums are injured by frost, resume growth following drought, have high soil nitrogen or low phosphorus levels and after 2,4-D applications. Having a good soil fertility program to ensure the conversion of nitrogen is most effective and will help minimize the risk of both nitrate and prussic acid poisoning. Excessive nitrogen applications will increase the risk for both types of poisoning.
Don’t graze the crop until it is 18-24 inches high. Young plants and regrowth have higher prussic acid levels.
Do not graze or green chop after a light frost. Wait 10-14 days before grazing or green chopping. After a killing frost, wait until the plant has completely dried for at least 10 days.
Prussic acid tends to accumulate more in shorter sorghums, less in taller plants. Leaves accumulate more prussic acid and fewer nitrates. Stalks are higher in nitrates and lower in prussic acid.
Testing is usually not useful. By the time lab results get back, the prussic acid will have dissipated.
Most prussic acid is lost during the curing process. Crops cut and allowed to wilt before chopping or ensiling and field drying will allow for the acid to volatilize from the forage.
Nearly all forages contain nitrates. Ruminants (via rumen microflora) are able to convert the nitrates to nitrites and then eventually to ammonia, which is usable by the animal. However, nitrites are also able to enter the bloodstream where they convert hemoglobin (an oxygen-carrying molecule) to methemoglobin (unable to carry oxygen). Thus, animals consuming forages with too many nitrates, especially over a short period of time, may produce high levels of methemoglobin, which can lead to reproductive loss and/or death.
Physical signs of excessive nitrates are difficult and rapid breathing, muscle tremors, low tolerance to exercise, incoordination, diarrhea, frequent urination, collapse and death. Abortions can happen following nitrate poisoning. Nitrates dilate blood vessels that lead to peripheral circulation loss and loss of oxygen to the fetus.
Nitrates are taken up by the plant and converted to plant products in the leaves. However, when normal plant processes are disrupted, nitrates concentrate in the stalk. Plant stressors include growing under shaded or low-light conditions, herbicide applications, diseases and detrimental weather such as drought, hail, frost and low temperatures. The amount of nitrates accumulated will also depend on plant species, stage of maturity and nitrogen fertilization.
If you have questions or concerns about prussic acid or nitrates, contact your MFA livestock specialist or AGChoice location.
Managing for Nitrates
Nitrates can accumulate when plants are stressed and in soils where ample nitrogen is available.
Best practice is ensiling to reduce nitrate levels. Allow three weeks for full ensiling to occur. Dilute high-nitrate silage with normal forage and/or grain.
Dry baling concentrates nitrates more. Nitrate doesn’t dissipate like prussic acid.
Do not green-chop or feed direct-cut forage if high nitrate levels are present.
Delay harvest several days after a drought-ending rain and right after herbicide application.
Cut high-nitrate fields at a high stubble height. Nitrates tend to accumulate in the lower third of the stalk.
Younger plants will be higher in nitrates than mature plants, unless mature plants are under stress and/or in high-nitrogen soil.
Species such as sorghums/sudangrasses store high levels of nitrate, and brome and orchardgrass have very little under normal growing conditions. Small-grain annuals and millet that are hayed will have more nitrates if harvested immature. Legumes generally do not contain high levels.
It’s best to test for nitrates to ensure they are at safe levels.
One of the great challenges the dairy industry faces, especially during the summer, is heat stress. Increased temperatures, together with higher humidity, result in a decrease in milk production, feed intake, feed efficiency and growth rate in heifers. Reproduction and health are also negatively affected by heat stress.
There are different ways to reduce the effects of heat stress on cows, such as fans with water sprayers or cow housing and shading. However, not all operations are able to implement such management systems, and even with these measures, cows can still experience a certain amount of heat stress.
The thermal comfort range of lactating dairy cows is estimated to be from 32 to 75 degrees. Temperature, however, is not the only factor that plays a role in heat stress. An increase in relative humidity also increases heat stress in animals. Both temperature and humidity are used to calculate Thermal Heat Index (THI). The comfort threshold is considered to be a THI of 72, but high-producing milk cows start to experience heat stress from a THI of 68. The estimated response is that milk yield drops by half a pound for every unit increase in THI above 72.
Effects on production will not necessarily be directly after cows experience heat stress. There is often a lag time between increase in THI and the full effects on production. The first day of stress is not so bad, but dry matter intake is most sensitive to the mean air temperature two days earlier.
Lactating dairy cows produce a large quantity of metabolic heat and accumulate additional heat from the environment. A dairy cow produces more heat than a 1,500-watt hair dryer running full blast. Cattle decrease feed intake in an attempt to create less metabolic heat, as the heat increment of feeding is a large portion of whole body heat production. In addition to reduced nutrient intake, heat-stressed cows have an increase in maintenance cost. Maintaining body temperature has a large energy cost. Because of decreased energy availability and increased energy utilization, heat-stressed cows enter into negative energy balance. Methods to counteract the negative energy balance include increasing energy density of the diet or improving digestibility of feed components. Inclusion of feed additives, such as ionophores, yeast or MFA Shield Technology can improve nutrient digestibility.
Three management strategies to minimize the effect of heat stress are:
Physical modification of environment
Genetic development of heat-tolerant breeds
Improved nutritional management practices
Since I’m a ruminant nutritionist, I am after the third strategy. If I only have a hammer in the toolbox, everything looks like a nail.
Feed intake plays a significant role in production—both the amount of feed being consumed per day and the feed intake pattern. Uneven feed intake during the day can have a negative effect on the rumen environment by increasing the fluctuation of rumen pH. During heat stress, cows will have decreased feed intake. As a result, cows tend to consume more feed during the night with cooler temperatures, causing increased variation in feed intake.
When adding Shield to the diet of heat-stressed cows, it is common to see dry matter intake increase by 8 to 10 percent, or rather come back two-thirds of where we would expect cows to be if they were not stressed. Also, we see a reduced size in the first morning meal. I am not certain if there is increased meal frequency or not; some farmers report “yes” and others “no.”
Water is arguably the most important nutrient for dairy cows. Shield Technology tends to increase water intake, similar to what we see with niacin. Both have a vasodilation or increased blood flow effect. Increases in water intake, especially during heat stress, can have a positive effect on the decrease in body temperature as well as an increase in performance. In dairy cows, Shield has also been shown to increase saliva production during feeding compared to TMRs without Shield components.
Heat-stressed cattle show a reduction of antioxidant activity of plasma, which means they are experiencing an increased oxidative stress. Oxidative stress can lead to damaged molecules and disruption of normal metabolism and physiology. Feeding
Shield components has been shown to reduce oxidative stress.
Visit with your local MFA feed specialists for more information on how Shield Technology can help mitigate the effects of heat stress this summer.
Tall fescue covers more than 17 million acres in Missouri and has been the cornerstone forage for beef cattle production since the Kentucky 31 variety was released in the mid-1940s—and for good reason. Fescue sod reduces erosion on hilly pastures, tolerates intensive grazing and produces good-quality forage in the spring, fall and even part of the winter if properly managed.
However, fescue presents two main challenges to cattle producers: very little growth when weather gets hot and dry and the well-documented fungal endophyte that produces alkaloid compounds that are toxic to livestock. The heat of the summer along with concentrated amounts of the alkaloids in fescue stems and seed heads intensify the negative impact. These effects include increased body temperature, increased respiratory rate, low weight gain and reproductive problems, often referred to as the summer slump.
What you need is a summer slump buster. You can try adding diversity to fescue pastures to dilute the toxic effects, manage it for reduced endophyte concentrations or supplement with a grain-based feed. But the best way to get full performance potential out of your cattle is grazing them on non-toxic, warm-season forages in the summer.
A great choice is a mixture of native warm-season grasses such as switchgrass, little bluestem, big bluestem, Indian grass and eastern gammagrass. Using a more diverse mix—including native cool-season grasses, legumes, and wildflowers—provides even more benefits but requires more careful management.
These native forages are a subset of the plants that were once present in grasslands across much of Missouri, which means they are adapted to grow well in our soils and climate. In addition to being free of toxic alkaloids, they bring some other great benefits to a grazing program.
During the summer when fescue shuts down, native grasses will produce up to 4 tons per acre of forage. The quality of warm-season grass forage is best early in the summer and decreases as it matures, so it’s best to adjust the stock density and duration to keep the plants vegetative without grazing them too short. During the summer grazing season, steers and heifers can be expected to gain between 2 and 2.5 pounds per day on native grass pastures. Grazing cow/calf pairs on native grasses instead of endophyte-infected fescue can increase milk production and weaning weights.
The metabolism of native warm-season grasses is different from cool-season grasses such as fescue. This allows them to better handle summer dry spells and droughty soils because they are more water-efficient. Native grasses also have remarkable rooting depths, as much as 10 to 12 feet. Such deep roots allow these drought-hearty species to find water not available to shallower-rooted grasses such as fescue.
In addition to being a superior summer forage, native warm-season grasses are also great for increasing infiltration rates, stopping erosion, providing buffers along streams and creating wildlife habitat. For decades, biologists have been planting native grasses on conservation areas and providing technical assistance for private landowners who want those benefits on their property. As a result, Missouri Department of Conservation, Natural Resource Conservation Service, Soil and Water Conservation District, U.S. Fish and Wildlife Service, Quail Forever and other agencies and organizations are available to provide expertise on selecting, establishing and managing native grasses.
Getting more native grasses on Missouri farms and ranches for more efficient livestock production and natural resource benefits is a top priority for all conservation partners, and they are putting their money where their mouth is. There are numerous cost-share programs that will cover most of the cost to convert existing vegetation to native grasses. To learn more about how native grasses can benefit you, visit with the experts at your local USDA Service Center. Your local MFA will also have everything you need to establish native grasses.
When reviewing the numbers on a forage analysis, most producers pay close attention to the crude protein and fiber levels of hay they’re feeding to their livestock. But are you checking the ash?
The ash content in harvested forages can have a significant role in animal performance. In the lab, the amount of ash in a forage sample is determined by burning off the organic material and weighing the residue that is left. Much of the ash will be made up of minerals, such as phosphorus, potassium, calcium, magnesium and others. These minerals are essential for both plants and livestock.
However, a potentially large fraction of ash in the feed can be from soil contamination. This shows up principally as silica, which is not digested by the animals. Silica isn’t necessarily detrimental, but it does dilute the nutrient content and contributes nothing to feed value. Ash takes the place of nutrients on approximately a 1-to-1 basis. Further, added ash can bring greater mold and yeast counts, which are soil-borne organisms.
High forage ash content is consistent with drought, dry weather and dusty conditions as well as flooding, wet soils and mud. Heavy rains have the potential to splash soil particles onto forage. Rodents, gravel roads and aerobic deterioration have also been associated with higher ash values.
Looking at large numbers of samples from the lab, we see the ash content range from 5 to 18 percent. Values trend in the lower end of that range for grasses and haylage. The objective is to keep external soil contamination below 3 percent of the mass, which roughly means the forage should test under 11 percent ash. Values above that represent external sources and are negatively associated with forage quality and animal performance.
The way forage is harvested can increase the external component of forage ash content. A June 2017 article in Hay and Forage Grower offers these management practices that can minimize ash percentage:
Consider different cutting height. Though a low cutting height offers more yield potential, it also results in more soil being incorporated into the forage. A cutting height of 3 inches for alfalfa and 4 inches for grass is a good compromise.
Make wide swaths. This will not only speed the drying rate but also keep the wilting forage on top of the stubble and off the ground.
Use flat knives on disc mowers. These create less suction and introduce less soil into the forage than angled knives.
A mower’s cutterbar setting affects the amount of dirt pulled into the cut crop. Be sure to keep the angle of the cutterbar as flat as possible. If the cutterbar is tipped too far forward, it will force the knives to scalp the soil surface.
Make sure rakes and tedders are properly adjusted and maintained. The goal is to move forage, not the soil. This is easiest when the tines are adjusted so they barely touch the ground, where they will hit a sheet of paper, but not scrape dirt.
Rake as little as possible. Often hay has to be raked, but use strategies that minimize hay movement over the ground. Mergers are much more effective in this regard as the hay is actually picked up before being moved. The forage mat should be flipped, with the intent of allowing sunlight to hit earlier shaded material.
Widening the swath or windrow can reduce the ash level. Packing all of the cut crop into a narrow, heavy windrow usually causes it to sink through the stubble and sit directly on the ground. A wider swath will spread the weight of the cut crop across a larger surface area, helping it sit on top of the stubble.
Control rodents. In addition to the damage they do to fields and plants, their dirt mounds are easily incorporated into forage windrows.
Keep storage areas clean. Dirt can be added at the storage and loading site as easily as in the field. Keep silage bags and silo piles on well-drained, solid surfaces.
It is important to note that the sum of minerals on most forage reports is not total ash content because mineral analysis usually does not include silica, which is the largest proportion of ash. So look for an “ash” value on the report. The greater attention to ash content has now led many forage laboratories to offer a neutral detergent fiber (NDF) analysis that is ash-free. This is designated as NDFom or aNDFom on the forage analysis report. For samples with low ash, the NDF and the NDFom will be similar.
Producers who are successful in raising heifers follow similar management practices. They feed high-quality feedstuffs and don’t feed too much forage too soon. They feed to maximize animal productivity. They have good records on animal performance and health.
One of the most important factors is avoiding the post-weaning lag. Some producers observe diminishing animal performance when calves are moved from hutches to group pens. Calves that are eating 2 pounds of starter feed a day often will fall behind when moved to the group housing, but those eating 6 pounds do not. Waiting for a couple of weeks to introduce hay to group-housed calves is usually helpful. The rumen won’t be fully developed until the calves are 400-450 pounds, so they will be 4-6 months old before the rumen is large enough and developed enough to handle a diet high in forage. Forage quality and availability need to be adequate. Clean, fresh water needs to always be available.
Group size can be a factor. Smaller groups mean fewer friends to deal with and usually cause less stress. Providing adequate shelter also helps. Protecting calves from weather extremes reduces their feed needs and improves performance. Calves will lay down in a dry, draft-free, well-bedded area, if available. Ambient temperature, moisture, hair coat and wind directly influence the calves’ nutrient needs. This is a winter time concern as well as a summer concern.
From the time heifer calves are weaned until they reach about 450 pounds is not the time to skimp on feed quality. They can gain 2.5 pounds a day and have been shown to have better lactation performance when provided adequate amounts of quality rations. The principle of “that which is cheapest wins” is always a temptation, but reducing ration costs doesn’t need to come at the cost of animal performance. For example, if I feed too much forage to small calves, their average daily gain (ADG) drops. When I divide the daily feed cost by a smaller amount of gain, I often see an increase in cost of gain. That will get a nutritionist fired.
Pre-weaning starter feeds, such as MFA StandOut, and grower feeds, such as MFA Trendsetter, will have:
Palatable and digestible sources of protein, proving adequate metabolizable protein
Vitamins and minerals
Refined functional carbohydrates
Appropriate feed additives, e.g. Rumensin, Shield Technology
Adequate heifer growth means heifers achieve height and weight goals. They should be ready for breeding at the targeted time. Moving heifers to the breeding group should be based on weight and hip height, rather than age. The current recommendation is to breed heifers at about 55 percent of the dam’s mature bodyweight.
Holsteins should be 51 to 52 inches at the hip and 750 pounds before being put in the breeding group. Jerseys are smaller and should be 40 inches at the hip and 600 pounds. Even though we see some heifers—one out of every five or six—start to cycle at 9 months of age, it is recommended to not breed heifers younger than 10 months.
The ADG objective of a bred heifer is about 1.75 pounds per day. If we feed high-energy diets—particularly if the diet is high energy and low in protein, such as high-yield corn silage or a feedlot type diet—the heifers will get fat. This is particularly detrimental. With these types of feedstuffs, heifers may need their feed restricted. Feeding about 85 percent of free-choice intake achieves the performance goals but does not over-condition them. For bred heifers on a grass forage base, I tend to see 66 to 85 percent of the diet as forage.
Holstein heifers should be eating about 22 pounds of dry matter a day when they are ready to calve; Jersey heifers will be eating about 17 pounds. The preference is to have heifers on the close-up diet the last month of pregnancy. The close-up diet should be more concentrated than the grower diet. At the end of pregnancy, the fetal tissue and mammary gland are soaking up a lot of nutrients. The heifer has continued nutrient needs for growth and maintenance. Her dry matter intake declines as calving approaches. If she can’t eat enough to meet the energy and protein need, she will start to mobilize muscle and fat. This is not good. Excessive weight loss predisposes the animal to fatty liver. Ensure the diet is adequate.
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