Hay Moisture Levels

With the limited opportunities and short windows many have had to make hay so far this year, some hay may have been made at higher moisture levels than we would like. Moisture levels have a direct effect on hay quality. What we have found to be a consistent number in the literature is 20% moisture maximum. To be more specific:

    1. Small squares to be 20% or less,
    2. Large round, 18% or less and
    3. Large squares, 16%

Hay baled at 20% moisture or higher has a high probability of developing mold, which will decrease the quality of hay by decreasing both protein and total nonstructural carbohydrates (TNC) AKA energy! The mold will also make the hay less palatable to livestock and could potentially be toxic, especially for horses. Even hay baled between 15%-20% moisture will experience what is known as “sweating.” Sweating, in regard to hay bales, refers to microbial respiration, which will create heat and result in dry matter (DM) loss. A good rule of thumb is that you should expect a 1% DM loss per 1% decrease of moisture after baling. As an example, hay baled at 20% moisture that is stored and dried down to 12%; will result in 8% DM loss.

What happens if we bale hay and the moisture content is too high? Bad things. If lucky, maybe the hay will only mold, but if it is too moist and starts heating, it could catch fire. If the hay heats to 100-120 degrees F, it will be fine; if it goes above that, monitor daily. Once it gets to 140 degrees F, consider tearing down the stack. At 150-160 degrees F, call the fire department, and once it gets to 160 degrees F, there will be smoldering pockets and hot spots, and gases will ignite hay when exposed to air (source: Washington State University Extension, Steve Fransen and Ned Zaugg).

It can be a double edged sword in regards to losing quality by not baling, or losing quality by baling with moisture levels that are too high. Therefore, our recommendation to ensure adequate livestock nutrition this winter is to have a forage analysis done on the hay baled this year. Once you have those results, develop a corresponding supplemental feed program, if necessary, based on the nutritional requirements of your livestock.

The two short videos below by Clif Little and Rory Lewandowski will answer questions regarding forage testing, and subsequently interpreting the results of the test(s).

To bloom or not to bloom?

By Kassidy Buse

A common recommendation of agronomists is to let one alfalfa cutting reach bloom each year.

Ev Thomas, retired agronomist from the Miner Research Institute in Chazy, N.Y., says otherwise in The William H Miner Agricultural Research Institute Farm Report.

“For many years, I’ve said that in managing alfalfa for dairy cows, you should never see an alfalfa blossom, from seeding to plowdown,” says Thomas.

Thomas also notes there’s room for difference of opinion due to no research supporting either opinion.

But, if one cutting is to bloom, which cutting should it be?

The first cut of alfalfa-grass typically contains the most grass. Grass, even the late-maturing species, is close to heading when alfalfa is in the late bud stage.

The second cut is exposed to long, hot June days that result in highly lignified, fine stems. A Miner Institute trial found that the stem quality of bud-stage second-cut alfalfa was no better than full-bloom first-cut alfalfa.

The third cut can be influenced by prior harvest management. If it was a late second cutting, the third cut was growing during midsummer heat. This cut would also have highly lignified stems.

The fourth cut often takes a long time to bloom, if it makes it there. A killing frost might arrive first.

For any cutting, the more grass in the stand, the lower the forage quality if alfalfa is left to bloom.

“The objective of letting alfalfa bloom is to improve root reserves, and therefore extend stand life,” says Thomas. “We need to balance the impact of delayed harvest on plant health with the economics of feeding alfalfa of lower quality that is needed by today’s high-producing dairy cows,” Thomas adds.

How alfalfa and alfalfa-grass is managed depends on if the goal in mind is long stand life or high milk production potential.

Avoid Barn Fires, Let Hay Dry All The Way

Not only can wet hay catch fire, but it can mold. Hartschuh says bale temperatures of 120° to 130° F often results in mold growth and makes the protein less available to animals. ( Farm Journal )

Farmers across the country have either finished putting up their first cutting of hay, or they are in the process of doing just that. While it can be easy to get in a rush, avoid barn fires by ensuring your hay is dry enough before you bale it.

“When [hay] is baled at moistures over 20% mesophilic bacteria release heat causing temperatures to rise between 130°F and 140°F. If bacteria die and bales cool, you are in the clear, but if thermophilic bacteria take over temperatures can raise to over 175°F,” according to Jason Hartschuh a guest contributor to Ohio State University Extension’s Ag Safety Program.

Most wet bales catch fire within six weeks of baling, Hartschuh says. Here are some things to consider when determining if your hay is at risk of fire. Did the field dry evenly? Were moisture levels kept at or below 20%? If moisture was higher than that, was a hay preservative used?

If you are concerned that your hay is a fire risk, monitor it twice a day for the first six weeks or until low temperatures stabilize, he says. Temperatures should be taken from the center of the stack or “down about 8 feet in large stacks.”

Not only can wet hay catch fire, but it can mold. Hartschuh says bale temperatures of 120° to 130° F often results in mold growth and makes the protein less available to animals.

“While those temperatures are not high enough to cause hay fires, the concern is if the mold growth continues and pushes temperatures upward into the danger zone,” he says.

According to research from OSU, if the temperature in the hay continues to rise, reaching temperatures of 160° to 170° F, then there is cause for alarm.

“At those elevated temperatures, other chemical reactions begin to occur that elevate the temperature much higher, resulting in spontaneous combustion of the hay in a relatively short period of time,” Hartschuh says. “If the hay temperature is 175° F or higher, call the fire department immediately, because fire is imminent or present in the stack.”

 

Critical Temperatures and Actions to Take

The team from OSU extension recommends monitoring the following temperatures and taking appropriate action.

125° – No Action Needed

150° – Hay is entering the danger zone. Check twice daily. Disassemble stacked hay bales to promote air circulation to cool the hay outside.

160° – Hay has reached the danger zone. Check hay temperature every couple of hours.  Disassemble stacked hay to promote air circulation to cool hay have fire department present while unstacking from here on.

175° – Hot pockets are likely. Alert fire service to possible hay fire incident. Close barns tightly to eliminate oxygen.

190° – With the assistance of the fire service, remove hot hay. Be aware the bales may burst into flames.

200°+ – With the assistance of the fire service, remove hot hay. Most likely, a fire will occur. Keep tractors wet and fire hose lines charged in the barn and along the route of where bales are to be stacked.

 

Cutting Height in Hay Fields: How Low Can You Go?

The second consequence for mowing too close to the ground is increased ash content of the forage. All forage has a natural ash content of approximately 6%. However, mowing too closely with disk mowers can add soil to the crop, and increase the ash content by as much as 10-12% (18% ash content in total analysis). If we all had table-top smooth fields, it would also be much easier to make a closer cut across all fields. However, things such as groundhog holes and the unevenness of fields can add to increased ash content of our harvested forage.

So, the million dollar question is how low can you go? The best answer is…it depends! The first question I always ask is – is it a solid stand or a mixed stand? If you have grasses involved, you must keep cutting height higher than a pure stand of legume, if you want to keep the grass in the stand. Keep in mind these are minimum recommendations; it’s okay to mow higher than the numbers below. Here are my minimum cutting height recommendations:

Alfalfa or Clover

  • 2” minimum. Some literature shows a cutting height of 1” will not reduce stand longevity, but remember the increased ash content issue. Also, keep in mind that frequent cutting at early maturity will continue to deplete carbohydrate reserves. One cutting of alfalfa should be allowed to reach the bloom stage each year.

Cool Season Grasses (Orchardgrass, Timothy)

  • 4”during the establishment year
  • 3” minimum during production years. This is where we see most of our stand longevity issues. Frequent cutting of cool season grasses at a low height will continue to deplete energy reserves.

Mixed stands

  • You must manage for the predominant species. Do you have a grass stand with some alfalfa, or an alfalfa stand with some grass?
  • Alfalfa with some grass: 2.5” minimum
  • Grass with some alfalfa: 3” minimum (if you want to keep the grass sta

Hay Cost Calculator

Hay season is around the corner and many producers are likely greasing the wheels, sharpening blades, checking belt tension, and settling in for a long hay season. However, it may be wise to do some calculating and revisit some management decisions to determine hay needs and to see if there is a way to reduce hay needs. This could be important considering the tremendous cost of feeding cattle 365 days per year and knowing hay tends to be one of the most expensive feeds available.

In order to achieve the task of determining how much hay is needed and what the potential cost will be, Mr. Kevin Ferguson, Ms. Rebekah Norman, and Ms. Tammy McKinley developed an Excel based “Hay Calculator” to help with the calculations. That file can be found at https://ag.tennessee.edu/arec/Pages/decisionaidtools.aspx. The tool takes into account storage losses, feeding losses, bale size and weight, cattle weight, consumption, number of days fed, and hay price to determine hay needs and total cost. The calculator can also assist with hay quality analysis.

Based on several pieces of research, the method of storing and feeding hay significantly increase costs. Average storage losses for hay stored six months or longer range from 5 percent for hay in a barn to 30 percent for hay stored outside and uncovered. Hay stacked and covered with a tarp on a rock pad or pallets results in 12 and 14 percent loss respectively. Additional storage methods include a plastic sleeve and net wrap which result in average losses of 19 and 23 percent respectively.

Similar to storage, the method of feeding hay can influence hay loss. Feeding losses from feeding hay in a cone ring range from 2 to 5 percent while feeding hay in a conventional ring results in 4 to 7 percent hay loss. The use of a hay trailer generally results in 10 to 13 percent hay feeding losses while the use of a cradle will result in 15 to 20 percent losses. Unrolling hay on the ground has the most variability with losses ranging from 5 percent to 45 percent. Hay feeding losses are likely more a function of how much hay is fed at a time as opposed to the method. For instance, feeding a week’s worth of hay in a cone ring will result in more feeding loss than feeding one day of hay in a cone ring.

For illustration purposes, consider a producer with 30 cows averaging 1,200 pounds and feeding 2.5 percent of the cows body weight for 150 days. This would result in each cow needing 30 pounds of hay each day on a dry matter basis. Assuming 11 percent moisture would result in the herd needing 76 tons of hay or 152, 1,000 pound bales. If the bales cost $35 per bale then the total cost to the herd would be $5,320. However, storage and feeding loss have not been considered.

Now consider two management options with this herd: storing hay in a barn and feeding in a cone ring or storing net wrapped hay outside and feeding in a conventional ring. The first system of storing hay in a barn and feeding in a cone ring results in a total loss of 6.4 tons of hay or 13 bales of hay for an additional hay cost of $451 for the herd. The second system of storing net wrapped hay outside and feeding in a conventional hay ring results in a total loss of 21.6 tons of hay resulting in the need of 43 additional bales of hay and adding $1,513 to herd hay cost.

This basic illustration demonstrates changes in feed costs from differing hay storage and feeding management. Producers should consider methods of reducing hay storage and feeding losses to reduce total costs. Producers should also consider grazing management practices that reduce hay needs which have a potential of reducing feed costs.

Planning for the Alfalfa Growing Season

Planning for the growing season this year has been a little different than in previous years. The winter season seemed to be longer than usual and has producers wondering when they would be able to access their fields. Here is a bit of information for those producers that are considering planting alfalfa this year.

Field Selection

Establishment of alfalfa seed require a well-drained soil for optimum production. A germination soil temperature of 45oF is adequate for alfalfa establishment. Achieving a profitable stand of alfalfa is the result of proper field selection utilizing proven production practices to ensure germination and establishment. Poor soil drainage can cause problems with soil crusting which may cause poor soil aeration, micronutrient toxicity, and ice damage during winter.

Soil Fertility

It is important to remember to ALWAYS take soil samples before planting to determine pH and nutrient status of the field. Overall, there are 18 nutrients (macronutrients and micronutrients) essential for alfalfa growth. Some of these nutrients include:

  • Phosphorus: Helps root growth and increase seeding success. Low fertility soils can be improved with an application of 30-50 lbs per acre of P2O5, depending on soil test results.
  • Potassium: Research suggests that potassium has little effect or influence on improving stand establishment, however, adequate potassium should be added to meet the needs of alfalfa and even a companion crop.

Planting Alfalfa

Failure to successfully establish alfalfa can be expensive and may lead to issues related to production soil erosion. Some considerations for planting alfalfa include: (1) seedbed preparation; (2) seeding dates; (3) seeding depth and rate; (4) whether or not to seed with a companion crop; (5) 100% alfalfa seedings vs. alfalfa-grass mixtures.

  1. Seedbed preparation 
    Having a firm seedbed is a critical step to ensure good germination of alfalfa seed. Firm seedbeds will reduce the possibility of planting too deep and will help hold moisture closer to the surface. Packing the soil will help to insure a firm seedbed and good soil moisture retention.
  2. Seeding dates
    Determining when to plant alfalfa depends on several factors such as soil moisture and cropping practices. For best results in South Dakota alfalfa should be seeded between mid-April to mid-May. This all depends on weather conditions as well. This year might be safe to say that seeding alfalfa in mid-May might be the best option for producers.
  3. Seeding depth and rate 
    Seed should be covered with enough soil to provide moist conditions for germination. Seed placement of ¼ to ½ inch deep is appropriate on most soils at rates from 10 to 25 lb seed/acre.
  4. Seeding with or without a companion crop 
    Seeding alfalfa with a companion crop such as annual ryegrass, oats, spring barley, or spring triticale can help to minimize weed competition during establishment. However, planting alfalfa without a companion crop allows producers to harvest more alfalfa with higher quality in the seeding year.
  5. 100% alfalfa seedings vs. alfalfa-grass mixtures 
    Pure stands of alfalfa will produce the highest quality forage and for that reason has the highest demand from the dairy industry. Other producers whose animals’ nutrient requirements are lower may be interested in using alfalfa/grass blends to take advantage of improved persistency while still meeting the nutrient requirements of their livestock. Alfalfa-grass mixtures also offers some advantages such as reduced weed pressure and soil erosion.

The Bottom Line

It is always handy to remember that the first harvest seeding year is when alfalfa is seeded in the spring and considerations of taking one or two cuttings in the same year need to be made by then. The first harvest should be done after the flowers begin to appear, allowing greater energy reserves in the roots. Generally, alfalfa will reach this stage of development 60 to 70 days after emergence. Harvesting delays during this stage will cause large reductions in quality and a decline in total yield over the season because fewer harvests are possible.

I hope this growing season is another successful one. We might be a little slow this year; but that does not mean we won’t be able to achieve the goals for production.

Time to Check for Winterkill Injury

Winterkill Injury

There is a wide range of winterhardiness among alfalfa varieties. Some varieties may have suffered winterkill injury this winter, especially where the crop had no snow cover. Like in wheat, winterkill in alfalfa occurs when the crown is frozen. When this occurs, the taproot will turn soft and mushy. In the early spring, check for bud and new shoot vigor. Healthy crowns are large, symmetrical and have many shoots. Examine them for delayed green-up, lopsided crowns and uneven shoot growth. If any of these characteristics are present, check the taproots for firmness. Some plants may even begin to green-up and then die. Plants putting out second leaves are likely unaffected.

Interseeding alfalfa to thicken an alfalfa stand will generally not work. If the stand is one year old or less, plants will generally come up and then be outcompeted by the survivors from last year. Large dead spots should be disked first and then seeded. If the stand is two or more years old, interseeding alfalfa will not work because of autotoxicity.

Heaving Effect

As the soil freezes and thaws, alfalfa stands can be damaged by the heaving effect. This will be more likely to occur where soils are not under continuous snow or ice cover and where temperatures have been in the single digits at night. This winter has been cold enough to freeze the soil where it is not under snow cover. Soils with high levels of clay are especially prone to winter heaving.

If heaving has occurred, dig up some plants to determine if the taproot is broken. Plants with broken taproots may green-up, but they perform poorly and eventually die. Slightly heaved plants can survive, but their longevity and productivity will be reduced. Crowns that heaved 1″ or less are not as likely to have a broken taproot. With time, these plants can reposition themselves. Raised crowns are susceptible to weather and mechanical damage. Raise cutterbars to avoid damaging exposed crowns.

Evaluating Plants and Stands

Producers should start to evaluate the health of their alfalfa stands as soon as the soil thaws.

  • Look at the crowns and roots.
  • Buds should be firm, and white or pink in color if they have survived with good vigor.
  • The bark of roots should not peel away easily when scratched with a thumbnail.
  • When cut, the interior of healthy roots will be white or cream in color.

When alfalfa growth reaches 4 to 6″, producers can use stems per square foot to assess density measure. A density of 55 stems per sq. ft. has good yield potential. There will probably be some yield loss with stem counts between 40 and 50 per sq. ft. Consider replacing the stand if there are less than 40 stems per sq. ft., and the crown and root health are poor.

If an established stand was injured by winterkill or heaving, and large patches are dead, producers may want to buy some time before replacing the stand by temporarily thickening the bare areas with red clover. Red clover is not as susceptible as alfalfa to the plant toxins released by alfalfa (allelopathy) and helps provide good quality forage.

 

Test Hay, Don’t Guess

November 25, 2017 01:19 PM

Fall is here and the weather reminds us of the changing of the seasons. This is the time of year when many producers are hauling hay home for the winter as well as pricing and purchasing hay. There is a tremendous range in hay quality depending upon level of maturity, fertilization, growing conditions, harvest circumstances and storage methods. Accurately sampling and testing hay is the only way to get a real understanding of the nutritive value of feed. Using values from previous years or a “book value” can be costly since a producer may incorrectly develop a ration using values that aren’t representative.

Guidelines for sampling

When sampling hay, getting a representative sample is a critical first step. Samples must accurately represent the entire lot of hay. When obtaining a sample for analysis, it should be kept separate from other lots of hay. The UNL NebGuide “Sampling Feeds for Analyses” (PDF version, 655KB) states that a “lot” of hay should be harvested from the same field consisting of similar types of plants, cutting dates, maturity, variety, weed contamination, type of harvest equipment, curing methods and storage conditions. When these conditions differ, feed should be designated and sampled as a separate “lot”.

Hay samples should be taken using a hay probe or a core sampler. The hay probe should penetrate at least 12-18 inches into the bale and have an internal diameter of at least 3/8 of an inch. Using your hand to grab a sample will not consistently provide reliable results. Tips of hay probes should be kept sharp to cut through hay and prevent selective sampling. Avoid getting hay probes hot when using a drill to drive the probe into the bale, since friction from high speeds can heat the probe to a point where it damages the hay sample.

To get a representative hay sample from a “lot” of hay, select 15-20 bales in the lot. Knowing the total number of bales that are present can help identify a random method that should be used (such as sample every fourth bale) to obtain an accurate sample. Once all of the samples for a “lot” have been collected, the samples may need to be sub-sampled to get the feed down to a sample size that can be sent in for analysis. The UNL NebGuide “Sampling Feeds for Analyses” walks through a step-by-step process to do this. Being careful to ensure the sub-sample submitted is representative is important.

Once hay samples have been taken store in a plastic sealed bag in cool dry place until the sample is ready to be submitted. Samples that contain over 15% moisture should be frozen. Make sure to label the bag with your name, address, lot identification and feed type. Most commercial labs provide an information submittal form that allows producers to select a standard feed test for forages. Whenever possible, send samples into the lab early in the week to avoid having the samples sit over a weekend.

Analyze for moisture, protein and energy

Cattle feeds should be analyzed for moisture, protein and energy. Producers may also want to have forages tested for key minerals. Feed sample results are usually reported on an as-is and dry-matter basis.

When developing a ration for cattle or comparing feeds to one another, always utilize the nutrient analysis on a dry-matter basis. After formulating a ration on a dry-matter basis, the values can then be converted to an as-is basis using the moisture content of the feed to determine the actual amount of feed that should be fed to the cattle on an as-is basis.

Analyze forages for nitrates

In addition to moisture, protein and energy, annual forages harvested for hay such as foxtail millet, oats, sudan grass and sorghum-sudan hybrids should be analyzed for nitrates. These annual forages can accumulate high levels of nitrates under various growing conditions that can potentially reach toxic levels. The only way to know if high levels of nitrate accumulation have occurred is to test for it. See the UNL NebGuide “Nitrates in Livestock Feeding” (PDF version, 319KB) for additional information. For additional information on understanding the results from a hay analyses, please see the “Understanding a Feed Analysis” Learning Module on the UNL Beef website.

Conclusion

Accurately testing hay takes time and money. However, the value of this information is critical in accurately and cost-effectively formulating rations. Don’t let the small investment of time and money discourage you, it may be some of the best time and money you can invest in your operation.

Forage Analysis: What Numbers Do I Need

One the more common questions I receive with regard to analytical testing of forages and other feedstuffs is, “I have the sample, now what do I test for or what analysis package should I select?”

The basic components that nutritionists need to evaluate a feedstuff or develop a ration are dry matter or moisture, crude protein, an estimate of the energy content of the feedstuff — Total Digestible Nutrients (TDN), Net Energy for Maintenance (NEm), Net Energy for gain (NEg), and the macro minerals, Calcium and Phosphorous. These are the most basic numbers that are required but including some additional analyses in the report can give us additional insight into the quality of the feedstuff or improve our ability to predict animal performance, which is the primary reason we analyze feedstuffs.

I recommend that the report include acid detergent fiber (ADF) and neutral detergent fiber (NDF).  The amount of NDF in forage reflects the amount of cell wall contents (hemicellulose, cellulose, and lignin) within the sample. The NDF fraction is often associated with the respective bulkiness of forage and is correlated with dry matter intake of the forage or feedstuff. Therefore, the amount of NDF may be used to estimate the expected dry matter intake associated with the forage.  The ADF number represents the amount cellulose and lignin within the forage and is correlated with the respective digestibility of the forage.  In general, a higher ADF value is associated with forage that has a greater proportion cellulose and lignin and would likely be a more mature. Additionally, the ADF fraction is used to calculate the energy estimates TDN, NEm, and NEg that appear on the report. There are a number of different mathematical equations that the testing laboratory may use to calculate these numbers, based on the type of sample (corn silage, alfalfa, grass hay, etc.). If the ADF is included in the report, the nutritionist can adjust or recalculate the energy estimates if necessary.

If the forage will be fed in combination with a byproduct feed such as wet distiller’s grain, including an analysis for sulfur can be beneficial if the forage will be used in a growing or feedlot ration.  Additionally, if the forage is a known nitrate accumulator (forage sorghums, sudangrass) or may have been stressed due to drought, including a nitrate analysis should always be considered, especially if the forage will be fed to pregnant cows.

Most analytical laboratories have a number of different analysis packages which encompass the most common procedures or numbers that a nutritionist or producer needs to know about their feeds. These packages will typically include the basic procedures (DM, CP, TDN) and then add on specific analyses such NDF, or the Macrominerals (Ca,P, Mg, K, Na, Cl, S). Some laboratories may group analysis packages by the type of sample (Forage, vs. mixed ration) or production purposes (dairy vs. beef).

The objective of analytical testing of forages and feedstuffs is to improve our ability to meet the animal’s nutrient requirements and ultimately predict animal performance. The unequivocal best method of evaluating the quality of a feedstuff is feeding the feedstuff to an animal and evaluating performance over a set period of time, under a specific set of conditions. Since that would not be cost effective or timely, analytically evaluating feedstuffs in a laboratory is the next best the thing and although it is not perfect, it is unequivocally better than the “this looks like really good stuff” method of evaluating feedstuffs.

Prussic Acid and Nitrate Poisoning are Concerns After a Light Frost

Although late October has been very warm and “summer-like”, the average first frost date for much of the Southern Plains is here.  Soon a cold front will bring near-freezing to sub-freezing nighttime temperatures

It was discovered in the early 1900s that under certain conditions sorghums are capable of releasing hydrocyanic acid or commonly called prussic acid.  Prussic acid when ingested by cattle, is quickly absorbed into the blood stream, and blocks the animal’s cells from utilizing oxygen.  Thus the animal dies from asphyxiation at the cellular level.  Animals affected by prussic acid poisoning exhibit a characteristic bright red blood just prior to and during death.  Lush young regrowth of sorghum-family plants are prone to accumulate prussic acid especially when the plants are stressed such as drought or freeze damage.  Light frosts, that stress the plant but do not kill it, are often associated with prussic acid poisonings.

Producers should avoid grazing fields with sorghum type plants following a light frost.  The risk of prussic acid poisoning will be reduced, if grazing is delayed until at least one week after a “killing freeze”.  As the plants die and the cell walls rupture, the hydrocyanic acid is released as a gas, and the amount is greatly reduced in the plants.  One can never be absolutely certain that a field of forage sorghum is 100% safe to graze.

Cattle that must be grazed on forage sorghum pastures during this time of year should be fed another type of hay before turning in on the field, and should be watched closely for the first few hours after turn in.  If signs of labored breathing, such as would be found in asphyxiation, are noted, cattle should be removed immediately.  Call your local veterinarian for immediate help for those animals that are affected.  Be certain to read OSU Fact Sheet PSS-2904 “Prussic Acid Poisoning” before turning cattle to potentially dangerous fields.

Frosts also stress the plant before a hard freeze kills it.  Plant stress from frosts will impair the normal metabolism of the plant.  Therefore the plant continues to take up nitrates from the soil but is inefficient at converting the nitrates to protein.  Therefore nitrate accumulations may reach dangerous levels.  Testing the forage before grazing or cutting for hay will provide important knowledge about the safety or danger in the forage.  Visit with an OSU County Extension office about testing procedures and read OSU Fact Sheet PSS-2903 “Nitrate Toxicity in Livestock”.