This fall has provided some grazing and harvesting opportunities that aren’t available every year. Some of the ‘opportunities’ have turned out quite well as far as livestock and managers are concerned, while others have turned into another ‘learning experience’.

One particular situation has fascinated me. Many alfalfa fields were left with quite a bit of vegetation available. The typical practice is to turn cattle or sheep in to graze these fields after they have frozen. Waiting until freezing occurs seems to reduce the chance of bloat. A reasonable amount of grazing provides the animals with high quality feed and still allows the alfalfa plants to store nutrients for the following year. If grazed right down to the ground, the plant may suffer winter damage as well as reduced production the following spring.

This year, rather than grazing, some farmers decided to harvest the frozen feed and store it as silage. Some of the bags of alfalfa still appear to be in the same condition that they were on the day they were cut. A physical check 3 weeks after the alfalfa was put in the bag found no change in color, odor, or temperature. It appeared that the plants were sitting there wondering ‘what now?’ I haven’t had much success finding research data on this subject, but it appears that freezing has killed many of the organisms on the plant necessary for fermentation. It may also have reduced the soluble carbohydrates that drive the fermentation process. Moisture varies from one part of each plant to another after freezing, so that some of the forage mass will be quite dry while some will be very wet. This also leads to poor fermentation and a high concentration of mold and fungi. I contacted several experts in silage fermentation and found their solutions interesting. One gentleman suggested that the ‘non-silage’ frozen alfalfa be fed up as rapidly as practically possible. He believes that allowing it to remain in the bag for an extended period of time may lend itself to the growth of molds and fungi, and that the organisms that eventually grow will be soil bacteria rather than plant bacteria, that could lead to clostridial fermentation which is very undesirable. This gentleman also believed the same would occur if a grass was harvested and bagged while still frozen. Another gentleman believed that the bag might begin to ensile when the weather warmed up, if the farmers had added one of the bacterial inoculants.

My understanding is that some of the fellows have decided to let the bag sit until it warms up next spring and see if the temperature change might trigger the start of fermentation. It would be interesting to know if anybody that bagged the alfalfa tried one of the silage inoculants mentioned above. Many of these products are made up of strains of bacteria that are beneficial to the fermentation process.

Years ago, when it got really cold in the Columbia Basin, we had many of our high moisture ingredients freeze so solid that they couldn’t be loaded or fed. Potato waste, carrots, cull spuds, apple pomace, corn silage, and potato waste slurry were completely solidified. Crews were divided into water and feed. All worked virtually around-the-clock making sure that every pen had feed and water. We had to feed the cattle hay for several days until it warmed up. Then we had to feed all of the cattle as if they had just arrived or risk digestive diseases such as bloat, acidosis, or enterotoxaemia. This involved feeding the starter ration, then the intermediate ration, and finally the finish ration for most of the cattle. Each ration was fed for 3-5 days before switching the cattle to the next higher energy ration. Not only did we lose gain during the frozen days, but also it took two weeks or more to get the cattle back on feed…it was a very expensive cold spell. If nothing more, that event made me appreciate the cattle feeders that operate in very low temperatures every winter.

Corn grown for silage also undergoes some undesirable changes after a killing frost. The rule of thumb is to harvest it as rapidly as possible after the frost so that a minimal amount of sugars are lost. Moisture content is still very important, so harvest may have to be put off for several days until moisture reaches about 70%.

One interesting note I found in an extension publication from Iowa was the difference in plant response to freezing. Alfalfa was damaged quite quickly, orchard grass was next, and ryegrass held it’s nutritional value the longest. Based on this info, the authors recommended grazing alfalfa first, followed by orchard grass, and ryegrass after a
hard freeze. The damage was expressed as reduction of protein and TDN.

The most common questions I get relative to the freezing issue are in regard to sudan grass and its hybrids that tend to accumulate toxins when they are frozen. Sudan grass seems to go in and out of favor in the Northwest in no particular pattern. Lots of people grow it following early crops for a few years, and then no one grows it. It yields a tremendous amount of dry matter per acre, second only to corn. It is very palatable to livestock, and has a decent concentration of nutrients. Its biggest single problem is that it concentrates prussic acid immediately after it is frozen. Prussic acid is another name for hydrocyanic acid (cyanide), a deadly poison to livestock. There are several ways to protect your livestock. You can collect samples from the lower parts of the plant and send them to a feed lab to test for the concentration of prussic acid. Sampling the lower part of the plant is important because that’s the part that may remain green and also is where the toxin will be concentrated, if present. If the sample comes back negative, or low, the field should be safe. Secondly, you can delay turning the cattle into to the suspect field until all plant parts are brown. This may take several weeks depending on the weather. The third means is by dosing the cattle with a paste that has bacteria in it that actively feed on the toxin reducing any danger. When I was much younger, we turned a few ‘expendable’ head into a field, and if they made it for 3 or 4 days, it was deemed to be safe for the rest of the herd. One year that turned out to be a pretty expensive field check because it killed all the animals the first night. I was accused of selecting the wrong animals, however nobody suggested which the ‘right’ animals were!

Cows or calves eating snow for water is another area that offers some challenges. Research conducted in Canada indicates that the both groups of animals can survive by eating snow in place of drinking water. Performance of the calves was reduced somewhat and the cows lost more bodyweight than the group with access to an ice-free water trough. There were no problems with calving or breeding back the following spring. The calves were turned out to graze in the spring and showed no adverse effects. The big ‘watch out’ was a layer of ice on top of the snow. Whenever that occurred the cows seemed to be able to paw through the ice, but expended quite a bit of extra energy just trying to get to snow. The calves were quite hesitant. It was as if they didn’t have any idea of what to do, which makes sense if we believe that animals learn by experience. Rather than stress this group, they were given water within 24 hr. of the formation of the ice.

Winter often brings weather events for which we are never completely prepared. I was quite surprised to find the lack of research information on frozen plants. As you might expect most of the info found was about corn plant response to frost, and what should be done to minimize nutrient loss. I would like to hear from anyone who has had some
serious winter weather events that affected the feed or the animals and how they dealt with the problem. I’d be happy to pass this info along.

Thanks to Carl Jensen, Univ Id.; Rick Weber, Pioneer Hybrid, Mike Hutjens Univ Il., Mike Gamroth Or State, for their input to this article.

Michael J. Mehren, Ph.D. is a livestock nutritionist who appreciates frozen cubes in his liquid diet when near Hermiston, Oregon.

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