Source: Government of Saskatchewan
Animals need time to adapt to changes in feed. Ruminants especially need to be gradually switched from high roughage rations to rations containing high levels of grain or concentrates. Sudden changes may cause acidosis or other digestive upsets in cattle and sheep.
Feeding hay to cattle and sheep before allowing them to graze green crops or lush pastures can prevent some of these digestive problems. Alternatively, animals could be allowed to graze only a few hours a day for several days until they have adapted to the new feed.
Some animals may develop allergic reactions to substances in fresh, lush, green feeds, and it is always prudent to turn cattle onto new pasture when their stomachs are full.
Mould and ergot
Mould, toxins and ergot can poison animals. Pregnant animals are most susceptible to these toxins. If these toxins are consumed at high levels, they may cause abortion, vaginal or rectal prolapse, internal bleeding, dry, gangrenous symptoms and even death in cattle. Weak and starving animals are less able to detoxify these toxins.
Addition of vitamins A, D and E may help the animals tolerate these toxins. Diluting the mouldy feed with clean feed may bring the toxin concentration down to a safe level. Dilute ergot-contaminated feeds to less than one ergot body per 1,000 kernels.
Feeding excessive amounts of low-quality hay or straw to cattle without adequate grain supplementation to provide energy and protein can leave the forage undigested and/or slow to digest and cause rumen impaction. Lack of water may also contribute to compaction.
Processing low-quality forage with a hammer-mill or bale shredder can increase the amount of forage eaten, but, if the ration is low in energy or protein, can also lead to impaction. You must be particularly watchful to ensure adequate energy intake during periods of severe cold weather.
Problems due to water
Clean snow has been successfully used as the winter water source for beef cows and sheep. The snow should be easily available and not hard-packed. The best type of snow is crystal-grainy and deep enough that cows can eat it. It may take several days for cattle to become accustomed to eating snow. Give cattle access to fresh water about six weeks prior to calving.
If you are concerned about the quality of water, if animals are eating or drinking less or have scours, a water analysis should be carried out to determine the level of minerals present.
Pesticides and herbicides
If crops are to be salvaged for feed but have been treated with pesticides or herbicides, ensure that the label restrictions have been complied with. Never feed seed grain treated with fungicides or insecticides.
Dicoumarol poisoning or “Sweet Clover Disease”
Mouldy sweet clover hay or silage may contain dicoumarol. Dicoumarol prevents blood from clotting, so animals may bleed to death internally or from external wounds.
Feed sweet clover to cattle for seven days and then switch to different forage for 14 days, then back to sweet clover for seven days and repeat. It is advisable to avoid feeding sweet clover for six weeks prior to castrating or dehorning. Do not feed any sweet clover to cows during the last three months of pregnancy.
Frost, drought and the application of herbicides may be factors in high nitrate accumulation by plants. Oat straw and oat hay are most affected. Green oats should be cut either immediately after a frost, before nitrates build up, or after seven days with no frost (assuming the plants were not killed) to allow any nitrate built up to be cleared by the plant’s system. Green feed cut after a frost should be tested for nitrates. If nitrates are suspected, the amount should be determined by a feed analysis performed at a feed testing laboratory.
Forages containing nitrates may kill cattle and sheep by interfering with the transport of oxygen by the blood. Symptoms of nitrate poisoning include rapid breathing as the animal struggles to get enough oxygen, frothing from the mouth, a bluish tinge to the mucous membranes, muzzle and udder, and brown-coloured blood. Treatment requires early intravenous injection of a 40 per cent solution of methylene blue at the rate of 100 cc per 100 pounds (45 kg) of body weight.
The rule of thumb for feeding is to dilute the nitrate-containing roughage with nitrate-free roughage so that the total feed contains no more than 0.5 per cent nitrate. For example, if green oats has one per cent nitrate (100 per cent Dry Matter Basis), it should be diluted by one-half with nitrate-free roughage. This should be done with each feeding to prevent over-consumption by any individual animal. Dilution does not work if high-nitrate feed is fed one day and nitrate-free feed the next.
Prussic Acid (Hydrocyanic Acid) Poisoning
Flax that has been frozen or severely affected by drought may contain toxic quantities of prussic acid (0.03 to 0.04 per cent or higher). Symptoms of prussic acid poisoning are similar to nitrate poisoning, except the blood remains bright red.
Death usually occurs before treatment is possible, although early intravenous injection of sodium nitrate and sodium thiosulfate by a veterinarian may be beneficial. Where prussic acid may be a problem, feed should be analyzed by a feed testing laboratory and suitable precautions taken. Prussic acid in cured forage gradually disappears over time.
Nutritional deficiency diseases
Poor-quality feeds provide livestock with fibre, but are low in energy, protein, minerals and vitamins. Inadequate amounts of nutrients may lower conception rates, and disease and parasite resistance. It may result in weak calves and lambs, and sometimes in still-born offspring.
When low-quality forages are fed, you must provide mineral and vitamin supplements. Ensure that you feed a balanced diet to provide adequate energy and protein. Pay particular attention to supplying adequate vitamin A and minerals, either through free-choice or force-feeding.
The following problems pose higher risks during very dry periods:
Blowing dust and dusty, dry feed can irritate the respiratory tracts of cattle and cause an increase in cases of pneumonia.
Poor pasture conditions increase the risk of plant poisoning. Many poisonous plants are unpalatable but, when the quantity of grass is in short supply, cattle will eat things such as chokecherry leaves, marsh arrow grass, water hemlock, etc., which can result in poisoning.
Soil-borne diseases such as Blackleg can present a higher risk because cattle are grazing closer to the ground.
Grass Tetany/Atypical interstitial pneumonia (AIP)
Severe drought followed by heavy rain may result in rapid, lush growth of cereals and/or seeded pasture. This has the potential to cause grass tetany. AIP is another disease that may occur when cattle are moved from poor pasture into an area with lush growth.
Veterinarians can provide additional information regarding these and other diseases.
Cattle should be fed before being turned out onto new pasture, otherwise their hunger may lead them to eat poisonous plants. They should be watched carefully for digestive upsets or AIP during the first few days on new pasture.