Oxalic acid and oxalate are anti-nutritional factors widely present in plant feeds. They can significantly reduce the utilization rate of mineral elements by animals and It can cause damage to many organs and cause poisoning. Therefore, attention should be paid to preventing the harm of oxalate to animals in production practices.
Source and physical and chemical properties of oxalate
Oxalic acid is also known as oxalic acid. It exists mostly in plants as grass ink adhesion promoter acid salts. Oxalates are widely found in the plant kingdom. A survey on the distribution of oxalate in the plant kingdom shows that among 93 genera, except for 11 genera that do not contain oxalate, most species of the remaining genera contain large amounts of oxalate. Common oxalate-rich forage plants and wild plants include the following:
Feeding beet
Fresh stems and leaves contain a large amount of oxalate, especially the leaves. Harvested in the early flourishing period have higher levels than those harvested in the later stages. Its oxalate content can reach 0.3% to 0.9%.
Pasture and wild plants
Such as sheep’s hoof, sorrel, cool sorrel, bluegrass, halophyte, purslane, setaria, etc. The oxalate content (fresh weight) in these plants can reach 0.5% to 1.5%.
Leafy vegetable feed
Such as spinach, spinach, amaranth, cowhide, etc. It has been reported in China that feeding raw spinach to Leghorn breeder chickens has caused calcium deficiency in the breeder chickens (eggshells have become thinner, the breakage rate has increased, and some breeder chickens have produced soft-shelled eggs), and has caused a decrease in hatchability of the eggs. Feeding spinach to pigs and poultry can also cause reduced growth and reduced calcium stores.
Straw
Hay made from rice straw and ratooned rice after harvesting contain large amounts of oxalate. In India, there have been reports of imbalances in calcium balance in the body due to the consumption of rice straw by cattle.
Sesame cake
Sesame husks contain oxalates, so the husks in sesame cakes must be completely removed.
Water lotus
Water lotus belongs to the aquatic plant of the Araceae family and was widely used as pig feed in southern provinces of my country. Some pig farms have been poisoned by feeding water lilies, with neurological symptoms such as empty mouth chewing, nervousness, and convulsions. The cause of poisoning has not yet been determined. Some studies believe that it is caused by the large amount of oxalate contained in water lilies.
Oxalic acid in plants exists in the form of free acid, but generally exists in plant cells as soluble potassium salts, sodium salts and insoluble calcium oxalate crystals. Oxalate can be present in the entire plant, with the highest content in plant leaves, followed by flowers, fruits and seeds, and the lowest content in stems. The oxalate content in plants also changes with the growth stage of the plant and the cultivation environment. Some people have found that the oxalate content in beet leaves can decrease with the passage of seasons; the oxalate content in wood sorrel changes day and night.
In addition to coming from plants, oxalates can also come from microorganisms in nature. It has been reported that fungi of the genera Aspergillus, Penicillium, Pythium, Sclerotinia, Phytophthora, Agaricus, Rhizoctonia, Pythium and other genera can secrete oxalic acid. Many pathogenic fungi (such as Sclerotinia sclerotiorum) injure plants by secreting oxalic acid toxins.
The harmful effects and mechanisms of oxalate
After oxalate is ingested by animals, it can form insoluble compounds with divalent and trivalent metal ions such as calcium, zinc, magnesium, copper and iron in the digestive tract. The oxalate is precipitated and excreted with feces, thereby reducing the utilization of these mineral elements. For example, adding 1% oxalic acid to a small horse diet containing 0.45% calcium can significantly reduce calcium utilization.
Oxalate has a strong stimulating effect on the mucous membrane. Therefore, when a large amount of oxalate is ingested, it can irritate the gastrointestinal mucosa, causing diarrhea and even gastric irritation. enteritis. Oxalate can be degraded by ruminant microorganisms and converted into carbonate and bicarbonate through metabolism. Therefore, ruminants are more tolerant to oxalate than non-ruminants. Poisoning occurs only when ruminants ingest a large amount of oxalate in a short period of time (such as when they are hungry) because part of the oxalate cannot be converted in time and enters the abomasum and is absorbed by the animal. When ruminants ingest small amounts of oxalate for a long period of time, rumen microorganisms can gradually adapt, improving the ability of the rumen to decompose oxalate. Therefore, newly introduced animals are more sensitive to oxalate than local animals. When the animals first graze on oxalate-rich grasslands, they are not adapted to the ingestion of oxalates. After being ingested multiple times and gradually adapting, their tolerance to oxalates can be improved. Oxalate tolerance. However, if ruminants continue to consume slightly higher levels of oxalate, due to changes in the pH value of the rumen contents (increased from the normal pH value), this may cause the oxalate to decompose into bicarbonate and carbonate.�Feeding amount
When feeding feed and forage rich in oxalates, the feeding amount should not be too much and should be fed in conjunction with other feed and forage. Equine animals are sensitive to oxalates, and feeding amounts must be strictly controlled. Feeding amounts of ruminants can be gradually increased to improve their tolerance to oxalate. At the same time, attention should also be paid to preventing animals from eating wild plants rich in oxalates, especially if animals are hungry and cannot graze in areas where oxalate-rich plants grow.
When adding feed and forage rich in oxalates, calcium supplements (such as calcium hydrogen phosphate, calcium carbonate, etc.) can reduce the body’s response to oxalic acid. Absorption of salt and alleviate the harm caused by oxalate
Information source: China Breeding Network
