Because of the different dietary formulations, the carotene content of dairy cows is also different. When vitamin A enters the rumen, 40%-80% of them are destroyed by nitrate and various microorganisms. In the small intestinal wall of dairy cows, carotene can be converted into alcoholic vitamin A, which is absorbed by the body to form ester-type protein complexes, which are transported to the whole body along with blood and lymph circulation, and stored in the liver when vitamin A is excessive.
For dairy cows, vitamin A is one of the necessary low molecular organic compounds. Vitamin a function is to maintain the integrity of epithelial tissue structure and promote the normal development of bone and visual function. Stimulate the synthesis of mucopolysaccharide in connective tissue, while keeping the membrane structure of cells and organelles such as lysosomes and mitochondria normal. Vitamin A deficiency will influence milk nutrients.
Therefore, a reasonable dose of vitamin A should be added or supplemented to ensure that it meets the needs of dairy cows. The best way is to vitamin a soluble in water.
Dairy cows fed poor-quality forage for a long time, seriously lacking enough carrots vitamin A, such as forage harvested on rainy days in summer and autumn and grass growing poorly in early summer, together with carotene destroyed due to improper operation in the preparation and processing of forage, or grain and silage during long-term preservation. It receives rain, sunshine and heats up. It loses its activity due to oxidation and destroys the carotene contained in it.
Some dairy farms only pay attention to the feeding and management of lactating cows but do not pay attention to signal of disease in young cattles. They only feed the dairy cattle with green fodder, especially fresh green fodder. However, cow babies are not fed or fed less, which often leads to vitamin A deficiency, especially fluffy cow. When the digestive and absorption function of the dairy cow's gastrointestinal tract is disordered, such as Fasciola hepatica, other intestinal parasitic diseases, gastrointestinal catarrh, etc., more concentrates are still fed, especially too much phosphorus-deficient feed and nitrate-containing feed, or naphthalene chloride poisoning occurs.
Because of the disorder of digestive function, Hu can not be made. All of the carotenes are converted to vitamin A and are difficult to absorb. The physiological functions of cows were abnormal, such as the increase of body temperature in late pregnancy and lactation, the decrease of liver function, the injection of diethylstilbestrol and hyperthyroidism, which reduced the content of vitamin A. Calves are unreasonably fed, do not drink colostrum in time or do not drink enough colostrum. They are weaned too early and are mainly fed with milk substitutes.
Besides, when they are heated and modulated, they destroy the activity of vitamin A and make them unable to get enough vitamin A, which causes the disease.
The diseased cows showed ataxia, aimlessness, unstable gait, limb weakness, occasional convulsions, lasting about 2 to 8 minutes each time, some even suddenly fainted, limbs and neck were stiff. Short breathing, prominent eyeball, but body temperature remains normal. In the spotted cow, the cornea of both eyes is not glossy, the reaction to light is slow or disappears completely, the symmetry of the pupils of both eyes appears moderate or extreme divergence, and then develops into blindness.
The optic nerve papillae were blurred, and there were color differences in the quadrants from the posterior pole of the retina to the surrounding edge, showing different shades of light gray or light blue, venous enlargement, and pink retina. Dairy cows are prone to miscarriage, stillbirth or preterm birth during pregnancy. Producing dairy cows often have reproductive disorders and reproductive tract diseases, and postpartum placenta retention.
To investigate the composition of diet, morbidity, abortion, neurological symptoms and blindness in dairy cows, and to make a preliminary diagnosis based on the changes of characteristics such as optic nerve papilla edema. Besides, the contents of carotene or vitamin A in the diet, liver tissues and blood of dairy cows were also determined.
Normally, healthy dairy cows contain about 601 U of vitamin A per 100 mL of blood and about 10-50 mg of vitamin A per gram of liver tissue. If the determination results are lower than the standard, the diagnosis can be made.
Prevention and control
If dairy cows suffer from vitamin A deficiency, the composition of forage and feeding should be adjusted immediately. Green and juicy feed such as alfalfa and carrot should be increased. When necessary, 4401U of vitamin A can be injected into muscles in time according to the weight of each kilogram, and 20-60 ml of fish liver oil can be given to them every time.
Besides, vitamin A preparation can also be used, such as vitamin A injection, 10-15 ml per muscle injection for adult dairy cows, 2-5 ml for calves, once a day, for 7 consecutive days. Besides, due to the synergistic and mutually protective effects of various vitamins and their common and similar roles, supplementation of vitamin A to diseased cows should be accompanied by appropriate supplementation of other vitamins, to ensure that all kinds of trace elements needed by dairy cows are met.
In the prevention and treatment of vitamin A deficiency in dairy cows, zinc and vitamin A should be supplemented at the same time, to improve the curative effect. It is necessary to mix cow feed reasonably, make nutrition balanced, and ensure that it contains an adequate amount of carotene and vitamin A. For dairy cows at different stages, the content of vitamin A required is different, basically about 2200U per kilogram of diet.