Vitamin A deficiency in beef herds lingering effect of drought

2013-04-25T12:46:00Z Vitamin A deficiency in beef herds lingering effect of droughtBy Jane Fyksen Crops Editor Agri-View
April 25, 2013 12:46 pm  • 

It’s been a tough calving season weather-wise, what with colder-than-normal temperatures, snow, rain and everything in between. Some beef producers may also be seeing the lingering effects of last year’s drought as well. An earlier-than-normal start to feeding stored feeds last fall due to droughty pastures, coupled with lower-quality hay during the winter feeding period, is resulting in calves showing vitamin A deficiency.

That’s according to Grant Dewell, Iowa State University beef veterinarian, who reported last week an uptick in the number of calf health problems submitted to the Iowa State Veterinary Diagnostic Lab due to cows without normal liver stores of vitamin A.

Doug Lyman, diagnostic pathologist at the Wisconsin Veterinary Diagnostic Lab, says Wisconsin’s lab is also on the lookout for vitamin A deficiencies this spring. Two weeks ago, the lab received two aborted calves that were below the detection level for vitamin A. “It wouldn’t surprise me,” says Lyman, to see more vitamin A deficiency problems from herds in the state. Lyman was previously in private practice working primarily with dairy cattle in northcentral Wisconsin.

“Typically calves have been submitted with a history of being either stillborn or weak at birth. Some veterinarians have reported blindness, neurologic signs or diarrhea that can also be associated with vitamin A deficiency,” reports Dewell in Iowa. “Severe vitamin A deficiency can result in abnormal bone development in fetal calves. Other calves may be born weak and fail to thrive. Additionally, poor immune function can lead to increased infectious disease incidence.”

Vitamin A is necessary for vision, maintenance of epithelial tissue and mucous membranes, bone development and immune function. While vitamin A usually isn’t a big concern for mature cows, deficiencies can show up late-winter/early spring when cattle have been eating hay for a long period.

Dewell recommends cows receive supplemental vitamin A either through oral supplementation or injection. Calves may benefit from an injection of vitamin A at birth and potentially a second dose two to three weeks later, especially if cows have not been supplemented.

Dewell says that unlike many vitamins produced by rumen bacteria, cattle have a requirement for vitamin A. They convert carotene from plant leaves to vitamin A in the wall of the small intestine. Since vitamin A is a fat-soluble vitamin, cattle can store it in their livers when their daily intake is 3 to 5 times greater than their requirements. Mature cows, he notes, can store this vitamin up to four months. Under better conditions, cattle fed good-quality hay during the winter will have adequate vitamin A levels from carotene in the hay and their accumulated liver stores. However, with longer-than-usual winter, a considerable number of producers are short on hay. Some may have purchased less-than-optimum hay due to the hefty price tag for hay.

Dewell says that “under less-than-ideal situations, vitamin A supplementation may be required to maintain proper health and reproductive performance of the cow and normal development and health of calves. Drought conditions that decrease the amount of carotene in plants limit the ability of cows to accumulate liver stores during grazing.

Additionally, harvested forage during a drought will have extremely low carotene levels, decreasing cows’ ability to consume their requirements during winter feeding.

“Another complicating factor is that many drought-stressed forages have elevated nitrate levels. High nitrate levels lead to destruction of carotene and vitamin A in the digestive tract, and increasing requirements for vitamin A by depressing thyroid function,” Dewell discusses.

In drought situations where plants become dead or dormant, the carotene content becomes practically devoid and may lead to a deficiency of the precursor to vitamin A. Carotene is very low in mature, weathered forages, grains and many crop residues, and will be lost in stored hay crops over extended periods of time. Hay that was stored throughout all of last winter was finally fed this winter, the vitamin A content will be considerably less than when that forage was originally harvested. Some 2-year-old hay was even being fed this winter and spring; vitamin A content is decreased markedly in older, more-weathered hay.

Dewell says late-pregnant cows this spring are apt to be at risk due to last year’s drought and the resulting springtime feed shortage (i.e. some are being fed corn stalks or stemmy or weather-damaged hay). They might also have had minimal green-grass intake last year due to drought. In hindsight, those cows should have been supplemented with vitamin A (either a liquid supplement, mixed in feed or added to mineral, or administered via an injection).

Common signs of vitamin A deficiency in cattle include: Reduced feed intake and growth, rough hair coat, night blindness, edema, diarrhea, seizures, increased susceptibility to infection, abnormal sperm, abnormal bone growth, low conception rates, abortion, stillbirths and weak calves.

According to the University of Arkansas, sub-clinical vitamin A deficiency may also result in a lower calf-crop percentage or a later calving season next year. Vitamin A deficiency can result in poor conception rates, abnormal embryonic development, and fetal death. Reduced maintenance of epithelial tissues (including the lining of the respiratory/digestive system) can increase infections. Clinical deficiency symptoms, as noted, include night blindness in older animals.

Specifically, Dewell says adequate vitamin A is critical for fetal and neonatal calves. Low levels can lead to calf losses from abortion and stillborn calves. Calves born alive from cows with low vitamin A levels may be blind from microphthalmia or constriction of the optic nerve, have deformed bone development or weak uncoordinated muscles, resulting in the inability to nurse. Neonatal calves without adequate vitamin A may seizure or show other neurological signs (from increased cerebrospinal fluid pressure). Continued low vitamin A can also lead to severe diarrhea that’s often fatal.

“Additionally, these calves may be at risk for increased infectious diseases because of poor immune function,” this Iowa veterinarian adds.

Vitamin A injection is a “very efficient way” to increase liver stores compared to oral supplementation, says Dewell. However, one injection may not be enough, as cows that are already deficient in vitamin A have a reduced ability to store vitamin A in the liver. It may be necessary to repeat the injection monthly until adequate stores are achieved or sufficient oral supplementation can be attained, notes Dewell.

“Calves that are born with signs of vitamin A deficiency due to abnormal development will probably not benefit from supplemental vitamin A,” he says. “Abnormal bone development that constricts the optic nerve leading to blindness or muscle incoordination from spine abnormalities will probably not respond to vitamin A.”

However, other calves not as severely affected will benefit from an injection of supplemental vitamin A at birth to prevent further detrimental effects of low vitamin A levels. Normal calves will be born with adequate levels of vitamin A, but require additional vitamin A from consumption of milk that has satisfactory vitamin A levels. Therefore, it may be necessary to repeat injection of vitamin A in two to three weeks. As it takes two to four weeks for cows to respond, calves may need that second injection.

It is also important to remember that cows and calves that are deficient in vitamin A are probably deficient in other vitamin and minerals, especially vitamin E (as well as possibly copper, manganese, selenium and zinc). Thorough evaluation of vitamin and mineral status should be done routinely. Liver biopsies can be performed on cows in mid to late-gestation to assess and correct vitamin and mineral status prior to calving.

Calves that die either from abortion, still birth or from other causes after birth should have a complete diagnostic work up including liver mineral and vitamin levels (especially vitamins A and E). Cattle producers can then cost effectively supplement the necessary vitamins and minerals to help ensure a healthy beef cow and calf, Dewell says.

Producers should consult with their own veterinarian and/or nutritionist if they suspect a vitamin A deficiency this spring in their herd. Lyman says liver samples from dead calves can be submitted to the Wisconsin lab through a local veterinarian. He says his lab can also run vitamin A blood serum tests on cows, as well as from weak-but-still-alive calves.

Lyman tells producers who suspect a problem to inject both cows and calves with A and E, and start supplementing with 100,000 to 150,000 units in the mineral mix. As soon as cattle get on green, growing pasture, vitamin A (and E) deficiency is no longer a threat.

According to the University of Arkansas, mineral designed for 4-ounce intake that contains 150,000 International Units (IU) of vitamin A will deliver about 75 percent of a mature, lactating beef cow’s vitamin A requirement. Cattle consuming a mineral with this level of vitamin A or greater would not be expected to exhibit vitamin A deficiency unless they are consuming the mineral at less than the expected rate and the mineral has been stored for a long period of time, resulting in the degradation of vitamin A. If a complete mineral with a high level of vitamin A has not been offered to the herd, an injectable form would be the preferred option if the spring breeding season will begin soon.

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