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Areas from Calgary to Winnipeg are either abnormally dry or facing drought conditions, according to Agriculture Canada’s Canadian Drought Monitor. Producers over much of the Prairie region are anxious about pasture quality and sufficient feed supplies to get them through winter. An open fall in many areas has supported extended grazing on poor pastures, post-harvest stubble fields and drought-starved crops. Many producers suffered through dry pasture conditions, needing snow cover and spring moisture to replenish grasslands. Quality of winter feed supplies, when available, varied greatly. Vitamin A deficiencies are a real possibility.

One of the essential nutrients cattle fall short of grazing dry pastures and consuming crop residue is vitamin A. Cattle on green grass get plenty of vitamin A, an important nutrient, often overlooked through fall and winter. Cattle and sheep cannot generate their own vitamin A; they need to eat green plants containing carotenoid precursors such as, carotene — found in the orange-yellow pigments in green leaves of plants. Ruminants then convert carotene to vitamin A in the wall of the small intestine. During Prairie winters and long open falls in drought years, vitamin A in rations is often deficient and needs to be supplemented. Including vitamin A in mineral mixes, incorporating it into grain rations or by injection are common and effective methods of ensuring cattle get the vitamin A they need for health, reproduction and growth.

Vitamin A is a fat-soluble nutrient that plays a role in many vital functions — especially related to health, reproduction and growth. It plays a role in low-light vision, normal kidney function, development of bones, teeth and nervous tissue. Vitamin A maintains delicate tissues lining the respiratory, digestive and reproductive tracts — keeping them pliable and in good working order. Vitamin A deficiency thickens these tissues, causing them to become more brittle and increasing susceptibility to infection because the lining loses its effectiveness as a barrier to pathogens. In addition, a hard and brittle gut cannot absorb nutrients, resulting in poor gains.

Vitamin A deficiency also impairs reproduction. A shortage of vitamin A reduces spermatogenesis (sperm production). Low vitamin A levels account for resorption of fetuses in pregnant females and abortions. Calves do not grow well without vitamin A.

Cows need 30,000 to 50,000 international units of vitamin A/head/day. Injectable vitamin A is a quick method of returning the cow’s vitamin A status to normal. A dose of 1.5 million IU of vitamin A is needed for adult cows. If severely vitamin A deficient, multiple injections over time may be needed.

Deficiency symptoms include loss of appetite, rough hair coat, reduced feed intake, reduced growth, night blindness, edema, diarrhea, low conception rates, abortions and stillborn or weak calves. Calves born to cows deficient in vitamin A often have trouble mounting a normal immune response. Response to vaccines is, therefore, impeded.

Many fields were dry going into fall. In areas affected by drought, snow reserves over winter or precipitation last spring failed to replenish deficits. During drought, available carotene in forage is low. Therefore, whether cows are grazing dry grass or consuming hay made from drought-stressed forages, vitamin A intake suffers. Even when hay is made from good green forages, carotene is unstable and declines over time.

In a normal pasture season, the daily intake of carotene converted into vitamin A is three to five times the amount required. Cattle store up to four months of vitamin A in the liver during this period and under ideal conditions, cattle fed good-quality hay during the winter maintain adequate vitamin A levels. Drought conditions decrease the amount of carotene in plants, limiting the ability of cows to accumulate liver stores during grazing. Additionally, harvested forage during drought has extremely low carotene levels, contributing to the inability of cows to consume their requirements during winter feeding.

Another complicating factor is that drought-stressed forages have elevated nitrate levels. High nitrate levels are thought to lead to the destruction of carotene and vitamin A in the digestive tract. Depressed thyroid function also plays a role in increased vitamin A requirements.

Drought compounds vitamin A deficiency because plants go dormant early in the year and it’s a long time before animals eat green grass again. Producers need to pay attention to the vitamin A status of their cattle when feeding hay. Storage conditions affect vitamin A levels. Carotenes deteriorate during storage. Vitamin A levels vary tremendously throughout a bale. There is virtually no carotene in the outside layers of brown and sun-bleached bales. Internally, green and preserved forage contains plenty of carotenes. Ultraviolet light from the sun destroys vitamin A. Heat and humidity increase the rate at which vitamin A breaks down.

Supplementing cattle with vitamin A is relatively easy and cost-effective. But by the end of winter in Western Canada, vitamin A deficiencies usually exist without supplementation. This year will be worse.

With calving season approaching, it’s time to review feeding programs. Adequate vitamin nutrition is key to a successful calving and rebreeding season. Another factor might come into play: Due to global supply chain challenges and increased demand, product shortages are a possibility.

For more content related to drought management visit The Dry Times, where you can find a collection of stories from our family of publications as well as links to external resources to support your decisions through these difficult times.

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).

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