Strategic use of Vitamin A and E for Ruminant Livestock

Vitamins are essential nutrients required by ruminants during all stages of production. There are certain times in the year when vitamin supplementation is required. During the summer, actively growing plants in hayland and pasture have high levels of vitamins A and E precursors. These naturally occurring precursors convert to their active form and available form to the animal. The amount of vitamin supplied from the growing plants is more than adequate to meet requirements. When forages are cut for hay or grazed after plants have gone dormant, the vitamin precursors oxidize and the potency or availability of the vitamins decline over time. When hay is cut or the forages are dormant for six months, a majority of the vitamin precursors have lost their activity and do not supply adequate amounts of vitamins to meet animal needs. Two-year-old hay cannot be expected to have any vitamin precursors remaining. The ensiling process for either bagged or chopped silage destroys the vitamin precursors in the forage and should be considered to supply minimal amounts to the ration. It is when these preserved and stored feeds are being used that supplemental Vitamin A, D and E should be added to diets to avoid deficiency disease symptoms. Effects of not feeding vitamins will be discussed later in this article.

Many commercial mineral mixes have vitamins A, D and E added at sufficient levels to meet requirements. Most mineral and vitamin supplement tags will include a guaranteed analysis that will list the amounts of individual minerals and vitamins. Vitamin quantities are expressed as International Units (IU), which are set amounts defined for each specific vitamin form. Reasonable rates of vitamin supplementation for cattle consuming a 3-4-ounce (0.19 – 0.25 lbs.) daily intake of mineral and vitamin supplement are: Vitamin A, 500,000 IU/kg; and Vitamin E, 1500 to 2500 IU/kg. By using Guaranteed Analysis levels, vitamin content of the supplement can be compared to cattle requirements to determine if the product matches up well with animal needs. Vitamins A and E degrade over time so purchased products that are stored for several months before use may not supply adequate vitamin levels when fed. Storage in a dry cool area will help prolong shelf life. CFIA recommends vitamins are used within 6 months from date of manufacture.

Vitamin A can be stored in the liver for use over a three- to four-month period. Vitamin E is only for two to four weeks. Therefore, it will take a shorter time for the animal to become Vitamin E deficient. It is best to supply vitamins as required on a regular basis. Injectable vitamins have a high availability for the first week or two after injection but levels quickly drop in the body and even though some level of vitamins are available for the period indicated on the label, may not be sufficient to meet requirements after the initial peak has passed. Some injectable products are currently out of stock. There is no injectable Vitamin E product registered for use in Canada.

Risk Factors for Vitamin Deficiencies

There are many animal and environmental factors that influence vitamin requirements.

Animal factors:

A thin animal has less body fat as a percentage of body weight compared to an animal in good condition. Vitamins are stored primarily in the liver, but some is stored in body fat. Therefore, a thin animal has less storage capacity. This may result in an animal becoming deficient sooner.

Size and age of the animal and production (e.g. stage of pregnancy, bulls during breeding season, stage of lactation, etc.) Requirements vary with use and deficiency risk (i.e. needing to release enough vitamin A and E in milk to meet nursing calf requirements.

Environmental factors:

Variable weather patterns last year (precipitation – a lack of or excess, temperature and sunlight intensity) may have had an impact on the formation and storage life of precursor in forages and hay. Any stress factor that reduces the plant efficiency could reduce precursor formation. These levels could also be reduced due to late cutting or other harvest problems.

The main risk factors that could contribute to a feeding program that is deficient in Vitamin A are:

• bleached pasture or drought-grown hay
• "heated" or caramelized forage
• high concentrate diets
• weathered forages (excess sunlight, moisture or heat)
• harvested crop residues
• feeds with increased oxidation (processing and inclusion of minerals)
• feeds subjected to prolonged storage
• feeds with increased oxidation (processing and inclusion of minerals)

The main risk factors for a Vitamin E deficiency include feeds that contain:

• high nitrate concentrations
• prolonged storage or weathering
• increased oxidation (processing and inclusion of minerals)
• higher levels of polyunsaturated fats

Vitamin A: Main Deficiency Symptoms

• Reduced feed intake resulting in reduced performance
• Night blindness (unique to Vitamin A) and total blindness
• Rough hair coat
• Reduced immune function
• Joint and brisket edema (swelling)
• Diarrhea
• Tearing and dry eye
• Seizures
• Improper bone growth
• Low conception rates (cows cycle but don't conceive)
• Abortions
• Retained placenta
• Stillborn calves
• Reduced bull libido
• Reduced sperm numbers, motility, and normal sperm

Studies indicate that the majority of vitamin A is transferred to the fetus during the last three months of pregnancy and by the colostrum in the first 12 hours post calving.

Vitamin E: Main Deficiency Symptoms

• Reduced immune function in calves
• White muscle disease (selenium also involved)
• Reduced calf growth rates
• Reduced reproductive efficiency

Vitamin E is transferred to the colostrum four to eight weeks prior to calving and is only transferred to the calf by colostrum. Therefore, females in late pregnancy require higher levels of vitamins A and E approximately eight weeks before calving and for the first three to four months of lactation or until calves are eating significant amounts of growing forage. Vitamin E has less storage capacity in the animal. It can be expected that deficiency symptoms or reduce performance can be expected sooner with Vitamin E than Vitamin A.

Producers can assess herd health status by contacting their local veterinarian and if necessary, conduct a blood test for vitamins A (retinol) and E (alpha-tocopherol). That testing for Vitamin E would be more beneficial because storage in the body is for a shorter time and would become deficient sooner than Vitamin A. Deficient animals should be provided with supplemental vitamins at recommended amounts.

If vitamin supplies are deficient or suspected to be deficient, it is recommended to start vitamin-feeding programs as soon as possible. Supplementation should continue until animals are turned out onto green grass. Vitamin requirements are higher for breeding cattle to maintain milk levels for calves and avoid reproductive failure.

Level of concern:

High risk animals are those that grazed dry or dormant grass since last July and have received a silage based or straw-grain ration after coming off pasture as well as animals on hay or greenfeed harvested last summer and produced under the same stress conditions. In addition, no supplemental vitamins have been provided to date, calving is to start within a few weeks and breeding season starts well before the animals are turned onto fresh grass. Under these conditions, body stores of vitamins have been depleted.

It is possible for calves to be born dead. Calves born alive are likely to have greater health risks such as white muscle disease or higher rates of infectious diseases such as scours or pneumonia because of poor immunity. A lack of vitamins will persist until calves start consuming substantial fresh forage (three to four months of age). Cows are at risk of poor conception rates due to reduced fertility for either cows or bulls at the start of the breeding season prior to turnout on fresh grass.

Medium risk animals are those that grazed forages that went dormant in September and have received medium to marginal quality forage after coming off pasture. Animals on swath grazing or grazing corn for the majority of the winter are in the same situation. Animals may have some reserves to draw on. Vitamin supplementation should start a minimum of four to eight weeks prior to calving. Calving starts four to six weeks prior to turnout on grass and breeding season starts one month after turnout to grass.

Low risk animals are those that have been fed appropriate amounts of vitamins since fall and are in good body condition. For example: backgrounding steers in good condition that had been receiving adequate levels of vitamins in the diet or supplement and have been well vaccinated and will be returning to spring pasture. Non-breeding animals have lower requirements than breeding animals.

In the short term, vitamin deficiencies in individual animals over the next three to six months may not be noticeable, especially for herds that have been provided vitamins and minerals as part of a balanced diet to date. These herds are unlikely to experience effects of a Vitamin A deficiency and may be at some risk of a Vitamin E deficiency due a more rapid metabolism and shorter storage duration in body tissues. Herds that start calving in March or April may experience more problems because the vitamin content in the mineral products has been reduced because of the shortage.

Vitamin deficiencies may result in small changes in performance over the short run. Lower milk production, reduced average daily gain and a slight increase in open cow rates, which are difficult to notice. If deficiencies continue, the losses in performance and in livestock deaths become more severe. It is possible to have a serious problem if body vitamin stores are depleted and the situation is not corrected. Even though products have increased in price, it is prudent to continue feeding vitamins.

Contributing authors:

Hushton Block, Ph. D., Agriculture and Agri-Food Canada
Murray Feist, Saskatchewan Ministry of Agriculture
Barry Yaremcio, Alberta Agriculture and Forestry
Jennifer Heyden, Saskatchewan Ministry of Agriculture
Andrea Hanson, Alberta Agriculture and Forestry
Naomi Paley, Saskatchewan Ministry of Agriculture