Vitamin A is important for many body functions, including growth, immune function, skin and hoof health, and reproduction. Vitamin A deficiency in beef cattle can result in decreased overall health and performance, blindness or night blindness, decreased fertility, higher incidence of retained placenta and stillborn or weak calves.
The following article was written by Chelsey Siemens, livestock and feed extension specialist with the Saskatchewan Ministry of Agriculture in Kindersley.
Vitamin A is transferred to calves through colostrum, so cows must have sufficient vitamin A stores to produce good quality colostrum. If cows are deficient in vitamin A, or if calves don’t receive enough colostrum, calves are likely to be vitamin A deficient.
Actively growing green plants contain beta carotene, a pigment which is converted to vitamin A in the body. During the summer months, cows usually consume more than enough beta carotene to produce the vitamin A that they need. This vitamin A will be stored in the cow’s liver and fat tissue for a period of two to four months. During fall and winter, cattle are consuming dormant forages or harvested feed in which the beta carotene content is much lower, making it necessary to supplement vitamin A in the ration. Even feeds that were harvested green will gradually decrease in beta carotene concentration during storage.
Challenging environmental conditions impact pasture and forage quality, including vitamin A content. During dry years plants may go dormant earlier in the season, extending the time period that cattle go without green forages. Cattle may be taken off pasture earlier in the fall and begin grazing later in the spring when moisture is in short supply. Pasture and hay shortages may also result in cattle being fed crop residue, high concentrate rations, and other diets that are naturally low in beta carotene. These conditions all contribute to an increased risk of vitamin A deficiency, and the need for supplementation.
Many commercially available mineral mixes and supplements include vitamin A. Look for the guaranteed analysis on the label, where vitamin quantities are expressed as International Units (IU) per kilogram of supplement. To ensure that cattle are receiving the desired quantity of vitamin A, they must consume the supplement within the recommended range. For example, a pregnant cow requires approximately 60 IU of vitamin A per kilogram of body weight (Nutrient Requirements of Beef Cattle, 8th Revised Edition). This works out to 38,100 IU of vitamin A for a 1400 lb cow. If we assume that the forage and concentrate in her winter ration contains very little vitamin A, the bulk of this needs to come from a supplement. If a mineral mix containing 500,000 IU/ kg of vitamin A is provided at 100 g per cow per day, each cow will receive 50,000 IU of vitamin A per day, which exceeds her requirement. However, if each cow only consumes 50 g per day, the requirement for vitamin A will not be met. Use caution if feeding more than one ingredient containing supplemental minerals, as some minerals are toxic at high levels or when present in the wrong proportions. Contact a nutritionist or livestock and feed extension specialist for advice on balancing your particular ration.
Other considerations to keep in mind include the shelf life of supplements. Vitamins will degrade over time, so keep an eye on the manufacture date of any supplements containing vitamins and aim to use these products within one year. Injectable products containing vitamin A are available, but delivery must be timed carefully to cover the crucial time when stores of vitamin A need to be available to the animal. Unnecessary injections should be avoided whenever possible, so dietary sources are the preferred method of vitamin A supplementation.
Creating a plan for appropriate vitamin A supplementation is a relatively easy and inexpensive step which can have a significant positive impact on cow health and productivity.
For more information, please contact your local Regional Services office, or call the Agriculture Knowledge Centre at 1-866-457-2377.
