From pasture to the packer
Vitamin A critical for beef cattle
By Hannah Speer
Vitamin A plays a fundamental role in beef cattle health and performance. It supports vision, cellular generation and differentiation, immunity, epithelial integrity, reproduction, and fetal growth and development. The best dietary source of vitamin A for cattle is fresh green forages, which are high in beta-carotene, a compound that is converted to usable forms of vitamin A by the body. Any excess vitamin A not needed by the body is stored in the liver for later use during times when dietary vitamin A intake is low, such as during fall or winter when dormant forages are grazed, or when stored forages and grains make up the majority of the diet.
Lack of access to fresh green forage for long periods of time puts cattle at risk for developing a vitamin A deficiency if proper supplementation is not provided. This is especially true for cows, where a deficiency can have negative outcomes on both the cow and her calf. Beyond deficiency prevention, vitamin A can also impact carcass quality, particularly marbling development in cattle. Both excessive and restricted vitamin A intake can alter carcass characteristics, depending on when the provision of excess or restriction occurs during a calf’s lifetime.
Despite its importance, research on vitamin A requirements in modern cattle production systems remains limited. This article will explore the importance of vitamin A in different segments of the beef industry, current supplemental recommendations, and will perhaps raise important questions about the optimal timing and dose of vitamin A needed to achieve production goals.
Forms, functions of vitamin AVitamin A is a generic term that covers structurally related compounds that possess biological activity of parent substance named retinol. There are several forms of vitamin A, each having a unique function in the body. Retinol is the transport form of vitamin A that circulates throughout the body to be delivered to different tissues. Retinyl esters, or retinol bound to fatty acids, is the primary storage form of vitamin A, and is also the form commonly used in livestock vitamin supplements. Retinal plays a key role in vision, while retinoic acid is the form that controls cell differentiation and gene transcription.
Given the functions of vitamin A, it makes sense where we would start to see signs of a deficiency in cattle. In a severe deficiency, night blindness occurs. This is a symptom that is unique to vitamin A deficiency. Other symptoms of a vitamin A deficiency are more difficult to pin to vitamin A directly. Vitamin A deficiency can weaken the immune system and epithelial barriers protecting the gut and respiratory tissues, thereby increasing susceptibility to disease. It can also cause birth defects and impair reproduction in both males and females. In cows, depending on the timing and severity of deficiency during gestation, it can cause abortion, fetal resorption, or a failure to conceive entirely. For bulls, vitamin A deficiency has been noted to reduce testosterone production and negatively impact sperm production and quality. Young calves are especially prone to experiencing vitamin A deficiency because they are born vitamin A deficient. This is because placental transfer of vitamin A is very minimal during gestation.
Vitamin A needs of cattle: how much, and when?For all vitamin A recommendations for cattle discussed in the following sections, it is important to note that these are supplemental recommendations, and do not account for any vitamin A found in the basal diet.
CowsEnsuring cow receive enough vitamin A in late gestation is very important, as it can impact vitamin A concentrations in colostrum. Calves will rely on colostrum to provide the vitamin A they need to start building their own stores. Cow vitamin A liver stores contribute about 40% of the vitamin A found in colostrum, while the other 60% comes from the cow’s diet, so it benefits the calf if the cow has both adequate liver vitamin A stores and receives adequate supplemental vitamin A in late gestation. Low vitamin A levels in colostrum could cause a deficiency in the calf, which could lead to calf health issues given vitamin A’s role in the immune system. It is also important for maintaining tissue lining the gut, so a primary symptom of a vitamin A deficiency in a calf will be diarrhea in the first two weeks after birth.
Supplemental vitamin A needs of cows will vary depending on production system. The current recommended amount of supplemental vitamin A for pregnant and lactating cattle is 1,273 and 1,773 IU/lb of dry matter intake, respectively1. These recommendations have not been updated since they were published in 1976 and assume cows have been on green grass for 5 months out of the year building vitamin A stores to pull from when dietary intake is low. These recommendations will not work for the cow whose time on green grass has been cut short and has been consuming stored forages for a large part of the year or being fed primarily in confinement. Cows that have not had the opportunity to build vitamin A stores are going to require more supplemental vitamin A.
If cows are currently on green grass, they are probably getting more than enough in their diet to meet their needs and could get by with minimal vitamin A supplementation. Moving into fall and winter from consuming less green grass and more stored forages, 36,000 IU/day for pregnant cows is recommended. This means a vitamin/mineral supplement fed at 4 ounces/head/day would need to contain 144,000 IU/lb. For cows who have little to no access to fresh green forage throughout the year, the amount of vitamin A supplement needed to ensure adequate vitamin A status is increased.
A study conducted at the University of Nebraska-Lincoln assessed the effect of different supplemental vitamin A levels on vitamin A status of cows and their calves managed in long-term confinement, where cows were receiving a diet consisting of wheat straw, corn silage, and wet distillers grains2. They found that the current recommended supplemental amount for pregnant cows, if provided from late gestation to early lactation, was not enough to achieve adequate liver vitamin A concentrations for cows or calves. It actually took 3 times the current recommended amount, or 93,000 IU/d, to get liver vitamin A concentrations of both cows and calves into adequate ranges. Thus, if cows have not had much access to green forage throughout the year prior to late gestation, the current recommendation is that at least 93,000 IU/d, or 372,000 IU/lb in a 4-ounce mineral, should be provided during late gestation to ensure both adequate status in the cow and her calf.
Vitamin A for calves: impacts on carcass qualityIn addition to being beneficial for calf health, recent research has suggested that vitamin A supplementation to young calves who are destined for the feedlot may improve carcass quality, specifically marbling. Marbling, or intramuscular fat content, can be affected by either an increase in cell size (hypertrophy), or an increase in fat cell numbers (hyperplasia). Retinoic acid, the form of vitamin A that controls cell differentiation and has been shown to stimulate hyperplasia early in life, meaning that there are more potential sites for fat deposition as the calf matures and is placed on a high energy diet in the feedlot. Conversely, vitamin A restriction during the finishing period has been shown to increase marbling. This is because retinoic acid prevents fat cells from maturing, so less vitamin A during the finishing period will actually stimulate hypertrophy.
Before birthA study in Canada was recently conducted that evaluated the effect of late gestation vitamin A supplementation to beef cows and how that influenced carcass quality of steer calves3. What they found was that calves who were born to dams receiving 3,600 IU/lb of dry matter intake of supplemental vitamin A during late gestation had more intramuscular fat compared to calves whose dams did not receive supplemental vitamin A. These calves maintained this advantage of greater intramuscular fat all the way through the finishing period. No differences in subcutaneous fat thickness were observed between calves. Authors attributed the increase in intramuscular fat observed in the vitamin A treatment to calves being born with more immature fat cells within the muscle.
Administration at birthOne study showed that a dose of 150,000 IU provided to Black Angus steer calves at birth and again at 1 month of age via an injection resulted in an increase in intramuscular fat at the start of the finishing period compared to calves receiving no injectable vitamin A4. The calves receiving the vitamin A injection also had greater carcass marbling scores. Intramuscular fat percentages were greater in both males and females at harvest in a study conducted in Brazil when a single dose of 300,000 IU was administered as an injection at birth to steer and heifer calves5. In both of these studies, intramuscular fat was increased by vitamin A while no appreciable differences were observed in subcutaneous fat thickness between calves receiving or not receiving vitamin A.
In the feedlotThe supplemental vitamin A recommendation for feedlot cattle is 1,000 IU/lb of dry matter intake1. This level seems appropriate for optimizing cattle performance and carcass quality, and some studies have even evaluated supplementing less than the recommended amount for the entire finishing period and noted improvements in quality grade and marbling scores without any adverse consequences on animal health or performance. However, the effects of vitamin A restriction in the finishing period on carcass quality seem to vary by breed. Cattle with a lower genetic potential for marbling may take more days of vitamin A restriction to see improvements in marbling compared to breeds with greater marbling potential. More research is needed to understand how supplemental vitamin A amount interacts with breed type to influence carcass characteristics in feedlot cattle.
Take home messageVitamin A is essential for optimal health and performance of beef cattle at any production stage. Supplementation strategy for vitamin A, however, may depend on production stage, diet, and management goals. It should not be a “one-size-fits-all” supplementation approach. The current recommendations for supplemental vitamin A may not fully reflect the needs of modern beef cattle, especially cows raised in production systems where access to green grass is limited. The calf is at greatest risk for vitamin A deficiency, so providing adequate supplementation to the cow in late gestation will ensure the young calf gets the vitamin A it needs (which may also lead to improvements in carcass quality later on).
Going forward, vitamin A requirements should be refined considering different diet types, breeds, health implications, and production goals in all segments of the beef sector. The definition of a requirement may change based on the goal you are trying to accomplish─the requirement that is trying to optimize immune function or health is likely different than the one that tries to maximize carcass quality.
References1NASEM. 2016. Nutrient Requirements of Beef Cattle. 8th rev. ed. Natl. Acad. Sci., Washington, DC.
2Speer, H. F., K. H. Wilke, and M. E. Drewnoski. 2024. Effects of vitamin A supplementation on liver retinol concentrations of beef cows and their calves managed in confinement. Appl. Anim. Sci. 40:619-626.
3Dean, S., M. Gomes, W. Silva, M. Steele, K. Wood, M. Du, T. Costa, N. Serão, M. Gionbelli, and M. Duarte. 2024. Vitamin A-enriched diet at late gestation affects intramuscular fat deposition in beef offspring. Meat Muscl. Biol. 8:17646, 1-12.
4Harris, C. L., B. Wang, J. M. Deavila, J. R. Busboom, M. Maquivar, S. M. Parish, B. McCann, M. L. Nelson, and M. Du. 2018. Vitamin A administration at birth promotes calf growth and intramuscular fat development in Angus beef cattle. J. Anim. Sci. Biotech. 9:55.
5Maciel, F. C., O. R. M. Neto, M. S. Duarte, M. Du, J. F. Lage, P. D. Teixeira, C. L. Martins, E. H. R. Domingues, L. A. Fogaça, and M. M. Ladeira. 2022. Effect of vitamin A injection at birth on intramuscular fat development and meat quality in beef cattle. Meat Sci. 184:108676.
Speer is an assistant professor of animal science at the Northern Agricultural Research Center in Havre, Montana.
