The Importance of Vitamin A in Goats
- Kendra R. Shatswell
- 12 minutes ago
- 9 min read
For the sake of simplicity, this piece will usually refer to the precursors to synthesize Vitamin A as Vitamin A. As with many subjects, research in goats specifically can be sparse - so I have added quite a bit of information found in cattle research. Nutritional requirements might differ, but the function of vitamins and minerals in most ruminants is very similar. My goal is always to provide plentiful information because that means you can ask more questions and because sometimes it's the rabbit trail that leads us to answers. As always, I am not a vet or researcher, just a girl that loves goats and wants answers.
Vitamin A, a fat soluble vitamin, is stored in the liver and in body fat (1). A good diet provides adequate Vitamin A to goats; according to the Goat Extension website, “Vitamin A is synthesized from carotene, the pigment that gives grass and hay their green color.” There are many carotenoids found in plants that can be transformed into Vitamin A but beta-carotene is the most important. In feeds and minerals, Vitamin A might be provided in the form of synthetic retinols.
Possible Symptoms of Vitamin A Deficiency
Vitamin A is necessary for many functions in goats, including reproduction, eye, skin, and bone health, as well as immune function. An article in Small Ruminant Research also indicates that “...Vitamin A enhances the absorption and utilization of nutrients” (12) likely because Vitamin A is essential to a pliable rumen lining and a pliable rumen lining is essential to nutrient absorption (14).
An older study found a deficiency in Vitamin A can potentially increase the chance of urinary calculi in a very interesting way - the skin in the urinary tract essentially sheds more because it isn’t as healthy when Vitamin A deficient and this shedding skin makes a safe spot for bacteria to form, which can eventually create an environment favorable to crystal formation (11).
Nightblindness and weeping eyes are a likely symptom of Vitamin A deficiency and goats deficient in this vitamin are at higher risk of eye infections such as pinkeye (10).
Unfortunately, other symptoms of deficiency are quite vague - among the most notable are diarrhea, slow growth, low fertility and general susceptibility to illness. A couple sources point to hair loss or scruffy hair coat, as well, with source seventeen noting a deficiency of copper, zinc, and Vitamin A in goats with sarcoptic mange (2, 9, 17).
In cattle, especially young deficient stock in the advanced stages, “staggering gait, lameness or stiffness in knee and hock joints, and swelling of the legs and brisket (and sometimes in the abdominal region)” have been noted but there was less information on these particular symptoms in goat and producers would do well to rule out other culprits (14).
In cattle, the fertility decrease when deficient is due to the vitamin's numerous important contributions to reproductive tissues and “overall defense against oxidative damage;” conception rates especially might suffer as this vitamin plays an important role in follicular development (13). The same seems to be true in goats. This study showed beta-carotene was especially helpful in improving “follicular development and ovulation rate” in young does outside of a typical breeding season, though the “how” was not entirely understood (6).
Vitamin A - Important During Pregnancy
Of special interest is the role of Vitamin A in the health of pregnant does and newborn goats. “Prepartum vitamin A enhances goat doe health status and kid viability and performance” is worth reading in its entirety at the number twelve source. In summary: newborn kids ingest Vitamin A via colostrum, so a dam with inadequate stores will mean the kid doesn’t receive enough, either. Supplementing does with Vitamin A before kidding increased both the dam’s and kid’s health, specifically increased weights, gains, and body temperatures in the kids and “enhancing the does’ immunity and reducing kidding-induced stress” (12).
How does Vitamin A help with body temperature? Goat kids are born with brown adipose tissue, a type of fat that is mostly around the kidneys but also found in the neck and around the heart. The process isn’t entirely understood, but this brown fat will eventually change to white adipose tissue after about a month (25). While it is brown adipose tissue, it serves an amazing purpose - thermoregulation. In very simple terms, it converts chemical energy into heat energy, increasing the kid’s body temperature without shivering. Source twelve goes into greater detail as to the process, but it is known that Vitamin A supplementation enhances this process (12, 13, 24).
Dietary Sources of Vitamin A
Quantities of the vitamin in both pasture and hay are highly variable. In drought conditions, dry pasture will contain significantly less carotene. There are also differences among types of plants - legumes typically have higher concentrations of Vitamin A than grasses. Both legumes and grasses provide more Vitamin A in the early growth stages than at maturity (9). Hay put up in drought conditions or hay left too long between cutting and baling is also lower in beta-carotene (4). In fact, leaving it in the sun for too long or the unlucky cutting that gets rained on might result in hay lacking in Vitamin A at all (9). Stemmy hay is a poor source of Vitamin A because most carotene is found in the leaves (blades of grass) rather than the stem. Long term storage depletes Vitamin A stores in hay, especially if it is stored outdoors or subjected to sunlight, heat, humidity, and even oxygen - think of it as a very “sensitive” vitamin (3). A general rule of thumb is hay over a year old might lose as much as half of its original Vitamin A and the Pickworth et al study - source four - usually found some degradation as soon as four months. In that study, out of orchard, fescue, and alfalfa hays, the Vitamin A content of fescue degraded the most. With all this in mind, producers are more likely to see deficiencies in the winter or when feeding hay, especially older grass hay, for long periods of time (5).
In addition to loss via the modes listed above, pressure such as turning alfalfa into pellets, also reduces Vitamin A content dramatically. Don’t count on it providing any unless the manufacturer has specifically added some back to the final product (22).
To complicate matters, the level of carotenoids in the diet is not always an accurate representation of what is actually being converted by the ruminant into Vitamin A; some is “lost” in the process but to date there’s not a clear understanding as to why (9,18). Additionally, several sources indicate there’s disparity among carotenoid utilization among breeds in dairy cattle though I could find no mention of this in goats (8,14). Thankfully, sheep and goats convert Vitamin A more readily than cattle (29).
As far as why carotenoids might not be converted so efficiently, this cattle study describes reasons why:
Several factors affect the absorption of vitamin A in cattle, such as dietary fat content, intestinal health, and the presence of other micronutrients. Higher dietary fat content can enhance vitamin A absorption, while intestinal diseases can impede it in animals (Reboul, 2013; Amimo et al., 2022).
Sources note that in cattle diets heavy on grain, silages, or haylage were likely to be deficient. Grazing fertilized fields or a diet otherwise high in nitrates can also be problematic (15). To reiterate - it is thought goats are quite efficient at converting carotenoids to Vitamin A but there’s not a lot of goat-specific research out there to date.
In mineral mixes, Vitamin A can suffer from oxidation caused by other minerals so it's best to avoid prolonged storage to minimize loss (16). For a more detailed explanation, this source is worth the read - Understanding vitamin stability in animal feed premixes. Because of all these caveats to Vitamin A supplementation, absorption, and quantities, it is highly unlikely Vitamin A toxicity will occur outside of a mixing error (10).
How Much Vitamin A is Necessary?
Due to deficiencies in both the diet and conversion, it is often necessary to provide Vitamin A via synthetic supplement, most usually a quality loose mineral. How much Vitamin A does a goat require? Sheep Goat and Cervid Medicine by Pugh suggests “...105 IU/kg BW/day for nonlactating animals. During late gestation, the requirement increases to 150 IU/kg/day, and for lactation, 175 IU/kg/day” (9). “IU” is short for international unit, which is how most minerals will list Vitamin A, “kg” is kilogram, and “BW” is body weight. Remember that a kilogram is approximately 2.2 pounds.
The 2007 National Research Council lumps sheep and goats together with a requirement of 104.7IU/kg for maintenance. As mentioned earlier, pregnant does will have higher requirements to provide adequate amounts in colostrum. NRC recommends a bit over 178 IU/kg for lactating animals, with pregnant and growing animals falling in between the maintenance and lactating recommendations (10). For example, a lactating doe weighing 110lb would require around 8900IU of Vitamin A per day.
According to Goat Medicine by Smith and Sherman, there is proof kids battling coccidiosis have a higher Vitamin A requirement, presumably because of incurring gut damage (10). As mentioned earlier, this vitamin is stored in the liver and in body fat. Various sources point to stores lasting anywhere from 4-6 months. These stores are readily utilized when the diet is not meeting the animal’s requirements.
Testing for Vitamin A
Vitamin A status can be checked by blood serum or by a sample of liver tissue, though the liver tissue method is not applicable in kids that died before nursing since colostrum is the primary source of Vitamin A. There are varying viewpoints on how accurate these tests are.
While the website description is specific to cattle, Michigan State University offers this sort of testing here - Vitamin A and E Diagnostics | College of Veterinary Medicine at MSU as does the veterinary diagnostics lab at Colorado University - Veterinary Diagnostic Lab USALIMS Test Information and Iowa State University - Tests/Fees – Veterinary Diagnostic Laboratory. (Author’s note - if you’re aware of other labs offering this service, feel free to let me know so I can add them to the list!)
Supplementing Vitamin A
Supplementation may be provided by improved diet or oral supplementation or injection. There are few injectable Vitamin A supplements in the U.S. and those that are on the market are typically not labeled for goats. The second edition of Goat Medicine by Smith and Sherman also prefers oral supplements due to “rapid peroxidation at the injection site” which means that the injection might be less effective and potentially cause oxidative stress (10). Due to these shortcomings, oral supplements or an improved diet are the preferred methods of supplementation for most producers. In oral supplements where Vitamin A is listed in mg, the conversion factor is dependent on the form of Vitamin A - either various forms of retinol or beta-carotene. If it isn’t listed on the product, sometimes the more detailed manufacturer's label on the product website will go into greater detail or provide IU equivalents.
As mentioned, good quality alfalfa (leafy and dark green) or other legume hay is a good source of beta carotene. Raw carrots are another good source of Vitamin A, though they should be fed in moderation and, if chopped, in pieces small enough to prevent potential choking. Dr. Sandra Baxendell recommends a cup or two of raw, peeled carrot slices in her webinar on Pregnancy Toxaemia (23).
One “home remedy” is cod liver oil, though I was unable to find any research pertaining to goats as far as using it as a Vitamin A supplement specifically. It is high in the vitamin and there are multiple livestock and horse supplements containing it; some producers opt to use the human varieties. One very old study in 1938 from the Journal of Dairy Science proved supplementing fish oil to dairy cattle or dairy goats “markedly reduces the fat percentage of the milk” and a later study in dairy cattle found the same thing to be true but “the Vitamin A content of the milk fat and blood plasma was increased by feeding cod liver oil” (20). A newer study also found the fat was lower in cod-liver oil fed goats but this was at over 1% of their diet, not as a short-term supplement, and the fish oil did increase some beneficial fatty acids (21). Certainly an area worthy of additional research.
It may not be talked about as much as Vitamin B or Vitamin E, but I hope this piece gives goat producers a new appreciation for Vitamin A!
Concentration of pro-vitamin A carotenoids in common beef cattle feedstuffs - PMC
Long-term hay feeding may lead to vitamin A deficiencies in cattle | Farm Progress
Chapter 2. Balancing Vitamin A Supply for Cattle: A Review of the Current Knowledge
Pugh, D. G., Baird, A. N., Edmondson, M. A., & Passler, T. (2021). Sheep, Goat, and Cervid Medicine (3rd ed.). Elsevier.
Smith, M. C., & Sherman, D. M. (2009). Goat medicine (2nd ed.). Wiley-Blackwell.
Evaluate Vitamin A Supplementation for Beef Cattle — Extension and Ag Research News
Chapter 2. Balancing Vitamin A Supply for Cattle: A Review of the Current Knowledge
Alexandria Journal of Veterinary Sciences www.alexjvs.com The Relationship between Serum Zinc, Copper and Vitamin A Concentration
The Influence of Tocopherols and Cod-Liver Oil on Milk and Fat Production.
Neonatal Hypothermia in Small Ruminants - Alabama Cooperative Extension System
