Understanding how important vitamin A is and making sure ruminant livestock get enough of it during winter can keep them healthy and productive. Dr Sakhi Nkosi, a veterinarian at Afrivet Technical and Training Services, gives farmers practical tips for keeping vitamin A levels right for their animals.
During winter, one of the most critical nutritional deficiencies observed in ruminants is a lack of vitamin A. This fat-soluble vitamin, along with vitamins D, E, and K, plays a crucial role in maintaining the health and well-being of these animals.
Vitamin A is essential for various physiological functions in ruminants. It is vital for proper bone formation, vision, and the health of the respiratory, digestive, and reproductive tracts.
Additionally, it contributes significantly to sperm development, energy metabolism, skin maintenance, and immune system support through antibody production.
Clinical signs of nutritional deficiencies in winter
During winter, ruminants may display various clinical signs indicative of nutritional deficiencies, particularly when vitamin A is lacking. Key symptoms to watch for include:
- Lower growth rates: Animals may experience stunted growth and fail to reach their expected size.
- Night blindness: Difficulty seeing in low light conditions is a common symptom of vitamin A deficiency.
- Increased susceptibility to diseases: A weakened immune system makes animals more prone to infections and illnesses.
- Keratinisation: Hardening of the respiratory, digestive, and reproductive tracts can occur, leading to various complications.
Health conditions resulting from vitamin A deficiency
- Pneumonia: Respiratory infections are more likely to occur due to the keratinisation of respiratory tract tissues.
- Diarrhoea: Digestive issues arise from the hardening of the digestive tract lining.
- Reproductive issues: These include stillbirths, abortions, and keratinisation of the reproductive tract, affecting fertility and offspring viability.
- Unusual gait: Neurological issues can lead to abnormal walking patterns.
- Rough coat: The skin and coat of the animal become rough and less healthy-looking.
Specific manifestations in calves
- Microphthalmia (small eyes): Calves may be born with abnormally small eyes which ultimately affects their vision.
- Diarrhoea and pneumonia: Calves are particularly vulnerable to digestive and respiratory issues.
- Weak immune system: Calves with vitamin A deficiency are more susceptible to infections and illnesses due to an underdeveloped immune system.
Understanding vitamin A sources and storage in ruminants
Vitamin A is available in green vegetation as β-carotene, which ruminants convert into its active form retinol/vitamin A. During good seasons with abundant green pastures, cattle can absorb and store vitamin A in their livers for up to four months, while sheep can store it for up to six months.
Pregnant cows, in particular, require high levels of vitamin A during the last stages of pregnancy.
Since calves are born with low vitamin A levels, often considered to be deficient, they rely on vitamin A in the colostrum from their dams to meet their requirements.
The vitamin A content in colostrum is directly influenced by the cow’s nutritional status at the time of calving. Deficiencies are more likely during drought or winter seasons when green vegetation is sparse and carotene levels are low.
Additionally, vitamin A is highly oxidisable and unstable, losing its potency during storage. Cut hay, for example, loses about 6 to 7% of its carotene content per month.
Therefore, vitamin A supplements should be stored for short periods, and even good hay from drought-stressed forage will have low carotene levels.
Pastures that have been overfertilised with nitrogen can also interfere with vitamin A absorption in the gut of the animal.
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Effective strategies for supplementation in animals
To maintain adequate vitamin A levels during dry or winter periods, supplementation is crucial. This can be achieved through various ways. When choosing a product for vitamin A supplementation, it is important to consider the stability and oxidisability of the vitamin.
Some products cannot be stored for long periods due to these properties. For instance, premixes may be used, but one must consult with an animal nutritionist on the use, stability and storage of these products.
Water-based injectable products offer a more stable form of vitamin A, which is readily absorbed by the animal and can last up to three months in the body compared to oil-based injectables.
Other available products include those that can be dosed orally, or mixed with water, often containing additional essential minerals for animal health. It is especially important to supplement through periods such as pregnancy and lactation since many of our cows calve down before green grass is abundant.
Ensuring proper vitamin A levels in cattle is crucial for their overall health and productivity. Farmers should consult with veterinarians or animal nutritionists to assess the vitamin A status of their herd and determine the best supplementation strategy. This proactive approach will help prevent deficiencies and support the well-being of their livestock.
- Dr Sakhi Nkosi is a veterinarian at Afrivet Technical and Training Services.
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