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  • Hypovitaminosis Vitamin A Deficiencies in Drought Conditions

Hypovitaminosis Vitamin A Deficiencies in Drought Conditions

Rumen bacteria are reasonable for the synthesis of many essential vitamins (Dewell 2014, p. 1). Most vitamins are not required in the diet as they become the by-product of rumination (Dewell 2014, p. 1). Vitamin A however, is a dietary requirement as it is a vital component for growth (bone development), reproduction, vision and disease resistance in ruminant animals (Dewell 2014, p. 1). It has an essential role at a cellular level where its main function is to sustain membrane integrity (Charlton & Ewing 2007). This is a negative contributory factor in successfully diagnosing Vitamin A deficiencies as it has the ability to influence a variety of systems, organs and pathways in the body (Charlton & Ewing 2007).

The primary roles of Vitamin A include:


  • Assists in spermatogenesis.
    • Spermatogenesis refers to the formation/production of sperm. Without Vitamin A normal sperm cells cannot be created. Abnormalities can occur causing reduced fertility and effective conception.
  • It is important for the growth and differentiation of embryonic tissue after conception.
  • Involved in the biosynthesis of reproductively essential hormones.
    • The presence of Vitamin A helps to improve ovulation, ovum implantation as well as foetal and embryonic development. The activation of the appropriate hormones for pregnancy establishment can be influence by a deficiency. Vitamin A deficiencies can ultimately result to reduced conception.
  • The presence of adequate Vitamin A helps improve ovulation, implantation of the ovum, embryonic development


  • Involved in genetic expression at growth stages.
    • Controls growth and differentiation during genetic expression.
  • Controls resorption and deposition of skeletal bone as well as the development of teeth and normal nerve tissues.
  • Essential for healthy kidney function.
  • Major component of epithelial cells.
    • It is involved in the formation and protection of mucus membranes and tissue cells.


  • Impaired vision.
    • Vitamin A is a major component of Rhodopsin; the component which effectively receives lights in the eye. In the absence of dietary Vitamin A, Rhodopsin cannot be created, resulting in blindness.
      • Night blindness is often the first symptom exhibited and often goes unnoticed until symptoms progress into daylight hours also.


  • Influences antibody response and disease resistance.
    • Vitamin A is a vital nutrient in the immune system which assists in maintaining protective mucus membranes in the respiratory and digestive tract. In its absence, the invasion of bacteria and viruses can occur more readily.
  • Acts as a natural antioxidant.

(Charlton & Ewing 2007)

How do deficiencies occur?

Vitamin A in its complete elemental form does not occur specifically in plant material (Dewell 2014, p. 1). Instead plant material contains of Vitamin A precursors; carotenes and carotenoids (Irsik 2011, p.1). These precursors are converted to Vitamin A through the walls of the small intestine where systemic absorption occurs (Irsik 2011, p.1). Carotenes, in particular, are high in green pasture (Dewell 2014, p. 1). This substance is quickly destroyed by sunlight and hot air temperatures rendering the amount available less than their requirements in most cases (Irsik 2011, p.1). In addition to the presence of prolonged dry pasture, deficiencies in Vitamin A can also occur under the following conditions:

  • Prolonged periods of dietary inadequacy.
  • Systemic infections.
  • Calves/lambs born with low liver stores.
  • Calves/lambs starved of colostrum.
  • High concentrate diets.
  • Feeding hey grown in drought conditions as the primary diet.
  • Feeds that have been stored for long periods of time with deplete in Vitamin A reserves.

(Irsik 2011, p.1)

When precursors are abundant in green pant material, 90% of converted Vitamin A is stored in the liver and the rest is dispersed to fat reserves and other organs (Charlton & Ewing 2007). The mobilisations of these reserves are easy and occur readily when the precursors are at inadequate levels in the pasture and do not meet the animal?۪s requirements (Charlton & Ewing 2007). Systemic store of Vitamin A are often depleted quickly in the absence of green grass (Charlton & Ewing 2007). These rates of depletion vary based on the type of animal and its requirements. This can be seen the table?۪s below.



Mature cows/bulls






Adapted from (McKiernan & Blackwood 2006, p. 1)







Adapted from (McKiernan & Blackwood 2006, p. 1)

Supplementation should occur before Vitamin A stores begin depleting as the effects of deficiencies can adversely influence livestock productivity and the overall success of the enterprise Adapted from (McKiernan & Blackwood 2006, p. 1).

Signs/Symptoms of Vitamin A. deficiencies:

As Vitamin A influences several vital pathways in the body, signs and symptoms are not specifically associated with one category e.g. Symptoms can be varying and often in drought situations, can be mistaken for other drought associated conditions. The main signs and symptoms of Vitamin A deficiencies are and not limited to:

  • Night blindness
  • Ill-thrift and scouring on dry pastures
  • Reduced appetite
  • Rough coat/hair loss
  • Calf/lamb retardation ? blindness and inability to suckle
  • Joint swelling
  • Reduced libido
  • Abnormal semen
  • Slow or abnormal bone growth
  • Poor fertility
    • Low conception rate
    • Abortions/stillbirths
  • Heightened disease susceptibility
  • Staggering gait

(Charlton & Ewing 2007)

Cattle in particular affected by Vitamin A deficits will often still appear in a good body condition score but will be expressing abnormalities such as these (Charlton & Ewing 2007). These symptoms can range in severity based on the extent of the deficiency. Prolonged deficits untreated or in the event of prolonged dry feedstuff can result in death in acute cases (Charlton & Ewing 2007).

How can Top Country help?

Maintenance supplementation during drought conditions has become an essential practice in extensive animal production to assist in utilising dry feed reserves. Top Country manufactures high quality dry loose lick supplements to meet the specific requirements of your livestock. Our range is able to be fully customised and with the support and knowledge of our qualified nutritionists, Top Country can provide a unique nutritional program specifically designed to meet the expectations of your enterprise. Under drought conditions where extended dry periods are common, Top Country dry lick supplements can form an effective carrier for the delivery of Vitamin A. Additional vitamin inclusions can assist in meeting vitamin deficits for less than 1 cent/head/day when carried in dry lick supplements.

The signs and symptoms of vitamin A deficiencies can be quite hard to pin point as it influences many systemic pathways at a cellular level. Symptoms can be highly variable in their effect as well as their severity. In addition to providing vitamins in supplements, Top Country nutritionists can effectively help in meeting the requirements of your current situation as well as assisting in the determination of deficiencies. Serum sampling is the most effective and accurate way to determine whether there is a vitamin deficit and the extent to which it exists. The costs associated with this type of testing can become quite costly as labour intensive if livestock are not already yarded. Alternatively, Top Country nutritionists can collect a pasture sample specifically targeting Vitamin A content and provide a comprehensive interpretation of these results. This is a cost effective option as it can depict the levels of dietary Vitamin A livestock are exposed to under their current situation for only the cost of the sample when analysed at Feed Central.

In any instance being proactive in drought conditions is often an effective tool in minimising economical losses associated with these difficult times. Contact a Top Country nutritionist today for a product recommendation or an on farm property assessment; we?۪d be more than happy to help!


Charlton, SJ & Ewing, WN 2007, The Vitamins Directory, 1st edn, Context, England.

McKiernan, B & Blackwood, I 2006, ?Vitamin and mineral additives for sheep and cattle in drought?۪, NSW DPI ? Prime facts, issue. 294, pp. 1-2.

Irsik, M 2011, ?Vitamin A for Beef Cattle?۪, University of Florida College of Veterinary Medicine, pp. 1-2.

Dewell, G 2014, ?Vitamin A Deficiency in Beef Calves?۪, IOWA State University - Veterinary Diagnostic & Production Animal Medicine, Iowa.

Flynn & Rossi, n.d., ?Hypovitaminosis A in Pasture Fed Cattle?۪, pp. 1-11.

Author: Emma Turner (BAppSc)

Tags: Supplements Deficiencies Vitamin A

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