There’s No A or E in Drought!
Drought Conditions & Vitamin Deficiency
When facing a drought one usually thinks first about forage and water shortages. Protein, energy, and minerals are the nutrients most often considered. There are other highly essential nutrients however that may be critically short under these conditions and that we are seldom worried about. We oftentimes take vitamins for granted for example, but truth be told, not all vitamins are going to become a problem. The B vitamins for example are mostly synthesized by the cow provided her rumen is working properly. A couple of the fat-soluble vitamins (A, D, E, and K) on the other hand, can and usually pose a problem. Vitamins D and K are not as critical since they are readily synthesized, the first one initially by the action of the sun irradiation on the skin, and the second one by the microbes in the lower gut. Vitamins A and E, however are a different story.
Vitamin A is critical to many functions in the body particularly the surfaces (epitheliums) of many body systems. As such it plays a critical role in vision, growth, and reproduction (embryonic development). Its deficiency has also been associated with abortions, retained placentas, and compromised immune function, as well as an increase in the number of sick (morbidity) and dead calves (NRC 2001). There is no vitamin A as such in the normal diet of the cow, aside from mineral supplements that may be fortified with it. Cows need to ingest its precursor, the pigment known as beta carotene (or pro-vitamin A) abundant in “green plants”, to be able to synthesize this vitamin. Once absorbed through the intestine beta carotene is converted to retinol or the active vitamin A. Vitamin A is stored in the liver, a strategy animals have evolved to capture the ample presence of pro-vitamin during the spring and cope with the deficiencies over the dry season and the winter. Variations of the beta carotene in pastures and hay can be corroborated by the seasonal changes in color from green in the spring to yellowish in the summer. When most of the diet consists of dry summer pasture or dry, bleached hay the deficiency becomes likely. Since there are liver reserves, this may not happen immediately unless they are already coming from a deficient situation on the previous season.
However, if the deficiency is hitting the cows early in the summer, once they have been inseminated, the odds of maintaining the pregnancy are decreased. In cows supplemented with beta carotene pregnancy rate doubled particularly in the second and third cycles (22 vs.11%). One thing to remember is that carotenes act as antioxidants reducing the negative impact of oxidizing free radicals that affect all body membranes. In essence they are the first “line of defense” of the immune system protecting the membranes of the negative effects of these radicals. However, they accomplish this with the ultimate sacrifice, since they destroy themselves in the process.
Cow/calf pairs challenged by the environment either by disease or other stress, with no enough green pasture, rely on the vitamin A stored in their liver or the one supplied with the minerals for their protection.
Vitamin E complements the antioxidant functions of vitamin A. It helps maintain the integrity of the keratin, and as such it helps protect the eyes from pinkeye, a common problem oftentimes also observed during the summer. The most common vitamin E we find in animal feedstuffs is alpha tocopherol. Again, its concentration is high in green forage and diminishes drastically after harvest and during storage. This vitamin helps maintain the integrity of the cell membrane and is essential in boosting the immunity. Around calving time for example, high levels of this vitamin have been associated with boosting white blood cells (macrophages) necessary to fight infections. As a result of their antioxidant properties both vitamin E and selenium react with free oxidative radicals preventing cell and tissue damage, and protecting from the invasion of pathogens.
Other factors can compound the stress of dry forages during a drought. Aflatoxins in supplemental feed also contribute to oxidative stress, reducing the reserves in the cow of both vitamin A and E. Water quality can also compromise the immune system. For example, high iron concentrations (greater than 0.3 ppm) in drinking water which are highly oxidative, lead to the overuse of vitamin E that again acts as anti-oxidant. Supplementing with vitamin E then becomes important with poor water quality, and/or when pastures are dry and bleached during the summer. If cattle in the range is supplemented with distillers grains this becomes an additional challenge to vitamin E stores since the free radicals in the DDGS fat will increase the use of this vitamin.
In summary, cow/calf pairs grazing dry summer pastures need supplementation with protein and energy, but also minerals and vitamins, particularly A and E. Verifying mineral supplements have adequate concentrations of vitamins A and E boosts cattle’s immunity and helps withstand stressful conditions. Shades of green in forages are associated with higher concentrations of pro-vitamin A and vitamin E. If that type of baled forage is available in the farm, it can be used strategically as a source of these essential nutrients for those categories that will benefit the most.
Source: Alvaro Garcia, South Dakota State University