Animal Health Matters: Nitrates are the toxic side effect of summer – Farm Forum

Russ Daly| Special to the Farm Forum

As students filter back to South Dakota State University this week, I harken back to my own days as a student and the courses I took as a pre-veterinary student. Some of the most memorable class experiences were not necessarily the most pleasant ones. Included in that list are the chemistry courses, which always seemed to require an inordinate amount of work.

Five semesters of chemistry are on our pre-vet students list. It starts with inorganic chemistry, progresses through organic chemistry, and ends with biochemistry. As I did back then, current students question the necessity of all this chemistry. After all, what does biochemistry have to do with being a veterinarian and keeping livestock healthy?

The answer, as Ive come to realize, is … everything!

Biochemistry underlies everything we expect from our animals. Reproduction, immunity, milk production, growth:they all rely on a usually-taken-for-granted complex system of nutritional compounds being taken in, broken down, put together, metabolized and utilized by the animal.

Biochemistry class got more interesting after I realized that. Even more interesting was learning animal examples of when this biochemistry gets messed up: acidosis, ketosisand milk fever, for example.

This summer, as in most South Dakota summers, another example of messed-up biochemistry is playing out in some areas: high forage nitrates and their potential to poison cattle.

Nitrate poisoning involves biochemistry problems in plants as well as the animals that consume them. Nitrates might get bad press among cattle producers, but theyre essential.

When moisture is plentiful and growing conditions are good, plants take in nitrogen through their roots in the form of nitrate salts. These compounds are drawn up into the stem and leaves where they serve as building blocks for amino acids, which get tied together to form proteins. Like a refinery where crude oil comes in and gasoline comes out, the plant refines this nitrogen into the protein that will nourish a hungry cow or calf.

But what if, just when this refinery was working at full capacity, the soil around the roots dries up, with insufficient moisture to move the nitrates through the plant tissues? The raw materials (the nitrates) still come in, but theyre not able to be processed into proteins anymore accumulating like crude oil in a refinery holding tank, especially in the lower stalks and stems.

Cattle need nitrogen building blocks for amino acids and proteins, too. Consumed plant proteins are broken down into nitrogen that can be utilized by rumen bugs. They then produce protein for the animals use.

The unprocessed nitrates from stressed plants can serve as a nitrogen source too, but once inside the rumen, they first get converted to a form called nitrites. These nitrites are then absorbed into the bovines bloodstream.

This is not good. Nitrite molecules readily bind to iron in the blood, which is an essential component of oxygen-carrying hemoglobin in the red blood cells. Nitrite blocks this oxygen-carrying capability.

Oxygen breathed in by the cow becomes useless because it can no longer get to the body cells. The animal starts to suffocate from within.

If a person is around to witness it, they might notice the cow becoming anxious, breathing faster and faster, with the heart beating faster and faster in a futile attempt to get oxygen to the bodys cells. In acute nitrate poisonings, this progression is quick enough that animals are simply found dead. A blood sample taken from affected animals looks dark chocolate brown, devoid of the red tint of healthy oxygen-carrying hemoglobin found in a normal animal.

Lower levels of nitrates can cause chronic, non-fatal poisoning problems: miscarriages in pregnant cows, for example. Younger animals show poor growth and performance.

Dry conditions are the typical root cause of nitrate accumulation in plants, some of which are more prone to accumulating nitrates than others. Corn and sorghum have been a frequent source of questions this summer, but oats, wheat, and many other crops and weeds can also be problematic. Nitrate accumulations can be spotty within locales and even individual fields.

SDSU Extension centers can perform rapid tests for nitrates on forage material, or can direct you to labs for more complete analysis. Nitrate testing risky forages can be a pretty cheap insurance policy when the risk of nitrate accumulation exists.

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Animal Health Matters: Nitrates are the toxic side effect of summer - Farm Forum