by: Stephen B. Blezinger
PhD, PAS
Part 2
In the last issue we began a discussion of a variety of issues that have to be considered when working through drought periods and low forage situations. Moderate to extreme drought conditions create a series of challenges well beyond a shortage of forage. In the first installment of this three part series we discussed buying hay and other forages, other roughage sources, supplementation using urea inclusive feeds and the potential pitfalls of feeding �cheap feeds.� In this part of this series we will continue this discussion and attempt to provide information on other areas to which attention should be given.
Water
One of the absolutely most basic issues is the water supply. In many areas, the extended drought has resulted in stock ponds which have dried up as well as problems many conventional water wells where the water table has dropped below the intake pump's intake level. Many producers are drilling new wells, deepening existing wells, connecting to community water supplies (if available) digging out stock ponds or in some cases hauling water to cattle. None of these are desirable and all are expensive. Water is, however, an absolute requirement and while an animal can, in some cases go weeks with little or no food, it can only live a very few days without water. This is especially true given the temperatures that many areas have been experiencing.
Livestock drinking water (especially in stock ponds) may be contaminated by a number of factors including minerals (total dissolved solids, or TDS), manure, microorganisms, and algae. These contaminants can impact the appearance, odor, and taste of drinking water as well as its physical and chemical properties. Some contaminants may directly impact animal health by causing disease and infection; others have a more indirect effect and may cause cattle to decrease their overall water intake. When water intake is reduced, feed intake will also decrease, and, as a result, animals will gain less weight. One important thing to remember is that as drought periods extend and water levels drop, the concentration of contaminants increases, sometimes to very critical levels. Consider this as you read the following paragraphs.
When the mineral content of water exceeds safe levels, animal performance can suffer. High levels of sodium (salt) depress water intake and result in weight loss and diarrhea. Animals exposed to water that is high in sulfur have increased incidences of polioencephalomacia (PEM) and experience higher mortality rates. Salinity of water, the concentration of dissolved salts in water, can be expressed as either TDS or TSS (Total Soluble Salts). Electrolytes or ions that regulate or affect metabolic processes, such as magnesium (Mg+), calcium (Ca+), sodium (Na+), and chloride (Cl-), contribute to the salinity of water. At certain high levels, these electrolytes can, in fact cause toxic effects by themselves or by interfering with the absorption of other important nutrients. Alone, however, TDS, TSS, or even EC tell us little about the quality of any water sample. However, these are indicators that when elevated give us a clue that some minerals may merit further and more precise analysis.
Manure is a common contaminant in cattle drinking water, particularly when the primary source of water is a pond where cattle may spend a good deal of time loitering. Manure is carried into drinking water on the cattle's hooves and is deposited directly when the animals defecate. Livestock drinking water that is contaminated with manure can become a hotspot for bacterial growth, which in turn can cause animal disease. High levels of bacteria have been found in cattle watering ponds where they may contribute to outbreaks of coliform related illnesses caused by E. coli, E. aerogenes, and Klebsiella species. These can lead to mastitis, urinary tract infections, diarrhea and numerous other unsavory and often lethal infections.
Fecal contamination of livestock drinking water can cause algae blooms through a process known as nutrient loading. Blue-green algae are common contaminants in standing water. When ponds become overgrown with algae, cattle will avoid drinking from them in favor of other water sources, if any exist. If no other source of fresh drinking water is available, they will decrease their overall water intake, which results in poorer performance. In addition to blue-green algae, other water-borne microbes can negatively impact animal health. Leptospirosis, which causes reproductive loss in cows, is spread by a microorganism found in water contaminated by urine. The soil-borne microbe believed to be primarily responsible for foot rot (F. necrophorum) can also be spread by consumption of contaminated water.
The minimum requirement of cattle for water is a reflection of that needed for body growth; for fetal growth or lactation; and of that lost by excretion in the urine, feces, or sweat or by evaporation from the lungs or skin. Water requirements are affected by many factors, and it is impossible to list specific requirements with accuracy. The major influences on water intake in beef cattle fed typical rations are dry matter intake, environmental temperature, and stage and type of production. Water quality is important in maintaining water consumption of cattle. Factors such as pH, total dissolved solids, hardness, odor and taste as well as compounds present in excess (nitrates, iron, sodium, sulfates, and fluorine), toxic compounds (arsenic, cyanide, lead, mercury, hydrocarbons, organochlorides and organophosphates) and bacteria are criteria for evaluating drinking water for humans and livestock. Water components can also have a direct effect on mineral balance and status in the animal. As mentioned previously, in many cases minerals such as Sulfur are more soluble than in feeds or forages and thus can have a greater antagonistic affect on the absorption of other minerals such as Copper or Selenium.
Some parameters we use to indicate water quality include salinity, total dissolved solids, hardness, nitrates and mineral levels. For a more extensive discussion of water issues as well as specific guidelines please visit https://cattletoday.com/archive/2009/March/CT1910.shtml.
Toxic Compounds
Under the right (maybe wrong) conditions, different compounds can prove toxic to cattle. Drought conditions can also contribute significantly to these problems. While this list can be extensive, find below a brief review of the most common problems.
A. Nitrates
Nitrate poisoning in cattle is caused by the consumption of an excessive amount of nitrate or nitrite from grazing crops, hay, silage, weeds, drinking water, lubricating oil, fertilizer, etc. In addition, drought is also a major cause of nitrate poisoning. All plants contain some nitrate, but excessive amounts are likely to occur in forages which have been grown under conditions of excessive fertilization and/or stress. The buildup of nitrates in soil brought on by excessive fertilization with poultry litter or animal manure is a common cause of nitrate accumulation in plants. Commercial fertilizers aren't likely to cause excessive nitrate accumulation in plants when recommended application rates and practices are followed. Any stress condition which causes an abrupt decrease in plant growth may contribute to plant nitrate accumulation, even with a normal nitrogen supply. Adverse conditions may include but are not limited to detrimental weather such as drought with high temperatures or low humidity, cold temperatures, hail damage and frost may slow or stop plant growth and cause nitrates to accumulate.
Nitrate toxicity in cattle is primarily a problem associated with some annuals, certain perennial weeds and some cool-season grasses (fescue, bromegrass, orchardgrass, small grains and ryegrass). Warm-season grasses generally cause fewer problems. Corn and sorghum have occasionally caused problems. Sorghum-sudan hybrids and johnsongrass have probably caused more problems than any other summer annual forage. Weeds are also nitrate accumulators and can cause problems since some weeds tend to be more drought tolerant than grasses and in a young, succulent stage can be a problem.
The effects of nitrate levels of forage, feed and water (as mentioned above) are additive. So, both feed and water must be considered when evaluating a nitrate problem. Nitrates may reach dangerous levels in ponds, shallow wells or streams that collect drainage from manure, highly fertilized fields or industrial waste. Again, this is especially true during drought conditions when decreasing pond levels result in a greater concentration of problem compounds. Deep wells are usually safe sources of water. No safety standards have been set for livestock water, but it has been suggested that up to 100 ppm of nitrate nitrogen in water should be safe if cattle are consuming an adequate ration that is free of nitrates.
B. Prussic Acid
Because of potential prussic acid content, sorghums, sorghum-sudangrass crosses, sudangrasses and johnsongrass may be poisonous if grazed or fed improperly. The danger of prussic acid poisoning is greatest when livestock graze forage sorghum varieties and crosses, less when they graze sorghum-sudangrass crosses, and least when they graze sudangrasses.
The greatest number of livestock losses occur when grazing after a period of drought or a series of frosts. Also, after cutting or grazing, young re-growth forage, especially sorghum and sorghum-sudangrass crosses, can be very toxic. The young, dark green growth or re-growth is potentially dangerous to livestock. Shortly after frost, prussic acid release potential increases slightly. However, they can be safely grazed a few weeks after freezing if there is no substantial regrowth.
As plants mature and plant height increases, the risk of prussic acid poisoning is reduced. Only during times of stress, such as drought or frost, will toxicity remain high in maturing plants. This is primarily due to the interruption in the plant's normal growth pattern.
Since prussic acid poisoning is very fast-acting on high-risk forage, death will occur quickly. Watch animals closely for any signs of toxicity. If there is any question that there may be poison in a stand, secure a good uniform sample from throughout the field, collecting mainly stems randomly, then package them in a good plastic bag and mail or deliver them to a diagnostic laboratory. If possible, he adds, keep the sample cool and, if frozen, be sure it remains frozen until it arrives at the laboratory. However, given the volatile nature of prussic acid, even if the lab analysis indicates a potential for prussic acid poisoning the actual forage may be safe to eat after the stems have become dried, cracked and have allowed the toxic gas to escape.
The active compound is hydrocyanic acid (HCN). Symptoms of HCN poisoning are gasping, staggering, trembling muscles, convulsions, and death resulting from respiratory failure. The mucous membranes of the mouth and eyes may have a blue coloration as evidence of cyanosis. In cases of recovery, there appears to be no permanent effects.
Hay maybe be dangerous when cut but becomes safe in time through volatilization of the HCN. Hay stored for two or more months gradually losses all its cyanide potential.
C. Mycotoxins
Mycotoxins are chemical agents (toxins) produced by a wide variety of naturally existing fungi. The word mycotoxin comes from �myco� which refers to fungi and the metabolites it may produce that are toxic to other organisms. There are about 100 types of fungi that grow on standing crops or stored feeds and produce toxic substances. Approximately 20 of these have been associated with naturally-occurring diseases. Toxigenic (toxin producing) fungi spores are present almost everywhere, and they can germinate, grow, and interject their toxins into a variety of substrates when moisture, temperature, and aeration conditions are favorable. Optimal conditions for toxin production by different fungi may be quite variable. In many cases, the production of one of the most well-known of these toxins, Aflatoxin, is associated with drought stress in corn and cotton (cottonseed and other cotton products). In addition to Aflatoxin, other mycotoxins include T-2 fusarium, Zearalenone, Fumonisin, Vomitoxin and DON (Deoxynivalenol). This is only a short list of the variety of fungi produced toxins which can affect livestock. In general, most of these mycotoxins affect monogastrics (pigs, chickens) more severely than cattle. However, their affects on both beef and dairy cattle can be extensive and profound.
Mycotoxins affect cattle in a variety of ways. The fact that there presence is wide ranging implies that their occurrence in feeds cannot be overlooked. Additionally, the fact that profound reductions in performance as well as the adverse affects these compounds can have on animal health also supports the need to recognize their potential presence in grains and feeds. The affects of mycotoxins can be seen in reproductive function, immune response and animal growth and performance (gains, milk production). As noted previously these compounds can affect the animal in different ways. Mycotoxins can be highly reactive in mammals and may destroy different tissues. This is most true of liver tissues. The liver is the central organ in the body and the presence of different mycotoxins has been shown to be highly toxic to the liver.
Conclusions
In the final part of the series we will continue to discuss the list of issues that must be considered when managing during drought periods.
Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at [email protected]. You can also follow us on Facebook at Reveille Livestock Concepts.
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