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DROUGHT CONDITIONS CAN LEAD TO AFLATOXIN POISONING

by: Stephen B. Blezinger
Ph.D, PAS

Sometime back we had a lengthy discussion of the causes and effects of Aflatoxin in grains and feeds provided to cattle of all classifications. Given the environmental conditions we have experienced across the country this year, the incidence of Aflatoxin will be much higher than normal and producers need to be aware of this situation.

What is Aflatoxin?

In order to understand how to manage this toxic compound, we must first understand what it is and where it comes from. Aflatoxin is a highly carcinogenic compound produced by several species of fungi. Aflatoxin B1 is considered to be one of the most highly toxic, naturally produced compounds known to man. The main causative fungal species are Aspergillus flavus (A. flavus) and Aspergillus parasiticus (A. parasiticus) during growth on some feeds or foods. Aflatoxin is a secondary metabolic by-product of the growth and development of these fungi in materials such as corn grain, grain sorghum, cottonseed, peanuts and dry beans. Corn has been found to be an especially good substrate for aflatoxin production because of its high carbohydrate and low nitrogen content. To a lesser extent it can be found in soybeans and small grains such as wheat, oats and barley. It can also be found in corn or other grain silages as well. A complicating factor is that the fungi of concern are normal, soil-borne microorganisms in the environment and are found on both living and decaying plant matter in virtually all crop production systems. Although mycotoxin contamination occurs across most of the U. S., aflatoxin contamination appears to be the most prevalent in the southeastern and southwestern states although midwest corn production is also susceptible. Although it is not understood what triggers the production of aflatoxin by the organism, environmental factors influence the production of aflatoxin in the field and during storage when conditions are favorable. Studies have shown that water activity, relative humidity, temperature, light and pH affect aflatoxin production. Presence of aflatoxin becomes much more prominent in drought years when crops are damaged by the dry weather conditions. The drought conditions allow access of the fungi to the susceptible parts of the plant such as the corn kernel, cottonseed, etc., by increasing the permeability of the seedcoat. Drought conditions are typically in conjunction with high temperatures as well as high relative humidity, all conditions conducive for the growth of the fungi which produce aflatoxin. As this statement makes clear, the development of aflatoxin is largely a matter of uncontrollable natural events. It has been shown however that grain which has been stored and remoistened increased in aflatoxin contamination. Grain that has been processed by rolling or grinding, in which the starchy interior is exposed is highly susceptible to growth and proliferation of the fungi.

Effects on Cattle

As stated, aflatoxin has been identified as one of the most toxic, naturally occurring substances known to man and is found in several forms, most commonly identified as B1, B2, G1, G2. This statement regarding the level of toxicity is quite profound and redeemed only by the fact that it is not terribly common to find aflatoxin in very high concentrations.

The effects of aflatoxin consumption are relatively similar in most animals. The animal's susceptibility to aflatoxin, however, varies by species, age and individual. Consumption of high levels of aflatoxin creates a condition referred to as aflatoxicosis. Specific liver conditions created by aflatoxicosis can include acute necrosis, cirrhosis and carcinoma as well as systemic effects such as blood cell fragility, immune system degeneration and other conditions which can lead to lost production and even death. In beef cattle it will commonly cause reductions in feed intake, rate of gain, feed efficiency, reproductive function, rectal prolapse and abomasal cavity edema. These symptoms are also found in dairy cattle in addition to suppressed milk production and the conversion of aflatoxin to aflatoxin M1 that is secreted in milk. It has been shown that consumption of even small amounts of aflatoxin by the lactating cow could lead to decreased milk production in addition to contaminated milk. Also, abortions of fetuses in breeding cattle have also been reported due to aflatoxin consumption.

Young calves are especially susceptible to these toxic effects. This may be largely due to the underdevelopment of the rumen which, in its fully developed state, may have at least some detoxifying effects. The clinical symptoms of aflatoxicosis in younger cattle are similar to more mature animals and include decreased growth rate and feed intake, rough hair coats, anorexia, reluctance to move, grinding of the teeth, apparent blindness, diarrhea and rectal prolapse.

Obviously the research has shown that the effects of aflatoxin on cattle, beef and dairy, are profound. The cost is staggering once the level of lost production in terms of reduced feed efficiency, reduced gains and reduced milk production, not to mention the loss of the animals themselves in many cases, are considered. A relatively unmeasured expense is that of production losses due to long-term low-level ingestion of aflatoxin contaminated grains. This is an area which requires substantial research.

How can this problem be managed?

As with many situations, the best defense is a good offense. A number of steps can and should be taken to reduce potential aflatoxin contamination in feed and grain supplies. They include:

1) Make sure that grains and feeds do not contain excessive moisture. If the grain samples test higher than 14 to 15 percent moisture the load should not be accepted.

2) Set up an extensive quality control procedure which utilizes appropriate and detailed sampling. This should be standard in most feedmills, especially those located in the southern United States. Aflatoxin contamination is not an analytical problem. Quick, relatively inexpensive assays exist which can effectively be used to quantify aflatoxin levels in a sample. The root of the problem is in sampling. This is primarily true because aflatoxin is not uniformly distributed throughout a field or a load. Improper or inadequate sampling tends to be one of the greatest problems in most grain elevators and feed mills. Simply taking one or two "hand-grab" samples will not provide a representative sample for testing. Even use of an approved grain probe will not effectively provide a representative sample when only probing a load two to three times. Loads of grain should be probed multiple times with a standard grain probe and these subsamples combined to produce a gross sample which can be tested. This will help to locate and target any "hot spots" which may be found within a load of grain. Although not fool proof by any means, this method greatly reduces the chance of missing highly contaminated areas in the load. Finally, elevators and mills need to employ testing procedures which are quantitative, meaning the test gives a fairly accurate indicator of the level of aflatoxin in the sample, not just an indicator that something is there. A number of testing kits and procedures are available at varying cost of set up and per sample. Blacklighting, which was once the industry norm should no longer be considered.

3) Keep bins and equipment (mixers. etc.) clean and free from grain and dust build-ups where moldy feed might accumulate and subsequently contaminate clean grain or feed.

4) Any feed or grain which smells or looks musty or moldy should be rejected. These outward signs provide a strong indicator for other more serious conditions.

5) Retain samples of grain and feed for a period of time. Different facilities will retain samples from 3 months to two or more years. This simply provides a way to go back and double check a given load should a problem arise.

6) If a problem with Aflatoxin is found, especially in stored grains, the grain can still be used as long as it is fed in a diluted manner. In beef cattle (cows, finishing animals) the level of aflatoxin intake needs to be kept below 300 ppb. In younger or growing cattle, this level should be even lower (<100 ppb) or eliminated altogether if possible. In newly received cattle or stressed cattle, obviously it is best if affected grain is not used. This means that if you have a supply of affected grain, depending on what the level is, you should feed another, clean source of grain along with the tainted product to dilute the overall amount down as far as reasonable.

Other steps may also be employed but these are some of the most basic. Nothing can replace a good quality control program either at the elevator, the feed mill or on the farm or ranch.

Conclusions

Aflatoxin may potentially be one of the most serious problems affecting the livestock as well as the feed and grain industry. In order to effectively combat contaminations it is necessary for the industries to involve all levels from grain production through grain feeding in order to detect and handle grains which are heavily infested. This requires that the farmer, grain handler, feed manufacturer and producer each assume responsibility in determining that the product utilized is clean and uncontaminated in order to maintain efficiency and provide a safe world food supply.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, Texas. He can be reached at Route 4 Box 89 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at sblez@peoplescom.net.

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