Aflatoxin risk in lower income countries

Aflatoxins are by-products of Aspergillus fungi, and ubiquitous contaminants of many crops, with common ingredients of animal feeds, such as maize, ground nuts and oilseeds, being the worst affected. Aflatoxins consumed by cows are either degraded by the microbial flora in the rumen, or eliminated through urine and faeces. A small amount (typically 2-3%) of aflatoxin B1 (AFB1) is metabolised to aflatoxin M1 (AFM1) in the liver and excreted in the milk of lactating animals.

In low and middle income countries (LMIC) there are some regulations for aflatoxins in foods and feeds, but these regulations are often adopted from other countries, and do not take into account local contexts, such as, if it is appropriate for smallholders, the national ability to enforce and comply, and the general food security situation in the country.

With limited resources for testing and enforcing the standards, many products on both the formal and the informal market exceed the limits for aflatoxins. While the negative effects of aflatoxin exposure in livestock has been documented in many experiments, these have been conducted in controlled laboratory settings, or in high-income countries.

In LMIC there are often multiple factors contributing to reduced productivity in livestock, including different infectious diseases, heat stress, lack of water and inadequate feed. Under these circumstances it is reasonable to assume that the effects of aflatoxins are not the same as in livestock under optimal conditions, and it is also difficult to assess the impact. The typical symptoms of aflatoxicosis in animals, include decreased appetite, decreased reproductive function, decreased growth, decreased production and immuno-suppression are common, but this could be caused by many other hazards.

It is difficult to estimate the economic impact of aflatoxins in the livestock production in LMIC, but there has not been many attempts to understand this. In addition to the impacts on productivity, a major concern with aflatoxin exposure in cattle is the contamination of milk with AFM1. Kenya is the East African country with the highest milk consumption, and therefore AFM1 contamination has been a major cause of concern.

Aflatoxins in the dairy value chain in Kenya

Several studies have indicated the extent of aflatoxin contamination in different products in Kenya. Dairy feed samples were collected from farmers, retailers and manufacturers in 5 different counties in the country. It was found that feed could contain as much as 9661 ppb, and within the 5 counties, the proportion of positive samples ranged from 47.8 to 90.3%. 83.3% to 100% of the feeds from retailers exceeded 5 ppb, and 28.6% to 100% of the feeds from manufacturers.

In the same counties as the feed was tested, milk was also found to be contaminated, with more than 25% of samples in some counties exceeding 50 ppt, and the highest observed level was 6999 ppt. However, when studying milk contamination levels in the capital Nairobi, contamination rates were often even higher. Among samples from urban milk traders, 55% of raw milk samples exceeded 50 ppt. Similarly, when sampling pasteurised milk, more than 50% exceeded this limit, as was the case with more than half of the samples of pasteurised yoghurt. Using data on milk consumption in Kenya, it was calculated that an average adult consumes 45 ng AFM1 per day. These results suggest that aflatoxins are likely to be a very big problem in the growing dairy industry, and a limiting factor for more efficient milk production. The exposure to AFM1 through milk is non-negligible, and it was also found to have an association to stunting in children, which is a common phenomenon in Kenya, where more than 40% of children in low-income settings having stunted growth.

Managing contaminated crops

A lot is known about how aflatoxins could be prevented in the field and in storage, including good agricultural practices (GAP), improved drying technologies and biological control using atoxigenic fungus. However, uptake has been limited in low-income countries and these methods have not yet managed to make neither food nor feed safe. In Kenya, as in other LMIC the problem of managing contaminated crops remains, and alternative uses must be explored. The recommended actions can be more difficult to accomplish than in countries with more resources:

1. Adjusting different levels depending on species susceptibility: While this would be economically beneficial, the different levels may be even harder to control and enforce.
2. Binding: If the legal framework could allow the use of proven, efficient toxin binders or substances added to feed which tie up toxins so they can’t be absorbed, this could be a way for mitigation.
3. Blending or diluting more contaminated with less contaminated: if there could be sufficient control to ensure that the resulting product is not exceeding levels, this method could be useful in low-income settings.
4. Sorting, trimming and cleaning: While this potentially can reduce the contamination levels of the selected grains, there are concerns that the rejected grains may somehow find a way into the feed or food chain again.
5. Mitigating the negative health effects: There are indications that increasing proteins could reduce the harmful effects on animal productivity, however, since many farmers are struggling to provide sufficient feeds anyway, this may be a less effective way to mitigate.
6. Destruction of highly contaminated feed: in areas were resources are limited, destruction of feed is always debatable, since many animals are getting too little feed anyway. In addition, this may be costly.
7. Diversion from feed use: While there are still some gains from biofuel or other alternative uses, the same problems applies as to ‘destruction’.
8. Extrusion and heating: This may reduce aflatoxin contamination, but the method is too costly to be generally applicable.
9. Chemical treatment: These methods are still too expensive for scaling out in most LMIC countries.

Ways forward

In spite of decades of research there are still many unknowns regarding the impact of aflatoxins in dairy production in LMIC. It is likely to contribute to both reduced livestock productivity as well as to human exposure, and we know that the current level of enforcement of standards is not sufficient to alleviate the situation. In addition, the lack of alternative uses of contaminated crops reduces the incentives for authorities to actively enforce the legislation, since they deteriorate the food security situation. It is therefore necessary to critically review standards and explore ways forward that take the specific circumstances into consideration.

Author: Johanna Lindahl, International Livestock Research Institute, Kenya