As a poultry and egg producer one is used to ups and downs in income and costs. However, when income is low and costs are high, the continuation of an enterprise is at stake. Then it is wise to be extra alert on subclinical dangers that might threaten a company's liveability. One of those unnoticed threats is often a low level infection of mycotoxins.
Feed safety is more than ever before gaining ground in poultry production and trade. Factors driving this not only include pathogen issues but also economics. It is not anymore just a concern for the food chain but also an aspect that can promote or hinder the bottom line. Feed safety is in fact very crucial in today’s highly volatile and competitive business environment. In this applicative discussion the target is to highlight the mycotoxicologic safety of feeds having direct correlation to food safety and the economic bottom line. Mycotoxicologic safety herein relates to the inevitable contamination hazards arising from mycotoxins, the toxic byproducts of fungal metabolism. In poultry mycotoxins often affect productivity and egg quality.
Often producers and especially the nutrition managers working with them fret about the feeds’ nutrient levels produced or used in their operations. This is easy to comprehend in these times because major nutrition errors may affect over 60% of the total production cost. And if we are speaking about aqua nutrition, in which feeding programmes are highly dependent on fish meal, then one may be risking over 70% of production cost. Such cost indeed is enormous. But is the first love of nutrition about cost, even under commercial setting? I believe it is not. It is first about biology and of course cost. And this I am sure also considers the welfare of animals. You see, everyone is on board now. Then, one may pose the question ‘what then is a nutritious feed’? The typical answer is one that contains essential nutrients in the right balance. Essential nutrients normally refer to dietary protein or amino acids (AA), vitamins and minerals, and energy as a nutrient attribute. Truly so, but it’s not the complete picture, as experience shows that dietary specs alone do not guarantee optimum nutrition of birds. And whether you believe in feed safety or not, mycotoxin control needs to be integrated along with essential nutrients.
Mycotoxin effect on amino acids
To show that nutrient value of diets may be diluted by mycotoxins, a study investigated the effect of Aflatoxin (AFL) on the utilisation of Lysine (Lys) or Methionine (Met) (Mills et al., 1989). Their approach was to feed day old broilers with one of 80%, 100% and 120% of NRC (1984) recommendations for Lys or Met, at 0 or 3.5 ppm of AFL. After 21 days of feeding, performance results shown in Table 1 varied according to diet.
As expected, it was observed that body weight (BW) of birds increased with increasing dietary Lys concentration, while response to Met was similar across diets. On the other hand, AFL contamination blunted the response to Lys and Met at all AA density, reducing BW by 26% on average. This showed that aflatoxicosis alters the protein value of feeds and thus the AA requirement of the birds. These modifications arise because mycotoxins such as AFL act as immunogen which increase inflammations and immune cost. Metabolically, they also disturb assimilation of absorbed feed nutrients. The net results of these events are a repartitioning of ingested nutrients to service increased maintenance requirements relative to needs for growth or production. The feed conversion worsened by as much as 0.6–8%, depending on AA treatment. To extrapolate to practical condition, a 26% reduction in BW or high inefficiency in feed conversion is not warranted considering that feed protein and essential AAs such as Lys and Met make up 35-55% of feed cost. In any case, this data underscores the point that dietary AA inefficiency could be a price to pay to eliminate toxin problems. To avoid these kind of losses means that nutritionists should prioritise the pursuit of feed safety in their operations. This demands the integration of feed mycotoxin control with other routine feed formulation operations. For instance reliable routine and simultaneous analysis of nutrients and mycotoxins in feed ingredients. Such programmes should also be complimented with preventive usage of in-feed proprietary mycotoxin adsorbents. This is because mycotoxin analytical data whether from smart test kits or elaborate HPLC procedures still suffer uncertainties. Supplementation of adsorbents makes feed safety rather flexible, promotes the feed quality, safety of poultry foods and is rather economic.
Synergy in a negative way
The synergy that may occur with co-occurrence of mycotoxins is also of economic importance. An elegant investigation with broilers by Hamilton et al. (1992) illustrates this. They observed that BW was depressed by 14%, 8% and 24% in the presence of 2.5 ppm AFL, 2.5 ppm OTA and 2.5ppm AFL+OTA, respectively, compared to uncontaminated diet. This showed that the effect of the mixed toxins was more than the sum of the effects of each toxin. Effects on carcass yield (important in birds destined for processing plants) indicate a similar trend (Hamilton et al., 1992). These synergistic effects make mycotoxin co-occurrence more lethal in poultry feeds, and should be accounted for when treatment or preventive strategies are being formulated.
Apart from direct effects of mycotoxin contamination via feed, there is an indirect mode of action, which is often overlooked. This relates to the potential of mycotoxins to increase disease virulence in farm birds, further complicating food safety issues. In this mode of action, mycotoxins by affecting the immune system, compromise the ability of birds to combat diseases. This interference with the immune system may be manifested as depressed lymphocyte activity, suppressed antibody production or impaired macrophage function. A challenge study conducted by Kumar et al. (2003) illustrated in Figure 1 showed that broilers’ BW was only 69% of control after simultaneous E. coli and dietary OTA challenge compared to single challenged with E. coli (82%) or OTA (84%). The conclusion was that pathogenicity of E. coli was accentuated in the presence of dietary OTA contamination.
Previously Swamy and Devegowda (1998) confirmed that dietary AFL exposure interferes with the immune system based on antibody response to Newcastle and Infectious bursal diseases vaccinations in broilers. They observed (re-expressed in Figure 2) that with increasing (100 – 400 ppm) AFL ingestion, IBD and NCD antibody titre dropped to between 36 -61% and 32-52% of uncontaminated diet, respectively. These data suggest that AFL reduces the efficiency of vaccination via inducement of low antibody response.
Poultry genetic sensitivity
While AFL and OTA are mycotoxins of tropics or subtropical areas, common in the southern hemisphere, northern hemisphere climates often favour Fusarium toxins like DON and ZEA. Moreover level of exposure and poultry genetics may be a factor in how mycotoxins impact productivity. A recent 12 months trial with hens of two divergent genetic backgrounds found significant interaction between DON and breed on feed consumption, egg mass and laying intensity (Ebrahim et al., 2011). These scientists also found that DON reduced eggs by as much as 0.33% to 2.36% depending on breeds and exposure level. Whatever the climate might be, already poultry feeding is being impacted by international trade in crop feedstuffs, thus geographical classification of mycotoxins are only of academic value. In concluding these aspects, it is appreciated that the level of mycotoxins normally tested in control studies like those cited here, may be uncommon in practice. Nonetheless, raw material surveys teach us that it is safe to expect sporadic contaminations. Higher than minimum permissible levels of AFL levels have been reported in commercial poultry feeds in several tropical areas. Placinta et al. (1999) also summarised data from both temperate and tropical regions, showing very high Trichothecenes and Zearalenone levels in crop grains and animal feed samples. Apart from climate, these contaminations also reflect poor feed safety control, and low feed manufacturing technology.
Indeed as today’s hikes in price and scarcity of raw materials intensifies, we can expect sporadic contamination, high variation in batch to batch quality, likelihood of poor quality being traded or diverted to poultry feeds and substitution of conventional ingredients with alternative feedstuffs in the formulations. To exemplify the latter case soybean meal price has suffered more than 40% increase in certain regions, creating a situation whereby less quality but cheaper alternatives are becoming more attractive in least cost formulations. Given these scenarios the gap between artificial control trials and field exposures could be narrowing.
Economics of mycotoxin response
Putting figures to mycotoxin menace is practically relevant. Not only can this assist in process audit but also in choosing and evaluating management strategies. As an example we chose AFL, since its quantitative impact on BW gain in broilers is well documented and has greater geographical spread than most common toxins. Moreover the figures are applicable to growing conditions since toxins are produced within the grower house. A scenario is presented in Table 2 using gradual low increases in AFL ingestion to simulate linear depression in broilers’ BW gain and FCR. Low levels of AFL were chosen as they have been shown to be typical even in professional grow out operations using quality diets and healthy birds (Jones et al 1982).
The rate of depression was computed at an incremental rate of 0.2 ppm based on a relationship of 1 ppm ingestion to reduce BW by 5%. Also an endpoint BW of 1.8 kg was chosen. Results show that with increasing intake of AFL daily BW gain and BW at 37 days decrease and days to end point BW increase.
To apply these parameters, assuming a grower operation produces one million birds/month, a loss of 90 tonnes of live weight/month at an exposure level of 1.02 ppm could be expected. Moreover there were subtle but serious impacts on days to finishing weight and FCR (figures not shown), and the cost of medication and labour figures will further add to these losses. Such is the power of toxins. For the producer it might well be that the fear of toxins is the beginning of wisdom.
Dr Olayinka Akinde, Fusion BioSystems, is a nutritionist based in Germany. References available on request. Contact: Olayinka@fusionbiosystems.com