Mycotoxins’ impact on poultry gut health

The hidden threat of toxins from mould is well recognised, with many countries and regions having controls in place to limit animal exposure by testing raw materials or applying proven mycotoxin binders in feed. Mycotoxins are secondary metabolites produced by moulds that grow on crops in the field or on stored feed materials post-harvest. It is common for feedstuffs to be contaminated with multiple mycotoxins, as the analysis of one mycotoxin was shown to indicate the presence of others and many moulds produce toxic metabolites under similar environmental conditions. When animal feeds are formulated using various sources of grain, they can be contaminated by a variety of mycotoxins because moulds can also be specific to certain plants.

Mycotoxins can cause conflicting symptoms in birds

Mycotoxins cause a variety of sometimes conflicting symptoms in birds, ranging from reproductive to immunity problems. Many mycotoxins have pro-oxidation properties, which can affect organs and damage tissues on contact. This article covers the current level of the mycotoxicosis threat, as shown in the 2015 European Grains Harvest Analysis, and talks about how this can impact gut health and, subsequently, growth performance in poultry.

2015 harvest toxin contamination

Mycotoxin risk varies year to year and between regions. In a recent survey conducted by Alltech, the presence of up to 38 mycotoxins and their co-occurrence in the 2015 grain crops in Europe was analysed to provide a risk assessment for poultry diets. In 2015, large areas of Europe were affected by high temperatures and dry conditions, especially when summer crops were at the grain-filling stage. In southern Spain, crops were impacted by very high temperatures and in Italy the grain yield expectations were low due to drought. High temperatures and poor rainfall caused problems in eastern France, southern Germany and Poland. Similar weather problems impacted the production of maize grown in the Czech Republic, northern Austria, Slovakia, Hungary, Romania and Bulgaria.

Figure 1- Occurrence of various mycotoxins from the 2015 European harvest.

The yield of winter cereals in northern Europe improved towards the end of the growing season thanks to better weather. In eastern Europe, however, high rainfall delayed grain harvesting and increased the potential for mould growth post-harvest, especially during storage. The testing of feedstuffs was conducted via ultra performance liquid chromatography, coupled with tandem mass spectrometry (UPLC-MS/MS) methodology developed at Alltech’s Global Research Headquarters in Lexington, Kentucky, USA. The results were used to determine the risk of mycotoxicosis from feedstuffs.

The figures below show the frequency of each mycotoxin group (Figure 1), the average risk analysis for feed contamination (Figure 2) and the percentage of samples in high, medium or low risk categories for broiler chickens (Figure 3).

Figure 2 – Mycotoxin risk assessment for broilers from results of the 2015 crop.

These analytical results show that more than 90% of samples tested positive for mycotoxins, with Fumonisins and Type B Trichothecenes, e.g. deoxynivalenol (DON), being the most prevalent in the European 2015 grain crop samples. Although mycotoxin levels were lower on average, the occurrence of multiple mycotoxin contamination in feedstuffs led to a higher risk category being advised. These Fusarium mycotoxins can have a variety of effects in poultry, especially at a gut level.

Figure 3 – Percentage samples presenting high, medium or low risk from Mycotoxicosis in poultry.

Gut damage by mycotoxins

Gut mycotoxin exposure can cause oxidative damage to cell membranes and reductions in cellular protein synthesis, which can produce lesions in various parts of the gastrointestinal tract. Specific research has shown that exposure to Fusarium damages the gut tissue and reduces nutrient digestion. This can result in necrosis, gizzard erosion, haemorrhaging and the mal-absorption of nutrients. Externally, this damage may manifest itself as an increase in the feed conversion rate (FCR), a reduction in performance, as well as in watery faeces, with poorly digested feed particles.

One of the main symptoms of mycotoxin damage is the appearance of lesions in the gastrointestinal tract. This starts in the bird’s mouth, where the mucosal membranes can become inflamed and develop lesions. With regard to the crop, lesions can affect the holding capacity and grinding of feed, especially in whole grain diets. This loss of activity may expose chickens to higher levels of pathogens, as the crop has been implicated in controlling pathogen carriage into the gut. Lesions cause pain and can limit feed intake, reducing the ability for the bird to attain its genetic capacity for performance.

Feeding trials with DON concluded that exposure to DON impaired the glucose transport systems across the gut wall in the jejunum, a major site of absorption. The same researchers revealed that DON contamination in feed significantly reduced villus height and surface area in the jejunum. Similar trials using Fusarium toxins in chickens showed that ileal proliferating cells were significantly reduced in the presence of contaminated feeds. These cells are important in the growing bird for the development of the gut and maximum nutrient uptake. Compromising their proliferation can have an effect on the animal throughout its entire growth period.

Damage and erosion of the gut lining can facilitate the invasion of gut tissues by pathogenic bacteria, such as Clostridium perfringens and Salmonella spp. Such pathogens are encouraged to proliferate by a reduction in feed digestibility, which is caused by various problems associated with mycotoxicosis, leading to undigested nutrients passing down the intestinal tract. These nutrients are utilised by bacteria in the caecum, which can then spread back up the tract into the ileum, the main area of absorption. Published trials discuss how eight-week-old broilers reacted when exposed to Eimeria spp. and fed Fusarium contaminated feeds. These studies reported that exposure to the mycotoxins retarded recovery from the coccidial lesions caused by the challenge. As seen in other trials, birds exposed to the toxins had lower villi height, thus reducing the absorptive surface area in the jejunum and ileum. Other re-search confirmed such findings, with trials showing that chickens fed diets contaminated with DON had a higher occurrence of necrotic enteritis when exposed to Clostridium perfringens, increasing sub-clinical cases from 20% to 47% of the flock.

Impact of storage

In a report written by Santin, the appearance of lesions and gut damage coincided with the peaks of mycotoxin contamination in grain during various seasons. The main danger period was between December and February, following harvest. This was due to the storage of grain, which potentially exposed the cereal to moisture damage and subsequently a potential increase in mould growth and mycotoxin production. This is a particular risk following a wet harvest, as seen in various European countries in 2015. Hence, the real impact of mycotoxins in terms of gut damage, impaired digestion, altered nutrient uptake and subsequent performance loss may only now become apparent for producers.

Conclusions

Gut health is a major concern for all poultry producers, especially broiler producers. Lesions caused by the toxins can be seen throughout the digestive tract, starting in the mouth, with the subsequent discomfort reducing feed intake. The irritation and injury caused by oxidative damage to the cells lining the gut wall can reduce digestion and lead to increased nutrient availability for disease-causing pathogens. These organisms can then reproduce to form large colonies that invade the upper reaches of the gastrointestinal tract, leading to diseases such as necrotic enteritis.

Analysis of the 2015 European cereal harvest showed that 20% of the feedstuffs sampled presented a high risk and 18% a medium risk to poultry. Due to the multiple contaminations of many samples, especially those with Fusarium moulds, which are implicated in immunosuppression, this led to an overall high-risk analysis for poultry from harvest samples in 2015. This was due to the poor weather conditions that occurred in many regions in Europe during crop growth and harvest. Drought followed by wet harvesting weather has a major impact on grain quality, promoting the growth of mould and the production of mycotoxins. The impact of these conditions may become even more apparent after storage. The promotion of mycotoxin production during storage is particularly manifested by losses in bird production due to poorer feed intakes, lower rates of digestion and absorption in the gut. These symptoms are typically noticed five months after harvest. Therefore European producers should use mycotoxin binders at such times of the year following a poor growing season.