Mitigating mycotoxins in swine diets with clay

Since the ban on antibiotics in the European Union, intensive research has focused on the development of alternative feeding strategies that can maintain animal performance and health. One product class that has been suggested as an alternative feed additive for use in the pig industry is the inert clays. Clays are crystalline, hydrated aluminosilicate molecules composed of alkali and alkaline earth cations along with small amounts of various other elements. The best-known are montmorillonite, smectite, illite, kaolinite, biotite and clinoptilolite. The molecules in these clays are arranged in three-dimensional structures creating internal voids and channels capable of trapping a wide variety of molecules. As a result of this structure, clay minerals are regarded as a simple and effective tool for the prevention of the negative effects of many toxic compounds. The adsorption capacity for any specific clay is determined by the fine structure of the clay particles, their surface properties and exchangeable ions. Clays have also been shown to have a significant influence on growth, nutrient digestibility and the reproductive performance of swine.

Improved pig performance

The strategy of using clays to improve pig performance has been given considerable attention in research. Many studies have documented a significant improvement in weight gain and feed conversion in pigs fed diets supplemented with clays. Improvements have been noted for both weanling pigs and growing-finishing pigs. Where improvements in performance have been noted, one of the most likely explanations for the improvement is the fact that clays increase nutrient digestibility. Clays reduce the speed of passage of feed along the digestive tract which allows more time for digestion. Feeding clays also causes morphological changes in the intestinal mucosa such as an increase in villus height and an increase in the villus height to crypt depth ratio. These changes increase the surface area of the gastrointestinal tract thus increasing nutrient digestibility. Several studies have indicated that feeding clay reduces the incidence, severity and duration of diarrhoea in pigs. The mechanism for the reduction in diarrhoea is likely due to increases in the numbers of Bifidobacterium and Lactobacillus and decreases in Clostridia and E. coli in the small intestine of pigs fed clays. In addition, the numbers of pigs born alive and weaned, birth weight and weaning weight have been shown to be higher for sows fed clays.

Reducing the effects of mycotoxins

One of the most important roles of clays for pigs however, is their ability to mitigate the effects of mycotoxins. Mycotoxins are toxic secondary metabolites of fungi commonly found on grains, which can cause severe negative impacts on swine health and performance. Clays may have the ability to diminish the impact of mycotoxins through their binding properties. Lindeman et al. reported that inclusion of 0.5 % hydrated sodium calcium aluminosilicate or sodium bentonite in a diet with 840 ppm aflatoxin prevented most of the reductions in weight gain and feed intake observed in weanling pigs. Wang et al. reported that the addition of montmorillonite clay to the diet can ameliorate the negative effects of dietary zearalanone and accelerate recovery of zearalanone toxicity in weaning pigs during and after zearalanone challenge (Table 1). In their experiment, nursery pigs were fed diets contaminated with 0, 0.2, 0.4 or 0.8 ppm zearalenone which depressed weight gain and negatively impacted feed efficiency.
The addition of montmorillonite to the diet significantly improved the feed efficiency of pigs fed zearalenone. In addition, the total tract digestibility of nitrogen was improved by supplementation with montmorillonite while dry matter and energy digestibility were unaffected. Montmorillonite clay also improved the performance of growing gilts fed zearalenone contaminated diets. Wang et al. reported significant improvements in weight gain and feed efficiency as a result of including 2 g/kg montmorillonite in diets contaminated with 0, 0.2, 0.4 or 0.8 ppm zearalenone. Zearalenone causes infertility, abortion and breeding problems in swine and can be found in cereal crops like maize and its by-products. Zearalenone and its metabolites bind competitively to oestrogen receptors which causes hypertrophy of the uterus. Feeding clay resulted in a significant reduction in vulva length, width and area in gilts fed zearalenone (Table 2).

Increased nutrient digestibility

Where improvements in nutrient digestibility have been observed, several mechanisms have been proposed to explain the effect. As already suggested, it has been proposed that clays reduce the speed of passage of feed along the digestive tract which would allow more time for digestion. Secondly, some authors have put the improvement in protein and energy retention as a result of clay supplementation down to increased activity of pancreatic enzymes. The increased activity is proposed to result from the fact that pancreatic enzymes bind to the surface of the adsorbents and form complexes that are active within a wider range of pH in the digestive tract. Finally, feeding clay minerals can cause morphological changes in the intestinal mucosa. Xia et al. reported that the villus height and the villus height to crypt depth ratio were 19.1 and 37.1% higher in pigs fed diets supplemented with 0.2% montmorillonite compared with a control (Table 3). An increase in villus height increases the surface area for nutrient absorption thus increasing nutrient digestibility.
A further advantage of feeding clay to pigs is that this may help to minimise the impact of swine production on the environment. Shurson et al. and Poulsen and Oksbjerg reported that the amount of nitrogen excreted in faeces was significantly higher while urinary nitrogen excretion was lower in pigs fed zeolites. As urinary nitrogen is more volatile than faecal nitrogen, this change in excretion pattern would tend to reduce the amount of nitrogen lost to the environment from a swine operation.

References available on request.