Mycotoxins and eggshell quality: cracking the problem

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1 World Mycotoxin Journal, May 2008; 1(2): Wageningen g Academic P u b l i s h e r s Mycotoxins and eggshell quality: cracking the problem G. Devegowda 1 and D. Ravikiran 2 1 Former Head, Division of Animal Sciences, University of Agricultural Sciences, Bangalore, India; 2 Ph.D. scholar, Department of Poultry Science, Karnataka Veterinary, Animal and Fishery Sciences University, Bangalore, India; gdevegowda@gmail.com Received: 1 March 2008 / Accepted: 30 April Wageningen Academic Publishers Abstract Good eggshell quality is essential for preservation of egg contents and embryonic life. Eggs with poor shell quality are rejected both as table eggs and as hatching eggs, leading to heavy economic losses. Dietary mycotoxins in laying hens can predispose them to or precipitate eggshell defects. Effects of various mycotoxins on poultry eggshell quality are reviewed. Methods in practice for alleviation of these effects have been discussed. Keywords: poultry, eggshell quality, mycotoxins, mycotoxin decontamination 1. Introduction The avian egg is basically an embryonic chamber essential for the propagation of the species (Peebles and McDaniel, 2004). Eggshell is a sophisticated bioengineering product designed to perform the following crucial functions: (1) protecting the egg contents from the microbial and physical environment; (2) controlling the exchange of water and gases through pores during the extra-uterine development of the chick embryo; and (3) providing calcium for embryonic development once the yolk stores are depleted (Nys et al., 2004). The egg is a fragile commodity and the industry suffers enormous losses from the breakages of table eggs and hatching eggs (Hunton, 2005). Major influences on the quality or structure of the eggshell during the reproductive life of the hen are genetic constitution, diet, climate, housing, and age (RIRDC, 2000). Several dietary factors, singly and in interaction with other factors, contribute to eggshell quality. Certain mycotoxins are found to have an adverse effect on eggshell quality, in a direct or indirect manner which is reviewed in this paper. 2. Eggshell quality Most shell defects can be classified under five major categories, viz. defects associated with egg shell integrity, texture, shape, colour and cleanliness. Defects considered under the category of egg shell integrity include gross cracks, hairline cracks, star cracks and thin shelled or shell-less eggs (Anonymous, 2002). The difficulty in storage and transport of cracked eggs, and restrictions on their sale for human consumption have a severe negative impact on the profitability of egg producers. Shell quality expressed as shell integrity is relative in its expression. For a commercial table egg, the shell provides mainly a physical protection against the onslaught by extraneous environment and microbes. For a hatching egg, however, the shell also has to serve a physiological function of optimum gas exchange. Therefore, while a thick eggshell is a synonymous with good shell quality in a commercial table egg, it may not be so in the hatching egg. However, the eggshell quality is traditionally measured as the ability to resist breakage (Peebles and McDaniel, 2004). Parameters like porosity of the shell and relative vapour conductance of the shell may be more relevant and reliable measures of shell quality (Peebles and Brake, 1985). However, due to their cumbersome nature they are not widely followed. Measurement of percentage shell (Peebles and McDaniel, 2004) and specific gravity of egg (Hamilton, 1982) are two other methods which make evaluation easier. But again, data relating to the interaction of these factors with mycotoxins is limited. Direct measurement of shell ISSN print, ISSN online 203

2 G. Devegowda and D. Ravikiran thickness after removal of shell membranes is a common method adopted to ascertain shell quality (Peebles and McDaniel, 2004). 3. Mycotoxins affecting eggshell quality Shell integrity is the parameter of eggshell quality most commonly affected by mycotoxins. However, mycotoxins also greatly affect other parameters such as shape, texture and cleanliness. Effects of aflatoxins and cyclopiazonic acid Aflatoxin B 1 and cyclopiazonic acid are the most common mycotoxins implicated in eggshell quality. Several studies have shown a clear positive correlation between aflatoxin B 1 and cyclopiazonic acid contamination of feed and poor shell quality. Dietary aflatoxin B 1 causes reduction in eggshell weight of laying hens. Zaghini et al. (2005) reported a reduction in the eggshell weight of laying hens exposed to 2.5 mg/kg of dietary aflatoxin B 1. Aflatoxins at 1 mg/kg levels have been shown to reduce the levels of circulating calcium and phosphorus content in the blood of broiler chicken (Eraslan et al., 2005), a metabolic situation that could reduce the shell quality in laying hens. Aflatoxins were also found to reduce the eggshell calcium content in laying hens (Abdelhamid and Dorra, 1990). Zinc plays a very significant role in eggshell formation. Conversion of bone calcium (a phosphate salt) to eggshell calcium (a carbonate salt) requires enormous quantities of bicarbonates. Bicarbonate generation from carbon dioxide and water is catalysed by a zinc dependent enzyme, carbonic anhydrase (Figure 1) (Joosse, 1983). Aflatoxin B 1 inflicts hepatic damage, reduces the hepatic zinc levels and reduces bone breaking strength in birds (Maurice et al., 1983). Aflatoxin B 1 is known to affect several other factors contributing to eggshell quality. Feeding aflatoxin B 1 contaminated diets resulted in depletion of hepatic vitamin Blood plasma Carbonic anhydrase (zinc dependent enzyme) Shell gland CO 2 H + + H 2 CO 3 + H 2 O - HCO 3 Egg shell Ca 2+ Ca 2+ Ca 2+ Figure 1. Carbonic anhydrase, a zinc dependent enzyme essential for shell formation targeted by mycotoxins. A in poultry (Pimpukdee et al., 2004), a vitamin crucial in maintaining the mucosal secretory activities of several organs including the shell gland. Aflatoxin B 1 reduces the utilisation of cholecalciferol in poultry (Rama Rao et al., 2007). Dietary aflatoxin B 1 results in decreased plasma 25- hydroxy vitamin D and 1, 25-dihydroxy vitamin D levels within five days of feeding. Aflatoxin B 1 also reduced the urine flow rate, sodium excretion and potassium excretion while increasing calcium excretion and reducing total plasma calcium, clearly indicating a negative relationship between aflatoxin B 1 and calcium metabolism. These effects are attributed to altered vitamin D and parathyroid hormone (PTH) metabolism. Aflatoxicosis is thought to decrease endogenous PTH synthesis and the renal sensitivity to PTH. Also, the decrease in glomerular filtration rate exhibited 10 days after toxin removal indicates that aflatoxin B 1 may cause prolonged alteration in renal function. (Glahn et al., 1991). Cyclopiazonic acid produces a marked deterioration in the eggshell quality in laying hens (Bryden, 1991). Hens receiving daily doses of 5mg/kg body weight (b.w.) laid eggs that were either badly cracked or shell-less and all the exposed hens died within seven days. At 2.5mg/kg b.w. there was no mortality but the eggs had significantly thinner shells which were often cracked (Cole et al., 1988; Suksupath, 1993). In a study in breeder hens Suksupath (1993) observed that at 2.5mg/kg b.w. ingestion level the eggshell thickness was reduced considerably, which was reflected by the reduced number of settable eggs. Since cyclopiazonic acid and aflatoxin B 1 exert similar effects metabolically and toxicologically, some of the mechanisms detailed for aflatoxin B 1 may also be true for cyclopiazonic acid (Figure 2). Effects of trichothecenes The major trichothecenes, T-2 toxin, diacetoxyscirpenol and deoxynivalenol elicit oral lesions leading to lower feed intake, low egg production and poor shell quality. Diacetoxyscirpenol has been found to reduce egg production and increase the percentage of thin-shelled eggs in laying hens (Anonymous, 2007). Wyatt et al. (1975) reported reduction in egg production and incidence of shell thinning upon feeding T-2 toxin contaminated diet to hens. T-2 toxin is shown to cause mouth lesions associated with reduction in egg weight and also shell weight. The percentage shell was not affected significantly, but concurrent suboptimal management practices resulted in a reduction in shell surface density (Grimes and Bridges, 1992). Hamilton (1987) reported a 22% drop in egg production, 12% increase in cracked eggs, incidence of blood spots and a further 18% egg breakage during transit in T-2 toxin fed hens. In a similar observation Jewers (1990) has reported an increase in egg breakages from a normal 3% to 15% with T-2 toxicosis. This author also reported a 204 World Mycotoxin Journal 1 (2)

3 Mycotoxins and eggshell quality: cracking the problem Gut Liver Kidney Poor calcium and vitamin D3 absorption. Lower vitamin A, E and zinc levels. Poor vitamin D3 conversion and calcium binding protein synthesis Low vitamin D3 level. Increased calcium excretion. Plasma Low calcium and phosphorus levels. Bone Increased calcium mobilisation. Reduced calcium deposition. Shell gland Low secretory activity. Low bicarbonate levels. Poor shell deposition. Figure 2. Common metabolic effects of mycotoxins responsible for poor shell strength. further 18% of eggs being broken in transit to customers, suggesting that the effect of T-2 toxins on eggshell quality can be extensive. Manoj and Devegowda (2000) have reported a decline in shell quality, besides other adverse effects, in laying hens fed diets containing T-2 toxin. Chowdhury and Smith (2004), studying the effects of grains naturally contaminated with Fusarium, manifesting several Fusarium mycotoxins concurrently with predominant activities of deoxynivalenol and fusaric acid, have reported a reduction in egg production, egg mass, egg weight and egg shell weight. Increase in plasma uric acid levels and relative kidney weights were also noted suggesting renal damage. In another study, Chowdhury and Smith (2005) have shown that hepatic protein synthesis is reduced by feeding naturally contaminated grains containing multiple Fusarium toxins. Hepatic tissue is the major site of synthesis of calcium binding vitellogenins (phosvitins) and Fusarium toxicity may reduce the egg shell weight by reducing the synthesis of phosvitins. Effects of zearalenone Zearalenone is a mycotoxin with oestrogen mimicking effects. In White Leghorn hens, zearalenone is shown to reduce egg specific gravity, egg shell thickness and interior egg quality. Concurrent reduction in serum calcium and increase in serum phosphorus have also been reported (Hoerr, 2003). It is reported that exposure of avian embryos to oestrogenic influences causes histological changes and disrupts the localisation of carbonic anhydrase in the shell gland in the adult birds, implying a functional disturbance in the shell gland at the laying stage (Berg et al., 2004). Since zearalenone is an oestrogenic mycotoxin, this observation acquires greater significance. Effects of other mycotoxins Ochratoxin A is associated with impairment of kidney functions. Ochratoxin A may thereby indirectly hamper the eggshell quality. Shirley and Tohala (1983) have reported poor shell quality and eggs with blood spots in hens fed diets containing ochratoxin A. Jewers (1990) reported the occurrence of thin rubbery shells which break more readily than normal during field outbreaks of ochratoxicosis. Ochratoxin A is reported to cause stains on shell surface as well as poor shell strength (Hermann, 2002). Fumonisin B 1 too has been shown to cause a reduction in shell quality as represented by shell weight in quails (Butkeraitis et al., 2004). Co-contamination with mycotoxins is also shown, in many cases, to contribute to poor shell quality. Available data indicates that dietary aflatoxin B 1 (50 μg/kg and 200 μg/kg) and fumonisin B 1 (10 mg/kg) in combination have primarily additive adverse effects on quail egg weight, specific gravity and percent eggshell (Oliveira et al., 2002). Citrinin and patulin fed separately, were found to reduce the eggshell calcium content in laying hens, as did aflatoxins. Among these three toxins, patulin caused the highest reduction in calcium content of eggshell besides altering the shape of the eggs (Abdelhamid and Dorra, 1990). 4. Approaches to alleviating the adverse effects of mycotoxins There is no available technology which can fully prevent the mycotoxin contamination of animal feeds at preharvest or postharvest times. However, in animal feeds several methods of mycotoxin decontamination have been tried and are proven to be effective at varying levels (Devegowda and Murthy, 2005). The most effective method of neutralising mycotoxins already present in the feed is by binding them World Mycotoxin Journal 1 (2) 205

4 G. Devegowda and D. Ravikiran to organic or inorganic inert compounds before they can be absorbed from the intestines. Bentonites and aluminosilicate clays have been in use at different inclusion rates of 0.5-1% against aflatoxin B 1 (Huff et al., 1992; Phillips et al., 1988). However, these clays have disadvantages, including high inclusion rates and a narrow range of binding efficacy as only aflatoxin B 1 is bound significantly. Clays tend to offer little or no protection against zearalenone, ochratoxin A and trichothecenes (Girish and Devegowda, 2004; Kubena et al., 1993; Santin et al., 2002; Volkl and Karlovsky, 1998). Possible dioxin contamination and interaction with dietary trace elements are the other disadvantage associated with mineral clays (Chestnut et al., 1992; Kramer et al., 1993). Biological agents have been tried with varying degrees of success in decontaminating mycotoxins (Jouany, 2007). Biodegradation of trichothecenes by ruminal and intestinal flora (He et al., 1992; Kollarczik et al., 1994) and by a strain of Eubacterium (Binder et al., 2001; Fuchs et al., 2002) and of zearalenone by a strain of yeast Trichosporan (Molnar et al., 2004) have been tried. The limitations of such a biological approach are the specificity, concentration and optimum conditions of microbial enzymes as weighed against the wide variety of potential contaminants, the short interaction time and the influence of other dietary factors (Jouany, 2007). Nevertheless, the situation specific application of such strategies is a possibility, while further research in this area may lead to much better prospects. Yeast glucomannan (YGM), a biotechnological concept which is also organic, is a promising alternative that has gained acceptance in recent years (Devegowda et al., 1998). A derivative of the yeast cell wall, YGM has been shown to decontaminate several mycotoxins occurring in animal feedstuffs. Several researchers have proved decisively that the YGM is able to bind higher levels of several important mycotoxins at lower inclusion rates as compared to the limited narrow range binding abilities of inorganic binders (Deo et al., 1999; Pavicic et al., 2001; Raju and Devegowda, 2000; Yegani et al., 2006; Yiannikouris et al., 2004). Manoj and Devegowda (2000) reported that YGM reversed the suppression of egg production by T-2 toxin. Chowdhury and Smith (2004) have demonstrated that the addition of glucomannan to Fusarium contaminated diets reversed the reduction in shell weight and increase in uric acid excretion caused by the toxins. In another study Chowdhury and Smith (2005) observed that the suppression of the hepatic protein synthesis by Fusarium contaminated diets was fully alleviated by supplementing glucomannan. Yegani et al. (2006) have demonstrated that feeding glucomannan in Fusarium contaminated diets reversed the reduction in eggshell thickness caused by the mycotoxins in broiler breeder hens. 5. Conclusion Available data on the effects of mycotoxins on eggshell quality is not very extensive. In the case of several mycotoxins, there are either no reports on this parameter or the observations are scanty. More research is recommended into the interaction of mycotoxins and shell quality. Eggshell quality is an important economic parameter that comes under consideration post-production. However, the adverse effects of mycotoxins on eggshell quality and alleviation by mycotoxin adsorbents is taken relatively less seriously. It is desirable for more research to be conducted in these areas. References Abdelhamid, A.M. and Dorra, T.M, Study on effects of feeding laying hens on separate mycotoxins (aflatoxins, patulin, or citrinin)- contaminated diets on the egg quality and tissue constituents. 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