OT Mycotoxins impact egg production

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Date: 2006-05-01

Mycotoxins impact egg production

http://www.wattpoultry.com/eggindustry/article.aspx?id=7450

By Dr. Simon M. Shane

Aflatoxicosis results in lowered serum protein, lipoproteins and

carotenoids. Coagulation is adversely affected, leading to a greater

potential for hemorrhage.

The recent episode of multi-state mortality in dogs due to toxic

levels of aflatoxin highlights the problem of mycotoxicosis which is

both seasonal and regional in the USA.

Aflatoxin is the most common of the economically significant

mycotoxins and in the USA is most frequently associated with

contaminated corn. Drought exposes the developing ears to infection

with Aspergillus flavus and A. parasiticus. These fungi elaborate at

least four related toxins of which aflatoxin B1 is most frequently

associated with adverse effects centering on the liver and vascular

system of susceptible livestock.

Concurrent with the outbreak of aflatoxicosis in dogs, egg producers

noted an increase in blood spots ranging from pinpoint accumulations

of blood in the albumen adjacent to the vitelline membrane to blood-

filled eggs. Small blood spots should be differentiated from protein

inclusions ( " meat spots " ) which occur normally in up to 4% of brown-

shelled eggs. These particles are formed from the protein matrix of

the eggshell and have a characteristic tan to red color caused by

incorporation of porphyrin pigment which colors the shell. In fact,

the albumen of white-shelled eggs also contains protein particles,

but these non-pigmented inclusions are translucent and are virtually

invisible.

Blood spots occur as a result of hemorrhage at the time of ovulation

from ruptured small vessels adjacent to the stigma of the ovarian

follicle. This results in release of blood into the infundibulum of

the oviduct with subsequent appearance in the albumen, usually

adjacent to the vitelline membrane surrounding the yolk.

Causes of Blood Spots

Any factor which decreases the rate of clotting or impacts the

integrity of blood vessels will predispose to the presence of blood

spots. Aflatoxin binds to mitochondrial DNA, resulting in adducts

which impair oxidative phosphorylation, critical for synthesis of

proteins and the metabolism of lipids. Hepatic dysfunction as a

result of aflatoxicosis is indicated by elevation and disturbance in

the ratio of specific serum enzymes which can be assayed.

Aflatoxicosis results in lowered serum protein, lipoproteins and

carotenoids. Due to reduced synthesis of prothrombin, coagulation is

adversely affected, leading to a greater potential for hemorrhage.

The permeability of capillaries may also be increased due to

degenerative changes induced by toxins.

Aflatoxicosis is characterized in broilers by bruising, and in

highly susceptible immature species, such as ducklings, subcutaneous

hemorrhages are observed. It is evident that high-producing hens

will be susceptible to aflatoxicosis since the liver is responsible

for synthesis of the precursors of both yolk lipids and albumen

incorporated into eggs. Over short periods, hen-week production may

be maintained despite the presence of low to moderate levels (100

ppb) of aflatoxin in feed although egg weight is frequently reduced.

Chronic aflatoxicosis may affect shell strength as the rate of

conversion of dietary vitamin D3 (cholecalciferol) to the active

metabolic form is diminished. This decreases the efficiency of

calcium absorption since the activity of calcium-binding protein in

the intestine is reduced. Absorption of carbohydrates and lipid

nutrients is also impaired due to reduced output of pancreatic

amylase and lipase. Clinical problems associated with mycotoxicoses

in laying flocks also include the indirect effects of

immunosuppression manifested as septicemia and peritonitis,

deterioration in internal egg quality, reduced yolk pigmentation and

defective shells.

The differential diagnosis of blood spots includes vitamin A

deficiency and anticoagulant rodenticide toxicity, both of which are

extremely rare. Deletion of vitamin K from premixes fed to caged

hens will also predispose to blood spots. It is possible that

hyperexcitablity ( " flightyness " or " hysteria " ) among hens may result

in hemorrhage at the time of ovulation. Data obtained during the mid-

1990s in Pennsylvania showed that flocks infected with Salmonella

enteritidis had a 3 to 4-fold increase in the prevalence of blood

spots compared to non-infected flocks.

Occurrence of Blood Spots

The prevalence of blood spots in white-shelled eggs was determined

in North Carolina random sample tests conducted between 1980 and

1984. " Small blood spots " were present in an average of 0.93% of

eggs examined with an additional 0.88% classified as " large blood

spots " over 5 mm in diameter. In contrast, brown-shelled eggs showed

prevalence rates for small and large blood spots of 3.2% and 2.1%,

respectively.

Consumer complaints relating to the presence of blood spots and free

blood in eggs can be regarded as an indication of the severity of a

problem. Since approximately 1.5% of all white-shelled eggs have

detectable blood spots, any marked increase in complaints might

suggest a problem over and above the accepted normal prevalence.

A review of records maintained by a large integrator showed

considerable variation in the prevalence of blood spots among

various complexes in the group. Complaints ranged from zero to 7 per

10,000 cases marketed, with an average of 2.4 complaints per 10,000

cases. If random sample data are representative of US

production,10,000 cases would theoretically contain 3,000 dozen

cartons with at least one egg with a detectable blood spot, assuming

a 1% prevalence rate. The discrepancy between the average of 2.4

complaints recorded and the potential for 3,000 observations

suggests a high tolerance for blood spots among consumers.

Detecting Blood Spots

It is impossible to detect blood spots using conventional candling

as the opacity of even white-shelled eggs limits visual detection by

a candler observing 12 rows of eggs at a throttle setting of 300

cases per hour. Electronic blood detectors function by passing light

beams at two different frequencies through eggs to detect the haem

molecule of blood. Validation of the sensitivity and specificity of

a blood spot detector by breakout examination in two large plants

confirmed that among samples of rejected eggs, there were three

normal eggs for every egg with a visible blood spot.

A plant operating at 300 cases per hour over an 8-hour shift would

process 864,000 eggs. With a 0.5% rejection due to blood spots, the

plant would normally reject 360 dozen eggs due to apparent blood

spot defects. Of this quantity, approximately 240 dozen eggs would

be unjustifiably rejected as " false positives " each shift. Since the

manufacturers of commercial blood spot detectors cannot provide data

on sensitivity (the ability to accurately detect eggs with blood

spots) or specificity (the ability to accurately differentiate

between blood spots and other defects), it must be assumed that not

only is there false rejection but that a proportion of eggs with

blood spots are released to the market.

Prevention of Aflatoxicosis

Feed mills should be equipped to screen corn and other cereal

ingredients for the presence of aflatoxin. Any consignment of corn

with moisture content in excess of 12% should be regarded as suspect

and should be assayed using a commercially available rapid immuno-

based test kit. Levels in excess of 50 ppb aflatoxin B1 are regarded

as potentially toxic. It is noted that the uneven distribution of

mycotoxins within a consignment of an ingredient may lead to

considerable sampling bias and result in either false negative

assays or non-representative high values in a car or truck load as

delivered.

Commercial and state diagnostic laboratories are equipped with gas-

liquid chromatography installations to provide quantitative results

for a wide range of mycotoxins in feed samples. Although the cost of

assays is generally low, delay in receiving results creates logistic

problems of segregated storage of suspect batches of ingredients.

A number of feed additive compounds have been shown to inhibit

adsorption of aflatoxins by selective binding in the intestinal

tract. Although bentonite clays may inhibit uptake, their efficacy

both in vitro and in vivo is extremely variable. Natural and

synthetic hydrated calcium aluminum silicates are more efficient

adsorbers of aflatoxins than clays. Esterified glucomannans derived

from the cell wall of yeast (Saccharomyces cerevisiae) also are used

as aflatoxin binders, intended for action against aflatoxins as well

as fusariotoxins which are frequently co-contaminants.

Current FDA regulations prevent manufacturers of zeolites and

esterified glucomannans from promoting their products as mycotoxin

adsorbents or binders, which would constitute a health claim.

Compounds can however be purchased and incorporated in diets as anti-

caking agents at an additive cost of less than $2 per ton. Since

aflatoxin is usually accompanied by other toxic fungal metabolites

including fusariotoxins and ochratoxin, a broad spectrum mycotoxin

binder is recommended when aflatoxin is present in cereal

ingredients and as reports of blood spots are received from

consumers.

Updated: May 03, 2007

History: Mycotoxins impact egg production