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Seleniferous region has impacted on the poultry industry after poor hatchability, embryo deformities, malformed toes, legs, wings, etc. (Franke 1934; Franke et al. 1936; Franke and Tully 1936; Moxon 1937). However, it has been also reported that the toxicity of Se in poultry or any other animals depends upon the other several factors which are intimately associated with the nature of diet, gender of animals, any co‐exposure of other elements to the animals, etc. (Levander 1972). Selenate injection with 0.6–0.8 ppm in the air sac of poultry eggs before incubation caused the teratogenic effects on the developing embryo, such as malformed upper beak, missing eyes and legs, and stunted growth (Franke et al. 1936). The same type of results were reported by Sukra et al. (1976) and Khan and Gilani (1980). Poley et al. (1941) indicated that 4.0 and 10 ppm Se application by dietary grains caused lower growth rates for chicks. 15 ppm dietary application culminated in decreasing hatchability to zero (Poley et al. 1937). Trelease and Beath (1949) recorded Se toxicity embryo deformities, the toxicity caused by various chemicals exposure growing turkeys administered with 20 ppm Se in regular rations. 9.0 ppm Se application on laying turkey hens caused few embryonic malformations but this increased at 15.0 ppm Se application (Carlson et al. 1951).

One study reported that insertion of Se as selenious acid with 0.4 ppm into the yolk before the incubation caused toxicity and produced malformed embryos (Ridgway and Karnofsky 1952). Layed eggs of poultry reared after dieting with 8.0 ppm Se from wheat caused induction for necrosis in growing embryo, especially in the brain, spinal cord, and upper beak, and also decreased the growth of the embryo (Gruenwald 1958). This study was also supported by the findings of Rosenfeld and Beath (2013). Latshaw (1975) studied unequal distribution of injected Se in eggs, such as higher concentration in yolk than the albumen part of the eggs. Selenite injection of 18 pg Se/egg into the yolk caused abnormal changes in hematological profile after 19 days and a propensity toward malformed embryo formation was reported (Landauer 1940; Kury et al. 1967). One study reported that 2.0 ppm dietary Se did not produced any defective effects in the laying hens in terms of growth and egg laying, but administration of 8.0 ppm caused a reduction of egg laying and stunted body growth (Thapar et al. 1969). Ort and Latshaw (1978) administered 5, 7, and 9 ppm Se in laying hens. Results reported that a 5 ppm dose caused the reduce hatchability, a 7 ppm dose caused reduced egg weights, and a 9 ppm caused zero egg production. Selenite in a Torula yeast diet to chicks increased the chicks' mortality rate (El‐Begearmi and Combs Jr 1982).

Mertz and Underwood (1986) found that application of 8 ppm Se in diet caused higher bioavailability of Se in feathers. Supplementing emus with 1.4 ppm Se caused reduced hatchability from 52% to 40% with fatal egg deformities (Kinder et al. 1995). Another study reported that 2.0 ppm Se from the administration of selenite by drinking water has no effect on chick growth patterns (Cantor et al. 1984). Drinking Se‐containing 300 μgSe/l agricultural drainage water caused embryonic death and death of adult birds (Ohlendorf 1989). Kumar et al. (2018) conducted a study on the effects of sodium selenite on adult White Leghorn broiler birds. For 42 days they administered sodium selenite with 15 and 30 ppm. Results indicated that histopathological changes occurred in the liver, kidney, lungs, heart, and intestine (Figure 4.2a–d). There were diminished amounts of hemoglobin, packed volume of cells, ALT, and AST.

In one study, the following concentrations of inorganic selenium and selenized yeast were given to chickens: 0, 2, 5, 10, 15, 20, or 30 mg Se/kg for six months. Concentration with 10, 15, 20, or 30 mg Se/kg feed induced some pathological changes, such as renal edema; higher rates of dystrophy cells were found in renal tubules (Todorović et al. 2004). Ort and Latshaw (1978) found that 5 mg Se/kg administration reduced hatchability and deformed embryos (absence of eyes, beaks, wing and feet irregularities). Another research suggested that 4 mg Se decreases the appetite of deformed eggs in chickens for seven days (Poley and Moxon 1938; Landauer 1940; Cantor et al. 1984). Table 4.3 lists more research on the toxicity caused by Se.

Figure 4.2 (a) The liver section of poultry birds that had ingested selenium showing congestion in blood vessels, congestion in sinusoids, necrosis in the parenchyma, and connective tissue proliferation between the lobules

(Source: Adapted from Kumar et al. (2018)).

(b) Section of birds’ lungs showing congestion in the alveoli and oedema in the bronchi

(Source: Adapted from Kumar et al. (2018)).

(c) Kidney section of poultry birds that had ingested selenium showing degeneration of tubules, infiltrations of mononuclear cells

(Source: Adapted from Kumar et al. (2018)).

(d) Section of cerebellum of birds that had ingested selenium showing degeneration of Purkinje cells

(Source: Adapted from Kumar et al. (2018)).

Table 4.3 Se toxicity in poultry birds.

Chemical form	Age	Dose (ppm)	Toxic effects	References
Na2SeO3 + Se in wheat	Immature	10	Growth ↓	Carlson and Leitis (1957)
Se in wheat	Laying hens	10	Hatchability ↓	Moxon and Wilson (1944)
Se in corn, barley, wheat	Adult	5	Mortality ↑	Moxon (1937)
Na2SeO3	Adult	6.5	Deformed embryos	Moxon (1937)
Na2SeO3	One day	8	Body weight ↓	Moxon (1937)
Selenous acid	One day	8	Mortality ↑	Thapar et al. (1969)
SeO2	one day	5	Mortality ↑	Hill (1979)
Na2SeO3	Adult	8	Dead embryo	Gruenwald (1958)
Selenite	Adult	10	Growth ↓	Jensen and Chang (1976)
Selenite	One day	5	Growth ↓	Jensen (1986)

↑ – Increased; ↓ – Decreased; Na₂SeO₃ – Sodium selenite, SeO₂ – Selenium dioxide; ppm – parts per million.