ALLTECH 2002 CD: Practical applications for selenomethionine:
broiler breeder reproduction
Department of Poultry Science, North Carolina State University, Raleigh, NC, USA
Selenium: an essential trace element
Incorporation of essential trace elements into the diets of all animals is required for maintenance of health, growth and myriad biochemical-physiological functions (Scott et al., 1982). Among those essential trace elements is selenium (Se). Selenium was discovered in 1817 by J.J. Berzelius, in Stockholm, Sweden, but the biological significance of this element was not recognized until it was identified as the toxic agent associated with alkali disease, now called selenosis, in the Dakota and Wyoming territories in the United States in 1856 (Franke, 1934; Franke and Tully, 1936; Franke, et al., 1936).
Unfortunately, selenosis is induced in animals that eat plants grown on soils with extremely high concentrations of Se, and therefore, it was considered a dangerous element until 1957. In 1957, Schwarz and Foltz reported that Se was an essential trace nutrient, and nutritionists then initiated extensive studies to discover the metabolic function of this element and document the consequences of its deficiency in human and animal foodstuffs.
Selenium deficiency can manifest itself in many diseases and dysfunctions such as liver necrosis, muscular dystrophy, microangiopathy, exudative diathesis, pancreatic fibrosis,
poor feathering, retained placenta, mastitis, cystic ovaries, general unthriftiness, Keshan disease, Kashin-Beck disease, cancer, numerous heart diseases, immune deficiencies, reduced fecundity and many others and can affect humans and animals alike (Shamberger,
The discovery that glutathione peroxidase (GSHPx) contained an integral and stoichiometric quantity of Se demonstrated a biochemical role for this essential trace element and provided a tool for monitoring its status in all animals (Rotruck et al., 1973). Because of similarities between Se and sulfur, it has been a long-held belief that Se would follow the sulfur pathways in its metabolism. This concept was strengthened by the discovery that plants and bacteria metabolize Se to the organic selenomethionine and selenocysteine (Burnell and Whatley, 1977). Selenomethionine is readily utilized as a substrate by enzymes that use methionine, and selenomethio-nine may be more available than pure methionine (Markham et al., 1980).
However, the multiple roles played by Se in the maintenance of the homeostatic condition in animals are still being discovered (Arthur and Beckett, 1994). Clinical cases of Se deficiency are clearly recognized and are easily treated today. However, Se nutrition in both humans and food production animals appears to be less than optimal in many parts of the world (Rayman, 2000).
The functionality of natural organic selenium
It has been recognized for more than a quarter of a century that the selenoaminoacids, selenomethionine, selenocysteine and selenocystine, are the primary sources of naturally occurring Se in plant-based (Burk, 1976) and meat-based (Levander, 1986; Cai et al., 1995) feed ingredients. The selenoaminoacids are bound in protein, principally as selenomethionine and selenocysteine, and constitute 50 to 80% of the total Se in plants, grains (Butler and Peterson, 1967) and in Sel-PlexTM, the organic Se-enriched yeast (Kelly and Power, 1995).
Animals cannot synthesize selenomethionine, the primary selenoaminoacid, directly from selenite or selenate forms of inorganic Se (Cummins and Martin, 1967; Sunde, 1990). However, selenocysteine can be found in the body of animals fed inorganic Se such as
selenite and selenate. The presence of selenocysteine is due to synthesis of GSH-Px and other selenoproteins in which the selenocysteine is incorporated. The Se in selenocysteine is incorporated co-translationally using selenide and serine as precursors. The synthesis of selenocysteine involves a unique process in which selenide is phosphorylated under the influence of selenophosphate synthetase to selenophosphate.
The selenophosphate is made available to a unique seryl-tRNASEC that is recognized by selenocysteine synthetase. The selenocysteine synthetase converts seryl-tRNASEC to selenocysteyl-tRNASEC that allows insertion of selenocysteine into a peptide chain. The base triplet UGA that normally functions as a stop codon (Amberg et al., 1996) encodes this process of selenocysteine insertion at its appropriate site in the peptide. The selenocysteine insertion also requires a specific mRNA, an elongation factor, GTP, and the selenocysteine insertion sequence; and all of these factors interact at the ribosome to read the UGA selenocysteine codon (Low and Berry, 1996). This synthesis and conversion process is energetically expensive.
Selenomethionine is easily converted to selenocysteine via cystothionase (Esaki et al., 1981). Selenomethionine is readily converted to selenocysteine by poultry and other animals (Cummins and Martin, 1967; Esaki et al., 1981). This is a very important process
because selenocysteine can substitute for cysteine in proteins, and animals cannot synthesize cysteine de novo. Even though selenocysteine can be substituted for cysteine
in many structural proteins, it is not incorporated directly into specific selenoproteins (Sunde, 1990; Daniels, 1996).
In order for selenocysteine to be incorporated into specific selenoproteins, selenocysteine-®-lyase must react with free selenocysteine to release selenide in the presence of reducing agents (Sunde, 1990; Burk, 1991). Then, selenocysteyl-tRNA[Ser]SEC, which recognizes the specific UGA stop codons in the selenoprotein-mRNA, inserts the new, cotranslationally synthesized selenocysteine into the specific selenoprotein (Burk, 1991). Thus, organic Se must be converted from its original organic to the inorganic form then back to the organic form to fulfill its biological function (Arthur, 1997). This conversion is crucial with regard to synthesis of selenoproteins because it has been reported that 30 to 80% of the Se in the body may be selenocysteine (Hawks et al., 1985).
Selenomethionine is highly available and can substitute for methionine in the synthesis of all proteins (Daniels, 1996). If selenomethionine is substituted for methionine in a protein, such as GSHPx, there is no additional catalytic activity within the protein (Waschulewski and Sunde, 1988).
However, it has been demonstrated that the retention of selenomethionine in animal tissues is significantly longer than retention of Se derived from sodium selenite (Shan and Davis, 1994). Miller et al. (1972) compared the influence of sodium selenite, selenomethionine, fish meal, and fish solubles on Se retention in chickens. Selenium from fish products was only retained at 15% compare with 35% retention of Se from selenite and to a high of about 49% from selenomethionine. The availability of Se from fish meal can also be negatively affected by the method of preparation (Whitacre and Latshaw, 1982).
Cummins and Martin (1967) and Osman and Latshaw (1976) have demonstrated that Se derived from selenite was easily released from animal protein subjected to alkaline dialysis whereas Se from selenomethionine was retained as a part of the protein. Ort and Latshaw (1978) have shown that even when toxic levels of sodium selenite are fed to laying hens, egg levels and body tissue levels return to normal within two to four weeks after cessation of the feeding of toxic levels of sodium selenite. Selenium from selenite, therefore, only interacts loosely with the sulfur amino acids and Se in selenomethionine is a part of the protein. The stored form of organic Se is in a non-functional state, i.e. not used immediately for formation of biologically functional selenoproteins (Mahan, 1994; 1995).
Since this non-functional Se is better retained than inorganic Se, its conversion to selenide before conversion to selenocysteine and other selenoproteins, which are functional, appears to be more efficient. As a consequence of the large pool of stored Se
in protein, in times of oxidative stress, body protein can be degraded rapidly providing more than adequate concentrations of organic Se that can be used for synthesis of specific selenoproteins, such as Se-dependent GSH-Px enzymes. In cases where supplementation of selenomethionine is at a high level in feeds, it can be demonstrated that 40 to 50% of total body Se as selenomethionine can be found in muscle (Daniels, 1996). Selenocysteine is the pivotal amino acid in the synthesis of Se-dependent cytosolic glutathione peroxidase (Rotruck et al., 1973), but only about 30% of the body’s Se is incorporated into cytosolic glutathione peroxidase. About 70% of the body’s Se is incorporated into 30 to 100 other selenoproteins in mammals (Burk and Hill, 1993).
SELENIUM IS UNIQUE AMONG THE TRACE ELEMENTS
Mertz (1987) suggested that Se is unique among the essential trace elements especially in the manner in which its deficiency is expressed. In mammals, Mertz indicated that a Se deficiency was most likely to be manifest in the second generation of deficiency. However, rats experiencing Se deficiency, even though they showed no clinical signs of deficiency, die within a few weeks if they become deficient in vitamin E (Schwarz, 1951). If those rats that are in the first generation of Se deficiency are force-fed high levels of fats, they die within a few hours (Schwarz, 1954). These early observations by Schwarz and by Mertz point out the complexity of Se deficiency and that there is a great need to assure that humans and production animals alike always have an adequate dietary level of available Se.
The availability of organic Se from selenomethionine or inorganic Se from selenite or selenate, may be affected by numerous factors. Cantor and Johnson (1985) concluded that Se was made more available in diets that were low in protein, possibly as a result of increased feed intake, and decreased or constant protein intake resulted in increased egg production compared with pullets given increasing concentrations of dietary protein. The kind and quality of fish meal used in poultry diets also influenced the availability of Se for poultry (Miller et al., 1972, Whitacre and Latshaw, 1982). Thus, it is important to determine if there are factors that interfere with the bioavailability of Se either as sodium selenite that is passively absorbed by diffusion from the intestinal tract (McConnell and Cho, 1965) or selenomethionine that is actively absorbed over the methionine transport system (Spencer and Blau, 1962).
SELENOMETHIONINE MAY BE THE 21ST AMINO ACID
These observations have raised a question about whether selenomethionine, due to its essential nature in the synthesis of selenoproteins and its conversion to selenocysteine, may be the 21st amino acid. This issue will be resolved in the future, but the roles played by selenomethionine in all animals including poultry species must be clearly defined in order that it can be more effectively supplied in practical diets. One area of investigation that has been obscure is the role of Se, specifically selenomethionine, in the maintenance of reproductive status in poultry and other animals.
Selenium involvement in male fertility
In many animal species, Se will accumulate in high concentrations in endocrine glands (in decreasing order in chicken pituitary, pineal, adrenals, kidneys, pancreas, brain and ovary and testes (Vohra et al., 1973)) and reproductive organs in mammals (Allan et al., 1999; Behne et al., 1988). There is an unusually high concentration of Se in the testes and in spermatozoa. Similarly, Se accumulates in mammalian testes to a higher level than in other tissues (Behne et al., 1986; Hansen and Deguchi, 1996).
Since 1974, when Se was permitted by FDA to be used as a feed supplement in the US, it has been clearly demonstrated that this trace element is essential for male fertility (Hansen and Deguchi, 1996). Behne et al. (1982) has also shown that in conditions of Se deficiency, rat testes will preferentially retain Se. A deficiency in dietary Se can result in decreased numbers of normal spermatozoa per ejaculate, decreased motility and decreased fertilizing capacity. These phenomena have been demonstrated in rodents, humans and poultry such as chickens, turkeys and ducks (Surai, 2000; Surai et al., 1998a,b; Surai et al., 2001).
When semen samples were analyzed microscopically, it became evident that primary spermatozoal abnormalities were associated with spermatozoal head morphology and in the integrity of the midpiece that contains the mitochondria that function in the provision of energy that allows for sperm swimming and motility (Surai, 2000; Surai et al., 1998a,b; Surai et al., 2001). A spermatozoon that has an abnormal midpiece or head deformity is rendered permanently incapable of ovum fertilization (Froman et al., 1999; Sikka, 1996).
CELLULAR BASIS FOR SELENIUM INVOLVEMENT IN SPERMATOZOAL FUNCTION
Mammalian spermatozoa contain on a cellular basis some of the highest concentrations of Se found in the body. Sperm mitochondria-associated cysteine rich protein (SMCP), previously described as mitochondrial capsule selenoprotein (MCS) and mitochondrial capsule protein (MCP), is a major structural element of the mitochondria in the midpiece of the spermatozoon tail (Kleene, 1994; Ursini et al., 1999; Lenzi et al., 2000). The SMCP has a high concentration of Se contained in phospholipid hydroperoxide glutathione peroxidase (PH-GSH-Px) (Ursini et al., 1999; Lenzi et al., 2000), which makes up approximately 50% of the SMCP and acts as a structural protein and embeds the mitochondrial helix in the mature spermatozoon.
However, in the testis, the PH-GSH-Px acts as a powerful antioxidant in the developing spermatids and spermatozoa (Ursini et al., 1999; Lenzi et al., 2000). The dual role played by PH-GSH-Px in maturation and in the mature spermatozoon partially explains the mechanical instability of the mitochondrial midpiece of spermatozoa from Se-deficient animals.
ANTIOXIDANT ROLE OF SELENIUM IN THE MALE REPRODUCTIVE
Surai (2000) recently discussed the antioxidant system in avian testes and semen and established that the concentration of Se found in seminal plasma and spermatozoa is finely regulated, and if those concentrations are elevated or decreased, the function of the spermatozoon will be negatively affected. Most of the Se in spermatozoa is contained in SMCP as PH-GSH-Px, but a substantial portion of the Se is in GSH-Px and some other Se-containing proteins in the mitochondria and in seminal plasma. It appears that because of the high rate of metabolism in spermatozoa, a significant production of reactive oxygen metabolites (ROM) can occur; and these along with lipid peroxides must be reduced to prevent damage to spermatozoa (Lenzi et al., 2000; Surai, 2000; Surai et al., 2001; Surai et al., 1998a,b). This partially explains the need for high
levels of Se found in spermatozoa and seminal plasma.
The spermatozoa are subject to the damaging effects of high concentrations of polyunsaturated fatty acids that can be readily oxidized to peroxides in the aerobic environment of the testis, semen and in the uterovaginal sperm host glands in hens (Lenzi et al., 2000; Surai, 2000; Surai et al., 2001; Surai et al., 1998a,b). A balance between pro-oxidants and antioxidants must be established in tissues and body fluids with high metabolic rate to ensure the survival and function of cells in those aerobic environments. Oxidative stress, caused by peroxidation of polyunsaturated fatty acids in these tissues and fluids, can lead to irreparable damage in the spermatozoon cell membranes and render it incapable of ovum fertilization, the only function of the sperm cell.
Sies (1993) indicated that the physiological and pharmacological strategies for antioxidant defense are organized into the categories of prevention, interception and repair. In the context of antioxidant defense, Se and the glutathione system act primarily at the level of interception; and this leads to transfer of the pro-oxidant away from sensitive compartments in cells. Thus, if the pro-oxidant/antioxidant balance shifts toward the pro-oxidant condition in the testis, semen, or in the hen’s uterovaginal or infundibular sperm host glands, the function of spermatozoa will be rapidly degraded leading to infertility for the male.
HISTORICAL EVIDENCE THAT SELENIUM DEFICIENCY ALTERS
Experimental evidence indicates that spermatozoal morphology is severely altered in mammals (and now in poultry) that have been fed Se-deficient diets. In this case, the primary abnormality was shown to be a bent midpiece in which the spermatozoa swim with the acrosome pointed backwards, thereby essentially reducing the fertilizing capacity of the sperm cell to nearly 0%. In poultry, there has been little evidence presented to show that Se deficiency has affected fertilizing capacity of spermatozoa.
However, between 1968 and 1970, there were some studies conducted at Virginia Polytechnic Institute and State University (Edens, 1970) that provided evidence that dietary Se deficiency, which was manifest in breeder diets before 1974, did indeed cause a problem in breeder males. We were using White Plymouth Rock breeders that had been selected divergently for high or low body weight.
By today’s standards, both lines were experiencing reproductive problems, but the problems in the High Weight Line (HWL) were more severe than in the Low Weight Line (LWL) (Table 1). The data indicated that fertility was poorest in the HWL × HWL cross and the best fertility was in the LWL × LWL cross. Crossing HWL males with LWL females resulted in improved male fertility, but crossing LWL males with HWL females depressed male fertility. Thus, it was ascertained that genetic factors in both males and females could adversely affect fertility.
However, the focus of the work was on males. Continued study showed that the spermatozoa from HWL males had a reduced metabolism as indicated by lower oxygen utilization in at least two semen extender diluents with and without fructose, a major substrate for avian spermatozoal metabolism. Further examination of the semen was done by utilizing an eosin-nigrosin vital staining technique to determine live vs. dead spermatozoa and to characterize live spermatozoa according to morphological characteristics (Table 2).
These data indicated that the HWL males had greater numbers of abnormal spermatozoa,
especially in association with the midpiece and head, than did the LWL males. It is important to keep in mind that there was no supplemental Se given to those males. Any Se they had available had to come from feed grains, meat and bone meal and from fish meal. Those Se sources were most certainly providing some forms of organic Se, but all organic Se is not available, especially from meat and bone meal and from fish meal. If feed grains were grown in regions with low soil Se levels, those grains, the primary source of selenomethionine, selenocysteine, and selenocystine, would also be low in Se content rendering the birds to a state of Se deficiency.
EXPERIMENTAL EVIDENCE THAT SELENIUM DEFICIENCY ALTERS
SPERM MORPHOLOGY IN BROILER BREEDER MALES
Recently, a study was conducted to ascertain the influence of sodium selenite and selenomethionine (Sel-PlexTM) on the sexual development of young roosters. The males were reared to 14 weeks of age on a diet supplemented at 0.2 ppm Se with sodium selenite. The background level of Se in the male breeder diets was chemically determined to be 0.28 ppm. At 14 weeks of age, males were placed into individual cages. There were 10 in a group that continued to receive selenite Se (supplemented at 0.2 ppm; total Se was 0.48 ppm); 10 were given selenomethionine (supplemented at 0.2 ppm; total Se was 0.48 ppm); 10 were given only the basal diet with no supplemental Se (total Se was 0.28 ppm). The results from this trial are presented in Table 3.
Both selenite- and selenomethionine-fed males began to produce semen at 19 weeks of age, which was very early, but it was not until 26 weeks of age that the basalfed males produced semen. Additionally, it was evident that basal-fed males had delayed sexual maturation based upon development of secondary sex characteristics (comb and wattles), testicular size at 26 weeks of age, and delayed onset of crowing. The signs of secondary sexual development in the Se-supplemented roosters were an indication that hormonal development was advanced at an early age.
Behne et al. (1987) observed that testicular Se content is regulated by follicle stimulating hormone (FSH), which is also responsible for spermatogenesis in the seminiferous tubules of the testis. Burk (1978) found aspermatogenesis in first generation rats given a Se deficient diet, and Sprinker et al. (1971) reported consistent testicular atrophy and aspermatogenesis in second generation Se-deficient rats. Additionally, leutinizing hormone (LH) regulates the Leydig cells that produce testosterone in the testes, and when LH was given to Se-deficient rats, serum testosterone levels increased at a slower rate as compared with controls. Behne et al. (1987) concluded that Se deficiency affected Leydig cells and suggested a biological function of Se in the steroidogenic cells of the testes. Therefore, the advanced development of secondary sex characteristics in Sesupplemented roosters was normal while delayed development in basal-fed roosters was a sign of Se deficiency that impaired testosterone secretion.
However, these observations are contrasted with the conclusions of Combs and Combs (1986), who stated that there is no evidence that Se deficiency influences male reproduction in poultry. Data from the investigation reported herein clearly indicate that there is a Se influence on reproductive potential in roosters. We also performed the eosin-nigrosin staining technique on samples from these males (Table 4). When we examined the data for basal-fed males, we found a situation that was much like the condition found in the HWL and LWL males examined more than 30 years ago. Roosters fed diets that had no supplemental Se had significantly more abnormal spermatozoa, especially head and midpiece abnormalities, than those fed selenite or organic Se as selenomethionine. Additionally, it was evident that roosters fed the Se-deficient diet had smaller ejaculate volumes and decreased spermatozoa concentrations than those given Se supplements.
However, it was a surprising observation to find that selenite-fed males had more abnormal sperm cells in their semen than did those fed selenomethionine. Spermatozoal abnormalities, especially in the midpiece of the tail of sperm, found in association with Se
deficiency have been recognized for many years (Wu et al., 1979). The midpiece
abnormality was associated with a deficiency in the Se-rich SMCP that provides structural integrity to the midpiece (Kleene, 1994; Ursini et al., 1999). Therefore, one must extend the observations made in mammalian models and conclude that the midpiece of avian spermatozoa also contains SMCP or SMCP-like protein that is compromised by Se deficiency leading to increased numbers of bent spermatozoa and other abnormalities that were related to the midpiece (Figure 1). Again, it was surprising that there were more spermatozoal midpiece abnormalities associated with selenitesupplemented roosters than with the selenomethionine supplemented roosters (Table 4).
We have also examined histologically the testes from the roosters involved in this investigation. Our results have shown that testes in males given no supplemental Se were not committed to spermatozoal formation in the same time frame as were those given selenomethionine (Figure 2). In testes from Se-deficient roosters, there were fewer Sertoli cells and hierarchies of spermatogonia that were committed to spermatid formation as compared with those fed selenomethionine. Leydig cell formations also appeared to be less developed in the basal-fed birds. These observations conform with those made in Se-deficient mammalian models (Burk, 1978; Behne et al., 1987). This partially explained the delayed development of sexual maturity in the basal-fed birds.
Extension of laboratory studies to realtime field application of Selenomethionine
to broiler breeder reproduction
MALE REPRODUCTIVE PERFORMANCE
Two breeder flocks (Hubbard Ultra-Yield) are currently being examined for semen quality based upon sperm quality index and vital staining of semen smears. Early results from this investigation are shown in Table 5. The Sperm Quality Index (SQI) was determined with the Alpharma instrument and was used on fresh semen in the breeder houses. The SQI is an index of spermatozoon numbers and motility. In two separate measurements separated by a period of eight weeks, the SQI was greater for the selenomethionine-fed roosters and suggested greater motility and sperm numbers compared with the selenite-fed males. This observation was not unexpected, but when the vital staining of semen smears was evaluated, it was apparent that there were more normal spermatozoa and fewer abnormal forms in the selenomethionine-fed males.
An interesting observation focused on the normal decline in numbers of normal spermatozoa with aging in the roosters. Selenite-fed roosters had a greater decline in normal numbers than did selenomethioninefed roosters. These larger declines in normal spermatozoa from roosters fed sodium selenite may indicate that the antioxidant properties associated with selenite Se may not be sufficient to sustain the integrity of spermatozoa in the aging rooster testis, but with improved retention of Se in those given selenomethionine, there might be induction of more Se dependent PH-GSH-Px and GSH-Px in the testis, in SMCP and in seminal plasma. This hypothesized condition would then create an improved antioxidant environment that would promote spermatozoal integrity.
At this point, it is apparent that Se does indeed play a major role in the fertility of the avian male. Our results do not differ from earlier mammalian and avian studies. There is relatively little historical information to show the influence of Se deficiency in heavy breeder chicken males. However, our data extend the early work with selenite; and this work shows that organic Se found in selenomethionine may be superior to selenite in terms of maximizing rooster spermatozoal fertilizing potential.
Selenomethionine involvement in female broiler breeder fertility
In 1974 several scientific articles were published that emphasized the fact that Se was vital for production and hatchability of chicken eggs. Latshaw and Osman (1974) and Cantor and Scott (1974) demonstrated that as little as 0.1 ppm Se from sodium selenite prevented early egg production decreases (12 weeks after initiation of egg production) that were common in times before 1974. Latshaw and Osman (1974) reported that Se supplementation to the diets of layers improved egg production significantly as compared with layers given a low Se diet, but vitamin E only partially corrected the depressed egg production. Egg production was 54 to 58% in Se-deficient hens, while it was raised to 75 to 80% in Se-supplemented hens. Arnold et al. (1974) reported that sodium selenite supplementation increased numbers of fertile eggs but did not improve hatch of fertile eggs.
Arnold et al. (1974) also indicated that mortality of laying hens decreased with Se supplementation. Cantor and Scott (1974) reported that Se supplementation significantly raised hatchability of fertile eggs. Latshaw and Osman (1974) also demonstrated that hatchability was a very sensitive indicator of Se deficiency. Hatchability was elevated from 18% in Se-deficient hen eggs to over 88% with Se supplementation. A significant problem leading to decreased hatchability of eggs from Sedeficient hens was the extremely high rate of early dead embryos (less than 5 days of incubation), but Se supplementation corrected completely the high rates of early chicken embryonic mortality.
Additionally, the infertility level of eggs from Sedeficient hens (21.4%) was almost 5-fold greater than the infertility in Se-supplemented hens (4.4%). The performance and reproductive potential of laying hens was improved with low levels of Se supplementation (0.1 ppm). Cantor and Scott (1974) extended the work of Latshaw and Osman (1974) by incorporating selenomethionine into their experimental diets and demonstrated that sodium selenite and selenomethionine at 0.1 ppm Se improved performance of laying hens as compared with Se deficient controls; and selenomethionine decreased the incidence of exudative diathesis in growing chicks. Today, breeder hens in the US are provided Se, primarily as sodium selenite, in doses that range from 0.1 to 0.3 ppm Se, the legal limit set by the FDA. The allowable level of organic Se as selenomethionine is also set at a maximum of 0.3 ppm for poultry.
Vitamin E supplementation to Se-deficient hens only raised hatch of fertile eggs to 58%, partially alleviating infertility, but did improve the early dead embryo problem (Latshaw and Osman, 1974). Thus, it appears that part of the early dead embryo problem can be related to a pro-oxidant condition created in the incubating egg and embryo. This condition can be improved by the use of selenomethionine in breeder diets, which leads to greater chick embryo survival and increased rates of hatch of fertile eggs.
Based upon information derived from studies performed immediately before and after Se was approved for use in poultry diets in 1974, it becomes apparent that Se is essential in the reproductive processes of both layer and breeder chicken hens. However, the approval by the FDA of selenomethionine for use in poultry diets has renewed interest in selenomethionine as a safer Se source for poultry. Therefore, it was important to revisit the use of different Se sources in breeder hens and ascertain the influence of each source on the performance of those breeder hens.
However, the use of Se to enhance avian female performance was not without controversy. Cantor and Scott (1974) observed improved egg production and a trend toward improved fertility (not significant) when selenomethionine was provided to laying hens on a low Se-low vitamin E diet, but there was no consistent improvement in hatch of fertile eggs. Cregar et al. (1960) did not show an influence of Se on hatchability of eggs from turkey hens fed a low Se torula yeast diet. Cantor et al. (1978) demonstrated that Se did improve reproductive performance as indicated by improved hatchability of fertile eggs from turkey hens, but Se did not influence egg production rate or level of fertility.
Japanese quail respond to low Se, low vitamin E diets differently from chickens and turkeys. Selenium and vitamin E were equipotent in maintaining hatchability of the quail eggs (Jensen, 1968), but quail chicks from hens on a low Se diet had a high incidence of leg paralysis and degeneration of both smooth muscle in the ventriculus and in skeletal muscle in legs. These observations show that Se-deficient Japanese quail dams produce chicks that are not healthy, suffer and die from Se deficiency-related maladies similar to observations in mammalian species made earlier by Schwarz (1951; 1954) and Mertz (1987).
In the broiler breeder trials currently underway, the females were given supplemental sodium selenite or selenomethionine at the level of 0.3 ppm Se when they were placed at 21 weeks of age. At 11 weeks of production, selenomethionine-fed hens exhibited improved egg production, fertility, daily numbers of settable eggs and hatchability (Table 6). Egg production in selenomethionine-fed hens lagged behind the selenite-fed hens for about five weeks into the production period, but improved from then on. Improvement in daily settable eggs began around six weeks into production and persists to the current time in the selenomethionine-fed hens.
These preliminary data suggest that selenomethionine improves the performance of heavy breeder hens. In each category of performance, selenomethionine supplementation improved factors such as egg production, fertility, hatchability and daily settable eggs. Overall, there has been an improvement in chicks per hen capitalized on each of the two farms. On farm 1, the improved chick production is four chicks per hen and on farm 2 the number is 1.2 chicks per hen in favor of those fed selenomethionine. Hatch of fertile eggs over the life of the flock was improved by selenomethionine by 2.3% on farm 1 and 0.8% on farm 2. These data are comparable with those from UK commercial studies using Ross breeders fed selenomethionine in combination with sodium selenite.
In broiler chickens, we have determined that selenomethionine has the capacity to improve feathering in some commercial lines. Therefore, we attempted to determine if selenomethionine supplementation to broiler breeders had any influence on feather integrity and on re-growth of feathers on the saddle and back of breeder hens. Subjective observations indicated that selenomethionine-fed breeders were experiencing a faster re-growth of feathers in hens that had been in production for approximately 20 weeks. This work will be finished soon, and there will be another assessment of the feather condition in those hens given either selenite or selenomethionine.
It can be concluded that studies in field settings suggest that the use of organic Se as selenomethionine improves reproductive potential of broiler breeders. While the data are still sparse, they do show that both male and female broiler breeders benefit from the supplementation of natural organic Se in their diets. In males, semen production and quality are improved. This may be associated with earlier development of secondary sexual characteristics as well as hormonal development in the earlier maturing males. Furthermore, the improved structural integrity of the spermatozoon may be due to both improved antioxidant status in the seminal plasma and the sperm cells and also due to improved content of the modified Sedependent PH-GSH-Px in the spermatozoon capsular membrane. In the females, there was improved egg production, fertility, hatchability, settable eggs and chicks per hen capitalized. Improved fecundity of the female may also be related to improved antioxidant status due to the presence of organic Se in their diets. Additionally, re-growth of feathers on the saddle and back regions of female breeders is apparently stimulated by selenomethionine.
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