Maintaining high fertility is critical for successful hatching egg production. Changes in diets can be used to improve fertility. Selenium is an essential nutrient and is important for reducing cell membrane damage. Selenium is found in different forms. Organic forms are found in plant and animal materials and are generally easier for animals to absorb. Research has shown that selenium is essential for male fertility (successful sperm). This trial looked at the effect of selenium supplementation on fertility.
After mating, sperm can be stored by the hen in specialized tubules in her oviduct for up to two weeks. Following ovulation (release of a yolk from the henï¿½s ovary), sperm are released from sperm storage tubules and travel to the fertilization site on the surface of the yolk. The sperm digest a small portion of the layer (perivitelline membrane) surrounding the yolk, creating a small hole that allows the sperm to enter and fertilize the egg. Although only one sperm is needed to fertilize an egg, the likelihood of getting fertile eggs increases when more sperm penetrate the yolk.
In most cases many sperm penetrate the membrane surrounding the yolk. The perivitelline sperm hole assay is used to assess female fertility by counting the number of holes made by sperm attempting to fertilize an egg. A high number of sperm holes indicate high female fertility.
Why do the study?
Maintaining fertility in older hens is important because as age increases, fertility and hatchability decrease. Older hens have less ability to effectively store sperm. Past research has looked at improving fertility by adding selenium to male diets, but little work has been done using selenium to improve female fertility and egg quality. Recent research at the University of Alberta examined the effects of increasing the normal amount of selenium in layer diets by adding additional organic or inorganic selenium. This should improve fertility in older laying hens by increasing the length of time sperm can be stored.
How was the study done?
Seventy-five Shaver 2000 White Leghorn hens, 61 wk of age, were randomly divided into three groups of 25 hens each. One group was fed a standard diet with selenium-supplementation from a normal premix. The next group was fed a diet enriched with an organic form of selenium (Sel-Plexï¿½). Finally, the third group of hens was fed a diet enriched with an inorganic form of selenium (Bonus). These diets were fed for 3 wk. The birds were then artificially inseminated with pooled semen from 22 Shaver 2000 White Leghorn males fed the standard diet. Eggs were collected on days 2 to 7 after insemination. A section of the yolk membrane was removed from each egg and stained. Sperm holes were counted using a microscope (figure 1). Eggs were also collected on the first and last day of the trial, and for three days in each week to determine if there were any changes to egg quality.
What did we find?
This experiment showed that selenium supplementation increased the average number of sperm holes in the yolk layer. As seen in the figure below, the Sel-Plex group (supplemented with organic selenium) had the highest average number of sperm holes.
This may be the result of selenium improving the environment of the sperm storage tubules in the henï¿½s oviduct, allowing sperm to live longer. Although past research indicated that selenium had an effect on egg quality this study found very little improvement.
The bottom line
1. Feeding diets enriched with selenium (especially organic forms), can improve fertility.
2. Selenium seems to play an important role in the maintenance of fertility in laying hens.
3. Selenium supplementation could extend the life of the flock at higher production levels.
It should be noted that this was a short-term study; a longer trial may show higher sperm hole numbers and a greater improvement in egg quality with selenium-supplementation.
D. D. Agate, E. E. O'Dea, and M.E. Rustad AFNS, University of Alberta
Alberta Government, Agricultural and Rural Development website