The resounding acceptance of artificial insemination (AI) by commercial pork producers necessitates the need to manage boars for maximum fertility and semen production.

Several research groups have investigated the effects of supplemental selenium on reproductive characteristics of boars, and there is strong evidence to support the inclusion of this mineral in the daily ration.

Researchers at Ohio State University reported improvements in sperm production, sperm morphology and fertility for boars fed diets supplemented with the traditional, inorganic source of selenium (sodium selenite) at levels of 0.5 ppm. Because of environmental concerns, however, the Food and Drug Administration (FDA) allows a maximum of 0.3 ppm supplemental selenium in swine diets.

It has been suggested that selenium from sodium selenite may not be as biologically effective as the selenium indigenous in grains, which is incorporated in an organic form called selenomethionine. Sel-Plex (Alltech, Inc.) is an organic source of selenium that consists primarily of selenomethionine.

A working hypothesis is that because of greater bioavailability, an organic selenium source may be superior to an inorganic source when supplemented at the 0.3 ppm level in an effort to improve boar semen quality and fertility.

The objective of this study was to evaluate the in-vitro fertilizing capability of sperm cells from boars fed selenium from either organic or inorganic sources.

From weaning through the completion of the experiment, Yorkshire × Landrace boars were fed the following diets:

• Basal diets that met or exceeded the nutrient recommendations for boars (NRC, 1998) with the exception of selenium;

• Basal diets supplemented with 0.3 ppm selenium from an organic source (Sel-Plex), or

• Basal diets supplemented with 0.3 ppm selenium from an inorganic source (sodium selenite).

At sexual maturity, boars were trained to mount an artificial sow for semen collection. Ejaculates were collected and semen was diluted and stored at 65°F (18°C) in Androhep-Lite (3 billion sperm cells in 85 mL of semen and extender). Using in-vitro fertilization (IVF) procedures, sperm fertilizing capability was determined on Days 2 and 8, post collection (Day 1 = day of semen collection).

Fertilization rates were significantly greater for the Day 2 post-collection semen from boars fed the diet supplemented with organic selenium (Figure 1). Moreover, on Day 8 post-semen collection, fertilization rates tended to be greater for boars fed a diet supplemented with Sel-Plex compared with boars fed the control diet or the diet supplemented with sodium selenite.

Therefore, the use of an organic source of selenium in boar diets may result in greater conception and farrowing rates in swine operations employing AI. While the cost/benefit relationship of this research has not been addressed, it is assumed that a technology that increases conception and farrowing rates would enhance reproductive efficiency in the breeding herd, and thus increase profitability.

Additionally, research has shown that swine fed diets supplemented with organic selenium excrete less selenium into the environment than swine fed diets supplemented with inorganic selenium.

Researchers: Mark J. Estienne, Susan M. Speight, James W. Knight and Allen F. Harper, Virginia Tech, Blacksburg, VA. Contact Estienne via e-mail at: mestienn@exchange.vt.edu.