Genetics

Organic Selenium Enhances Boar Fertility

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: [email protected].

Marker-Assisted Selection Could Boost Sow Performance

The length of a sow's productive life (SPL) in a breeding herd is impacted by reproductive performance, locomotion and structural soundness.

SPL is usually defined as either the number of days that a sow remains in the breeding herd or the number of litters that a sow produces. Length of sow productive life or longevity is evaluated by removal, culling and replacement rates, percentage of gilts in the herd, average parity of females in inventory and average parity at removal.

Because reproductive traits carry low to moderate heritability, marker-assisted selection (MAS) may be an effective tool to reduce the culling rate of sows and improve SPL.

In this study, 119 single nucleotide polymorphisms (SNPs) from 95 genes were examined in a commercial sow population with recorded reproductive traits for six parities. SNPs are changes in a single, specific coding unit of the genetic code.

The SNPs association analyses revealed a number of potentially interesting genes associated with total number born, number born alive and with gestation length in several parities. These associated genes could be considered for marker-assisted selection to improve SPL in commercial sow herds.

According to the PigChamp 2007 benchmarking report (http://www.pigchamp.com/summary_archives.html) in the last 10 years, the average culling rate of breeding females was 49.7% and sow mortality rate averaged 9.2%. The two most prominent reasons for culling are reproductive problems and locomotion disorders. Both appear to affect a higher percentage of sows in early parities.

Reproductive traits are low to moderately heritable and have low repeatability across parities. Traditional phenotypic selection, based on reproduction records, is less effective. Marker-assisted selection (MAS) is one method to improve lowly heritable traits.

The identification of genetic markers significantly associated with high sow longevity would allow breeders to select gilts at early ages — prior to the entry of the herd — that would have the best opportunity for increased sow longevity. Genetic suppliers could use the markers to improve selection methods and possibly “fix” the important genes in the population.

The objective of this research was to identify genetic markers or SNPs associated with sow productive traits. A commercial herd involving 2,066 gilts supplied by Newsham Choice Genetics was included in the project.

Six reproductive traits were recorded: total number born (TNB), number born alive (NBA), stillborn number (SBN), mummy number (MN), gestation length (GL) and non-productive days (NPD). The study included six different parities that were comprised of gradually reduced numbers of sows. DNA was isolated and large-scale genotyping was performed.

Twenty-three genes showed significant associations with at least three reproductive traits. For Parity 1, six genes were significantly associated with both TNB and NBA, while four genes were highly significantly associated with SBN. Two genes were highly significantly associated with MN and NPD, respectively.

In later parities, the six genes had significant association with TNB and NBA. Four genes were significantly associated with GL in several parities.

Researchers also recognized four genes were simultaneously associated with reproductive performance, fatness and locomotion traits, implying that these genes have more than one genetic effect on sow longevity-related traits. The study verified that there are genes causing variation in sow productive life; therefore, the use of marker-assisted selection could improve sow longevity.

The National Pork Board, Newsham Genetics, Hatch funding and the State of Iowa and the College of Agriculture funded this research effort.

Researchers: Bin Fan, Suneel K. Onteru, Marja Nikkilä, Kenneth J. Stalder and Max F. Rothschild, Iowa State University. Contact Stalder by phone: (515)-294-4683 or e-mail: [email protected] or Rothschild by phone: (515)-294-6202 or e-mail: [email protected].

Frozen Boar Semen Use Shows Promise

The use of frozen boar semen technologies to preserve genetics, reduce risk when introducing new genetics into the breeding herd, allow international distribution of genetics and provide a reserve of semen to cover emergency needs has been a goal of the pork industry for many years.

A study conducted at the University of Illinois, in collaboration with the USDA and Purdue University, was designed to help establish the parameters for successful use of frozen boar semen. The fertility effects of 1, 2 or 4 billion thawed, motile boar sperm were studied using single or double inseminations in gilts.

Semen from six selected sires was collected and shipped by PIC to the USDA National Animal Germplasm Program laboratory at Fort Collins, CO, for freezing in ½ cc. straws. Frozen semen was shipped in liquid nitrogen tanks to the University of Illinois Swine Research Center for use in the fertility trials. The experiment was conducted in five replicates using terminal line PIC gilts.

At 180 days of age, prepubertal gilts were treated with PG600, followed by Matrix (Intervet, Inc.), to synchronize estrus. All gilts that expressed estrus following Matrix withdrawal were assigned to a treatment. Gilts were allotted to treatment with each boar represented across treatments.

Multiple straws of frozen boar semen were thawed into Minitube thawing extenders to create 80 cc. doses containing 1, 2 or 4 billion motile sperm/dose. Semen was used within one hour of thawing.

Estrous detection and real-time ultrasound were each performed at 12-hour intervals to determine onset of estrus and to verify fertility and time of ovulation. Gilts were inseminated once at 32 hours or twice at 24 and 32 hours after the onset of estrus using conventional artificial insemination (AI) catheters.

Data were collected for interval from AI to ovulation, pregnancy and number of fetuses at Day 24-35. The data were analyzed for the effect of dose, number of inseminations, replicate, boar, and interval from insemination to ovulation, where appropriate.

There was no effect of either dose or number of inseminations on pregnancy rate, number of healthy fetuses or embryo survival (Table 1). There was an effect of interval from insemination to ovulation on number of fetuses and embryo survival, but not on pregnancy rate.

Optimal insemination occurred within eight hours before ovulation. Boars significantly influenced number of fetuses and embryo survival, but not pregnancy rate.

Results suggest that limited numbers of thawed, frozen sperm can be used to establish acceptable pregnancy rates and litter sizes in gilts. There was little evidence that using double insemination at 24 and 32 hours after onset of estrus or using higher numbers of sperm was advantageous. This indicates that acceptable fertility can be achieved using a single insemination with 1-2 billion thawed, motile sperm. It was also evident that the boar impacted litter size and that selection for fertility and motility after freezing may be a necessary measure. Lastly, the interval from insemination to ovulation is an important limitation to fertility when using frozen boar sperm. Insemination within eight hours of ovulation has the greatest potential for fertility.

Researchers: K. Spencer, S. Breen, J. Taibl, B. Yantis and R. Knox, University of Illinois; P. Purdy, H. Blackburn, S. Spiller and C. Welsh, National Animal Germplasm Program, ARS, USDA, Fort Collins, CO; and T. Stewart, Purdue University. Contact Knox by phone (217) 244-5177) or e-mail: [email protected].

Table 1. Impact of Number of Thawed, Motile Frozen Boar Sperm and Number of Inseminations on Pregnancy Rate and Number of Fetuses at Day 30 of Gestation