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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].

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 ( 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].

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].

Crop Residues + Swine Manure Enhance Methane Generation

Co-digesting swine manure with crop residues shows great promise in boosting methane generation in anaerobic digesters.

The problem with using swine manure only for anaerobic digestion is its low carbon/nitrogen (C:N) ratio (6:1 to 8:1, normal range), while good digestion re-quires a C:N ratio between 16:1 and 25:1.

University of Minnesota agricultural engineer Jun Zhu says the use of crop residues can be an effective way to enhance methane production, and at the same time reduce the volume of crop residue materials for disposal.

In his research, the addition of the crop residues at all C:N ratios increased the total daily gas volume produced (Figure 1). Wheat straw didn't achieve the same increase in gas production compared to corn stalks and oat straw during the first two weeks of production, but surpassed corn stalks later for the C:N ratio of 25.

Corn stalks and oat straw performed equally well in increasing gas production when compared to the control group (Figure 1).

When the C:N ratio was increased from 16:1 to 20:1, there was a clear increase in gas volume produced for all of the materials tested (Figure 1). However, continuing to increase the C:N ratio to 25:1 didn't produce the same increase in gas production seen in the increase in the C:N ratio to 20:1.

Figure 2 shows the methane (CH4) content in the gas from reactors using different crop residues and C:N ratios. Not much difference was observed in methane production between wheat straw and the control. However, the difference was quite significant for the other two crop products tested. Oat straw showed quick success, achieving a 44.4% digestion rate on Day 1 for a C:N ratio of 20:1, and a 58.8% digestion rate and C:N ratio of 16:1 by Day 3.

Corn stalks also reached 45% methane content on Day 5 for C:N ratios of 16:1 and 20:1.

The increase in C:N ratio doesn't seem to correlate with an increase in methane production for wheat straw treatment as compared to the control when the digester enters into a steady state.

But methane content mushrooms for both oat straw and corn stalks during the same period at a C:N ratio of 20:1 with 57% for oat straw, 68.2% for corn stalks and just 46.5% methane digestion rate for wheat straw.

“Since the quantity of pure methane is a product of total gas volume and the methane concentration in the off-gas, the higher the methane content and gas volume, the more methane is produced,” Zhu explains.

“Therefore, it appears that oat straw and corn stalks perform better than wheat straw when co-digested with swine manure, from the perspective of pure methane productivity,” he concludes.

Researcher: Jun Zhu, University of Minnesota Southern Research and Outreach Center at Waseca. Contact Zhu by phone (507) 837-5625, fax (507) 835-3622 or e-mail [email protected].

Gas-Phase Biofilters Reduce Odor, Emissions

Alternative media are being tested for use in gas-phase biofilters in an effort to minimize pressure drop, lower operating costs and reduce the biofilter footprint. Improved biofilters will also be more resistant to rodents and extend the useful life through reduced maintenance costs.

Gas-phase biofilters are a proven method for reducing odor and other gaseous emissions from swine facilities. However, widespread adoption of biofiltration has stalled due to four issues:

  • The relatively large footprint needed to manage the media pressure drop;

  • The concerns about the biofilter media harboring rats;

  • The potential problem of long-term biofilter media compaction; and

  • The concerns about potential nitrate leaching from the biofilter media into the soil.

This project at the University of Minnesota, funded by Pork Checkoff, was designed to identify and evaluate alternative biofilter media that would solve some of these issues.

Six media were evaluated in Phase 1: bag mulch, lava rock, cedar chips, pine bark nuggets, western pine bark and wood shreds. Media sieve analysis (filtration process), porosity and unit pressure drop vs. unit airflow relations were determined.

Phase 1 testing was conducted in a biofilter media testing unit with six columns, including individually controlled airflow rates and moisture control (pictured above).

Phase 1 testing involved the air-cleaning performance and pressure drop characteristics of each media evaluated on the basis of hydrogen sulfide (H2S), and ammonia (NH3) removal.

In Phase 2, three media — wood shreds, pine bark nuggets and lava rock — were placed in similar columns and evaluated for pressure drop and reductions of H2S and NH3.

In Phase 3, pine bark nuggets were used in all six columns and H2S, NH3 and odor removal were analyzed.

Overall, pine bark nuggets and lava rock scored the highest by recording the lowest unit pressure drops vs. unit airflow rates.

Results from Phase 1 indicate that all six media supported microbial growth if seeded, and were effective, reducing H2S concentrations between 21-75% and NH3 concentrations between 43-80%.

All three media in Phase 2 performed well in the study.

Some biofilter media in Phase 3 had lower percent H2S, NH3 and odor removal than others.

Researcher: Kevin A. Janni, University of Minnesota. Contact Janni by phone (612) 625-3108, fax (612) 624-3005 or e-mail [email protected].

Electrostatic Collection System Reduces Barn Dust

Test results in a hog finishing barn demonstrate that the Electrostatic Space Discharge System (ESDS) maintained a significant level of dust reduction compared to the control group.

The ESDS reduced 63% of total particle sizes (expressed as “total spatial particulates” or TSP) of dust and 47% of smaller particles less than 10 microns in size (PM-10). The 10-micron and smaller dust particles are the size inhaled by workers in hog barns.

Dust is a mixture of very small particles and liquid droplets that can cause or worsen health conditions in people and pigs. The PM-10 and smaller particles are of most concern because they can settle in the bronchia and lungs.

The ESDS reduces dust by negatively charging particles and causing them to attach to walls and equipment in the barn. This reduces the dust concentration in the room air as well as the air exhausted through the ventilation fans.

The ESDS has been shown to reduce dust levels in poultry buildings with great success — but little is known about the advantages in swine confinement facilities, the main goal of this research project.

To evaluate ESDS, a 1,000-head, two-room finishing barn was tested. Each room contained 24 pens, 12 per side. One room was equipped with an ESDS unit and the other served as a control.

The ventilation in each room included four pit fans and six wall fans. The ventilation controller was set to run through six stages. Fresh air entered the room through quad ceiling inlets for stages 1-3, and entered through wall inlets near the ceiling during stages 4-6.

Ventilation air flow ranged from 8 to 22% less than fan manufacturers' published data, probably due to the dirtiness of the fans.

The ESDS consists of an electrical multiple wire design, which maximizes the ions created by the 30,000 volts in the ESDS.

Air samples in each room were collected using MiniVol portable air samplers suspended 6 ft. above the slotted floor. The system samples air at 1.3 gal./minute, collecting in three different particulate categories: total spatial particulates (TSP), particles less than 10 microns (PM-10) and particles under 2.5 microns (PM-2.5). Particle size separation is achieved through impaction and collection on 2-in. filters.

Dust samples were collected over 24-hour periods. The collection process was repeated three times at about six-week intervals: first for 29- to 48-lb. pigs, then for 150- to 169-lb. pigs and finally for 240- to 260-lb. pigs. Each filter was weighed before and after sampling to get the mass of the dust particles on the filter.

In all three dust removal particle size test groups shown in Figure 1, Figure 2, Figure 3, the ESDS room reflected a significant advantage in total dust removal over the control room.

The greatest amount of TSP removal occurred in all three finisher weight groups (Figure 3).

Also, the first group of finishing pigs weighing 29-48 lb. showed a greater percentage reduction of dust particles.

Concentrations of dust removed were less in general for the middle weight group (150-169 lb.) because outside temperatures were warmer, increasing fan operation and decreasing dust concentration because of greater air exchange.

The application of the ESDS technology needs further study to determine the impact on other hog barn issues, such as odor, pathogens and gases, researchers note.

Dust will continue to be an issue in swine barns. Efficient and effective ways of removal will be key to maintaining a healthy working environment for the workers and for swine.

Researchers: R.E. Nicolai and B.J. Hofer, both of South Dakota State University. Contact Nicolai by phone (605) 688-5663, fax (605) 688-6764 or e-mail [email protected].

Waterer Bowl Location In Nursery Pens Tested

Pigs' preference for the location of drinker bowls was tested in a commercial nursery barn near Jefferson City, MO. Twenty-five, 7-week-old crossbred gilts were allocated to one of nine pens, configured with three treatment options:

Treatment 1 had one water bowl located on the same side of the pen as the feeder, close to the back wall (F).

Treatment 2 pens were equipped with two water bowl drinkers. One bowl was positioned as F (above), and the second was located across from the feeder along the back wall (O).

Treatment 3 had three water bowl drinkers/pen. Two were positioned as F and O, and the third bowl was located across from the feeder, but next to the alleyway (A).

Pigs preferred the drinker along the back wall (O), when given three choices (Figure 1). But when offered two water bowl drinker locations, they did not show a preference (F vs. O).

The least preferred location for a water bowl was next to the alleyway (A).

The number and length of aggressive interactions around the water bowl drinkers did not differ among treatment groups (Figure 2).

Researchers: C.J. Jackson, A.K. Johnson, L.J. Sadler, K.J. Stalder and L.A. Karriker, DVM, Iowa State University; R.E. Edler and J.T. Holck, Boehringer Ingelheim Vetmedica, Inc.; and P.R. DuBois, DVM, Cargill Pork. Contact Johnson by phone (515) 294-2098, fax (515) 294-4471 or e-mail [email protected].

Alternate Tail Docking Procedure Cuts Stress

The use of the cautery iron rather than the conventional blunt trauma cutting method of tail docking can reduce the elevated stress response seen in newborn piglets without the use of analgesics or anesthetics.

Tail docking is routinely performed on piglets to prevent tail biting behavior.

Because analgesics and anesthetics are not routinely used to relieve the pain associated with tail docking on commercial hog farms, research was conducted to compare the stress response to tail docking using two methods: cautery iron (CAUT) and the more commonly used blunt trauma cutters (BT).

Six-day-old piglets' tails were docked using CAUT, BT or sham tail docked, where pigs were handled as if docking tails, but leaving their tails intact (CON). Blood samples were taken prior to tail docking and at 30, 60 and 90 minutes after tail docking to evaluate the effect of the procedure on cortisol concentrations, commonly used to assess stress levels (Figure 1, page 24). Piglet behavior was also recorded in the farrowing crate using one-minute scan samples via live observations for 60 minutes prior to and 90 minutes after tail docking.

Sixty minutes after tail docking, pigs tail docked using CAUT and CON had similar cortisol levels. Therefore, tail docking using cautery may reduce the acute stress response to tail docking.

Piglets tail docked using CAUT and BT spent more time posterior-scooting compared with CON piglets between 0 and 15 and 31 and 45 minutes after tail docking (Fiqure 2).

Elevated blood cortisol can be reduced with cautery iron rather than the BT method of tail docking. Although the tail docking-induced rise in cortisol was prevented by using CAUT, the behavioral responses to BT and CAUT docking methods were similar.

Researchers: M.A. Sutherland, P.J. Bryer, N. Krebs and J.J. McGlone, all of Texas Tech University. Contact Sutherland by phone (806) 742-2805 (ext. 253), fax (806) 742-4003 or e-mail [email protected].

Transport Space Allowances Studied for Weaned Pigs

Because the optimum space allowance required for weaned pigs during transport is unknown, Texas Tech University scientists sought to establish a first estimate of their space requirements based on measures of animal well-being.

A commercial livestock trailer was divided into compartments fitted for 100, 11.5-to-22-lb., weaned pigs at a space allowance of 0.5, 0.6 and 0.7 sq. ft./pig. Instruments recorded environmental conditions. Digital scans recorded the frequency of standing or lying behaviors of pigs every minute during the trip.

Prior to transport, blood samples were taken from four pigs per compartment for physiology and immune measures, and weight and lesion scores were recorded.

Pigs were then transported two hours to the wean-to-finish site using the same route for each of the four replications during winter.

At the finishing site, blood samples were again taken from the same experimental pigs.

Space allowance influenced the behavior of weaned pigs in the last 15 minutes of transport (Figure 1). Pigs transported at 0.6 sq. ft./pig spent less time standing than pigs transported at 0.5 and 0.7 sq. ft./pig.

Reduced standing behavior in pigs transported at 0.6 sq. ft./pig suggests that these pigs may have been in a more “relaxed” state during the last 15 minutes of transport, or became habituated to transport conditions sooner than pigs transported at 0.5 or 0.7 sq. ft./pig.

Researchers contend pigs appear to spend the majority of their time during transport active. However, pigs transported at 0.6 sq. ft./pig appear to spend more of their time resting than the other two treatment groups.

Cortisol concentrations and the neutrophil-to-lymphocyte ratio both increased during transport regardless of space allowance, trailer deck or gender (Table 1).

Increased cortisol concentrations and neutrophil-to-lymphocyte ratio in transported weaned pigs suggests these pigs experience stress, but the stress was not impacted by the space allowances tested.

Albumin concentrations were increased after transport, suggesting that these pigs were slightly dehydrated. Increased concentrations of create kinase and aspartate aminotransferase after transport suggest that these pigs were somewhat fatigued as a result of the two-hour transport. However, there was no effect of space allowance on any of these measures (Table 1).

No pigs died or were injured during the transport study. Body weight loss during transport did not differ among space allowances tested.

Researchers: M.A. Sutherland, N. Krebs, J.S. Smith and J.J. McGlone, all of the Pork Industry Institute, Texas Tech University. Contact Sutherland by phone (806) 742-2805 (ext. 253), fax (806) 742-4003 or e-mail [email protected].

Hydrogen Sulfide Detector Warns of Dangerous Gas Levels

A research team at Iowa State University (ISU) has developed a wireless hydrogen sulfide (H2S) detector that successfully detects the potentially fatal gas released from manure in deep-pit barns during slurry agitation and pumping events. This project was funded by the National Pork Board.

Lethal concentrations of H2S can develop rapidly and vary spatially in a swine barn during manure agitation and removal.

It is estimated the lost market value of 20 or more hogs to H2S poisoning during slurry agitation would pay for the new detection system in one year.

Personnel should never enter a swine barn during slurry agitation. The Occupational Safety and Health Administration's (OSHA) limit for immediate threat to life is 100 ppm of H2S. Field studies have shown that H2S concentrations can exceed this level quickly during slurry agitation with concentrations recorded as high as 1,300 ppm.

Researchers at ISU have the following objectives for this project to reduce the risk of human or animal fatalities from H2S gas:

  1. Develop and test a wireless hydrogen sulfide detection system for use during hog manure agitation and removal;

  2. Better establish building ventilation management strategies to increase human safety and maintain animal health during the manure agitation and removal process; and

  3. Add to the knowledge base about the development of hazardous conditions due to H2S from manure.

Initially, six commercially available H2S sensors were tested in ISU's Agricultural Waste Management Laboratory.

The prototype consists of a sensor/transmitter and a handheld receiver. The sensor/transmitter is equipped with the H2S sensor, a wireless communication system and battery power. The unit is placed inside the swine barn before agitation begins. The receiver remains outside so the operator can safely monitor H2S gas levels inside the barn. Both an audible and visual alarm are activated when a predetermined H2S concentration is detected.

The prototype matched performance of a research grade H2S analyzer.

To better understand H2S burst formation and distribution in swine facilities, the prototype system was used to detect concentrations at various locations in a swine finishing facility. While using surface agitation with splashing (agitation that disturbs the slurry surface), measurements were collected simultaneously from the pit below the slats and just above the slats in the same location. The use of stir fans equalized H2S concentrations above and below the slotted floor. By using stir fans, the operator can obtain a representative sample of room gas levels using a single point detection system.

H2S gas levels from above and below the slats in the same location can be collected during subsurface agitation (no disturbance of the slurry surface). While H2S concentrations were detected below the slats, no measurable H2S concentrations were detected above the slats. These results suggest that subsurface agitation should be used whenever possible to minimize H2S burst releases.

In a third test, H2S gas data was collected simultaneously from different areas within the barn just above the slats. In less than 10 minutes after vigorous surface agitation, the H2S gas concentration had exceeded the maximum range of the gas detector (500 ppm), demonstrating the dangers of H2S gas emissions during slurry agitation.

Researchers: Ross Muhlbauer, Randy Swestka, Robert Burns, Hongwei Xin, Steve Hoff and Hong Li, all of Iowa State University. Contact Burns by phone (515) 294-4203, fax (515) 294-4250 or e-mail [email protected].