The Research Boar Stud at Virginia Tech's Tidewater Agricultural Research & Extension Center
Livestock Update, January 2002
Mark Estienne, Swine Research Physiologist and Allen Harper, Extension Animal Scientist-Swine, Virginia Tech Tidewater AREC, Suffolk, VA
The use of artificial insemination (AI) on swine farms continues to increase. Nationwide, 47% of sows and gilts were bred using AI in 1997. A recent study of the pork industry, however, revealed that nearly 70% of the nationžs sow herd was bred via AI in 2000 (Lawrence and Grimes, 2000).
In a typical AI situation, semen is collected from boars trained to mount an artificial sow. Because an ejaculate contains many more sperm cells than are needed to impregnate a single female, semen is diluted with commercially available extenders to create multiple insemination doses and enhance the efficiency of reproduction. The advantages of AI compared to natural mating systems, however, are tempered when boars consistently display a reluctance or refusal to mount an artificial sow and/or ejaculate mediocre or poor quality semen (low volume, low sperm concentration, etc.).
Little research information exists regarding nutritional strategies and management techniques that optimize semen quality and libido in boars used for AI and few land grant institutions have the resources or facilities to conduct requisite research in this important area. However, the Virginia Swine Evaluation Station (VSES) at Virginia Techžs Tidewater Agricultural Research and Extension Center (TAREC) in Suffolk was recently renovated into a boar stud to be used for research purposes. The goal of research conducted in this facility is to develop techniques for optimizing sperm cell production and libido in boars used for AI.
Virginia Swine Evaluation Station Research Boar Stud
The VSES was constructed in 1967 and was originally used to evaluate, in a central location, growth rate, feed conversion efficiency and body composition of boars from independent seedstock producers. In 1995, the boar-testing program was discontinued, a major reason being a trend in the swine industry toward producers procuring boars or semen from larger, genetics companies.
Renovations of the VSES into a research boar stud began in the late fall of 2000 and were completed in the early spring of 2001. The John Lee Pratt Animal Nutrition Research Program and Virginia Techžs College of Agriculture and Life Sciences, Department of Animal and Poultry Sciences, and TAREC provided funds for the renovation. Major improvements included painting of the entire facility, refurbishing the office and restroom, repair of the roof, and replacement of the ceiling, metal flooring, and doors. The electrical wiring of the VSES was upgraded to conform to modern standards. Old cinderblock pen partitions were removed and replaced with modern hot-dipped galvanized metal panels. A semen collection room equipped with an artificial sow, and a semen analysis laboratory was established.
The VSES research boar stud is a passively ventilated, curtain-sided building. Four stirring fans improve animal comfort during the summer months and four heaters provide supplemental heat during the winter. The renovated facility can accommodate 40 mature boars, housed individually in pens measuring 12 x 4.5 feet. The pen floors are partially slotted which allows for manure collection under grated metal, and feeding and resting of animals on solid concrete. Each pen is equipped with a nipple drinker and a sprinkler cooling-nozzle.
In April of 2001, the facility was stocked with Ham-line boars generously donated to TAREC from National Pig Development-USA (NPD-USA) of Roanoke Rapids, NC. These are lean-type (.4 in. of backfat at 250 lbs. of body weight and 177 days of age) boars characteristic of genetics packages used in the modern swine industry and that will serve as experimental subjects for research studies conducted at the facility.
Recent Research Completed at the VSES Research Boar Stud
Previous work from TAREC demonstrated that intramuscular treatment with 10 mg Lutalyse (Pharmacia & Upjohn, Kalamazoo, MI) decreased the number of sessions required to train sexually active boars (i.e., boars experienced with natural mating) (Estienne and Harper, 2000) and sexually inexperienced boars (Estienne et al., 2001) to mount an artificial sow and allow semen collection. The objective of a study completed this past spring at the VSES research boar stud was to extend our previous findings by determining the effects of different doses of Lutalyse on the ability to train for semen collection, boars that had not previously experienced natural mating.
Boars were moved individually into the semen collection room twice weekly for six weeks (total of 12 training sessions). Upon entering the semen collection pen, boars received intramuscular injections of either deionized water (4 mL, n = 10) or Lutalyse at doses of 5 mg (n = 10), 10 mg (n = 10), or 20 mg (n = 10). Each training session lasted a maximum of 10 min. Semen was collected via the gloved-hand technique and boars that had not mounted the artificial sow and allowed semen collection after 12 training sessions were classified as untrained.
The percentage of boars trained for semen collection during the experimental period was similar for controls (20%) and boars receiving 5 mg (30%), 10 mg (20%), or 20 mg (10%) of Lutalyse. For each training session, libido was scored using a scale of 1 to 5 (1 = showed no interest in artificial sow, 5 = mounted artificial sow and allowed semen collection). There were statistically significant effects of treatment on libido scores as depicted in Figure 1.
Figure 1. The effect of Lutalyse treatment on mean libido scores (1 = no interest in the artificial sow; 5 = mounting artificial sow and allowing semen collection). Means without common superscripts (a, b, c) differ (P < .05). Standard error was .08. The 0 mg dose of Lutalyse was 4 mL of deionized water.
The 10 mg dose of Lutalyse enhanced libido somewhat during the experiment. However, in contrast to previous investigations (Estienne and Harper, 2000; Estienne et al., 2001), Lutalyse failed to increase the number of sexually inexperienced boars trained for semen collection during the experimental period. An explanation for the discrepancy in results between the current and previous studies is not readily apparent, because similar methods were used for each experiment. Boars used in previous experiments were Hampshire, Landrace, or Yorkshire (Estienne and Harper, 2001), or Landrace x Yorkshire (Estienne et al., 2000), and thus differed in genetic composition from the boars used in the present study. Moreover, boars used in previous studies (Estienne and Harper, 2000; Estienne et al., 2001) were older and heavier than boars employed in the current experiment. Perhaps, the effectiveness of Lutalyse for training for semen collection is influenced by genetics or the age and size of the treated boar.
Wettemann et al. (1992) reported no effects of Lutalyse on mounting behavior in boars. Before beginning the experiment the boars utilized in that study, however, were characterized as lacking libido for failing to mount an estrous sow. It is doubtful that the lack of an effect of Lutalyse on the number of individuals trained for semen collection was a consequence of a group of inherently low-libido boars used in our experiment. Indeed, after concluding this experiment, semen was eventually collected from 90% of the boars using other husbandry techniques (e.g. allowing boars to mount estrous female, beginning semen collection, and then moving boar onto the artificial sow).
It is also doubtful that a higher dose of Lutalyse would have increased the number of boars allowing semen collection in Experiment 2. The 20 mg dose of the drug caused marked non-sexual behavioral changes and actually decreased libido scores below controls. One boar vomited within 5 min of treatment with the 20 mg dose during each of the 12 training sessions.
Ongoing Research at the VSES Research Boar Stud
Research studies have demonstrated positive effects of feeding a FDA-approved source of l-carnitine (Carniking; Lonza Inc., Fair Lawn, NJ) on sow reproduction. Additionally, in male rats and other species, l-carnitine increases sperm motility and sperm concentrations. Although limited data from field trials in Europe and the U.S. suggests similar effects in swine, the effects of l-carnitine on boar semen quality, as well as libido, have not been thoroughly addressed.
Thus, in an ongoing experiment at the VSES Research Boar Stud, boars trained to mount an artificial sow for semen collection are being fed a daily ration containing 0 or 500 mg L-carnitine (Carniking) (n = 9 per treatment). During the 16-week experimental period, semen is being collected from each boar once weekly and ejaculates are analyzed for semen volume, gel weight, sperm concentration, total sperm cells, and the percentages of motile and morphologically normal sperm cells. Various indices of libido such as time between the boar entering the semen collection room and the initiation of the ejaculation, and the duration of ejaculation, are also being evaluated. The effect of feeding L-carnitine on the maintenance of sperm motility during liquid storage in a commercially available semen extender is also being assessed.
Estienne MJ, Harper AF. PGF2a facilitates the training of sexually active boars for semen collection. Theriogenology 2000; 54:1087-1092.
Estienne MJ, Harper AF. Lutalyse enhances libido in boars being trained to mount an artificial sow for semen collection. Journal of Animal Science 2001; 79(Suppl. 1):23.
Lawrence J, Grimes G. Production and marketing characteristics of U.S. pork producers, 2000. Available at: http://agebb.missouri.edu/mkt/porkmkt.htm
Wettemann RP, Welty S, Bishop DK. An attempt to stimulate sexual behavior of boars. Oklahoma Agriculture Experiment Station 1992 Animal Science Research Report. 1992; 410-412.