REView: INTRAUTERINE (TRANSCERVICAL) AND

FIXED-TIME ARTIFICIAL INSEMINATION IN SWINE

 

B.A. Belstra

 

Summary

A large portion of the current swine artificial insemination (AI) research is focused on a means to reduce the number of sperm required per service (i.e. estrus) without compromising sow farrowing rate or litter size.  One strategy proposed to accomplish this is to decrease the number of sperm per insemination dose by depositing semen within the uterus (intrauterine), instead of the cervix, as is the case with natural mating and conventional AI.  Based on the limited available data, intrauterine insemination may reduce the number of sperm required to achieve fertilization compared to conventional AI, but it may also increase the chance of causing or aggravating an existing cervical or uterine injury (post-insemination bleeding) and introducing a uterine infection.  Insertion of an intrauterine catheter is more difficult in gilts than sows and requires a breeding technician to have more skill as compared to conventional AI.  However, the adoption of non-surgical intrauterine techniques could allow other technologies like embryo transfer, frozen semen, and sexed semen to be adopted on a larger scale.  An alternate strategy to reduce the number of sperm required per service is to reduce the number of inseminations by controlling the timing of the inherently variable processes of estrus and ovulation through pharmaceutical treatments (i.e. synchronization) and inseminating once at a fixed-time.  A gonadotropin preparation (P.G. 600Ò, Intervet, Inc.) is currently available, but more versatile and effective progestagen, GnRH, eCG, and hCG synchronization products exist that are not approved for swine use.  The extent to which hormone synchronization treatments are utilized in the future will likely depend on their cost, efficacy, and ethical implications.  At present, intrauterine and fixed-time insemination technologies are only being used for research and special genetic transfer situations in swine.  Some form of commercial application may be on the horizon, but at this point, there is not enough data to determine if the benefits of these techniques would outweigh the costs.  If a major reduction in the number of sperm required per service is achieved, it could substantially increase the economic and genetic efficiency of semen production, but it would also increase the need for accurate evaluation of semen quality. 

 

Introduction

During the 50’s and 60’s, research on the transport of sperm in gilts and sows inseminated with doses differing in volume and number of sperm suggested that approximately 5 to 10 ´ 10⁹ sperm in 100 mL was necessary to achieve optimal fertility (Stratman and Self, 1960; Baker et al., 1968).  Since then, the number of sperm per insemination dose has decreased primarily due to improvements in semen extender.  A recent review of the US swine AI industry suggests that AI accounts for an estimated 60% of all matings and that on average a sow receives 2.2 insemination doses per service containing 2.5 to 4 ´ 10⁹ sperm in a 70 to 100 mL volume (Singleton, 2001).  These numbers suggest that on average a sow mated by AI receives 7.2 ´ 10⁹ sperm per service (2.2 inseminations ´ 3.25 ´ 10⁹ sperm per dose).  If an average boar ejaculate contains 70 ´ 10⁹ sperm then only 8 or 9 sows could be inseminated 2.2 times each.  Singleton (2001) also estimated that on average AI boars are collected 4.7 times per month and 100 doses per boar per month is a common production goal.  There would be an obvious increase in economic and genetic efficiency even if the number of sperm per insemination dose could only be reduced a few fold.    

 

The outer (vaginal) end of the cervix is the normal site of semen deposition during natural mating and conventional AI.  Within 2.5 h of a conventional AI approximately 70% of the volume and 25% of the sperm inseminated are lost as they flow back out of the sow’s reproductive tract (Steverink et al., 1998).  Several different instruments have been developed to transverse the entire length of the sow’s cervix (» 6 in.) and deposit semen in the uterine body (intrauterine insemination, IUI) or anterior portion of a uterine horn (deep intrauterine artificial insemination, DIUI). 

 

Figure 1.  Diagram of the sow reproductive tract illustrating the site of semen deposition for 3 different types of artificial insemination.

 

 

Figure 2.  Several commercially available transcervical (intrauterine) insemination catheters designed to place semen 6 to 8 in. past the end of the cervix, in the uterine body.  Note the secondary catheter protruding through the tip of the primary catheter.  Photo courtesy Dr. Wayne Singleton, Deptartment of Animal Science, Purdue University.

The potential advantages intrauterine techniques are that they may allow fertilization results comparable to conventional AI with fewer sperm and could also bring other technologies like sexed semen (Johnson, 2000) and embryo transfer (Hazeleger and Kemp, 2001) closer to commercial application.  The potential disadvantages of these techniques are that they may increase the chance of causing or aggravating an existing cervical or uterine injury (post-insemination bleeding) and introducing a uterine infection.  In addition, intrauterine catheter placement requires more breeding technician skill (especially in gilts) and time compared to conventional AI, although the deposition of the semen is quicker because uptake is not dependent on sow uterine contractions. 

 

Review of the Available Data

There have been two basic strategies to reduce the number of sperm inseminated per service, either reduce the number of sperm per insemination dose or reduce the number of inseminations per service.  Several recent experiments have attempted to do both by bypassing areas where sperm are lost through intrauterine insemination and hormonally synchronizing estrus and ovulation to allow one fixed-time insemination.  Krueger et al. (1999) utilized surgical insemination of synchronized gilts and found that as few as 10 ´ 10⁶ sperm (in 0.5 mL) deposited near the utero-tubal junction (UTJ) of each uterine horn were sufficient to provide fertility comparable to one conventional AI with 3 ´ 10⁹ sperm (a 150 fold reduction; Krueger et al., 1999).  A similar study with synchronized sows using the same surgical DIUI technique confirmed this finding (Krueger and Rath, 2000).

 

Hancock (1959) and Hancock and Hovell (1961) performed some of the earliest non-surgical transcervical insemination experiments in swine.  Sows had a greater proportion of cleaved ova recovered 3 to 4 d post-insemination when semen was deposited in the uterus compared to the cervical canal (Hancock, 1959).  More recently, semen has been non-surgically deposited two thirds of the way up one uterine horn (» 10 in. from the UTJ) by inserting an expensive, flexible, fiber optic endoscope (Martinez, et al., 2001) or a less expensive, flexible, secondary catheter without an endoscope (Martinez et al., 2002) guided through a modified AI catheter.  Sow fertility results from these non-surgical DIUI experiments are summarized in Table 1.  It is important to note that in both studies DIUI sows were inseminated once at a fixed-time after hormonal synchronization and that the conventional AI sows received two inseminations but were synchronized only by their common 4-day weaning-to-estrus interval.  Both studies seem to suggest that one non-surgical DIUI of synchronized sows with as few as 50.0 ´ 10⁶ sperm can produce a farrowing rate and litter size comparable to two conventional inseminations with 3 ´ 10⁹ sperm in non-synchronized sows (a 15 to 20 fold reduction).  It was possible to successfully pass the long, flexible, intrauterine catheter through the cervix in 95% of the sows with an average time of approximately 3.7 minutes (Martinez et al., 2002).  

 

Unlike the DIUI studies by Martinez et al. (2001, 2002), the third set of data represents a commercial-based study that utilized non-synchronized sows, a commercially available intrauterine catheter, and trained farm employees to perform the inseminations (Watson et al. 2001).  In addition, the semen was deposited in the uterine body (IUI) instead of two thirds of the way up a uterine horn (DIUI) and the IUI sows were inseminated on the same schedule as the conventional AI (control) sows.  Only when the insemination dose was reduced to 1.0 ´ 10⁹ sperm did the conventional AI sows exhibit reduced fertility compared to the IUI sows (Table 1).  Even though the Watson et al. (2001) study was intended to demonstrate the benefits of IUI it also demonstrates that we may be able to reduce the number of sperm per insemination dose with conventional AI to some extent without affecting reproductive performance.  Field reports of herds that achieve a high level of reproductive performance (³ 85% farrowing rate and ³ 10 pigs born alive) with only 1.5 to 2.0 ´ 10⁹ sperm per insemination dose are becoming more common.  However, management may view 3.0 to 4.0 ´ 10⁹ sperm per insemination dose as a relatively cheap form of insurance to cover potential deficiencies in semen quality from the boar stud or deficiencies in insemination timing, technique, or quality at the sow farm.

 

Table 1.  Reproductive performance of sows mated by non-surgical deep intrauterine insemination (DIUI, uterine horn) and non-surgical intrauterine insemination (IUI, uterine body) compared to conventional artificial insemination (AI, cervix) at different sperm dosages in three different studies.  Other abbreviations: CR, conception rate; FR, farrowing rate; TB, pigs total born; BA, pigs born alive.

 

 

Increasing the synchrony of estrus and ovulation postweaning through pharmaceutical treatments is the other means to reduce the number of sperm required per service because it can allow one fixed-time insemination (Brϋssow et al., 1996; Hϋhn et al., 1996; Pereira et al., 2001).  A gonadotropin preparation like P.G. 600Ò (400 IU equine chorionic gonadotropin (eCG) and 200 IU human chorionic gonadotropin (hCG)) can speed the onset of estrus and ovulation and increase synchrony of these processes among treated females.  However, a high degree of synchrony is required for one fixed-time insemination and more versatile and effective progestagen, gonadotropin releasing hormone (GnRH), eCG, and hCG products (Regu-mateÒ, FertagylÒ, FolligonÒ, and ChorulonÒ, respectively, Intervet, Inc.) exist that are not approved for swine use, or just not approved for swine use in the US.  Even in the unlikely event that more synchronization products became approved for swine use, they would have to have high efficacy and low cost to be useful in commercial production. 

 

Implications

Improvements in semen evaluation, semen extender, detection of estrus, prediction of ovulation, and sow management will continue to allow moderate reduction in the number of sperm required per service with conventional AI.  The adoption of intrauterine and fixed-time insemination techniques may allow a much larger decrease in the number of sperm required per service but would also require increased training of breeding technicians and pharmaceutical use for synchronization.  Since few effective products for estrus and ovulation synchronization are currently approved for swine use, protocols that utilize multiple intrauterine inseminations are more likely to be implemented first.  Due to the lack of published data there is currently considerable controversy over the ideal intrauterine insemination device, optimal insemination dose (number of sperm and volume), and site of semen deposition (uterine body vs. uterine horn).  One thing that is certain is that if a substantial reduction of the number of sperm required per service is made, it will increase the need for accurate evaluation of semen quality and a high level of sow breeding management to maintain fertility. 

 

References

Baker, R.D., P.J. Dziuk, and H.W. Norton. 1968. Effect of volume of semen, number of sperm

and drugs on transport of sperm in artificially inseminated gilts. J. Anim. Sci. 27:88-93.

Brϋssow, K.P., W. Jöchle, and U. Hϋhn. 1996. Control of ovulation with a GnRH analog in gilts

and sows. Therio. 46:925-934.

Hancock, J.L. and G.J.R. Hovell. 1961. The effect of semen volume and number of

spermatozoa on the fertility of intra-uterine inseminations of pigs. Anim. Prod. 3:153-161.

Hancock, J.L. 1959. Pig insemination technique. Vet. Rec. 71:527.

Hazeleger, W. and B. Kemp. 2001. Recent developments in pig embryo transfer. Therio.

56:1321-1331.

Hϋhn, U., W. Jöchle, and K.P. Brϋssow. 1996. Techniques developed for the control of estrus,

ovulation, and parturition in the East German pig industry: a review. Therio. 46:911-924.

Johnson, L.A. 2000. Sexing mammalian sperm for the production of offspring: the state-of-the-

art. Anim. Reprod. Sci. 60-61:93-107.

Krueger, C. and D. Rath. 2000. Intrauterine insemination in sows with reduced sperm number.

Reprod. Fertil. Dev. 17:113-117.

Krueger, C., D. Rath, and L.A. Johnson. 1999. Low dose insemination in synchronized gilts.

Therio. 52:1363-1373.

Martinez, E.A., J.M. Vazquez, J. Roca, X. Lucas, M.A. Gil, I. Parrilla, J.L. Vazquez, and B.N.

Day. 2002. Minimum number of spermatozoa required for normal fertility after deep intrauterine insemination in non-sedated sows. Reprod. 123:163-170.

Martinez, E.A., J.M. Vazquez, J. Roca, X. Lucas, M.A. Gil, I. Parrilla, J.L. Vazquez, and B.N.

Day. 2001. Successful non-surgical deep intrauterine insemination with small numbers of spermatozoa in sows. Reprod. 122:289-296.

Pereira, C.Z., J.L.M. Vasconcelos, D.A. Berto, L.N. Vieira, and M.N.P. Morais. 2001.

Synchronization of ovulation and timed artificial inseminations in sow in an early weaning systems. Sixth International Conference on Pig Reproduction, University of Missouri Columbia. pp. 122.

Singleton, W.L. 2001. State of the art in artificial insemination in the United States. Therio.

56:1305-1310.

Steverink, D.W.B., N.M. Soede, E.G. Bouwman, and B. Kemp. 1998. Semen backflow after

insemination and its effect on fertilization results in sows. Anim. Reprod. Sci. 54:109-119.

Stratman, F.W. and H.L. Self. 1960. Effect of semen volume and number of sperm on fertility

and embryo survival in artificially inseminated gilts. J. Anim. Sci. 19:1081-1088.

Watson, P.F., J. Behan, G. Decuadro-Hansen, and B. Cassou. 2001. Deep insemination of

sows with reduced sperm numbers does not compromise fertility: a commercially-based field trial. Sixth International Conference on Pig Reproduction, University of Missouri Columbia. pp. 135.