"FUTURE" REPRODUCTIVE TECHNOLOGIES –
APPLIED RESULTS OF TRANS CERVICAL INSEMINATION
AND OTHER STUDIES RELATED TO ARTIFICIAL INSEMINATION
W.L. Flowers
Department of Animal Science
North Carolina State University
Raleigh, N.C. 27695-7621
Introduction
It was once said that the real benefit of solving one problem is that one becomes aware of other problems that need attention. This statement has particular relevance in terms of the development of reproductive technologies associated with artificial insemination in swine. The only difference is that the word "improvements" should probably be substituted for the word "problems". In essence, the primary goal of developing new reproductive technologies is to improve the biological and economic efficiencies of current mating systems. When improvements are made in one component of A.I., often times, this heightens the awareness for the need to change others. Two current examples of this are deep uterine insemination and the development of prospective tests for semen fertility. The primary objective of this presentation is to discuss current progress that has been made in these two areas. A secondary objective is to illustrate how implementation of these two technologies, when and if they occur, probably will necessitate improvements in other areas of breeding management.
Transcervical Insemination
A common goal for most swine operations is to improve efficiency. For artificial insemination, one of the most compelling ways to achieve this is to decrease the number of spermatozoa in each insemination dose without compromising fertility. This would result in more insemination doses from each collection, which should decrease variable costs associated with semen production. Currently, most insemination doses normally contain between 2 and 4 billion viable spermatozoa. In theory, if this could be reduced by one-half to1 to 2 billion sperm cells per dose, then the efficiency of semen production should double.
From a physiological perspective, the reason that such a large number of spermatozoa need to be inseminated in swine is that the site of normal semen deposition for artificial matings is the cervix. Anatomically, the cervix is muscular organ whose inner lining consists of many deep crypts or folds. After insemination, a large number of spermatozoa are trapped in these crypts and once they enter, it is commonly accepted that they usually become trapped and do not have an opportunity to fertilize eggs (Figure 1). The best way to compensate for this is to increase the number inseminated and, thus, increasing the number that actually make it out of the cervix and into the uterus.
Recently, several different types of A.I. catheters have been designed to allow deposition of the semen into the cervical end of the uterus. Most of these involve special modifications of conventional A.I. catheters, either foam-tipped or spirettes, that allow a smaller catheter or tube to be navigated through the cervix and into the uterus. These catheters provide a way to physically "by-pass" the cervical crypts or folds during insemination. With this technology, the loss of spermatozoa in the cervix, essentially is eliminated and, in theory, reduced numbers of spermatozoa should be required (Figure 1).
Figure 1. Diagrams of conventional (A) and trancervical A.I. (B). Notice how in conventional A.I. the end of the catheter is still in the cervix. As a result, semen is deposited in the cervix and a significant number of spermatozoa are trapped in the cervical crypts. In contrast, transcervical A.I. catheters (B) contain "extensions" that allow for semen to be deposited into the uterus.
At the present time, initial results from field studies using transcervical A.I. appear to be promising. Results from two studies are summarized in table 1. In both situations, farrowing rates and litter size with transcervical A.I. with reduced numbers of spermatozoa were comparable to conventional A.I. These data demonstrate that numbers of spermatozoa in insemination doses can be reduced without negatively affecting farrowing rate and litter size on commercial swine operations. Perhaps, the most impressive demonstration of this is from the results reported by Gall (2002). In his study, sperm cell numbers were reduced by almost 80% (3.0 to 0.6 billion) with no change in fertility. From a practical perspective, an ejaculate with 60 billion spermatozoa would yield 100 (60 billion / 0.6 billion) doses with transcervical A.I. compared with only 20 (60 billion / 3 billion) for conventional A.I.
Table 1. Fertility of Sows bred via Transcervical (T.C.A.I.) or Conventional A.I. (A.I.).
|
Study |
Treatment |
Sperm/ Dose (x 109) |
Volume (ml) |
Doses/ Sow |
No. of Sows |
Farrowing Rate (%) |
Number Born Alive |
|
Watson et al., 2001 |
A.I. |
3.0 |
80 |
2 |
> 500 |
91.1 |
10.9 |
|
T.C.A.I. |
3.0 |
80 |
2 |
> 500 |
90.5 |
11.0 |
|
|
A.I. |
2.0 |
80 |
2 |
> 500 |
91.8 |
10.9 |
|
|
T.C.A.I. |
2.0 |
80 |
2 |
> 500 |
92.5 |
10.8 |
|
|
A.I. |
1.0 |
80 |
2 |
> 500 |
65.8 |
9.0 |
|
|
T.C.A.I. |
1.0 |
80 |
2 |
> 500 |
86.9 |
10.9 |
|
|
Gall, 2002 |
A.I |
3.0 |
75 |
> 2 |
141 |
86.2 |
9.9 |
|
T.C.A.I. |
0.6 |
30+18 |
> 2 |
145 |
85.1 |
10.1 |
It appears that modifications in catheter design have led to A.I technologies that will allow reduced numbers of spermatozoa to be inseminated with no appreciable change in sow fertility. However, as mentioned earlier, this potential improvement also presents a new set of challenges. While numbers of spermatozoa per insemination dose definitely are important, the volume of extended semen is also important. It is generally accepted that the physical displacement of the uterus by the large volume of semen normally deposited during mating in swine is critical for effective sperm transport to the oviduct. Consequently, even in situations where sperm numbers are reduced, it still may be necessary to inseminate the same volume of liquid for optimal fertility. This is one reason why the volume of semen inseminated was not reduced in the study by Watson et al. (2001) and why in the study conducted by Gall (2002), 30 ml of semen extender was inseminated prior to the extended semen with reduced numbers of sperm. The importance of volume of the insemination dose may need to be revisited to determine the minimum amount and the best sequence in which it should be administered, i.e. - extender first and then semen or vice versa.
Furthermore, if it is discovered that the volume cannot be significantly reduced, then another pertinent issue that must be considered is semen to extender ratios during extension. For most boars, the optimal ratio of semen to extender is between 1:8 and 1:64. At ratios lower than this, there are not enough buffers and nutrients in the extended semen to maintain the viability of spermatozoa for long periods of time. In contrast, at ratios higher than this, spermatozoa are more sensitive to conditions that lead to osmotic shock, which can reduce shelf-life and impair fertility. The latter is of relevance to transcervical inseminations. In a normal situation, 1500 ml of extender would be added to a 100 ml ejaculate containing 60 billion spermatozoa to make 20 insemination doses containing 3 billion cells each. This would be a 1:15 dilution ratio (100 ml semen / 1500 ml extender). If the same ejaculate was used to produce transcervical insemination doses of 0.6 billion in 80 ml, then 7900 ml of extender would be needed. This would be a dilution ratio of 1:79 (100 ml semen / 7900 ml extender). Therefore, development of new semen extender or insemination regimens similar to that used by Gall (2002) would be needed to address the potential problems with high dilution ratios for successful transcervical inseminations.
Prospective Boar Fertility Tests (or Programs)
Another way to enhance reproductive efficiency is to ensure that only semen from the most fertile boars is shipped from boar studs to sow farms. From a practical perspective, this can probably only be achieved via the development of prospective fertility tests, because pooling semen is common within the industry. Another reason that prospective evaluations are important is that most boars leave production before they have bred enough sows to truly estimate their fertility.
One of the interesting things about boar fertility is that it is often viewed as a "yes" or "no" phenomenon. In other words, a boar is either fertile or infertile. A recent study conducted by Flowers (2002), examined boar fertility by making insemination doses between 1 and 9 billion spermatozoa to breed sows. The changes in farrowing rates and numbers of pigs born alive as the number of spermatozoa were increased were called "fertility curves". Examples of fertility curves from several boars are illustrated in figure 2.
The results from these studies demonstrate two very important concepts about boar fertility. First, as the number of spermatozoa per insemination increased from 1 billion to 9 billion, so did farrowing rates and litter size. However, the manner in which it changed varied among individuals. For number of pigs born alive, boar 2 reaches a maximum value of 10.8 pigs between 3 and 5 billion sperm cells. In contrast, boar 1 reaches his plateau of 11.3 pigs at insemination doses with more than 7 billion spermatozoa. Finally, the fertility curves for boars 3 and 4 do not appear to plateau, but, instead, continue to increase over the same range of insemination doses. Second, fertility is a relative term, even when it is measured by objective data such as farrowing rate and number of pigs born alive. If 3 billion spermatozoa per insemination dose were used for inseminations, the boars in figure 2 would rank 2, 1, 4, 3 from highest to lowest in terms of number of pigs born alive. In contrast, if 9 billion sperm cells were used instead, then the order would be 4, 2, 1, 3.
It is not prudent for producers to attempt to adjust the number of spermatozoa per insemination dose based on a boar's inherent fertility. However, what is practical is to develop tests that can identify boars that produce acceptable farrowing rates and number of pigs born alive at insemination doses between 1 and 3 billion spermatozoa. This is actually the basis for most prospective fertility tests or programs. Good fertility tests need to be able to do a minimum of two things. The first is to identify subfertile boars. These are boars that would produce results that are not acceptable, such as farrowing rates less than 80% or numbers of pigs born alive less than 10. The second is to rank or assess the relative fertility of boars deemed acceptable, i.e.- boars that normally produce results better than the minimum levels mentioned earlier. Most of the current evaluations used in studs such as motility and normal morphology assessments are excellent ways to achieve the first goal - identification of subfertile boars or ejaculates (Flowers, 1997). Therefore, the first component of such programs is already being done on most
operations.
Technologies for estimating farrowing rates and numbers of pigs born alive for boars deemed acceptable are not available at the present time. However, there are some interesting things being studied that prove to be very useful. One of these is quantification of seminal plasma protein profiles of boars. In addition to spermatozoa, semen contains secretions from the secondary sex glands such as the seminal vesicles and prostate gland. There are a large number of proteins in semen that might be involved in a number of important processes that sperm cells need to undergo before they acquire the ability to fertilize eggs. Recent studies conducted with boars in production in N.C. have shown a interesting pattern between fertility and levels of two seminal plasma proteins. Ejaculates that contain increased amounts of two proteins (see Figure 3), produced farrowing rates and litter sizes of 86.7+3.4% and 11.2+0.3 pigs, respectively, whereas those with reduced levels averaged 78.4+3.1% and 10.4+0.4 pigs (Flowers and Turner, 2001). These data were based on over 500 ejaculates and 700 sows per group. It is important to recognize that the exact relationships between the presence of these proteins and the fertility of spermatozoa is not known and still under investigation. However, the initial relationship holds promise for development of the second component of a prospective boar testing program based on fertility.
Figure 3. Seminal plasma protein profile of a boar with high levels of two proteins (I and II) associated with high farrowing rates and large litter sizes.
Summary
Reproductive technologies with potential to improve reproductive efficiency on operations using A.I. are being developed. Two, transcervical insemination and prospective fertility testing programs, appear to be developing rapidly. For transcervical insemination, insemination catheters that allow semen to be deposited in the uterus are available. However, there are still questions with regards to sow longevity, semen handling and extension, and insemination techniques that need to be answered before this technology will be used routinely. For the development of prospective fertility testing programs for semen, the ability to identify subfertile boars accurately and quickly is available and currently being used by the industry. In contrast, procedures for estimating differences in the reproductive performance of fertile boars are lacking. Analyses of seminal plasma protein profiles of ejaculates may prove to be one way to accomplish this task.
Literature Cited
Flowers, W.L. 1997. Management of boars for efficient semen production. Journal of Reproduction and Fertility Supplement 52, 67-78.
Flowers, W.L. and Turner, Z.A. 2001. Relationships between seminal plasma protein profiles and estimates of fertility for boars. Proceedings, VIIth International Conference on Pig Reproduction, University of Missouri, page 43.
Gall, T. 2002. Fertility of intra-uterine vs. intra-cervical insemination of semen in swine. Journal of Animal Science 80 (supplement 2), 46.
Watson, P.F., Behan, J., Decuadro-Hansen, G., and Cassou, B. 2001. Field studies with deep uterine insemination in swine. Proceedings, VIIth International Conference on Pig Reproduction, University of Missouri, page 135.
Back Up
|