Artificial Insemination of Cattle

Transcription

1 Artificial Insemination of Cattle Animal Reproduction: 3850N Jacky Whitehead Nicole Black April 5, 2006

2 With the global market becoming so interdependent, it has opened the doors for livestock producers, to increase the value of their operations by introducing particular desirable traits into their herds from all over the world. Artificial Insemination allows the introduction of these traits, in a timely fashion and offers the operator an alternative to natural breeding. Artificial Insemination has been in commercial use since 1937, but its origins can be traced back to 1667 when Leeuwenhoek saw the first spermatozoa through the newly developed microscope. This discovery would be built upon nearly a century later when Spallanzi an Italian scientist discovered that a dog could be impregnated with the cellular portion of semen. Along with this he also stumbled upon what has become the foundation of the A.I. business. He observed that the spermatozoa could be suspended or, inactivated, by cooling them and then could be inseminated at a later date. The idea of artificial insemination would be furthered by the Russians in the 1990 s when Professor Ivanov developed methods for collecting semen and inseminating horses, cattle, sheep and swine. This phenomenon of freezing and preserving semen would spread to North America in 1937, gaining particular interest in the dairy industry, which remains the biggest user of this method to date. It is estimated that approximately sixty percent of all dairy cows in the United States are artificially inseminated, with the numbers being even higher in Europe with over ninety percent of all dairy cows being in the A.I. program. Artificial Insemination is not only limited to domesticated livestock, but has also been applied to endangered species programs and has most recently gained momentum in the human sector, combined with In Vitro programs. Throughout the years there have been many advances to the industry and the methods in use today, provide producers with an effective alternative to natural breeding programs.

3 The first step in Artificial Insemination in cattle is the collection of semen from a bull. Semen collection can begin in bulls at 12 months of age and can be collected twice a day 2 times a week when the bulls are young. In a mature bull semen may be collected twice a day 2 to 3 times a week in order to collect a large quantity of semen to be frozen. There are two fundamental methods for the collection of semen, an artificial vagina and electro-ejaculation. Of the two the methods, the artificial vagina is the more commonly used method and consists of a cylindrical rubber tube with a rubber liner attached to a collection cone and vial. An insulated jacket is placed around the vagina and hot water at about 60 o C is placed between the rubber tube and liner to ensure that the vagina is kept at 45 o C. A constant temperature is needed to allow for ejaculation to occur and prevents cold shock of the semen. The actual collection of the semen occurs by allowing the bull to mount and diverting the penis into the artificial vagina. The second method, electroejaculation, is a technique reserved for injured or lame bulls or older bulls as it is does not involve the bull having to mount. Electro-ejaculation involves the introduction of a probe or finger electrode to the rectum where sensory nerves for ejaculation are located and low-voltage pulses are gradually increased until ejaculation is stimulated. In order for frequent collection of viable semen a bull should be sexually stimulated. There are three approaches to stimulation, introduce a new mount in the original location, change the location but keep the mount, and change both the mount and location. There are also three approaches to sexually preparing a bull for ejaculation using a false mount by diverting the penis, restraint by preventing the bull to mount, and both false mounting and restraint. A bull is usually subjected to 3 to 5 false mounts as well as active restraint before being allowed to ejaculate to increase spermatozoa output.

4 After semen collection and before processing, semen is evaluated for its quality and quantity. The volume of the ejaculate is recorded and a concentration of the sperm is calculated. The concentration of sperm can be examined through either a hemacytometer or a spectrophotometer. The hemacytometer is a glass slide that holds a set volume of semen. The sperm is killed with formaldehyde to prevent movement and counted with use of a microscope. A spectrophotometer on the other hand involves no counting and uses the amount of light absorbed by sperm to produce a standard curve of absorbance versus sperm number. The total number of sperm in the ejaculate can then be calculated by the using the concentration of sperm per ml multiplied by the volume of the ejaculate. From this initial sample the quality of the semen is evaluated on its appearance and motility. The semen appearance is examined for its color and lack of debris, puss, and urine. The most commonly used method to evaluate for sperm viability is its motility. Motility has been found to have a positive relationship with fertility as discovered by researchers such as M.P. Mostari, M.G.M. Fahman, M.A.M.Y. Khandoker, and S.S. Husain. 1 In order to examine the motility of sperm the semen must remain around 37 o C as motility is lost around 18 o C. It can then be examined under a microscope and a percentage of motile sperm can be calculated. A percentage of greater then 60% indicates good quality ejaculate but less then 50% indicates poor quality and will be discarded. While examining sperm motility abnormal sperm can also be identified. Abnormal sperm can originate in the testes or the epidimymis and may be classified as either head or tail abnormalities. Errors such as a coiled tail, detached head, and ruffled acrosome are only a few of the abnormalities that prevent fertilization. An acceptable percentage of 1 M.P. Mostari, M.G.M. Fahman, M.A.M.Y. Khandoker, S.S. Husain; Evaluation of Bulls Based on Semen Quality and Herd Fertility 2004 Pakistan Journal of Biological Sciences, Bangladesh

5 abnormalities is between 5-15% and anything above this is considered too high. Although semen is evaluated after collection it is also worth mentioning that the bulls should be assessed for disease and physical factors of good fertility such as testicular size before semen collection occurs. The process of preparing spermatozoa, in order to be used in artificial insemination has seen many changes since the 1900 s. Although methods for collecting semen and insemination have been available for years, there have been various obstacles that the industry has had to overcome in order to make the A.I. program accessible to the commercial market. Perhaps the most significant advancement was the resolution on how to store semen long enough for shipment. This breakthrough was achieved in 1939 by Dr. Phillips, when he discovered that egg yolk would protect sperm cells from temperature shock upon freezing, and that the amount of semen obtained could be extended, resulting in higher numbers of dosages from a single ejaculation. This technique would later become known as the extender, and perhaps has had the biggest impact on the A.I. business. The present day extender is composed of six components, which all aid in the preservation and motility of the semen. The first step in preparing an extender is to make an isotonic diluter to ensure that there is no movement of water in and out of the cells. The current diluter of choice is the yolk-citrate which maintains sperm motility and fertility as well as maintaining visibility. However, its most important aspect is in preventing cold shock to the semen, which is permanent injury to the sperm caused by sudden increases or decrease in temperature during freezing and thawing. This is done through the addition of egg yolks and milk which not only insure isolative properties but also provide the sperm with important nutrients necessary for metabolism. Another

6 property of the extender is to prevent marked changes in the ph that are caused by lactic acid produced by sperm activity. This is achieved through the use of a buffering solution, usually sodium phosphate. In 1946 another breakthrough occurred when the addition of antibiotics was added, this limited the number of organisms found within the sperm, which although not all pathogenic compete with the sperm for nutrients and therefore lowers the sperm count. With the introduction of penicillin and streptomycin, researchers saw a dramatic increase in conception rates. Today the most widely used antibiotics are Gentamacin, Tylosin, and Linco-spectin, which all aid in the control of major pathogens found within the semen such as Urea Plasmas. The final component of the extender is the addition of a cryoprotectant, which maintains the viability of sperm during freezing and thawing. There are two classes of cryoprotectants which are made up of cell penetrating groups which include glycerol and dimethyl sulfonate, and non-penetrating groups which are composed of milk protein and egg yolks. With preference given to the cell penetrating group, as it has a longer shelf life. All of these advancements have allowed for semen to be stored for extended periods of time, which has opened up a wider market compared to when semen had to be shipped and inseminated within days of extraction. Today semen can be stored for weeks to years, and has even been reported to have been kept for up to fifty years without observing any major defects to the sperms morphology. The actual processing of the semen is performed after the diluter has been prepared the day before. The diluter is then split into two parts; one containing a cryoprotectant and the other one lacking. The part lacking is first warmed in a bath of water and the semen upon collection is deposited into it. Once together antibiotics are added, and the semen must remain in contact for three to five minutes. The semen is then

7 treated with lecithin and lipoproteins to prevent further cold shock. The mixture is gradually cooled to 5 o C over a two hour period which slows down the sperm motility and therefore decreases the metabolism requirements. It is at this point that the semen can be used in liquid insemination and will remain viable up to a week in cattle and a slightly shorter time frame for other species. However, if the semen is to be frozen an equal volume of the diluter containing the cryoprotectant is added and the semen is packaged into semen straws, which are sealed and then stored for an additional four to six hours at 5 o C. After this interval has passed the semen is placed in tanks filled with liquid nitrogen which is maintained at a temperature of -196 o C and can be stored for extended periods of time. Early freezing techniques used dry ice as a coolant but this required constant monitoring and replacement and could only be effectively applied to liquid semen transport. Presently, liquid nitrogen is used as the coolant of choice because at -196 o C it provides longer storage intervals and only requires refilling every six to nine months. Thawing of the semen is a critical point in the insemination process and without proper precautions executed the semen can be damaged. Once the straw has been removed from the tank, it should be instantly placed in a water bath for ten to sixty seconds. The temperature should be gradually increased to around 90 o C and maintained at this temperature for a minimum of forty seconds. It is vital at this stage that all insemination equipment be clean, dry, and warm in order to minimize the impact on the sperm. Once thawed, the semen can be deposited into the cow. Estrus detection in the females is vital in properly executing an A.I. program. Signs that a cow is entering estrus can be observed by watching for increased activity, riding or mounting of herd mates, swelling and moistness of the vulva, and finally

8 standing to be mounted. After estrus has been detected, the procedure of Recto-Vaginal Insemination can be applied, which studies have shown to have the highest success rate. This method of insemination is done through inserting the instrument through the vulva into the vagina and then through the cervix channel and deposited into the uterine body. Insemination should occur approximately twelve hours following standing heat to result in maximum conception rates. The whole process of thawing and insemination should not exceed fifteen minutes in order to minimize any unnecessary environmental factors that may affect the quality of the sperm. The primary focus of Artificial Insemination is to increase genetic superiority by seeking out only the most desirable traits in order to maximize profits. At the same time controlling diseases, lowering breeding costs and possible losses associated with maintaining a natural sire. Currently 1.3 million beef cattle are being A.I. d each year and interest is growing in other sectors such as horses and swine. Artificial Insemination does have its drawbacks however, in that estrus detection must be good and for best results a trained inseminator should be utilized. With the recent Bovine Spongiform Enephalopathy (BSE) scare the cattle industry was hit hard and stricter regulations have been put on semen export abroad in attempts to minimize the possible spread of the debilitating disease. The International Animal Health Code established between Canada and the United States reads as follows, Regardless of the BSE status of an exporting country, Veterinary Administration should authorize without restriction the import or transit through their territory the following commodities semen and embryos. 2 Canada and the U.S. have recognized this agreement and semen export saw only a minimal decline, however many other countries did not accept this statement and trade 2 Quoted by Rick Rasby, Beef Specialist at the University of Nebraska.

9 was ceased, serving a major blow to Canada s international markets. Recent protocols, however, put in place by the government have made the export of semen easier and international markets are once again being opened to Canadian semen. Overall A.I. offers an acceptable alternative to the traditional natural way and as the demand for the highest quality product increases, the need for having only the best genetics at hand will become more vital to the survival of much of the commercial and private sectors.

10 References M.P. Mostari, M.G.M. Fahman, M.A.M.Y. Khandoker, S.S. Husain; Evaluation of Bulls Based on Semen Quality and Herd Fertility 2004 Pakistan Journal of Biological Sciences, Bangladesh E.S.E. Hafez, B. Hafez; Reproduction in Farm Animals Seventh Edition 2000 Lippincott Williams & Wilkins, Maryland USA P.L. Senger; Pathways to Pregnancy and Parturation 2 nd Edition 2003 Cadmus Professional Communications USA American Breeders Services: A.I. Managements Manual 2nd Edition DeForest WI Virginia Cooperative Extension Service: "Estrous Synchronization and Artificial Insemination in Beef Herds" Blacksburg VA Blockey. M.A The Influence of Serving Capacity of Bulls on Herd Fertility. Journal of Animal Science 46:589 Toelle, V.D. and O.W. Robinson: Estimates of genetic correlations between testicular measurements and female reproductive traits in cattle Journal of Animal Science 60:89 Ball, L., R.S. Otto, R.G. Mortimer: Manual for Breeding Soundness Examination of Bulls Journal of Soc Theriogenology 12:1-65 Blockey, M.A. de B. and E.G. Taylor: Observation on spiral deviation of the penis in beef bulls Aust Wet J 61: Animal Improvement Programs Laboratory, USDA, Beltsvile, MD Rick Rasby Beef Specialist Animal Science Building University of Nebraska Lincoln, NE.