A.I. (cattle)

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Comparative AI in pigs and cattle
By Stuart Revell - Senior Veterinary Surgeon (Research) Genus/ABS. When studying comparative reproduction in farmed mammals, they don’t come much more different than cattle and pigs.

 
These differences are related to very dissimilar natural lifestyles.

Cattle are herd animals, where the principal male cannot afford to spend too long mating each individual as he has to keep rivals away, and numerous, small ejaculates are the order of the day.

Pigs are more solitary woodland animals who are not pushed for time, so copulation can be prolonged and a very high volume ejaculate produced. Herd females, constantly on the move, can cope with no more than one or two offspring, whereas a sow with a well-chosen den can cope with more, less immediately mobile, young.

The bovine lifestyle has a number of advantages for AI. The volume of the ejaculate is low, but the sperm count is high, because the cow’s cervix presents a barrier to the male. Most sperm never make it through the cervix, but AI technicians can deposit semen in the uterus, thus stealing a march on nature and allowing a very low sperm dose to be used.

In pigs, the boar’s penis locks into the sow’s cervix, so ejaculation is into the uterus. Pig AI equipment gets no further into the female than the boar does, so the sperm dose and volume used must be closer to those of natural service. Boar semen collection and processing is a lot of work in relation to the reward.

The bovine advantages continue when freezing is considered. Bull sperm are resistant to the many stresses of freezing and thawing, and frozen semen can be as fertile as fresh. Boar sperm are much more sensitive, which greatly limits the usefulness of freezing and makes the process more complex.

However, cattle don’t have it all their own way. Dairy farmers turn envious eyes on the conception rates routinely achieved in pigs, and oestrus closely tied to a clearly defined event like weaning also has its attractions.

 

February 2007

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 Section:
 
Sexed Semen: Is it Finally a Reality?
By University of Minnesota Extension and presented at the University of Minnesota Dairy Days-2007. Most of us have heard the rumor that sexed semen is “just around the corner” for as long as we have been aware of A.I.

Through the years, countless numbers of techniques have been investigated with no potential application in the real world. However, in the 1980’s a breakthrough in semen sexing technology was made by USDA researchers in the Lawrence Livermore Laboratory in California. The patents for this technology were licensed to a company named XY, Inc. of Fort Collins, CO, which performed extensive research during the 1990’s to optimize efficiency of these sorting procedures. In 2001, Select Sires partnered with XY, Inc. to set up field tests on the flowcytometer processed semen.

Flow-Sorting Technology
One of only a few repeatable techniques to sex sort sperm at a high level of purity uses a device called a flow-cytometer to detect a 3 to 4% difference in DNA content between male and female sperm and sort them with upwards of 90% purity. The first step in this procedure is to dilute sperm to a very low concentration and stain them with a fluorescent dye. The sample is then sent through the flow-cytometer at 60 mph under 30 to 60 psi of pressure. As sperm pass through the internal laser beam, the fluorescent dye is excited. Because of the larger X chromosome, female sperm emit slightly more light than male sperm, which possess the smaller Y chromosome. Detectors measure the amount of fluorescence and assign positive or negative charges to each droplet containing a single sperm. Charged deflector plates then split the single stream into 3 streams: positively charged particles containing one sex go one way, negatively charged particles containing the other sex are deflected in the opposite direction, while uncharged droplets containing multiple sperm or unidentified sex pass straight through. Confirmed with tens of thousands of offspring born in worldwide research trials, the procedure separates sperm of the two sexes with ~90% purity. However, that still leaves 10% of the undesired sex available to compete for fertilization. The figure below illustrates the probabilities of all possible occurrences of offspring generated by 90% pure sexed semen.

Probablities of all possible occurances of offsping gender from 10 pregnancies generated by 90% pure sexed-semen.


Commercialization of sexed semen in the U.S. was initiated with a 2003 license granted to Genetic Resources International (GRI) in Navasota, TX. In late 2004, Select Sires partnered with GRI and sent four proven sires to Texas to begin collection and processing of sex-sorted semen. During 2005-2006, Select Sires conducted a nationwide field test and collected information on over 27,000 services. These trials were conducted in a random sample of herds with average or better reproductive efficiency in order to accurately assess product performance for the “average producer.” The resulting calvings have a current data set of nearly 7,000 offspring so far with a gender ratio of 89% heifers when using sexed semen.

Technology Limitations
There are several major limitations that have stifled implementation of sex-sorted semen. Without question, reduced conception rates have been a primary hurdle. As you can imagine from the description above, sex sorting of sperm is a highly invasive procedure that negatively impacts sperm viability and longevity compared to normally cryopreserved semen.

Gender Bias of Calves Reported To Date



Source: 2005-2006 Select Sires Field Data
In addition, the procedure is extremely slow and inefficient. To properly sort, sperm must be precisely oriented as they past through the laser and fluorescence detectors in the flow cytometer. Due to the flat shape of bovine sperm heads, only about 30% are correctly oriented and half of these are female. Thus, only 15% of the sperm going into the machine are recovered as a marketable, sexed product. The high rate of sperm loss precludes use of Select Sires’ “most elite” sires for production of sexed semen.

Conception Rates



Source: 2005-2006 Select Sires Field Data
Although the 3,000 to 5,000 sperm of each sex sorted per second sounds like a lot, this translates into ~1.3 hours of sorting to process enough semen for a standard 20 million sperm/straw dosage. Thus, due to the slow sorting speed, commercialization is only possible with very low sperm numbers per dose (~2 million). If these limitations were not enough, the high cost of flow cytometry equipment (~$250,000 per machine) and intensive amounts of highly skilled labor required to sort sperm dictates that sexed semen will not be inexpensive. Because of the low sperm numbers per dose and compromised sperm viability, Select Sires only recommends its use in well-managed, highly-fertile, virgin heifers. While many research herds have realized very acceptable conception rates, averages indicate well-managed herds that achieve 60 to 65% conception rates in virgin heifers with normal semen can expect 45 to 55% conception rates with sexed semen.

Based on the favorable field results, Select Sires began marketing sexed semen in the fall of 2005. In early 2006, four sorting machines were installed at Select Sires headquarters in Ohio to expand the sexed semen lineup. In the fall of 2006, two additional sorting machines were added to bring the annual production capacity to 350,000 straws. Orders for sexed semen have exceeded our expectations.

What Is The Return On Investment For Sexed Semen?
The return on investment for the dairy producer depends on a complex interaction between the initial conception rate with non-sexed semen, the percent reduction in conception (if any) due to use of sexed semen, the price differential between sexed and conventional semen, expected gender ratio for sexed vs. conventional, and the value differential between bull and heifer calves. Most of these factors will change considerably from herd to herd, which differentially affects the breakeven value of sexed semen to each respective producer.

To calculate a return on investment (ROI), Select Sires has recently developed a sexed semen calculator in Microsoft Excel format that incorporates more than 20 other variables, which will vary from herd to herd. It will assist you in determining how this new opportunity can best be utilized in your individual operation.

Based on the product available today, the best return on investment will be achieved by limiting this product to virgin heifers only and following the “Keys to Success” (see below) to ensure optimum probability for conception.

Keys To Success
Use of sexed semen will require a breeding gun designed to accommodate the smaller diameter ¼ cc straws. Straws are to be thawed and handled identically to their ½ cc counterparts. However, the smaller diameter and compromised semen quality will make them much more sensitive to coldshock and errors in semen handling. To maximize potential for success:

Thaw straws in 95°F water bath for 45 seconds.
Semen thawing and handling environments should be warm and draft free.
Warm all semen handling equipment including guns, sheaths, and paper towels prior to contacting straws.
Only highly experienced technicians should use this product.
Use only in well-managed, virgin heifers that have achieved greater than 60% of their mature weight by 14 months and in moderate or better body condition.
Inseminate heifers 8 to 12 hours after observed estrus (AM/PM Rule).
Use of estrus synchronization and breeding to observed estrus is encouraged, but use of timed-AI in the absence of observed estrus is discouraged.
Other Methods of Sorting Semen
A number of new sex-sorting technologies and companies have recently appeared. Other methods include gender specific antibodies, centrifugation, and free flow electrophoresis. As you evaluate other technologies, please take the time to be wary, and ask numerous questions in order to make informed decisions. If the sex-sorting technology is not based on flow-cytometry and the patents developed by USDA, you should ask for scientific evidence that the procedure can, in fact, sort sperm. Accept nothing short of hundreds of births to assess whether the procedure can effectively produce offspring of the desired sex. Similarly, conception data should be based on thousands of services and should be based on palpated pregnancy data, as simple non-return data may mask results and distort the success that can actually be achieved. To date, only flow cytometry provides the best combination of sorting purity and commercial adaptation.

Summary
There is no question sex-sorted sperm for gender selection is now a reality. The product currently offered by Select Sires is backed by over 5 years of extensive field research and has been rapidly accepted by the U.S. marketplace. Currently, 18 of the 23 proven Holsteins and 2 of the 3 Jersey sires in the Select Sires sexed semen lineup have demand that exceeds the supply.

Because of continuing research, there will likely be improvements to the product and there will be the potential to utilize sex-sorted semen on lactating cows but current fertility results indicate its best fit right now is on virgin heifers.

List of Articles in this series
To view the complete list of 2007 Dairy Days

October 2007

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Natural Service versus Estrous Synchronization and AI
By Ryon S. Walker, Regional Extension Educator, University Of Minnesota Beef Team. This time of year producers are planning their summer breeding season schedules.

 

In the months prior to the breeding season, producers are fine tuning their herd bull management. Every year the question always sits in the back of most producers’ minds whether they should try using estrus synchronization and artificial insemination (AI) this year. However, the lack of change and a producer’s management goals usually persuade the use of natural service breeding over estrus synchronization and AI from year to year. The question remains, if goals such as length of a calving season, reproduction, growth or carcass performance are being achieved with natural service breeding, why change. Remember there are pros and cons to both natural service versus estrus synchronization and AI. Utilizing natural service requires management of factors affecting fertility of bulls such as nutrition, health, injury and age and having to purchase herd bull replacements of superior quality and genetics can become costly to a producer as well.

While most producers continually use traditional natural service breeding, reproductive biotechnology has been introduced over the years to assist producers in becoming more profitable in their management decisions. Artificial insemination was first used in the U.S. ( Minnesota) in the late 1930s with estrus synchronization receiving some popularity in the early 1960s. However, it’s amazing to note that a 1998 national survey indicated less than 12% of beef producers in the U.S. use any means of estrus synchronization and less than 14% use artificial insemination. This study represented 85% of all U.S. beef cows and 66.3% of all U.S. beef operations as of January 1, 1997. This survey (conducted by the National Animal Health Monitoring System) also indicated that time/labor, the technology not working, lack of facilities, cost and the technology too complicated were five reasons for producers not utilizing these technologies with time/labor being the number one reason among beef cattle producers. Natural service, no doubt, may be the easiest method of breeding cattle for producers that may not have the time and labor required to implement estrus synchronization and AI; however, several production goals can be implemented into a management system with quicker results utilizing these reproductive biotechnologies.

The benefits of using a breeding system that incorporates estrus synchronization and AI can be tremendous. These systems allow producers to reach certain production or economic goals quicker than natural service and can open the doors to value added markets as well. These benefits include:

Shortening and concentrating the calving and breeding season


Increasing the time needed for postpartum recovery in cows and first-calf heifers


The ability to induce anestrous cows and prepubertal heifers to cycle


Moving the breeding season to an earlier time of year


Introducing new genetics into the herd


Improving the uniformity of a calf crop (weight, color, disposition)


Increasing calf performance and weaning weights with earlier birthdates
Estrus detection can be a time and labor consuming process, which makes artificial insemination programs impractical for some beef cattle producers. Estrus detection can be eliminated by breeding animals at a designated or pre-determined time, also known as timed-AI or mass mating. Estrus synchronization systems that incorporate timed-AI have advanced in their ability to control the estrous cycle and induce ovulation at a pre-determined time. Pregnancy rates to timed-AI have matched or exceeded pregnancy rates to AI and twice daily heat detection allowing producers the opportunity to incorporate these technologies without too much time and labor involved.

The use of estrus synchronization and AI has been advocated as a way to breed females in a shorter time period and improve the genetics of a cow herd and its progeny without the expense of buying superior bulls. Introducing specific lines of genetics provide openings for niche marketing and value added products. Opportunities for value added beef are increasing with demands from major retailers requesting source verification. Age verification from AI calves may become a requirement for the eligibility of beef products for overseas markets. Estrus synchronization, along with artificial insemination, can be a valuable tool for smaller operations where the number of cattle (1-25 head) may not justify the cost for purchasing a bull of superior quality and genetics. Synchronization programs are also available to be used for natural service breeding to concentrate the calving season further without the use of AI. There is a new user-friendly Excel software program (Estrus Synch Planner) available that allows producers to customize their breeding season to best fit his/her operation utilizing 22 estrus synchronization protocols and three different methods of AI.

Today, estrus synchronization and AI remain to be the most available and widely applicable reproductive biotechnology available to beef producers. However, the low adoption rates of these reproductive technologies question the direction of the beef cattle industry in the U.S. and competitive intuition among beef producers. The United States and Brazil are world leaders in total number of beef cows in production; yet, beef producers in Brazil are inseminating 3.5 times more cows annually than U.S. beef producers. Unless beef cattle producers in the U.S. become more aggressive in their approach to reproductive management and genetic improvement, the competitiveness for supplying high-quality beef with other countries will increase.

March 2007