How Many Straws Should You Thaw?

Dairy Herd Management

A fine line exists between taking a shortcut and finding a more efficient way to do a job. That is certainly true when it comes to preparing semen straws for insemination. Many AI technicians have found that thawing more than one straw of semen at a time helps them tackle big breeding assignments, such as groups of synchronized cows that all need to be inseminated.

However, thawing multiple straws doesn't mean taking shortcuts on other procedures.

"If inseminators do not follow the recommended semen handling procedures, they are destined for problems no matter how many straws they thaw, even one," says Mel DeJarnette, reproductive specialist with Select Sires, Plain City, Ohio.

Thawing multiple straws of semen can be a way for you or your AI technician to breed a large number of cows efficiently without compromising semen quality or the conception rate of inseminated animals. However, you must follow proper procedures for straw preparation, thermal protection and work within limited time contraints.

Study caused confusion

A paper presented at the annual meeting of the American Dairy Science Association in 1997 resulted in confusion regarding the ideal number of straws to be thawed prior to insemination.

The trial, conducted in Hawaii, evaluated fertility when four straws of semen were thawed at one time, placed into AI guns, and used to inseminate cows. Conception rates for the 89 inseminations declined from 47.6 percent for the first gun prepared, to 41.2 percent for the second, 37.5 percent for the third, and 25 percent for the fourth.

Yet, it cannot be concluded that the fertility decline resulted from thawing more than one straw of semen at a time, because the researchers did not maintain adequate thermal protection. Rising temperatures inside the barrel of the loaded AI gun - due to warm outdoor temperatures - were associated with a reduction in semen viability over time.

Other research has found that as many as 10 to 20 straws of semen (depending on the type of thaw bath used) can be thawed at 95 F at one time without compromising semen quality. However, the study, conducted at Washington State University and reported in the 1991 Journal of Animal Science, advised that straws of semen should not be allowed to touch one another during the thaw process, because that could slow thawing and compromise semen viability. Therefore, in most on-farm thaw baths - containing around 1 pint of water - about four to five straws can be thawed at the same time.

Skill level critical

Despite research proving more than one straw can be safely thawed, AI experts often caution producers about preparing multiple guns because of the skill and proficiency in semen preparation and thermal protection it requires.

For example, thawing multiple straws often drains heat from the thaw bath, says Neil Michael, veterinarian and director of technician services with ABS Global in DeForest, Wis. Inseminators must monitor temperature between batches carefully to ensure it's maintained at 95 F to 98 F, or sperm viability diminishes.

Similarly, researchers say that sperm can live for one hour after thawing if maintained at between 95 F and 98 F. Thus, loaded AI guns must be thermally protected until deposited in the cow. Failure to do so can decrease sperm viability also. However, the percentage of live sperm declines in that hour, leading AI experts to recommend getting semen into the cow within 10 to 15 minutes after thawing.

Field study shows consistency

When inseminators guard against mistakes in semen preparation and thermal protection, more than one straw of semen can be thawed without lowering the conception rate of cows. In fact, two field trials that monitored inseminations by professional AI technicians show consistent conception rates from the first to last straw prepared.

The chart on page 49 contains information on thousands of inseminations where multiple straws were prepared by AI technicans from ABS Global and Paddocks Breeding Service. Conception rates were consistent across guns - with both groups having an overall conception rate between 32 percent to 33 percent.

Mike Sprenger, a technician with Paddocks who has inseminated 125,000 cows in his career, monitored the time it took him to prepare and breed AI guns on 266 occasions (1,435 breedings), and found that he typically took just under eight minutes on three guns, and just under 14 minutes on seven guns. Despite the data, he says producers often tell him to thaw just two straws when breeding cows in their herd, in an effort to increase conception rates. This mandate often slows his work and does little to improve the conception rate in the herds, he says. That's because his conception rate on the first two guns is within one to two percentage points of his average on all guns.

Do you get consistent conception rates - similar to these field trials - when you prepare multiple straws? Do you have good semen preparation and thermal protection procedures? The only way to know for sure is to track the gun number and subsequent conception rate when inseminating cows.

Heat and cold stress create challenges

One of the biggest problems when artificially inseminating cows is to maintain semen temperature at 95 F to 98 F until deposited in the cow. Review the following thermal protection procedures to ensure that the semen remains viable after thawing:

1. Warm the AI gun. To ensure semen viability, AI experts recommend warming the AI gun prior to inserting the straw. Researchers at ABS Global have compared the difference between semen thawed to 98 F and placed in a cold AI gun (41 F) and semen thawed at 98 F and placed in an AI gun that had been pre-warmed by vigorous rubbing with a paper towel (98 F). After being exposed to the air temperature for one minute, the semen temperature in the cold gun dropped by 35 F, causing sperm damage, while the sperm in the pre-warmed gun dropped 21 F, causing no damage.

2. Thaw in 95 F water. To ward off cold shock, or the rapid cooling of semen, some inseminators in cold climates have tried skipping the thaw bath and placing the straw directly into the AI gun - in the belief that semen will thaw once it reaches the cow's reproductive tract. However, research conducted by Mel DeJarnette, reproductive specialist at Select Sires, has found that this practice - called air thawing - actually does more damage to sperm quality than cold shock.

"On a scale of one to 10, with 10 being a procedure most damaging to semen, cold shock is about a five or six, while improper thawing is a 12," says DeJarnette. "If you don't thaw semen properly to begin with, you don't have to worry. Dead sperm are not susceptible to cold shock."

3. Watch out for cold stress. It's difficult to pinpoint a specific temperature when cold shock occurs or how much damage will result. DeJarnette says the outdoor temperature, the amount of time the semen straw is exposed to these temperatures, wind speed, the speed and severity in which the semen's temperature drops, and even the individual bull, are all factors in the equation.

To combat cold shock, inseminators must place straws in the AI gun quickly and place the gun near their body to maintain a temperature of 95 F to 98 F while transporting the gun to the cow. In large dairies, where preparation and breeding occurs in unheated facilities, DeJarnette suggests converting an old van into a breeding center. This allows you to prepare semen in a heated environment, away from the elements and near the cows.

4. Be prepared for heat stress. Similar to cold stress, heat stress does not become a concern at a certain temperature. However, when temperatures rise above 100 F and/or the humidity is greater than 50 percent, you should take precautions says Arun Phatak, veterinarian with ABS Global. In these extreme conditions, cut back on the number of straws thawed at one time and try to load guns in a cool environment, such as a vehicle or room with air conditioning.