IMPROVE PREGNANCY RATES WITH PROPER SEMEN HANDLING

by: Whitney Whitworth

In addition to proper heat detection, the area in which operations can make huge strides in improving pregnancy rates to artificial insemination is in correct handling of semen. From the time semen is processed at the bull stud to the time it is placed in the cow, proper techniques must be used to ensure the highest rate of survival of sperm cells. The majority of bovine semen is packaged in .5 mL or .25 mL straws, which have advantages over ampules used in the past: more straws can be stored in a tank and they thaw faster due to the surface area to volume ratio.

When semen is purchased from a bull stud, breeder service or reputable breeder, it will be shipped to the operation in a semen shipper with enough liquid nitrogen for just a few days. It is imperative that the semen be put in a storage tank with adequate liquid nitrogen as soon as it arrives at the operation where it is going to be used. The same rule applies when straws are transferred from one tank to another, it should be done as quickly as possible. Two people should be there to facilitate the operation, with the main goal of keeping the semen from being exposed to elevated temperatures for extended periods of time. Any time that semen straws are not held at low temperatures can reduce the fertility of the sperm cells. Therefore, the faster and smoother the transition occurs, the more likely the straws retain maximum number of live cells when thawed.

Liquid nitrogen tanks should be closely monitored. It is recommended that the nitrogen level in the tank be checked daily or at least weekly. That can be done in a variety of different ways, even something as simple as placing a yardstick in the mouth of the tank once a week and recording the level in inches. Most tanks are designed to hold nitrogen well for several weeks, but it is common for them to lose their vacuum if they are not treated with care and maintained properly. As the vacuum and the heavy level of insulation in the tank allows for the capability to hold the nitrogen, anything which damages the vacuum will cause nitrogen loss. The inner liner of the tank which actually holds semen is suspended in the neck of the outer layer. Excessive jarring and shaking of the tank should be avoided so that the connection between the two layers is not damaged. When damage occurs, the tanks lose nitrogen faster than in a normal situation. If this goes unnoticed, a producer could lose thousands of dollars of valuable germplasm. If a tank shows excessive frosting or condensation on the outside, then the vacuum is most likely damaged. It is very important that the tank not be moved more than necessary and also that it is not stored directly on concrete. If tanks are maintained in conditions which are wet or not well ventilated, it will shorten their lifespan. Tanks should be kept in an area with good light, but out of direct sunlight. Good light will help a technician work in the tank without raising the canisters too high in the neck of the tank. There is a distinct frost line in the neck, and raising and lowering canisters above this line should be avoided. There can be over a 200 degree temperature rise going from six inches from the top of the tank to one inch from the top. Once the straws are exposed to higher temperatures, any damage to the cells is irreparable, even if the straw is placed back in the nitrogen.

When it is time to breed a cow, there is a series of steps which must be followed in order to keep semen quality as high as possible. The straw to be used in a particular cow will need to be located as quickly as possible. Having an up to date inventory of what is in each canister in the tank is critically important to facilitate timely removal of semen from the tank. To hold the canister in the neck of the tank, some technicians will use a clothespin to balance it so that they can use both hands to work. When removing a straw from the cane, tweezers should be used to grasp the straw. Bending the tab on the top of each cane is often beneficial so that a technician can determine which canes are in use or are not full. It is a good idea to shake each straw before placing it in the thaw bath in order to remove any excess liquid nitrogen. Thaw baths should be checked regularly to ensure that the water temperature is correct, between 95 and 98 degrees. Ideally, only one straw at a time should be thawed. If more than one straw is thawed at a time straws may actually ‘freeze' together in the thaw unit and be difficult to separate, even causing them be destroyed. It is also more difficult to judge how much time is needed for each straw, as placing several straws in the bath together can cause an excessive temperature drop, making conventional timing unreliable. Time a straw should be in the thaw bath varies depending on the stud or service who processed the semen when it was obtained from the bull and what extender was used. Times required will be at least 40 seconds, and in many cases, 60 seconds. Always check with the bull stud who processed the semen for the most accurate thaw time. Straws can be left in the thaw bath for a few minutes, but this is not normally desired.

The point where the straw is removed from the thaw bath and is readied for placement in the insemination gun is a critical control point. Special care needs to be taken in removing all of the water from the straw as it is spermicidal. It is also important that the straw not be cold shocked by placing it in an insemination gun which has not been warmed. Running a paper towel up and down the length of the gun to create friction will warm it up. Also, many inseminators will place the gun in their shirt both before and after the straw is loaded in it so that body heat will keep it warm. When placing the straw in the gun, pay attention to keeping it out of the light. Light, along with water and urine, are spermicidal. Cutting the end of the straw is also a control point. Scissors should not be used as they can crimp the end of the straw or not cut straight. If a straw is not cut straight, there is a chance that it will not fit squarely in the sheath and the semen will escape between the gun and sheath. Straw cutters should be cleaned and maintained properly to ensure their maximum useful life.

After the gun is prepared, cattle should be bred as rapidly as possible. This will ensure that optimum semen quality is maintained and animals remain calm. Females which are in the chute for short periods of time and handled quietly will be more likely to settle to insemination. Anything which can reduce stress will do nothing but enhance reproduction.

No matter how experienced the technician, it is always important to stay on top of the steps in semen handling. Artificial insemination is arguably one of the most powerful tools on the ranch which allows for the ability to make great changes in the herd. Any advantage which may be gained by being vigilant in your preparation will be well worth it. Best of luck with in the spring breeding season!

(Reprinted with permission from the March 2017 Beefmaster Cowman.)







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