by: Heather Smith Thomas

The first sex-selected calf conceived from frozen sexed semen was born in the early 1990's, and in 2004 this technology became commercially available. Sexed semen has been used the most by dairymen, since it's more desirable to produce heifer calves than bulls in that industry. The earliest research on semen sorting was done in the 1980's at Colorado State University (with a USDA grant) and this technology has been continually improving. Today you can figure that at least 9 out of 10 calves produced by use of sexed semen will be of the desired gender.

Currently, a growing number of beef producers are beginning to utilize this option. Depending on their needs they can tweak their calf ratio to have a higher number of bull calves from their best cows (if they are seedstock producers selling bulls) or more steers from a terminal cross, or more replacement heifers. This is an excellent way to raise good replacements from selected cows.

Seedstock producers may use bloodlines with maternal qualities for brood cows and other bloodlines they'd use for marketing bulls. In female sales, bred cows and heifers are often worth more if bred with sexed semen. Some buyers want heifers guaranteed to have heifer calves while others want females that will produce only male calves. There may be a good market for offering good female bloodlines in a 3-way package—a cow with heifer calf at side and bred back to have another heifer calf.

Sex determination can be an advantage for reducing calving difficult in first calvers, since heifer calves are typically smaller at birth than bull calves. You may also want your best cows to have heifers, giving you a chance to make faster genetic progress in improving your herd, enabling you to keep more good females and cull more deeply. Some producers may opt to get heifers from the top 10 to 15 percent of their cows and steers from the rest of the herd.

The University of Idaho Nancy Cummings Research Ranch at Salmon, Idaho has done a two-year study on the use of sexed semen to generate replacement heifers. Even though this was a research trial, the heifers produced are being utilized as replacements for the University ranch herd.

Dr. John Hall, Superintendent at the research ranch, explained that the original herd of donated cows represented many breeds and now the Center is trying to build more uniformity into the herd. “We want to eventually have a black baldy cow base. One of the stipulations for our herd is that it be functional and efficient, paying its way just like any other rancher's commercial herd,” says Hall. The cattle must make a profit, just like they would in the real world. They have to pay their own way, and generate the money to pay all cattle and ranch expenses as well as some salaries of the Center's employees. The sexed semen project was a way to produce a uniform group of heifers from the best cows on the ranch.

In 2008 they bred 37 cows with X-sorted semen from the Angus bull Bon View New Design 878, with semen supplied by ABS Global. They only bred the cows that were observed in natural heat, and had a 67 percent pregnancy rate, which is very high for sexed semen. “This high success rate may have been partly due to the fact that we pre-selected the cows, and we only inseminated the individuals that we observed in heat,” said Hall.

The rest of the cows in that group were bred to a cleanup bull introduced later into the herd. When the calves were born in the spring of 2009, there were 22 AI calves from the sexed-semen inseminations.

“Of the 22 AI calves, 21 were female and one was male, which is pretty typical for the ratio you'd see when using sex-sorted semen. In that small group of cows—some of which settled to the sexed semen and the remainder to the cleanup bull--we shifted the sex ratio to 77 percent female and 23 percent males,” said Hall. This kind of program would enable a producer to pick out his best cows and breed them with sexed semen from a bull with outstanding maternal qualities to sire replacement heifers—and have a greater probability of having heifer calves. Conversely, a rancher wanting mostly steers to sell could breed all his cows with sexed semen from a bull that sires offspring with outstanding growth and carcass traits.

“We are very excited about the possibilities for this, and have been working with ABS Global, the company that provides the sexed semen for us,” says Hall. In 2009, the research ranch bred 100 cows with X-sorted semen, using fixed time AI and heat synchronization (breeding the cows all at one time, on one day), as a test to see how well this might work in a more typical producer situation. In this research trial, the conception rate was only 48 percent, with the remainder of the cows settling a cycle later to the clean-up bulls.

The Center and various semen companies were interested in finding out how well this method might work. Even though sexed semen costs about double the price of regular semen, this may still be a tool some producers might choose if it means more guarantee of getting replacement heifers from their best cows, or more steers to market if this is their goal.

Adam Simmons, the ABS Global representative (from Idaho Falls, Idaho) who worked with the research ranch on this project says that any rancher can order sexed semen through his company. “There is some information that we give to the producer and require that they review before they purchase sexed semen—because you don't get as high a pregnancy rate using it, and we want our customers to be fully aware of this fact,” says Simmons.

For instance, customers need to realize that during the sorting process some sperm cells are lost and all cells of the undesired gender are discarded, leaving less total sperm cells. This lower sperm concentration may adversely affect fertility, resulting in lower conception rates.

“Currently we only recommend its use on heifers, in a natural standing heat. The university trials are being done to see how well it can do on cows that are synchronized, but due to the extra cost of sexed semen and the lower conception rate (not as high as with regular AI) we still just recommend it only for heifers—because the AI conception rates for them is typically better than for cows anyway, and conception on natural heat is better than with synchronized heats,” he explains. This would give a producer the most success for the dollars spent, since sexed semen is more expensive than regular semen and you don't want to waste this expense with a poor conception rate.

One of the questions asked by producers is whether semen from any bull can be made available for use as sexed semen or if only certain bulls' semen is available in this form. “In general, only certain bulls are being offered, by various semen companies. ABS has the broadest selection, of all the AI companies. But we also offer this service on any bull the rancher might want to try,” says Simmons.

“Most of our competitors outsource their sexing. ABS actually owns the technology and thus they brought the sexing facility right to our home lab in Wisconsin. We therefore have the capability to sort semen on any bull desired. There are always some exceptions, but basically if a customer wanted this service on a certain bull, and agrees to buy everything that is collected on that bull in one collection, we will do any bull you want—as long as that particular bull's semen will freeze and go through the sexing process. Thus a producer could purchase sexed semen (choosing male or female calves) from just about any bull that we offer,” says Simmons.

In general, however, ABS offers a fairly broad range of bulls to choose from, in which sexed semen is already readily available. “We have a regularly updated list of these bulls,” he says.

The costs for sexed semen will depend somewhat on the base cost for the semen from each individual bull, with an additional charge for the sexing. “Sexed semen is more expensive than regular semen, just because about 2/3 of the semen is wasted when it is sorted,” he explains.

“As a rule, conception rates are about 10 percent lower with sexed semen than with conventional semen. Producers always have to realize that conception rates in general will vary from ranch to ranch, depending on who is doing the AI work, the condition of the cattle, etc. Some ranchers will get only 40 percent conception while others get 70 percent conception rates with conventional AI. You can usually figure that sexed semen rates will be about 10 percent lower than that ranch's typical AI conception rate,” he says.

For best results, ABS recommends that producers carefully follow their published guidelines for semen thawing and handling, and use highly experienced and trained ABS professionals for the inseminations. Highest conception rates will be obtained on well grown, well managed virgin heifers, with the inseminations taking place 12 hours after the heifers are first observed in standing heat.

Some commercial producers are opting to use sexed semen because they can raise replacements from their best cows, knowing that almost all of the conceptions will result in heifer calves. These will be often be better than any heifers they could purchase—since they know the history on their own cows and can select the genetics and traits they want. They can also maintain a closed herd, eliminating the risk of introducing disease by bringing in purchased animals.

THE SORTING PROCESS – Semen can be sorted as to gender because the x (female) chromosome has 3.8 percent more DNA than the y (male) chromosome. The sorting machines can “read” this difference as the sperm goes though in a stream of single droplets. The semen is stained with a fluorescent dye just before it passes through the machine. The female-producing sperm with the x chromosomes are larger and absorb more dye, and thus shine brighter. A laser in the sorting machine illuminates the cells as they pass by the laser beam one at a time, and determines the gender of the sperm based on the amount of light it emits. The fluid stream of sperm goes through at about 60 miles per hour, with more than 4000 sperm per second being sorted and processed. This is 3 to 4 times longer than it takes to process conventional semen, however, and that's one reason it costs more to sort it.

The x-bearing sperm are sorted off in one direction, the y-bearing sperm in another direction, and any sperm of undetermined sex passes straight on through as waste. One advantage to the sorting process is that any dead or damaged sperm are also passed through as waste. A normal ejaculate always has a certain amount of dead, dying or damaged cells, and these are eliminated in the sexing process, making the remaining sperm more viable. Thus a straw of sexed semen is generally more successful in lower dose than regular semen.

There is some variability among bulls regarding how their sperm goes through the sexing process. Some bulls are better candidates for sexed semen than others.


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