Sex-sorted semen in dairy breeding – what’s the latest?

18-07 | |
Use of SS in Florida for example, is enabling genetic progress in dairy herds to improve at a rate twice as fast as a decade ago. Photo: Henk Riswick
Use of SS in Florida for example, is enabling genetic progress in dairy herds to improve at a rate twice as fast as a decade ago. Photo: Henk Riswick

There are many benefits to using sex-sorted semen. Obviously, its use allows dairy producers to lower the chance that bull calves will be born. They can also improve their genetics without exposing their animals to potential new biosecurity threats through the purchase of heifers from other farms.

In fact, the use of sex-sorted semen in Florida. for example, is enabling genetic progress in dairy herds to improve at a rate twice as fast as a decade ago, reports Professor Albert De Vries of the Department of Animal Sciences at the University of Florida in a comprehensive recent study.

It’s therefore no surprise that sex-sorted semen use continues to grow worldwide. The government of India, for example, has started funding the delivery of sex-sorted semen doses to farmers of both cattle and buffalo, as demand for milk in the country continues to grow. Some 50,000 doses of sex-sorted semen are being delivered to farmers each year for the next 4 years.

In North America, according to recent research by Dr George Seidel of Colorado State University and Dr J.M. DeJarnette of Ohio-based Select Sires, sex-sorted semen is rapidly approaching 30% of the total artificial insemination market share.

But the cost (sex-sorted semen is about double the price of conventional semen) remains a barrier. Seidel and DeJarnette note that “although cow conception success rates have improved over time, the primary cost of sexed semen continues to be the indirect costs associated with lesser conception rates, which are currently around 80% of those with conventional semen.”

Most dairies in Florida and across the US are using only sex-sorted semen and beef semen, but because fertility rates are good.

Fresh sex-sorted semen, they add, rather than frozen, boosts conception rates to about 95% of the control level, but various studies have found that fresh sex-sorted semen provides no better results than frozen. Dilutants may play a bigger role than is generally perceived in success rate.

To maximise conception, experts recommend using proven inseminator technology and handling frozen sex-sorted semen with extreme care (thawing it correctly and so on). And better conception rates – making the cost of sex-sorted semen more worthwhile – are generally obtained with heifers and second pregnancies versus older cows.

However, the verdict is still out about using sex-sorted semen in the overall breeding strategy, when to inseminate with sex-sorted semen and what insemination strategy to use.

Honing sex-sorting semen use in breeding

The use of sex-sorted semen is being combined on more and more dairy farms with beef semen inseminations in order to maximise profits. Beef semen provides calves with better slaughter value when a heifer is not desired from a particular cow, and sex-sorted semen use allows producers to increase the chance of a heifer calf (and lower the risk of dairy bull calves, which have a lower slaughter value).

A graduate student in the lab of Dr Paul Fricke, a dairy reproductive physiologist at the University of Wisconsin-Madison, is currently analysing a huge data set of about one-third of the Holstein and Jersey cows in the US to determine how semen (conventional, sex-sorted semen and beef semen) is currently being allocated.

But how can producers make the best decisions in terms of the number of sexed-semen inseminations on their specific farms that ultimately provide them with the correct number of milking heifers born on an ongoing basis?

With the right data, says De Vries, who is currently researching this issue with Ron Jackson at ST Genetics (a maker of semen-sorting technology). “Most dairies in Florida and across the US are using only sex-sorted semen and beef semen, but because fertility rates are good, we are producing more heifer dairy calves than are needed,” he says. “This is because you always want a buffer due to stillborns, abortions, heifer non-complete rates, cow cull risks and variations in conception rate. So, numbers of heifers for milking are increasing over time.”

Producers need confidence that the calculations for the proportions of sex-sorted semen and beef semen will really match their farm, says De Vries. He explains that in order to calculate this accurately for a specific farm, you need the farm-specific data for conception rates, abortions, stillborns and heifer non-completes. This data is not easily calculated from the farm’s records. All the better if you have data for a specific heifer on these parameters for her dam and dams going back further.

In terms of producers determining which heifers should be bred to improve herd milk production (inseminated with sex-sorted semen rather than beef semen), that involves genomic testing. De Vries says maybe 10% of producers in Florida currently use genomic testing due to the cost.

Most producers in Florida only look at lactation numbers and the number of breedings, whilst some look at the production history of the cows. Farmers rely instead on the production history of the heifer’s line, but De Vries notes that genomic testing is much more accurate.

When to inseminate

The insemination timing that achieves the best conception rates for sex-sorted semen has recently been studied by Fricke and his colleagues. It’s important that sex-sorted semen is administered at the right time, he says, as it’s been through the sorting process which can damage it a little.

Some studies have concluded that sex-sorted semen conception rates are better closer to the time of ovulation, but Fricke says these studies were flawed. His team and other teams have tested the idea, finding that when ovulation is induced earlier without changing the time of insemination, fertility decreases. Frick is therefore confident that the idea of breeding later relative to the time of ovulation has no value.

However, better conception rates can come from breeding later on activity of oestrus, he explains, due to shorter life span in the female reproductive tract of sexed sperm.

And he and his colleagues have found that timing of ovulation relative to the onset of activity associated with oestrus is greatly variable among dairy cows.

“This is especially true with high-producing cows in which the interval from the onset of activity to ovulation increased as milk production increased,” Fricke says. “Taken together, this is why I recommend the standard timing of AI in a timed artificial insemination protocol (because of the controlled timing of ovulation). This is also why breeding later might be better for high-producing cows inseminated to oestrus in which ovulation occurs later relative to the onset of activity.”

Fricke and his colleagues just completed a study of fertility of Jersey cows inseminated with sex-sorted semen or conventional beef semen after synchronised ovulation or a synchronised oestrus. They presented this data at the American Dairy Science Association annual meeting June 19-22.

Meanwhile, scientists in Turkey have compared conception rates of Holstein heifers inseminated with sex-sorted semen or conventional semen after oestrus detection or timed artificial insemination.

Overall, they found pregnancy per insemination was higher (61%) using an oestrus detection strategy than using a timed insemination strategy (54%), regardless of type of semen. (And as expected, pregnancy per insemination was higher by about 20% for conventional semen versus sex-sorted semen, regardless of insemination strategy.) This team therefore concludes that sex-sorted semen is better in terms of increasing female dairy calves born to Holstein heifers when used with a protocol that provides effective oestrus detection (5-d Cosynch+Progesterone protocol).

In terms of what Fricke and others would like to know in future with regard to sex-sorted semen use in dairy farming, two major topics come to Fricke’s mind. We still want to know how to optimise the use of sex-sorted semen for the best fertility outcomes, he says, and “we also want to know why sexed semen yields lower conception rates than conventional semen.”

Hein
Treena Hein Correspondent

Beheer