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Improving The Odds With Sex-Sorted Semen

Tuesday, January 12, 2010

In the right circumstances, using sex-sorted semen in virgin heifers can offer a financial opportunity, says Blair Murray - Dairy Genetic Improvement Specialist/OMAFRA.

Once considered a dairy farmer's pipedream, sexed semen for artificial insemination has become commercially available from all North American studs on a select basis at a premium price. Although this semen greatly improves your odds of producing a heifer calf, it is fair to ask whether the extra cost is worth it.

Sex-sorted semen debuted in 1989. That year, the first live offspring was born from a dairy animal inseminated with semen sorted by the flow cytometry process. The process consistently produced 90 per cent female offspring at that time. However, it severely reduced semen viability and quality. Also costly and slow, the sex-sorting technology took another 10 years to gain commercial acceptance.

Commercial applications and most research have focused on using sex-sorted semen in virgin heifers. They generally have a better conception rate than lactating cows, and offer a better opportunity for return on investment for your dairy herd.

First-service conception rates using sex -sorted semen averaged 47 per cent for Holstein heifers and 53 per cent for Jersey heifers in a recently published research study. That's 80 per cent of the rate achieved with conventional semen, according to the study, which looked into using sex-sorted semen in 211 commercial dairy herds, mostly Holsteins and some Jerseys.

Of the single births, 89 per cent were female. When researchers considered only those animals calving with a normal gestation length of 265 to 295 days, 90 per cent of births were female.

Stillbirth incidence among heifers delivering female calves was the same for sex-sorted and conventional semen. Heifers delivering bull calves seemed to have a higher stillbirth rate, but only 10 per cent of calves born during the study period were male. Other unrelated research has shown a higher stillbirth incidence among heifers than cows calving for the second or later time, especially for heifers delivering bull calves.

Heifers calving bull calves generally have the greatest incidence of calving difficulties. One study found difficult births occur 10.9 per cent of the time for bull calves versus 5.3 per cent for heifer calves. A process ensuring a high rate of female calves could help reduce dystocia and stillbirths.

Sex-sorted semen produced 117 sets of twins. Of those, 79 per cent were two heifer calves, 15 per cent were mixed and six per cent were two bull calves. The ratio of females to males was 86 to 14, close to the expected number.

The study shows this technology works as expected, but can you count on it to payoff on your farm? Another study, done in 2007, calculated net present values for options using sex-sorted and conventional semen to breed heifers. Some of the assigned values used by University of Michigan researchers were: bull calf, $110; heifer, $500; conventional semen, $15 per dose, and sex-sorted, $45.

The researchers mode led two levels of conventional breeding conception rates, 58 per cent and 65 per cent, and a range of success rates for sexed semen at 53 per cent, 75 per cent and 90 per cent of conventional rates in the modeled herds.

Conventional semen conception rates were 58 per cent for first breedings and 65 per cent for second breedings. Rates for sex-sorted semen as a percentage of conventional were 53 per cent for first breedings, 75 per cent for second breedings and 90 per cent for third breedings.

These researchers' calculations included increased breeding costs, increased days open and culling rates. Most systems use one or two breedings to sex-sorted semen, and then go back to conventional semen if the heifer still has not conceived.

A break-even analysis calculated the required conception rate for sexed semen versus conventional. With a lower base conception rate of 58 per cent, sexed semen must achieve 86 per cent of the rate for conventional semen. With a base rate of 65 per cent however, the breakeven point for sexed semen is 80 per cent of the rate for conventional semen. The 80 per cent of conventional rates is within reason-any higher is probably not.

With all factors kept constant for the sex-sorted semen strategy to break-even, the heifer calf's value must be $512.81. If the sexed semen conception rate falls below 75 per cent of the conventional rate, the heifer calf's value must be much higher.

Based on these studies, sex-sorted semen may be a break-even proposition if:

  • you use it on heifers;
  • your conception rate with conventional semen is already high and stillbirth loss low;
  • the value of heifer calves produced is above average.

Other aspects of sex-sorted semen make it an interesting option as well. It could reduce incidence of calving difficulties and stillbirths. You could increase herd size with your own breeding stock rather than buying females that increase the risk of introducing disease into your herd.

Consider the values used as approximate since they have not been altered to suit Canadian values and conditions. Also, your farm's performance will differ. When considering sex-sorted semen, bear in mind the increased cost and reduced conception rate. A 60 per cent conception rate in heifers with conventional semen could drop to 45 to 48 per cent with sex-sorted semen.

January 2010

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