The author is a retired extension dairy scientist in genetics and management at Virginia Tech, Blacksburg.

Many dairy farmers turned sour on sexed semen as 2009 unfolded. The reasons were obvious: Cash flows reduced discretionary spending, and sexed semen was viewed as discretionary, $30 more a straw compared to conventional. I also heard comments that sexed semen spoiled the well for sale of replacements. Both of these factors reduced the use of sexed semen in 2009, but the question of where this technology will fit into long-term herd management remains.

At this year's American Dairy Science Association (ADSA) meetings in Denver, Colo., I had the opportunity to participate in a symposium on sexed semen. This article summarizes some of what I learned, as well as shared, with that audience.

Sexed semen technology is "field ready" and has been marketed long enough to eliminate the possibility of major surprises. A.I. stud personnel know a lot about which bulls perform best after sexing. There are downsides.

Conception rates (CR) are lower:
About 39 percent for sexed versus 56 percent for conventional in heifers
25 percent for sexed versus 30 percent for conventional in cows.

Conception rates are from national data (see Norman, et al, J. Dairy Sci. 93:3880-3890). Sorting technology adds about $30 per straw to the value of the bull compared to the conventional format.

Recommendations for using sexed semen also are well established and favor a conservative approach. Sexed semen is recommended for use in heifers observed in standing heat (not synchronized) on first or second service. Herds should be able to achieve at least 60 percent CR in heifers with conventional semen before considering use of sexed semen. Herds with lower CR or using sexed semen on later services in heifers or in cows may be disappointed with results from it. In some cases, a more aggressive approach may be justified, but expectations must be tempered.

What about returns?
Albert DeVries of the University of Florida gave a presentation that dealt with the economics of using sexed semen. Results showed that the primary factor affecting use of sexed semen was the value of heifer calves relative to bull calves. Improved genetics is possible through more intensive selection of dams for replacements. The dam's performance is negatively affected through added rearing costs due to lower conception rates but positively affected due to reduced dystocia through birth of heifer calves. However, the relative value of resulting heifer calves is the major factor.

Food for thought: Jersey breeders may use sexed semen even when Holstein breeders say the market doesn't justify the investment because of good Jersey heifer markets and low value of Jersey bull calves.

DeVries showed some interesting results from using conventional beef semen on older cows no longer needed as dams of replacement heifers due to additional heifer calves from sexed semen in first-calf heifers. Dairy breeders would need good knowledge of the market for dairy-beef crossbreds, and it probably means raising the resulting calves to some minimum market age.

During the symposium, I was asked to talk about genetic implications. About half of the top-ranking bulls for Net Merit were sexed in August 2009 so dairy farmers don't have to sacrifice genetic merit.

Genetic merit of service sires is a major issue that cannot be overlooked. Any gains from selection of dams of herd replacements will be quickly lost if sexed semen on lower ranking bulls replaces higher ranking bulls with conventional semen.

Selection of specific females as dams of future replacements requires knowing the genetic merit of prospective dams. In general, younger animals tend to be genetically better than older ones. Many herds do not have or choose not to use such information. Further, some of those better animals will be older cows with conception rates of 25 percent or maybe lower from expensive sexed semen.

Many herds will reject the hassle of a mating list. However, any herd that uses A.I. and regularly buys semen from younger sires can improve genetic merit of replacements by using sexed semen on heifers.

How many more heifers?
Sexed semen for the first two services in heifers reduces the dam's average age for replacements from about 45.7 to 43.3 months. It raises the number of single heifer births per 100 births from 47 to 55 heifer calves. That surplus of eight heifer calves can be used for some extra income, for a little more culling in the herd, or for internal growth.

An alternative "use" of those extra eight heifers is to not use all cows in the herd as dams of replacements. About 40 percent of the oldest cows can be eliminated as dams of replacements while producing 47 heifer calves per 100 births. As a result, the average age of dam of replacements drops to 35.6 months. The 10-month advantage in age of dams of replacements is worth about $22 NM$ in genetic merit. Herds that achieve over 39 percent CR with sexed semen in heifers can do even better.

Sexed semen works and is here to stay. On a long-term basis, many herds will find an attractive market for surplus heifers. There is a limit to how many extra heifers can be absorbed by the industry, but that won't eliminate the opportunity for good managers to make money with sexed semen. As I see it, sexed semen adds value to good reproductive management in those herds.

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