Just a guess here. It might be that sperm that create females are more susceptible to dying from abnormal situations - such as temperature, time outside the male, air, or the quality of the ejaculate?

Is that so Suby ,well I never, I have no explanation whatsoever . How does this compere with natural birth ratings....

There is more that goes on with cows than making milk - think fast food.

Please don't take this as me saying "I don't believe you" because it really isn't a case of that. However, to begin to give a genuinely scientific answer to this I would need to see some actual data around the issue. Observations from a single source can be subject to numerous errors, of which the most likely is pure chance. If you consider the number of livestock farmers across the world who artificially inseminate their cattle, it would be very unsuprising to find some where the male:female ratio of the offspring was skewed. If, however, there was a large body of data from a high number of sources you could begin to calculate the statistical importance of the observation. So, I could begin to start making some educated guesses (I am a geneticist who works in cancer research, so I could make a stab at it if it turns out to be a true observation). But unless the observation itself is true, it would be difficult to guess at! However, you may find this abstract, although not strictly what you're asking about, of interest: http://www.ncbi.nlm.nih.gov/pubmed/10735110 *Edited to add*: Can I just clear something up: you are not saying that the sperm has been preselected to give male offspring are you? You are asking about a phenomenon of artificial insemination?

My daughter who is a qualified biochemist tells me that owing to the difference in mass of the X and Y sperm (Y is lighter because of its chromosome structure), you can actually separate X and Y sperms in a very high speed centrifuge; and once separated you can select the type you need. Try this link, Suby. There are dozens of articles on "sexed semen" especially for dairy farmers as well as "beef farmers."

On the lighter side... a sexually unfulfilled female is more likely to create one that will satisfy her cravings...