1. Bull semen has one use: the insemination of cows. As a dealer remarked: "If you can think of anything else to do with it, let me know." In this country about 75 per cent of all dairy cattle breeding is by artificial insemination: dairy cows must calve once a year if they are to keep up their milk output, so they are routinely impregnated by artificial means. It is quicker, simpler and more efficient than the natural way (and less dangerous, since dairy bulls are ferocious beasts). A measure of how efficient: in one American herd of 2,000 cows, every animal was inseminated up to three times over a period of nine weeks, and no fewer than 98 per cent became pregnant. All this was done by one expert, with the help of six cowboys. The breeding of beef cattle in Britain is still mainly by natural insemination, although that is changing.
2. Semen is sold through advertisements in the farming press and by travelling sales reps. (One of their chat-up lines: "Some men can't give their semen away; people pay me for mine.") It is kept in "straws", or plastic phials, containing a tiny quantity of semen diluted in albumen, or egg-white. The straws, frozen in liquid nitrogen, are stored in warehouses around the country. A single 0.25cc straw can cost anything from pounds 12 to pounds 120 and a farmer with an average herd of 72 cows will probably buy 180 straws a year.
3. As with some spirits, price depends on the "proof" of the product, though in this case proof means the proven ability of the bull to sire cows with high milk yields. For example, semen from a bull whose daughters produce 1,000 kilos of milk per year above average might sell for pounds 15. The bulls carrying the highest proof are as famous in the international dairy community as film stars. There are just a few dozen of them, but they have big families. "Black Star", from Washington state in the US, has daughters producing milk in 50 countries. A Dutch bull called "Sunny Boy" has 500,000 daughters in 22 countries.
4. Besides proof, another influence on semen price is availability. Bulls, which have three-foot penises, vary widely in the frequency with which they produce and in the quantity of semen that results. A single ejaculation can yield as many as 500 straws, or as few as 50. An industrious bull may perform every day; a lazy one only once a week. Thanks to the laws of supply and demand, a lazy bull with a low output but a very high proof will command the top prices. His semen is like gold dust.
5. You may be wondering how it is collected. Methods vary. Some bulls mount frames covered in cowskin and ejaculate into rubber tubes with bottles on the end. Some mount other males, known as "teasers", only to be interrupted at the crucial moment (which arrives quickly and is over even more quickly) by a man with a rubber tube. Other bulls mount and inseminate females in the natural way, and the semen is then extracted from the cow. When necessary, the bull can be excited artificially, with the help of an aerosol spray which reproduces the smell of a cow on heat.
6. The British market in bull semen is thought to be worth about pounds 50m a year, and is growing. In terms of international trade, although much fuss has been made lately about Britain's right to export semen wherever it wants, this country is overwhelmingly a net importer. In 1995, exports were worth just short of pounds 1m while imports, mainly from the US, Canada and the Netherlands, totalled pounds 15.5m.
7. Behind this trading weakness lies a tale of strategic miscalculation some would see as typical. Britain was a world leader as recently as the 1960s, but then things went downhill. While American and continental European dairy farmers increasingly moved towards specialised high-yield milk herds, British farmers were encouraged to compromise milk output by breeding dairy cows which could also produce strong beef calves. British herds were thus "dual-purpose". In the past 10 years, however, Britain has abandoned that strategy and switched wholeheartedly to the American- European way. It is still struggling to catch up.
8. Most of those black-and-white cows munching grass out in the fields are, we fondly assume, traditional, familiar Fresians. We assume incorrectly. Thanks to the recent change of policy, Fresians are being replaced all over the country, with astonishing speed, by Holsteins, a breed that originally came from Denmark but which has been refined to a high pitch of productivity by American farmers. This transformation has been made possible by imported bull semen, so in a great many cases those cows have American or Dutch fathers or grandfathers.
9. By a fine irony, another reason that Britain fell behind in the introduction of Holsteins - and thus in the international semen trade - was that in the 1980s the Ministry of Agriculture was extremely pernickety about the risk of diseases such as foot-and-mouth coming in with American semen. At a time when our European partners, unworried, were blithely importing US semen, Britain's veterinary experts banned it - a perfect reversal of today's BSE positions.
10. Now the Holstein herd is growing, a big effort is under way to produce high-proof bulls, establish an efficient domestic trade and turn Britain into a net exporter. The drive has been championed by the Duke of Westminster, one of the country's biggest dairy farmers. The BSE crisis has not only affected foreign sales, but this whole effort, because farmers have been reluctant to buy semen for cows which might have to be slaughtered. The lifting of the export ban, alas, will have only a small effect on this.