The first notable advance in animal breeding methods occurred about the middle of the eighteenth century in England. The red, black, and pied, short-horned cattle of northeastern England, interbred with cattle from Holland, became famous all over the British Islands. Certain individuals were exhibited in all of the important cattle raising districts. They came to be known by name. Farmers eagerly bought calves from these celebrated cows and proudly traced the pedigrees of their herd sires back to this foundation stock. From this source developed the system of recording pedigrees, and in 1822 the first English herd book was published.

Then followed the realization that the value of an animal for breeding purposes consisted in its ability to transmit good qualities rather than in its own appearance. Some of the finest individuals were failures as breeders of desirable offspring, whereas other individuals of poor appearance were the progenitors of splendid specimens of the animal breeder's art. Back of the poor breeders was usually noted some inferior stock, while the good transmitters usually came from a long line of good ancestry.

More recently it has been realized that good ancestry alone is not enough. In spite of illustrious forebears there are too many "black sheep" in animal families. One way to avoid undesirable offspring, science has learned, is to use tested sires. If high egg-laying hens are wanted, use cocks that are known to beget hens that lay many eggs. If the milk yield is to be increased, it is necessary to use a bull that has the ability to augment the milk yield of his daughters over the yield of their dams. Basing selection on progeny performance rather than upon the appearance of ancestors was the next forward step in animal breeding.

Although the best of the purebreds have desired qualities, they are not so generally used in everyday farm production as might reasonably be supposed. In 1920 the census reported less than 1 per cent of the horses to be purebred, 3 per cent of the cattle, between 1 and 2 per cent of the sheep, and 33½ per cent of the swine. Less than 4 per cent of all livestock in the country are purebred and registered. According to Wentworth, little more than half of all animals have sufficient characteristics of the recognized breeds to be classed as grades from registered stock. Why is there this apparent lack of appreciation of the value of selected and registered livestock? Wentworth says:

"Commercially, we . . . seem to have reached certain limits beyond which the methods of pure breeding are not practicable. There is no question as to the improvement that a purebred beef animal . . . shows over a grade animal . . . The characteristic differences are definite and well understood. Nevertheless, production costs have increased to such a point that the refinements of the purebred in beef conformation and finish subject themselves unfavorably to the law of diminishing returns, since consumers do not pay the price for fancy meats that ordinarily warrants their production. According to present methods of breeding, stimulation of demand for meats and further improvement of market stock require additional use of expensively produced purebreds. Hence we have arrived at the apparent impasse of requiring better breeding at lower price levels, whereas under practical conditions we can secure better breeding only through higher costs."1

It is becoming clearer and clearer that one of the best ways of using the inherent value of purebred livestock lies in a more extensive use of crossbreeding. The mule is the oldest example of a crossbred animal. This hybrid combination of the horse and the ass has long been appreciated, but, since it is physiologically sterile, it can never be used for breeding purposes. The blue-gray cattle of Scotland are famous. Their distinctive color comes from the genetic composition of black pelt from the Aberdeen-Angus, or Galloway, combined with the white of the Shorthorn. The quick growth and uniformly good meat quality of these mixed breeds are due to the phenomenon of hybrid vigor, commonly associated with the crossing of somewhat unrelated forms. Western sheep in the United States are almost exclusively crossbreds. Swine from Poland-China and Chester White combinations or Duroc-Jersey and Yorkshire matings are commonly seen in the Corn Belt. Since they can not be used for breeding purposes, there must be good reason for their production.

1 Record of Proceedings, American Society of Animal Production, Annual Meetings, 1925-1926, pp. 42-43.

The most extensive use of crossbreeding is made in Denmark. Danish bacon has an enviable reputation. It is sold in England in competition with the best from British farms. About one-third of this bacon from Denmark is produced by mating the English Yorkshire with the Danish Land-race. Purebreds only are used. Each farmer buys his breeding stock from breeders who are approved by the government. While English and American breeders have spent their principal efforts in producing animals for the show ring, Danish farmers have developed a system whereby a pound of pork is produced from a little more than three pounds of feed. Careful tests of this have been made at the leading swine stations. At Elsesminde the Landrace has averaged 3.79 pounds of feed for 1 pound of gain and the Yorkshire 3.69 pounds. The crossbreds have averaged 3.23 pounds or 13.6 per cent less.

In the Breeder's Gazette there is a report by Casement giving the results obtained on his farm where Duroc-Jersey and Poland-China sows were both mated with Yorkshire boars. Many such cross matings were made and hundreds of pigs raised. The crossbred pigs are compared with purebred litters from other sows of the same breeds as the dams. There were, in round numbers, 10 per cent fewer pigs dead at birth, 30 per cent more alive at time of weaning, and 5 per cent more raised to market, of the crossbreds than of the purebreds. No figures are given for Yorkshire purebreds, so that the figures are not directly comparable to the Danish results; but they indicate clearly that there is value from crossbreeding in viability and longevity as well as in economy of gain.