Cross-breeding

Cross-breeding for the production of market animals has been practiced for many years, particularly with swine, sheep, and beef cattle. By this method of breeding, producers have taken advantage of the increased productivity ( called hybrid vigor or heterosis) that frequently results from the crossing of distinct types and breeds.

The most extensive experimental work in this field has been with swine. J. L. Lush, P. S. Shearer, and C. C. Culbertson of Iowa State College have summarized the results of the important experiments in this field. They point out that any one piece of work, especially one in which small numbers of pigs were used, scarcely appears enough by itself to prove beyond question that there is a real advantage in favor of cross-breeding. Yet, almost every piece of work indicates that such an advantage is probable.

The Iowa workers conclude that the combined weight of all the scattered evidence is overwhelming in indicating that cross-breeding results in increased production. Crossbred pigs tend to be somewhat more Vigorous and thrifty than would be expected from the average of the two parent breeds. Because of this added vigor, crossbreds generally show a lower death rate up to weaning, and consequently larger and heavier litters are weaned. Also, they generally gain a little more rapidly on a little less feed than the purebreds. For the same reasons, the crossbred gilts or sows, when used for breeding, can be expected to wean slightly larger and heavier litters than purebreds. Lush and his coworkers emphasize that these are results that can be expected on the average, but they should not be expected to happen every. time a cross is made, any more than slightly loaded dice should be expected to turn up a winning combination every time they are thrown.

Three general systems of cross-breeding may be practiced by the producer of market hogs. Purebred or high-grade females of one breed and purebred boars of another breed may be used for the production of each crop of pigs. This plan is simple, but it means that replacements of sows must be purchased or produced in a subsidiary breeding program.

Another plan is called crisscrossing, in which boars of two breeds are alternated in producing each new generation of pigs from dams saved from the previous generation. This plan takes advantage of any hybrid vigor expressed in the ability of the crossbred dam to raise large, vigorous litters, and eliminates the necessity of purchasing sow replacements.

Still another plan utilizes three breeds of boars. It is similar in all other respects to the crisscrossing system.

Our knowledge of the results that may be expected from crossbreeding beef cattle has been increased in recent years through work conducted cooperatively at Miles City, Mont., by the Department and the Montana Agricultural Experiment Station. The experiment was planned to test the possibility of maintaining heterosis through three-breed crossing. The first cross was Shorthorn bulls on Hereford cows. The first generation, or F1, females (offspring of Shorthorn bulls and Hereford cows) were mated to Aberdeen-Angus bulls, and their triple-cross female offspring were mated to Hereford bulls. The latter phases of this work have not yet been completed, but results thus far indicate that three-breed crossing may be an effective method of increasing productivity in beef cattle. Some results :

Fifty-seven F1 steers (Shorthorn X Hereford) were compared with 67 Hereford steers. The crossbred calves gained more rapidly in the feed lot and were heavier at the time of marketing. Crossbreds had fewer digestive disturbances, and they also had higher dressing percentages. Differences in efficiency of feed utilization, slaughter grade and carcass grade were not significant.

Fifty-three F1 and 55 Hereford heifers were also compared. The crossbred heifers were heavier at birth and weighed 7.2 pounds more at weaning time. At 18 and 30 months the differences in favor of the crossbreds were 50.9 and 88.0 pounds, respectively.

Results with offspring produced by mating Aberdeen-Angus bulls to F, females show that the triple-cross steers weighed more at weaning and at the end of the feeding period, gained more rapidly during the feeding period, sold for more per pound and per head, had a higher dressing percentage, and returned more per head above feed and marketing costs than the Hereford steers with which they were compared. The triple-cross heifers also weighed more at weaning and at 18 months, and were given higher scores at 18 months than Hereford heifers raised under identical conditions. There were indications that the triple-cross calves had a faster rate of gain before weaning, but a slower rate after weaning than F, calves.

Further work is needed to determine the part that continued three-breed crossing can play in commercial beef production. Management of animals in several groups at breeding time may make it difficult for some producers to follow. Crisscrossing, in which only two breeds are used, should be more practical, and its use should be tested further experimentally.