Another indication of the superior heat-regulating ability of zebu cattle is found in their grazing habits on hot, sunny days. Under these conditions zebu cattle have been observed to continue grazing during much of the day while Angus cattle spent most of the time in the shade. Crossbreds were intermediate in this respect.

Other data collected at the Department's Iberia Livestock Experiment Farm at Jeanerette, when the average afternoon temperature was 93.2° F. and relative humidity 71.7 percent, showed an average heat tolerance of 89 for zebu, 84 for zebu-Angus crossbreds, and 59 for Angus. The figures are indexes indicating the relative abilities of the three types to maintain a normal body temperature of 101° F.

The reasons for the zebu's superior heat-regulating ability are not well understood. Perhaps several factors are involved: The extra skin of the dewlap and sheath that provides more surface per unit of body weight, light color, basic physiological differences, or ability to sweat.

Commercial cross-breeding of beef cattle has not been practiced so extensively in recent years as in other classes of livestock, particularly swine and sheep. It was common before ranges were fenced, or before cooperative associations controlled the breed and type of bull used in herds where cattle belonging to the members were grazed as a unit.

In the years since the type of bull used for breeding has been controlled, emphasis has usually been placed on the use of bulls of one breed so that the cows in any one range herd are now, for the most part, high-grade Hereford, Shorthorn, or Aberdeen-Angus stock. This shift from casual to well-regulated breeding methods has resulted in the production of more uniform feeder stock, and by careful selection of bulls, most range operators have improved the quality of their cattle. It is possible, however, that the productivity of range cattle may be improved by taking advantage of the hybrid vigor that usually results from cross-breeding. Some cooperative work has been done in recent years by the Bureau of Animal Industry and the Montana Agricultural Experiment Station to obtain more information on this point.

The experiment was planned to test the possibilities of maintaining heterosis—that is, hybrid or crossbred vigor—through continual crossing. The first cross was made by mating Shorthorn bulls to Hereford cows. The F, females were mated to Aberdeen-Angus bulls, and their triple-cross female offspring were mated to Hereford bulls. This work is being conducted at the United States Range Livestock Experiment Station, at Miles City, Mont. The breeding program with Hereford cattle at this station is designed to develop superior strains of purebred Herefords, and selection of bulls is based on the results of progeny tests. Data from these experiments also serve as the basis for comparison of crossbred and purebred offspring. This breeding trial has not been completed, but we have results on parts of it.

A study of 57 steers sired by Shorthorn bulls and out of Hereford cows brought out several pertinent points. The crossbred calves gained more rapidly in the feed lot than the purebreds, and were heavier at time of marketing. The differences between the purebreds and crossbreds in efficiency of gain, slaughter grade, and carcass grade were not statistically significant. The dressing percentage was higher in the crossbred than in the purebred steers. The crossbreds had fewer digestive disorders in the feed lot than the purebreds. In general, the crossbred steers were less variable than the purebred steers.

The performance of 53 heifers produced by mating Shorthorn bulls to Hereford cows was compared with that of 55 Hereford heifers. The crossbreds were heavier at birth, and at weaning time weighed 7.2 pounds more than the Herefords. At 18 and 30 months, the differences in weight in favor of the crossbreds had increased to 50.9 and 88 pounds, respectively. The heifers ran together on native range, as yearlings and 2-yearolds, and had access to the same kinds and quality of feed.

Preliminary analyses of studies with steers and heifers produced by Mating Aberdeen-Angus bulls to Shorthorn X Hereford 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, had a higher dressing percentage, and returned more per head above feed and marketing costs than did 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 the first-cross calves. The triple-cross steers had somewhat higher slaughter and carcass grades and the heifers had higher scores for type than the first-cross animals.

Further work is needed to determine the part that continued crisscrossing can play in improvement of beef production. The results obtained to date in this experiment indicate that the procedure has good possibilities. However, the management of animals at breeding time and the careful record keeping necessary in connection with a crisscrossing scheme involving three breeds will make it difficult to use on many farms and ranches. The use of crisscrossing in which only two breeds are involved should be tested further, using the several possible combinations of established beef breeds.