Breeding for Hot Climates

We have done considerable work to determine the type of breeding best adapted to beef production in the plain around the Gulf of Mexico, Which is hot and humid much of the year. This work has been carried out at the Iberia Livestock Experiment Farm, at Jeanerette, La. I summarize some results reported by A. O. Rhoad and W. H. Black.

Zebu, Aberdeen-Angus, Africander, Hereford, and Shorthorn bulls were used at Jeanerette. The females were native Louisiana stock, grade Herefords, purebred Aberdeen-Angus, and several generations of offspring of those cows and bulls. Comparisons were made on the basis of weights at birth, 6 months, and 2 years.

The procedure that gave best results in the early phases of the work, when Hereford bulls were used on native or grade Hereford foundation cows, was to mate the females to the Hereford bulls, then mate their female offspring to zebu bulls. The hybrid females were then mated to Hereford bulls, thus producing offspring that were five-eighths Hereford, one-fourth zebu, and one-eighth foundation breeding.

When Aberdeen-Angus cows were used as foundation female stock, best results were had by first mating them to zebu bulls, then backcrossing the hybrid heifers to Angus bulls, to produce offspring that were one-fourth zebu, and three-fourths Angus. Good results also were had with animals having three-eighths zebu, and five-eighths Angus blood. These were produced by mating first-generation heifers (one-half zebu, one-half Angus) to bulls having one-fourth zebu, three-fourths Angus blood, or by mating second-generation heifers (one-fourth zebu, three-fourths Angus) to hybrid bulls ( one-half zebu, one-half Angus).

Other animals having varying amounts of zebu blood also gave reasonably satisfactory results. This work indicates that the amount of zebu blood needed in beef cattle in the coastal area lies somewhere between one-fourth and one-half, but sufficient data have not yet been accumulated to determine the proportion that can be expected to give best results in continued breeding operations.

In another phase of the work at Jeanerette we sought to determine the relative merits of the offspring of Aberdeen-Angus cows mated to Angus, zebu, Africander, and zebu X Angus bulls, and to demonstrate the possibilities of polyallel crossing in this and similar livestock breeding experiments. The zebu bulls were mostly of Kankrej breeding, commonly referred to in the United States as Guzerat, but there was also a trace of Gir blood.

The breed of sire was found to be significantly associated with birth weight of calves when four types of bulls were mated to the same 9 Angus cows. The calves ranked as follows in birth weight, by type of sire : Zebu, Africander, zebu X Angus, and Angus. In a group of 19 cows mated to 3 types of bulls, birth weight was also significantly associated with breed of sire and the calves ranked, by type of sire, in the following order: Zebu, Africander, and zebu X Angus. The breed of sire also influenced weight at 6 months in an analysis in which Angus, Africander, and zebu bulls were involved. This variation was largely due to the relatively small size of the Angus calves, compared with those from the other types of bulls. Calves sired by zebu bulls were only slightly heavier than those sired by Africander bulls. In another study in which offspring of zebu, Africander, and zebu X Angus bulls were involved, the calves ranked in that order, bur the variation among the averages of the three groups was too small to be statistically significant.

The findings indicate that hybrid calves carrying zebu or Africander blood are superior to Angus calves under conditions prevailing in the area, measured by weight at 6 months. The difference between calves sired by zebu and Africander bulls was not so clear, but the averages favored those sired by zebu bulls. The same was true of differences in performance of the two types of hybrids as dams.

The warm-blooded animal can tolerate only relatively small variations in its body temperature, and physiological reactions in the body are tuned to the task of keeping heat production in the body and heat loss from the body in balance, or nearly so. Under tropical and subtropical conditions, the ability of an animal to keep heat production balanced by heat loss is often taxed to the utmost. Animals that have an efficient heat-regulating mechanism are therefore more apt to survive and perform satisfactorily than those not so efficient in this respect.

Zebu cattle (Bos indicus) seem superior to European cattle (Bos taurus) in ability to maintain a normal or nearly normal body temperature under tropical conditions. Body temperature and respiration rates of cattle rise and fall as atmospheric temperatures rise and fall during a summer day. One of the avenues by which heat is lost from the body is evaporation through the lungs, so an increase in respiration speeds up the loss of heat from the body. The temperature and respiration rate of zebu cattle rose less than that of European cattle (Aberdeen-Angus) when exposed to high temperatures. European cattle became feverish when exposed to direct sunlight in summer, under subtropical conditions in Louisiana, while zebu cattle were not so affected. Zebu X Aberdeen-Angus crossbreds were intermediate to the parent strains in ability to maintain a normal body temperature in the heat.