Reproductive Rates and Growth of Purebred Brown Swiss Cattle in Brazil

Summary Pertinent facts about the reproductive and growth rates of purebred Brown Swiss cattle in Brazil are described as a step in locating the influences which lower the adaptability of European breeds of cattle to tropical conditions. At two of the five publicly-owned farms, about 80% of the calvings occurred during the dry season. At the three other farms, the calvings were distributed nearly equally in the seasons. The sex ratio was 52,1% males among the purebred calves born. At the one farm which had complete data on calf mortality, 219 of the 467 born were abortions and stillbirths or died before reaching 24 months of age. At another farm, 89 of the 634 born alive had died by weaning time or shortly afterward. These two farms agreed fairly well on the amount of mortality before weaning among those born alive. It appears that only about 50 to 60% of the calvings result in animals which live to at least 2 years of age. A little more than half the total deaths before 24 months occurred between birth and 3 months. The other period when mortality was especially high was from 9 to 12 months, which coincides roughly with the period when the calves are turned out in the pastures. Year-to-year variation in the death rate was large and statistically significant, but irregular. According to the men in charge at these farms, the most important causes of death were: abortion, stillbirths, tick fever, pneumonia, congenital debility, and foot-and-mouth disease. The sires averaged 61.5 months and the dams 77.3 months of age when their offspring were born. This amounts to an average interval of 5.75 years between generations. The purebred Brown Swiss cattle population was expanding over this period and the generation interval was increasing at about 0.9 month per year as the population came to include a larger fraction of older breeding animals. If it is assumed that the bulls go into service at 24 months, their average productive life was 75 months and the annual replacement of those in use was about 16%. The average productive life of the cows from first calving to the date of their disposal or death was 62 months for imported cows and 55 months for those born in Brazil. This makes an annual replacement rate among cows of 21%, but this figure makes no allowance for heifers which were intended for breeding but never calved, or for the population being an expanding one. The heifers averaged 44 months old at first freshening. The average interval between consecutive carvings was 16.8 months. No significant difference in calving interval was found between imported and nonimported cows, and there was no clear evidence of calving interval being affected by the age of the cow. Little inbreeding has occurred among these Brown Swiss cattle in Brazil. On the two farms which recorded live weights, the males were significantly heavier, the difference generally being of the order of 5 to 8%. The calves grew well during the first 3 months but after that, and especially after weaning, the growth rates were much lower than those generally regarded as standard in the United States. Heritability of intra-year differences in live weight among the Brown Swiss heifers at 12 months was estimated at 0.26 on the basis of mean squares within and between sires within years, but this was not statistically significant and can be regarded only as a highly uncertain indication.