Milk records of individual cows and meteorological data for each day over a period of 24 years were extracted from the files at the Livestock Production Research Institute at Mpwapwa in Central Tanzania. The herd was composed of various crosses between Bos indicus and Bos taurus cattle, and carried on average about 20% taurus inheritance. Milk yields were accumulated for successive periods of 28 days from calving to end of lactation, and related to average temperatures and total rainfall in the same period (and/or in the preceding period). The relationship was studied by multiple regression analysis. The proportion of total variation in milk yield accounted for by the climatic parameters considered, was in the range of 5 to 10 per cent. The variation which could be ascribed to individual weather variables was small, partly because of the close correlation between most of the variables. High morning (09.00 h) temperatures had a consistently negative influence on concurrent milk yield. In contrast high minimum temperatures, and high afternoon (15.00 h) temperatures on the wet bulb thermometer, had a significant positive effect. Milk yield was also positively influenced by high rainfall both concurrently and in the preceding period. The apparently positive effect of high wet bulb temperature in the afternoon might be explained by the inverse relationship between humidity and solar radiation, a climatic factor which was not recorded in this set of data.
Sires of seven Bos taurus beef breeds were mated with Bos indicus Boran cows at two sites, one near sea level and the other at about 1000 m altitude, and over three years. Purebred Boran calves provided controls for comparisons between sire breeds for growth to 4 years of age, mortality and carcase characteristics in a range environment where all the animals were kept under a similar management regime. Numerous sire breed x site, sire breed x year of birth and site x year of birth interactions were established. Mortality was high, but there was no significant sire breed effect, although purebred Borans had a higher survival than crossbred calves. There was no significant difference between genotypes in birth weight. Generally, Bos taurus cross steers achieved greater live weight gains and heavier carcase weights at 4 years of age than did purebred Borans. Limousin-cross steers had significantly (p < 0.05) less fat in the tenth rib sample joint than any of the other genotypes. A productivity index that combined calf survival and carcase weight indicated that the Chianina crosses were more productive than any other genotype at either site. Purebred Borans were more productive than all the Bos taurus crossbreds with the exception of the Chianina crosses at site 1, but were only superior to the Limousin crosses at site 2, which was at the higher altitude. When lean meat yield was introduced into the productivity index, the Boran purebreds were the least productive at site 2.
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