Influence of various climatic factors on milk production in cattle in Tanzania.

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.

Influence of season of birth on weight for age in two genetic groups of cattle.

Body weights from birth to 756 days of age for calves of Mpwapwa cattle (12% Bos taurus inheritance) and backcrosses (34% Bos taurus) born in the wet or the dry season were analysed. The calves were weaned at 75 days of age and after that fed entirely on pasture. Backcrosses were heavier than Mpwapwa at birth and at 252 days of age but not at subsequent ages. Calves born in the dry season had slightly larger birth weights than calves born in the wet season. Weight differences were reversed from 252 to 504 days reflecting the seasonal fluctuations in grass growth. The effect of season of birth on long term rate of gain was negligible. No significant interaction between genetic group (Mpwapwa vs backcrosses) and season of birth (wet vs dry) was observed at any of the ages. The study thus did not confirm the hypothesis that backcrosses because of their higher proportion of Bos taurus genes were more sensitive to the nutritional stress of the dry season than were pure Mpwapwa calves.

Observations on the effect of sex, litter size, and age on the body weights of rabbits.

Female rabbits of the New Zealand White and Chinchilla crosses were always found to be lighter than the male rabbits at 21 to 98 days of age. Animals from litters of less than six were heavier than those from greater litters (98-day liveweight 1461.2 g as compared to 1119.9 g).