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.