Published online by Cambridge University Press: 27 March 2009
Using data (1950–64) from the government-owned herd of Jamaica Hope cattle at Bodles, Jamaica, it was estimated that the fraction of cows called on the basis of their milk production in any given lactation was of the order 0·00 to 0·05. Using data (1967–68) from ten high–and ten low-producing farmer herds of the same breed, it was found that the level of calling was low and that cows proceeding from one lactation to the next had a yield superiority over the total population of only + 4 gallons. It is suggested that one of the principal reasons for the apparent lack of response to selection in dairy herds in the tropics may be that little or no selection for production is in fact practised.