Published online by Cambridge University Press: 02 September 2010
The Milk Marketing Board's 23 artificial insemination (AI) centres which provide service in much of England and Wales are grouped into five geographical areas (Figure 1). Analyses of trials on commercial farms to study the effects of crossing Charolais bulls with dairy cows (Edwards et al. 1966), revealed significant differences between these areas in both gestation length and birth weight of crossbred calves. However, the Charolais bulls used in the trials were divided into five teams, each of three bulls, and each team was used only in a single area. Consequently, bull teams and areas were confounded. The purpose of the experiment reported here was to estimate the differences between areas in gestation length and birth weight independent of sire.