Factors Influencing Experimental Error in Field Trials in Artificial Insemination

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Abstract
In experiment I, with 96,565 services from 1080 collections from 90 bulls, error variances with 4 antibacterial-agent treatments were compared. Results were as follows: (a) With an average of 60 or more services per collection (not split) there were significant differences among variances for collections within bulls within treatments (error) for the 4 antibacterial-agent treatments studied with the lowest being with the sulfa-streptomycin treatment and the highest with no antibacterial agents, (b) With smaller numbers of services per collection differences in heterogeneity of the error variances could not be detected. (c)Error variance decreased rapidly as number of services were increased to 80. Above this number decrease in error variance was slight in proportion to increase in numbers, (d) There was a little evidence suggesting that there was more variation among collections within bulls known to be infected with pathogenic Vibrio than other bulls. In experiments II and III, with 34, 341 services, a study of the effect of experimental design upon relative efficiency indicated that, if collections average more than 160 services, they can be split into as many units as desired as long as each unit represents an average of 80 or more services. If collections average much less than 160 services, they should not be split and incomplete block or randomized complete block designs should be employed.