TUDIES ON THE DESIGN OF COMPARATIVE POULTR Y TEST S: 1. A COMPARISON OF THREE STRAINS OF WHITE LEGHORNS HOUSED IN REPLICATED FIFTY-BIRD PENS AND INTERMINGLED IN A LARGE PEN

An experiment was conducted to estimate the magnitude of the pen effects and to compare the performance of three genetically different S.C. White Leghorn strains in twelve small pens (50-bird size) and a large intermingled group (a pen of 677 birds).There were no significant pen effects for any traits. The repeatability (intra-class correlations) estimates for all traits measured were relatively high: hen-housed egg production,.83; survivor egg production,.77; 160-day body weight,.93; March body weight,.94; laying-house mortality,.47; and feed efficiency,.84.Although strain differences were highly significant, there was no difference in egg production or mortality between the birds in the small pens and in the large intermingled group, and no evidence of any strain × replicate interaction.On the basis of this study, it is concluded that there is no advantage to intermingling strains after housing in order to compare their genetic merit, when an adequate number of uniformly equipped small pens are available and the management of the pens is very similar. There are two main disadvantages to intermingling strains, namely, the loss of feed consumption data, and the cost of trapnesting the birds in the test.