In Ploufragan, comparison of the parental breeds, Fayoumi and R.I.R., and of the two reciprocal crosses showed a heterosis as the mean value of the crossbreds exceeded that of the parental breeds by about 10 p. 100 for egg number and laying percentage and by 6 p. 100 for food efficiency one the laying year. Differences appeared between the two reciprocal crosses, the a Fayoumi X 9 R.I.R. crossbreds exhibiting a higher laying persistency, a slightly higher egg mass, but a 1.8 g lower mean egg weight. It seems that with and additional selection effort, especially on the R.I.R. strain, the crossbreds may give good production results in laying batteries, especially at a high temperature.
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