Malpositions in chicken‐pheasant hybrid embryos

Synopsis

The occurrence of malpositions in hybrid embryos obtained by two‐way crosses between Ring‐necked pheasants (Phasianus colchicus) and Columbian Rock fowls (Gallus domesticus) was examined and the numbers of the various types of malpositions were recorded. Of the 230 unhatched embryos, the 178 embryos which were detected to be more than 18 d old were classified according to their position in the shell. Of those exhibiting malpositions 68 were males and 52 were females. A X² analysis revealed that the sex of the embryo and the distribution of positions (normal vs malposition) were not correlated, although there were significant differences amongst the frequencies with which the different malpositions occurred (P<0.001). Since some of the embryos in malposition 2, in which the head is in the narrower end of the shell, were alive at the time of examination, while those in malposition 3, in which the head is turned to the left, were all dead, it is postulated that the former malposition is not always lethal, whereas the latter may be. Possibly some of the malpositions observed in these embryos represent earlier stages, or minor deviations, of the normal position. Although the proportion of embryos showing malpositions was large (67.4% of all the unhatched embryos examined), malpositions 2 and 3 together amounted to only 23.4% of the total showing malpositions. These observations, and the fact that 32.6% of the unhatched embryos were in normal position, suggest that malposition per se is not the main cause of the poor hatchability of these hybrids.