The Relationship between Hatching Time and Sex-ratio in Chicks

Abstract

The relationship between hatching time and sex-ratio in chicks was investigated in connection with breed and age of their parents, laying season and egg size. The chicks used were 3 strains of White Leghorn (W.L.) and hybrids between Rhode Island Red (R.I.R.) male and Rhode Island White (R.I.W.) female and between W.L. male and Barred Plymouth Rock (B.P.R.) female, and the reciprocal hybrid of the latter. Chicks that hatched alive were classified according to time intervals of every 2 or 3 hours after the start of hatch and sexing was done immediately after hatch.Female chicks tended to hatch earlier than males and the difference in hatching time between males and females varied among the breeds or the strains used, especially in the hybrid between R.I.R. male and R.I.W. female.Female chicks hatched earlier than males in proportion to the increase of age of their parent stocks in the hybrid between R.I.R. male and R.I.W. female, whereas no difference was observed among the other breeds used.In general, hatching time also might be earlier during the hot season than during the cold. This was clearly shown in the R.I.R. male: R.I.W. female hybrid and the difference of hatching time between the two sexes was more distinct in the hot season than in cold in this hybrid.Large eggs tended to hatch earlier than small ones in the R.I.R. male: R.I.W. female hybrid and vice versa in the Shaver strain of W.L. Eggs of medium size showed less difference in hatching time between the two sexes than those of larger or smaller size in hybrid chicks from R.I.R. male and R.I.W. female.It might be concluded from the results that the hatching time and the sex-ratio are affected considerably by the breeds or the strains of their parents.