THE IMPORTANCE OF LENGTH OF INCUBATION PERIOD 

 IN RHODE ISLAND REDS* 



By F. A. Hays, Research Professor of Poultry Husbandry 



INTRODUCTION 



A limited amount of preliminary unpublished data on Barred Plymouth Rocks, 

 collected by Dove (1935) at the Maine Station, suggested that chicks emerging 

 early from the shell were more likely to be females than males and that such 

 chicks were probably more viable than chicks emerging later. It is also com- 

 monly observed, in chicks from the same setting of eggs, that those emerging late 

 are less likely to survive and often grow more slowly than those emerging early. 

 Such observations suggested the possibility that the length of the incubation 

 period might be a useful criterion of the future outcome of chicks. A study of 

 the length of incubation period for Rhode Island Reds in its possible relation to 

 sex, viability, and characters afifecting fecundity was therefore undertaken m 

 the spring of 1937 and continued through three hatching seasons. 



Data Available 



All chicks were pedigreed Rhode Island Reds hatched in the same forced- 

 draft electric incubator in 1937, 1938, and 1939. Observations covered si.\ 

 hatches obtained at weekly intervals between March 7 and April 23. Seven 

 emergent periods, each covermg eight hours, were included in the study. The 

 first chicks appeared during the last third of the 20th day and the last chicks 

 appeared during the last third of the 22d day under the methods of incubation 

 used. Data were secured on 4730 chicks in the three-year period. Records were 

 taken on sex, mortality at different ages, body weight at about six months of 

 age for both males and females and at sexual maturity and at the end of the first 

 laying year for females, age at sexual maturity in females, winter and annual egg 

 production, and the emergent period of chicks from sires and dams classified 

 according to their individual emergent periods. 



In order to reduce to a minimum the temperature shock to the newly hatched 

 chicks, it was necessary to keep the chicks out of the incubator for the shortest 

 possible time during each eight-hour observation. For purposes of identification 

 a series of water colors was used for marking. It was found that the color mark 

 was most satisfactory when placed beneath the wing with a small brush. The 

 pedigree baskets were opened at each eight-hour observation. All chicks that 

 were out of the shell at the first observation were marked; and at the second and 

 later observations, all unmarked chicks were given the respective color mark 

 for the period. When the hatch was taken out of the incubator at the end of 

 the 22nd day, the emergent period of each chick was recorded. It was found 

 that the chicks could be gone over and marked in a short time by this method. 



♦Special credit is due J. W. Locke, Plant Foreman, for assisting in the observations on time of 

 emergence. 



