BODY WEIGHT AND EGG PRODUCTION 5 



that in the various studies body weights were taken at various ages by different 

 investigators. 



In most cases there was no uniform measure of body weight such as maximum 

 weight in the first laying year or weight at the end of the first laying year. On 

 the other hand, a summary of Canadian National Egg Laying Contests from 

 1924 to 1928, reported in their Blue Book for 1931, showed a decided correlation 

 between weight of birds and egg production in Leghorns, Barred Plymouth Rocks, 

 White Wyandottes, and Rhode Island Reds. 



Birds Used for Study 



The birds used were hatched in 1934, 1935, and 1936. They were all Rhode 

 Island Reds that were used in various breeding experiments. The methods of 

 feeding and management were kept constant. All birds were placed in the laying 

 houses when about 170 days of age. Individual weights were taken on each pullet 

 when housed, and subsequent weighings were made on the same calendar date 

 each month for a full year. 



Body Weight During the First Laying Year 



1. Monthly Body Weight 



The frequency distribution in body weight for all birds weighed at monthly 

 intervals throughout three years and the weight at first egg are recorded graph- 

 ically in Chart 1. All individual weighings were included to round out the fre- 

 quency graphs, because the monthly means were not significantly changed when 

 only birds surviving the whole period were included. 



A study of the frequency distributions in body weight from September to 

 January indicates skewness in the direction of lighter weight. The graphs further 

 reveal rather compact distributions for body weight during the first half of the 

 laying year. There was some evidence of a bimodal distribution at this time 

 around one mode of about 6 pounds and another mode of about 6.75 pounds. 

 The exact meaning of this apparent bimodal distribution has not been determined. 



Beginning with the February weights there was a rather close approach to 

 a normal frequency distribution. This result is suggestive that adult growth is 

 attained at about this time. From April to the close of the first laying year there 

 was an increasing tendency for the curves to flatten out. Such distributions 

 suggest that after mature growth was attained part of the population added weight 

 in the form of fat and another part of the population declined in weight probably 

 because of adverse physiological conditions. This series of graphs illustrates 

 the behavior of a large population in body weight through the first laying year. 



CHART 1 

 FREQUENCY DISTRIBUTION IN BODY WEIGHT DURING THE FIRST LAYING YEAR 



