The Effect of Monthly Hatches on Performance Traits of White Leghorn Pullets

Abstract

The effects of monthly hatches on various performance traits were studied with pedigreed chickens originated from the same parents throughout a year. The characters analysed in this report are age of sexual maturity, body weight at first egg and at twelve months of age, egg weight at ten months of age, pullet year egg production, and adult viability.It is concluded that the age of sexual maturity depends primarily on changes in daylength occuring during the growing period, and thus should be longest for the June hatch and shortest for the December hatch under natural daylight. The dependency of the character on the day length is best explained by fitting a quardratic equation, y=161-2.05x+0.25x2in which y stands for sexual maturity in days and x for the difference between day length in hours at sexual maturity and hatching dates.Although body weight at sexual maturity shows high correlation with the age of sexual maturity, rather poor ranking correspondence of sire group's records of these two traits suggests that the genetic correlation may differ substantially from the phenotypic association. Body weight at twelve months of age was largest in the May hatch and smallest in the July, the difference being approximately 400 grams. Two measures of body weight were negatively correlated each other.Annual egg poduction starting from first egg was highest for the April hatch and lowest for the September, whereas egg size at ten months of age was largest in the Febuary hatch and smallest in the September. Thus, the Febuary hatch or early spring hatch is more profitable than fall hatches.Egg production pattern, defined as the pattern of average monthly production rate starting from onset of production up to 540 days of age of pullets hatched contemporally, shows distinct features characterized by one or two production peaks with or without a sharp decline occuring during winter season. When birds encounter winter before they go to their production peak, uni-modal production pattern which has only one peak is seen (i. e. June and July), while bi-modal pattern characterized by the winter decline will be observed otherwise (i. e. December through April). Some applications of the results to the techniques of artificial lighting were discussed.Sire by hatch interaction was significant only in age of sexual maturiurity (p _??_ .05) and twelve omnths body weight (p<.01). Genetic correlation of egg production between spring and fall hatches after pooling three months of data was practically none, which suggests ranking of sire groups hatched in spring and fall lucks its consistency. Implications to selection and performance test involving seasonal difference were also discussed.