On the Measurement and Inheritance of Sexual Maturity in Turkeys (Meleagris gallopavo)

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Statistical analysis of the trapnest records of turkeys extending over seven years shows that date of first egg is a better measure of sexual maturity in turkeys than age at first egg. Date of first egg is little influenced by variation in the time of hatch within the normal hatching season of almost two months, whereas age at first egg is influenced, the later-hatched birds starting to lay when younger than the earlier-hatched birds. Moreover, genetic differences in sexual maturity can more readily be demonstrated with date of first egg than with age at first egg. Selection for early and late sexual maturity was effective in establishing lines that differed significantly in date of first egg. When these lines were crossed the results differed according to which way the cross was made. The progeny of late male x early female laid earlier than the birds in the late-maturing line but later than the progeny of the reciprocal cross. In at least one case, the progeny of the latter (early male x late female) laid just as early as the birds in the early-maturing line. It is concluded from this that sexual maturity in turkeys is determined by both sex-linked and autosomal genes. The body weight of turkeys at the time they lay their first egg is usually near the maximum first-year weight, whereas chickens start to lay three to five months before they reach maximum first-year body weight. It is suggested that physical maturity is a less important factor in determining the onset of egg production in turkeys than in chickens and that turkeys have a higher threshold of response to environmental stimuli than do chickens.