STUDIES IN HATCHABILITY IV. THE EFFECT OF INTERCROSSING- INBRED STRAINS OF CHICKENS ON FERTILITY AND HATCHABILITY

In a previous paper, the author (1929a) presented data show-ing that as close inbreeding is continued in chickens hatcha-bility decreases. The kind of inbreeding practised was full-brother-and-sister and half-brother-and-sister matings. It was observed that hatchability results are affected to a greater ex-tent in the first year of such close inbreeding than in successive years, though there is a general decline in hatchability each year that such close inbreeding is continued. Similar results were secured in Barred Plymouth Rocks and "White Leghorns. In another paper, the author (1929b) determined that hatcha-bility decreases as the coefficients of inbreeding increase. Since the intercrossing of highly inbred strains of corn pro-duces a remarkable state of rejuvenation, as demonstrated by Bast and Jones (1919), it was decided to determine the effect of intercrossing the inbred strains of Barred Plymouth Rocks and White Leghorns. Originally four pens each of the two breeds mentioned were started in the inbreeding project but in two years two pens of Barred Plymouth Rocks had practically exterminated them-selves through decreased hatchability. Two more pens of fnll-brother-and-sister and half-brother-and-sister matings, however, were started to replace the two depleted pens. In 1928 two pens of Barred Plymouth Rocks had been in-bred for three generations so that their progeny represented the fourth year of progressive full-brother-and-sister and half-brother-and-sister matings; two pens of Barred Plymouth Rocks have been likewise inbred for one generation and four pens of "White Leghorns had been similarly inbred hj using full-brother-and-sister and half-brother-and-sister matings for three succes-sive years. In 1929 the inbred strains were intercrossed by ex-changing the males in the first and second and the third and fourth matings, respectively, of each variety