
TY  - JOUR
A1  - Morris, JA 
T1  - The effect of mild inbreeding in two lines of White Leghorn
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1962
VL  - 13
IS  - 2
SP  - 362
EP  - 375
KW  - 
UR  - https://doi.org/10.1071/AR9620362 
N2  - The reaction of two flocks of White Leghorn to slow inbreeding has been examined. One flock, the M line, has been subject to continuous selection for egg production or an associated character since 1947, and the other, the C line, has been propagated by means of random mating without artificial selection for a corresponding period. Mean inbreeding, as measured by Wright's coefficient (F), increased steadily in both flocks to reach a maximum of 25.1&#37; in the M line and 16.2&#37; in the C line. Significant intra-year regressions of survivors' production (72 weeks), hatchability of fertile eggs, and egg production during the winter months of June&ndash;July, on computed F values, were observed for both lines. In addition, significant regressions for the 72-week production index, age at first egg, and pauses during June&ndash;July were observed for the M line. Viability of chickens, both during early rearing (hatching date to 3&#189; weeks of age) and during adult stage (approximately 20 weeks to 72 weeks of age), was not affected by small changes in degree of inbreeding. Intra-year regressions on F of age at death and production up to time of death were non-significant for both lines. Highly significant differences between yearly regressions of egg production, and pauses during the two winter months, on F values were observed. These differences could indicate a differential sensitivity of response to inbreeding associated with seasonal adversity. It was not possible to substantiate the existence of a differential response to a stress factor when mortality during a severe heat wave was examined, as the mean computed F value of birds dying was not significantly greater than the corresponding F value of survivors. The stress was reasonably severe, as 15.4&#37; of all birds died within a couple of days. 
ER  -

