temperature generally inhibits ovulation, while in Western Aus- 
tralia, which ig relatively dry, rainfall stimulates egg 
production in some species. 
Other external factors that affect the beginning of 
egg production are: establishment of territory, availability 
of nesting site and building materials, abundant food supplies 
and for some bird species the necessity of being a member of a 
large breeding colony. Egg production is inherited in chickens 
as it probably is in most species; in poultry it is an extremely 
complex characteristic involving many genes; 
Briles (1956, 1960, 1961) has found a relationship 
between blood types and egg production. Over a period of three 
seasons, he found that the hens in two lines heterozygous for 
B blood group alleles were superior to the homozygotes. Ona 
survivor basis, in one of these lines the heterozygotes were 
4.5 per cent better and in the other line they were 6.9 per cent 
better egg producers. 
More recently, work at this station (Smyth, 1961) has 
shown a definite correlation between the degree of melanization 
of laying hens and their per cent egg production. The lighter 
birds had the highest production and the darkest birds had the 
poorest production. Melanization groups between these extremes 
fell right in line with the correlation. 
Now to consider some of the hormone manipulations of 
egg production-- A number of studies have dealt with the treat- 
ment of hens, their eggs or the developing pullets to determine 
the effects on reproduction. Adams et al. (1950) reported ab= 
normal reproduction from pullets which had developed from eggs 
from hens which had been fed various levels, ranging from 0.01 
per cent to 0.04 per cent of two synthetic estrogens. Glick 
(1961), using very small numbers reported the results of dip- 
ping eggs of three days incubation in 100 ml. solutions of 
ethyl alcohol, 670 mg. testosterone propionate, 2 gm. testo- 
sterone propionate and 670 mg. deHydroisoandrosterone. Pro= 
duction for the resulting pullets in the testosterone groups 
was lowered by 16 per cent. The hens produced no fertile eggs 
in the 2 gm. testosterone group and hatchability was lowered 
by 14 per cent in the 670 mg. testosterone group. 
Estrogens given to 9-week-old or older birds, either 
in the feed at .04 per cent level (Adams et al. ; 1950), or as a 
12 to 15 mg. diethylstilbestrol implanted pellet in chickens 
(Akpinar et al., 19533 Talmadge, 1959; Jeannout et al., 1959), 
or as a 24 mg. pellet in turkeys, or as an intramuscular in- 
jection at the rate of 4.16 mg./week (Herrick et al., 1955), 
all produced a marked depression in egg production. In most 
cases, the depression effect lasted only during the first three 
to four months of production. 
55 
