384 ABSTRACTS
The influence of intensity of egg production upon infertility in the domestic
fowl. W. F. LAMOREUX (1940). J.Agri.Res.
61, 191.
D URING a period of five years over 1200 selected White Leghorn females and 100
males were used in a study to determine whether the degree of fertility is influenced
by the intensity of egg production and to note the basis for such a relationship if it
exists. Artificial illumination was used to a limited extent. All eggs were incubated. To
determine infertility the eggs were candled or the appearance of the germinal disc of
the broken egg was observed after 18 to 25 hours of incubation.
Individual incubation records for the hens during February, March and April of
each year were studied by three measures of intensity of egg production : '(1) the number
of eggs laid during a specific period of 6 weeks ; (2) the number of eggs laid during each
week of the incubation period ;' i.e., from February 1 to April 30 and ' (3) the number
of eggs laid per clutch (number of eggs laid on consecutive days). '
After the first and last hatch of the season was eliminated, those hens which layed
during the remaining six weeks each year, numbering 856, were included in the study of
No. 1. Egg production varied from 13 to 40 eggs. The highest proportion of infertiles,
24.4 per cent, occurred among the lowest producers, whereas the smallest proportion of
infertiles, 13.0 per cent, was among the best layers. In studying No. 2 the incubation
record of each hen was divided into weekly periods : the first week was eliminated to assure
adequate time for mating with the males. Each weekly record was put into one of seven
groups according to the number of eggs laid during that week. The mean percentage
of infertile eggs by groups was 14.7, varying from 31.2 per cent in the one-egg group
to 11.8 per cent in the seven-egg group. Finally, in considering No. 3, all complete
clutches of 1178 hens were studied. Here also the lower the intensity of egg production,
indicated by the smaller clutch, the higher the proportion of infertiles ; and vice versa.
In each of the five years studied there were 1.5 to 6.7 per cent fewer infertiles in the larger
clutches than in the smaller ones.
The rate of ovulation cannot be influenced by the degree of infertility ; this rate does,
it appears, affect the fertility of the eggs laid. Other workers have shown that (a) estrogen
is probably secreted in the theca interna of the Graafian follicle, (b) although the ova of a
poor layer develop equally as fast as those of a good layer, the latter has more ova in the
final stages of development at any one time than the former, and (c) in the follicle of a
very young oōcyst there is no theca interna.
The influence on fertility of high estrogenic levels was studied experimentally. Three
possibilities were considered ; (1) increase in the ability of the ova to be fertilized, (2)
prolongation of the functional survival of sperm in the oviduct and (3) induction of greater
sexual receptivity in the female.
Susceptibility of ova to fertilization was difficult to measure. On the suggestion that
at the beginning of a clutch there should be larger ova in the ovary than at the end all
clutches of four or more eggs were studied. An insignificant difference of only 2 per cent
was found between the fertility of the first two eggs of such clutches and the last two.
The functional survival of sperms in the oviduct as influenced by the estrogenic level
in the hen was studied. Hens were divided on the basis of laying intensity, those above
and those below 55 per cent (100 per cent equals one egg each day). Half of each group
was injected with estrogen two days after being artificially inseminated. From observa
tions made thereafter it was concluded that : ' sperm tend to survive somewhat longer
in the oviducts of rapid than of slow layers. '
It was noted that in some hens fertility declines rapidly after insemination. Also,
it is generally believed that non-laying hens mate infrequently, if at all. Eleven hens
which produced very few fertile eggs were artificially inseminated. In the ten days pre
vious to this they produced 80 eggs of which 2.5 per cent were fertile : from the second
to the eleventh day subsequent to one insemination they produced 138 eggs of which
60.9 per cent were fertile.
Other workers have shown that hens which ovulate most rapidly also copulate most
frequently. The present worker found, after daily injections of larger doses of estrogen,
no relationship between the amount of hormone and the frequency of copulation in three
immature pullets 15 weeks of age, three nearly mature but non-laying pullets, four pullets
which had recently started to lay, four yearling hens which were laying at a rapid rate
and three hens from a strain bred for low fecundity.
[J. N. W.]