88 SEASONAL VARLATION IN SEMEN QUALITY [Vol. XXII, Part II
Estimation of sperm concentration at regular intervals as was done in this experi-
ment, provided a direct indication of the rate of spermatogenesis. Spermatogenesis
is controlled by the activity of the follicle stimulating hormone of the anterior
pituitary gland. For full manifestation of its activity, however, the secretions of
other endocrines are also necessary. Very recently it has been demonstrated that
in some farm animals the seasonal variations in fertility and semen characteristics
correspond with the seasonal activity of the thyroid gland and that this seasonal
effect can be controverted by artificially administering thyroid hormone in summer
and one of the depressant thiouracil drugs in winter [Berliner and Warbritton
(1937) Bogart and Mayer 1946]. It seems, therefore, that decrease in sperm con-
centration in summer and autumn may be due to mild hypothyroidism produced
due to the prevailing high environmental temperature and relative humidity.
Total number of spermatozoa
Sperm concentration is indicative of spermatogenetic activity but does not give
a true evaluation unless the total number of spermatozoa per ejaculate is also con-
sidered. The total number of spermatozoa per ejaculate when calculated from
data of two successive ejaculates from an individual animal gives rather an accurate
picture of semen quality of the animal for the particular period when the semen
was collected. Analysis of data for total number of spermatozoa in different bulls
showed no seasonal influence on this character. The present result is in disagree-
ment with those reported by Erb et al. [1942] and Phillips et al. [1943] but is in
agreement with that reported by Mercier and Salisbury [1946]. The latter authors,
however, expressed doubts about their results because the frequency of semen
collection in their study was not rigorously controlled. Consequently, they believed
that the variation due to seasons in this respect might have been obscured. They
have, therefore, suggested that ' before the question is satisfactorily answered it
will be necessary to establish a rigorous schedule for semen collection throughout a
year '. In this investigation, a definite schedule throughout the two consecutive
years was followed in collecting semen samples, and yet no significant variation
among seasons or among months within seasons was observed.
Abnormal spermatozoa
The result obtained in this respect show that bulls did not differ significantly
in production of abnormal spermatozoa. Regarding the effect of seasons it was
found that summer differed from the rest of the seasons in producing low percentage
of abnormality. Highly significant seasonal variations in abnormal spermatozoa
of bulls have also been reported by Erb et al. [1942], Phillips et al. [1943], Swanson
and Herman [1944] and Mercier and Salisbury [1946]. During winter and spring
more bent and coiled tail sperms were produced, whereas in summer and autumn
more tailless ones. Phillips and his collaborators while working with bulls and
rams [1943,a; and 1943,b] reported a high percentage of abnormality in tails during
winter. But they did not mention the types of the tail abnormalities observed.
They considered that cold weather might have adversely effected the tails after
the collections were made. To test the validity of this view a few fresh samples