Vle CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. Ii

BULL FERTILITY AS AFFECTED BY AN INTERACTION
BETWEEN MOTILE SPERMATOZOA CONCENTRATION AND
FERTILITY LEVEL IN ARTIFICTAL INSEMINATION

J. J. SULLIVAN and F. I. ELLIOTT
American Breeders. Service, Inc.
DeForest, Wisconsin, U.S.A.

The efficiency of sperm utilization and maximum fertility
of bulls is of a major concern for an A.I. organization. One
of the obvious ways to meet this obligation in a frozen semen
program is to provide only the necessary number of sperm per
inseminating dose for optimum fertility without the excess that
would constitute wastage. This study was designed to develop
data determining the effect of the number of progressively mo-
tile cells per dose upon non-return rate.

MATERIALS AND METHODS. Nine mature Holstein-Friesian bulls were
Used in a factorial experiment to study the effect of sperm con-
centration upon fertility of frozen semen used in artificial in-
semination. Each bull was on a twice-a-week collection schedule
and provided 48 semen collections for the trial. Sixteen of
these collections were processed so as to contain a concentra-
tion of five million progressively motile cells per inseminating
dose. Sixteen others contained ten million progressively motile
cells, and the remaining sixteen contained fifteen million such
cells.

The spermatozoal concentration was adjusted prior to freez-
ing. The prior survival rate of each bull's semen through the
freezing process was used to estimate probable survival, and
the extension was carried out accordingly. Because there is sub-
stantial variation in survival rate from collection to collection,
and it was impossible to predict exactly, a range of two million
cells above or below the intended level was accepted. In other
words, concentrations reported as five million might have been
as low as three million or as high as seven million. The same
principle applies for the other concentrations.

Of the sixteen collections of each bull at each concentra-
tion, four were collected during the winter season (January,
February, March), four during the spring, four during the summer,
and four during the fall season. One of the four collections
representing each of three concentrations harvested during each
season was used to inseminate cows during each of the four sub-
sequent seasons. Thus, the experimental design removed the

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