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

THE SYNCHRONIZATION OF THE OESTROUS
CYCLE AND FERTILITY

T. J. ROBINSON

Department of Animal Husbandry,
University of Sydney, Sydney,
N.S.W. 2006, Australia.

I. INTRODUCTION

In summing up the Second Brook Lodge Workshop on reproductive
biology, Dr. Roy Greep likened the proceedings to a jigsaw puzzle
with no design on the box and no known number of pieces. In con=-
sidering the large domesticated animals the situation is further
confused by false concepts of the size and shape of the pieces =
concepts derived by extrapolation from laboratory rodents. Because
of the preoccupation with laboratory rodents, and because also of
the difficulties and expense of working with large domesticated
animals, we are woefully short of gquantitative data concerning the
factors which control reproductive phenomena in such animals. We
have qualitative notions. We know that oestrogen triggers off
certain physiological and psychological events. We know that pro-
gesterone plays a role and that this role varies between species.
We know that follicle stimulating hormone and luteinizing hormone
are involved in follicle growth and in the formation and function
of the corpus luteum. We are learning more of the mechanisms
involved in phenomena such as the maintenance of the corpus luteum
and the suppressive actions on the pituitary of progesterone and
oestrogen. What we do not know are the quantitative relationships
between hormones and fertility. We have only limited data upon
the quantitative aspects of sperm transport and survival in the
female reproductive tract, and upon the relationship between numbers
of sperm in the tubes and the chances of fertilization. We have no
information on such relationships and the endocrine status of the
animal in so-called '"mormal' oestrous cycles.

A major difficulty which plagues this field is the nature of
fertility data, particularly in sheep and cattle which commonly shed
but one egg. Animals either are fertilized or are not fertilized.
A difference between 45 and 55 percent of cattle or sheep which
conceive is of enormous economic and practical significance but in
order to demonstrate such a difference we need no less than 400
animals, A further difficulty is that this animal requirement is
enormously increased if the experiments are not conducted under

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