Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF,, PARIS, 1968, VOL. li

HEAT SYNCHRONIZATION OF HEIFERS WITH NORETHISTERONE
(17- X - ethynyl-19-nortestosterone)

G. Astrém and A. Bane
Department of Obstetrics and Gynaecology, Royal Veterinary College,
Steckhelm 50, Sweden.

Six experiments in heat synchronization of 134 heifers of the Swe-
dish Red and White Breed were carried out in 1967 and 1968 in
three different herds (table 2). 0,2-1 mg/kg body weight of nore-
thisterone was administered pererally to the heifers once daily.
Treatment continued for 17 days except.in one group treated for

10 days only. In 83 heifers the course of the oestrus cycle was
followed by observations of heat signs, repeated ovarian palpation
and vaginal examination. In these animals hormone treatment began
at different stages of the cycle: early luteal, full luteal and
follicular stage. Before the first day of treatment (day 0) of 33
of these heifers and every 4th day during treatment, the ovaries
were examined for the existence of palpable fellicles and corpora
lutea(c.1.). The vestibulum, vagina and portio were alse examined,
and the colour ef the mucus membranes (m.m.) noted. The vaginal
mucus was judged according to gquantity, colour and viscosity and
the portio according to its corrugation and degree of opening.
Cervical mucus samples were taken for study of arborization. In
the other animals treatment began at a randem point in the oestrous
cycle. In 69 animals (trials IV, V and V1) the vulva and teat dia-
meter were measured.

In all experiments the heifers were inseminated with semen, used
in routine insemination and known to produce a good conception
rate.

OVARIES AND VAGINA Table 1 shows the incidence of follicles
and cerpora lutea at individual examinations when treatment began
at different stages of the oestrous cycle.

Development and regression of palpable follicles i.e. follicles
with a diameter > 7-8 mm occurred during the period of hormone
administration. The incidence of heifers with palpable follicles
increased during this period.

hormone treatment. Development eof cyclic c.l. was not prevented
by treatment. In all animals a c.l. was palpable after 8 days
treatment but in the majority this had regressed before treatment
was terminated after 17 days (table 1). Vagina and pertio demon-
strated slight changes fellowing the normal pattern. The colour
of the mucaus membranes became less pale than normal hewever. The
vaginal m.m. was pink and that of the portio pink to red. The
portio generally remained smooth and a little open with a string
of clear mucus in the external os.

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