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

weeks after treatment.

Mucus discharge appeared during treatment at about the time for
normal heat in more than half of the heifers. The amount was
slight to mederate, the colour generally greyish and the visco-
sity varied.

TEATS AND UDDER An increase in udder size was observed during
treatment in the majority of cases.

Teat diameter increased steadily during treatment and at termi-
nation was on average 1,4 mm larger than at the beginning of
treatment. The teats had generally returned to normal by the
6th week after treatment.

OESTRUS SYNCHRONIZATION EFFICIENCY It is evident from table 2
that the majority of heifers showed heat on the 3rd and 4th days
after termination of treatment. A lower dose of norethisterone
(0,2 mg/kg) and a shorter period of treatment (10days) produced
poorer heat synchronization.

FERTILITY Conception rate following inseminatien at the syn-

chronized heat varied between trials even when the same dose was

employed (table 2). Conception rates for 0,4 ng/kg were 11,1%

gnd 21,5%, for 0,6 mg/kg 41,7% and T1,4% and for 1 mg 41,7% and
145%.

Conception rates for the medium doses (0,4 to 0,6 mg/kg) on twe
different farms were 35% and 67%. The higher figure was obtained
on a farm employing open loose housing and a more intense feeding
regime.

CONCLUSIONS Norethisterone prevented heat and ovulation during

the actual period of administration, but signs of cyclic activity

were evident together with fellicular development and regression.

Spontaneously developing ¢c.1.°s and c.l. s developing after ovula-
tion during treatment, were not inhibited by the hormone.

Weak cyclic changes were observed in the vagina and portio. These
were characterized by reddened m.m. s and a partially open portio
with secretions from cervix and vagina.

Very good heat synchronization was obtained at termination of hor-
mone treatment.

Fertility varied. This was not related to either dose or stage

of cycle. Feeding intensity could be a contributing factor to
this variation.

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