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

ORAL PROGESTOGENS IN CATTLE
FOR CONTROL OF THE ESTROUS CYCLE

R. G. ZIMBEIMAN, Ph.D.
Agricultural Division, The Upjohn Company
Kalamazoo, Michigan, U.S.A.

As is evident from Professor Robinson's presentation and the
other papers relating to estrus synchronization, synthetic pro-
gestogens have proven useful by a variety of routes of adminis-
tration. 1In the United States, the oral route has been most ex-
tensively studied and offers a practical procedure under a variety
of conditions. Some management situations, however, are not as
adaptable to the use of the oral route for synchronization of
estrus as others.

The first compound to be extensively studied for cattle was
medroxyprogesterone acetate (MAP, Repromix'<). MAP was used at
a daily dose of 180 mg. per day. Control studies with cycling
animals indicated a 92% synchronization of estrus during days 1-5
after last feeding (ALF). The second estrous period occurred at
days 18-26 ALF.

In attempts to improve upon MAP, the unique oral potency of
melengestrol acetate (MGA ) was uncovered. MGA effectively in-
hibited estrus and ovulation at 0.5 mg. daily, but may be recom-
mended at 1.0 mg. per day for practical use. Return to estrus
following MGA is somewhat delayed in comparison to Repromix; namely,
days 3-7 and 21-28 after last feeding for the first and second
estrous periods, respectively.

Conception rates following MGA have been relatively similar
to those following Repromix as shown below:
Conception Rates(a): Ratios
First Cycle Second Cycle First Cycle T ;}/
Cl

Treated(Tl) Treated(T2) Controls(Cl) /C1l

Repromix
Upjohn Studies 47 78 69 208 ndlnelis
University Trials 36 54 25 .65 .98
MGA
Upjohn Studies 34 73 5, <601 128
Field Trials 58 59 47 s O SRR

(a) Percent of those bred that conceived.
Both drugs show a reduced conception rate at first cycle with a

tendency toward an improved conception rate at the second cycle.
Percent of total group which became pregnant also appears similar

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