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

REPRODUCTION IN EWES TREATED REPEATEDLY TO CONTROL ESTRUS
P. J. DZIUK, B. B. DOANE and T. J. REIMERS

Department of Animal Science, University of Illinois,
Urbana, U.S.A.

Interest in repeated treatments to control estrus and
shorten the interval between lambings has been stimulated
by the development of potent progestogens (1,2,3). The
following study was conducted to determine the effect of
repeated treatments to control estrus on reproductive
performance in the euwe.

MATERIALS AND METHODS. Fifty-seven Rambouillet ewes
managed under normal flock conditions were treated at
intervals of 8 to 12 months over a period of 53 months.
The number of treatments per ewe varied from 2 to 6 with

a total of 260 treatments giving a mean of over 4 treat-
ments per ewe. The ewes received one of the following
progestogen treatments for 14 days, 71 mg of 6-methyl-17-
acetoxyprogesterone (MAP) per ewe daily orally, 1 mg of
6-chloro- 5-17 acetoxyprogesterone (CAP) per ewe daily
orally, 200 ugm of 17-acetoxy-6-methyl-16-methylene-pregna-
4,6-diene-3,20-dione (MGA) per ewe daily orally, or a
subcutaneous implant of silicone rubber and 5% MGA (4).
Following treatment during January to July, 500 IU of PMS
were given subcutaneously whereas during August to December
no PMS was used. Groups of 8 to 10 ewes were penned with
one ram at the time of mating to maintain pedigrees. Data
were recorded on date of estrus, date of lambing and num-
ber and sex of lambs.

RESULTS. Three hundred sixty-three lambs were produced
following 243 of the 260 treatments to matings occurring
within 35 days after withdrawal of the progestogen. The
number of lambs per ewe lambing was 1.5 and the number of
lambs per ewe per year was 1.9 because intervals between
lambings were less than one year. Examples of euwes
lambing at less than 12 month intervals after repeated
treatments are shown in table 1.

 

TABLE 1. Examples of Reproductive Performance after
Repeated Treatment to Control Estrus

Interval between Lambs/
first treatment ewe/
Ewe and last lambing Lambings Lambs year
days no. no. no.
1 485 2 4 3i5:0
2 856 5 6 2.6
3 1216 4 7 2ier]
4 1378 B 9 2%4
5 1766 6 12 245

1429

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