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THE EFFECT OF CONTROLLING THE INTERVAL FROM MATING TO OVULATION ON PREGNANCY RATE IN EWES TREATED WITH PROGESTERONE

By J. F. Roche and J. P. Crowley

Abstract

Oestrus and ovulation can be controlled in ewes during the breeding season by administering progestagens (Lamond, 1964). However, fertility at the con-trolled oestrus (40 to 60%) is generally low, regardless of the particular pro-gestagen or the mode of administration (Robinson, 1968). The physiological basis for this subfertility at the controlled oestrus is not clear at present. Fertilized eggs transferred to ewes previously treated with progesterone developed normally (Schmidt, 1961; Shelton & Moore, 1966), indicating that the capability of such uteri to sustain normal growth and development of the embryo was not adversely affected. Quinlivan & Robinson (1969) found that the pattern ofdistribution and survival rate ofspermatozoa became progressively altered at the first oestrus following progestagen withdrawal when compared with the pattern in non-treated control ewes. A significant decline in the cervical population of spermatozoa occurred between 12 and 24 hr after insemination of progestagen-treated ewes. This decline occurred in conjunction with a rapid drop in the vaginal population and was probably responsible fo

Year: 1970
OAI identifier: oai:CiteSeerX.psu:10.1.1.1002.1802
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