Luteal regression and presentation of estrus in ewes after two injections of pgf2a applied eight days apart

Abstract

Hernández CJ, Valencia MJ, Zarco QL. Téc Pecu Méx 2001,39(1):53-58. The aim of this study was to evaluate the effect of a double injection of PGF2a (PG) administered 8 days apart on corpus luteum regression and estrus expression in the ewe. Fifteen cycling adult ewes received an injection of 15 mg of PGF2a followed by a second injection eight days later. One blood sample was taken daily from each animal starting before the second injection and continuing until estrus. Detection of estrus was performed twice a day using a ram fitted with an apron. Functional luteolysis was considered when progesterone concentrations were below 1 ng/ml and remained low until estrous behavior. Progesterone levels (>1ng/ml) showed that 93.3% (14/15) of the animals had a functional corpus luteum at the time of the second PG injection. There was a failure of corpus luteum regression after the second injection in nine ewes (64.3%), in these animals estrus occurred 138±13.7 h (mean±se) after the second injection. In the other five ewes, luteolysis occurred normally and estrus was present at 60±5.3 h. It is concluded that the regime of estrous synchronization based on two injections of PG applied eight days apart has a low efficiency in the ewe, because there is a large proportion of animals in which luteolysis does not occur after the second PG injection.