Abstract
A trial for synchronization of estrus cycle with single or double injection methods of PGF2α- analogue was conducted in fifteen Holstein heifers. The subsequent variations in levels of plasma progesterone were investigated to assess the correlation between progesterone levels and synchroniza-tion of estrus cycle.
The results obtained were as described below.
1) The profiles of plasma progesterone level in fifteen Holstein heifers following PGF2α-analogue injection could be classified into five types (type I-V). The type V in which three heifers were in-cluded was considered as abnormal, the other four normal types reflected the ovarian condition of the heifers when PGF2α-analogue was first injected: two heifers at estrus (type I), two heifers at about 3-4 days after ovulation (type II), four heifers at functional stages of corpus luteum (type III), four heifers either at late stages of estrus cycle or at early stages of luteal phase (type IV).
2) The heifers, which came into estrus after PGF2α-analogue injection, could be classified into three group: (1) the estrus cycle was induced with PGF2α-analogue injection, (2) the time of injection was happened to coincident with estrus, (3) injection was done at the late stages of estrus cycle.
3) In all of heifers excluding three heifers which were supposed to be abnormal, the concentra-tions of plasma progesterone at the second PGF2α-analogue injection increased up to the levels which was almost the same as these of the first PGF2α-analogue injections.
4) The rate of successive synchronization of estrus cycle after the second PGF2α-analogue injec-tions in fifteen heifers was 73.3% (11/15). Three heifers which were judged as abnormal based on the levels of plasma progesterone and one heifer failed to synchronize even after the second injection. The conception rate was 72.7% in remaining eleven synchronized heifers.
