HORMONAL MANIPULATION OF FOLLICULAR WAVES FOR IMPROVING THE SYNCHRONY OF OESTRUS INDUCED BY PROSTAGLANDIN IN DAIRY COWS

Abstract

This experiment was aimed to determine whether pre-treatrnent with Oestradiol
Benzoate (OB) on the PGF;.,-induced oestrus afiects the waves of follicular growth
(follicular waves) and the synchrony of oestrus in Friesian dairy cows. Six cows
were randomly assigned in cross-over design to either control (3 cows) or treatment
(3 cows) groups. Saline (control) or treatment of OB was administered on Day 5 of
the oestrous cycle (Day 0 = oestrus), and on Day 12 all cows were treated with
PGF;.,. Observation of ovarian follicular dynamics was ca.rried out by means of
ultrasonography. Blood samples for progesterone RIA were collected on Days 5, 7,
9, 12, 14 of the oestrous cycle and at oestrus. Oestrus was detected twice daily by
means of KaMaR heat mount detector. Oestradiol benzoate administered on Day 5 of
the cycle reduwd tlte diameter and regressed (P<0.001) the first dominant follicle. After regression, the second follicular wave in OB-treated was emerged earlier (P<0.001) and with better synchrony (P=0.03) than in control cows. There was no correlation between the day of emergence of the second follicular wave and the day of ovulation (r,=0.45, P>0,05). The time interval from the day of emergence of the follicular wave producing the ovulatory follicle to ovulation was longer (P=0.013) in OB-treated than in control cows. There was no alteration in the concentrations of plasma progesterone on Days 5, 7, 9, 12, 14 and at oestrus. The results indicates that hastening the onset of the second follicular wave can hasten the onset of oestrus, and that improved synchrony of day of emergence of the second follicular wave was not associated with improved synchrony of oestrus.