Last update: August 12, 2011 02:49:33 PM E-mail Print

 

EFFECT OF OXYTOCIN TREATMENT DURING OESTRUS ON THE OVULATION RATE IN MERINO EWES

 

P R King

Grootfontein Agricultural Development Institute, Middelburg 5900

W A Coetzer

Dept of Human and Animal Physiology, University of Stellenbosch 7600

 

 

The ovulation rate of Merino ewes mated to Ronderib Afrikaner rams is on average 19 percentage points higher than that of Merino ewes mated to Merino rams. The higher sexual activity of the Ronderib Afrikaner ram may result in higher peripheral oxytocin levels during oestrus in ewes mated to Ronderib rams than in ewes mated to Merino rams. Accordingly two experiments were undertaken to determine whether exogenous oxytocin injected during oestrus would influence the ovulation rate of Merino ewes. In the first experiment, executed during autumn, 108 oestrous synchronized two-tooth Merino ewes were randomly divided into two groups (A and B). From the onset of oestrus Group A was intravenously injected every 30 minutes with 0.1 I.U. oxytocin (Oxytocin Synth. Phenix ), for a 24 hour period. Group B ewes were also handled every 30 minutes but received no oxytocin treatment. In the second experiment, also performed during the breeding season, 90 adult and 48 two tooth oestrous synchronized Merino ewes were divided into two groups (C and D) on a stratified mass and age basis. At the onset of oestrus Group C was injected subcutaneously with a slow releasing oxytocin preparation containing 2  I.U. oxytocin while Group D served as control. The number of ovulations per \ewe in both experiments was determined laparoscopically. The ovulation rate of Group A and B was 174.5% and 144% respectively (P<0.01). The ratio of ewes displaying single and multiple ovulations in Group A (15:22) differed significantly (P<0.01) from the ratio recorded for Group B (28:22). The ovulation rate of the adult ewes of Group C and D was 179.1% and 159.1% [respectively (P<0.05). The ratio of adult ewes displaying single and multiple ovulations in Group C (10:33) differed significantly (P<0.01) from the ratio recorded for Group D (19:25). The ovulation rate of the two tooth ewes did not differ between Group C and D (P>0.05). From the present results it would appear that oxytocin plays a role in ovulation and that the administration of exogenous oxytocin during oestrus can increase ovulation rate.

 

Published

Proceedings 34th SASAS congress