Abstract :
The objective of this study was to explore the possibility of a recurrent increase in the ovulation
rate of Malpura sheep, a non-prolific breed, by immunization against inhibin-based
peptide immunogens over a period of 3 years. Adult ewes (4–7 years of age) and weighing
between 28 and 38 kg were randomly allocated equally to three treatment groups.
The immunization of the ewes was initiated during the autumn breeding season. Ewes
were divided into three groups (n = 5 ewes/group) and actively immunized against the synthetic
peptides from the C [bI (1–29)-Tyr30] (Group I) or N [bI-43-Tyr152(153-167)Cys168]
(Group II) area of the bovine inhibin -subunit, conjugated to ovalbumin or against ovalbumin
(control). Each ewe received a primary immunization of 400 g immunogen and
3 booster injections, 200 g immunogen each at 4-week intervals. Estrous was synchronized
in all the ewes by administering two doses of PGF2 at 10-day intervals for three
consecutive years. Ovaries of ewes were examined each year between days 4 and 6 of the
synchronized cycle, with the aid of the laparoscope to determine the ovulation rate. Active
immunization significantly (p < 0.05) increased the ovulation rate. The overall ovulation
rate, irrespective of the treatment period was 5.2±0.44, 2.3±0.38 and 0.9±0.11 in Group
I, Group II and the control, respectively. Although the beneficial effect of immunization on
ovulation rate persisted for the entire period of the study, the interaction between immunization
treatment and the time period was non-significant. The results clearly indicate
that the active immunization against inhibin peptides can induce multiple ovulations in
Malpura ewes and its effect on multiple ovulations is sustained for a prolonged period of
time after the initial immunization.
