Ovarian activity in the Booroola x Romney ewe possessing a major
gene influencing fecundity
K.P. McNatty, K.M. Henderson, S. Lun, D. Heath, L. Kieboom, N.
Hudson, J. Fannin, K. Ball, P. Smith
Wallaceville Animal Research Centre, Ministry of Agriculture and
Fisheries, Upper Hutt
Proceedings of the New Zealand Society of Animal Production.
1984, 44: 33-36
The pattern of ovarian follicular development in Booroola x
Romney ewes (6-7 y) with an ovulation-rate >/-3 (F+ ewes) differed from
that in Booroola x Romney ewes (6-7 y) with an ovulation-rate <3 (++).
The difference was not due to variations in the number of ovarian
follicles (>/-1 mm diameter) or in the proportion of healthy follicles
which were similar for both genotypes. It arose because follicles in F+
ewes produced oestradiol and reached maturity at a smaller diameter than
in ++ ewes. During a prostaglandin induced follicle phase, the
secretion rate of oestradiol from ovaries with 3 presumptive
preovulatory follicles in F+ ewes was similar to that from ovaries with
only 1 such follicle in ++ ewes. Moreover, the total number of
granulosa cells (i.e. the oestrogen-secreting cells) in 3 preovulatory
follicles from F+ ewes was similar to that in 1 such follicle in ++
ewes. In F+ ewes, the presumptive preovulatory follicles reached 4.6 ±
0.4 (s.e.m.) mm in diameter, whereas in ++ ewes, they reached 7.3 ± 0.3
mm in diameter.
It is hypothesised that the putative 'gene' effect is manifested in
small ovarian follicles (</-2.5 mm diameter) which results in their
maturation at a smaller diameter (i.e. 3 to 5 mm) than is the case for
++ ewes. As a consequence, the development of at least 3 preovulatory
follicles in F+ ewes may be obligatory to generate sufficient oestrogen-
secreting cells to initiate oestrus and ovulation.
Keywords: NZSAPAB;
Booroola x Romney ewes; genotype; ovaries; follicles; corpora
lutea; oestradiol; granulosa cells
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Last Updated 03-05-1997
