Ovarian follicular development in Booroola ewe lambs and in highly fecund Booroola ewes

K.P. McNatty, S. Lun, D. Heath, N. Hudson, J. McDiarmid, K. Ball, P. Smith and K.M. Henderson

Wallaceville Animal Research Centre, Ministry of Agriculture and Fisheries, Upper Hutt

Proceedings of the New Zealand Society of Animal Production. 1986, 46: 241-244

At 3 months of age, the ovaries of F+ Booroola lambs [i.e. those heterozygous for the fecundity (F) gene] were lighter (P<0.01) than those of ++ Booroola lambs (i.e. those without the F-gene) which were of similar age and body weight. However, the number of follicles (>/= 1 mm diam.) in the above F+ lambs was 1.5 fold greater (P<0.01) than that in the ++ lambs. In lambs of both genotypes, ovarian follicles were active in synthesising testosterone and oestradiol and of reaching diameters which were similar to those of preovulatory follicles in mature ewes. However, none of the ovaries showed evidence of recent ovulations.

In Booroola ewes (4 to 8 years of age), the proportions of small ovarian follicles (0.5 to 1.0 mm diam.) that synthesised progesterone, androstenedione and oestradiol in culture were related (P<0.05) to genotype (homozygous, FF > F+ > ++ ewes). Also in the above ewes, follicles in the FF and F+ animals reached maturity at smaller diameters than in ++ animals, namely 3.4 ± 0.3, 4.1 ± 0.2 and 6.8 ± 0.3 mm (mean ± s.e.m.; n=3 ewes/genotype) respectively. During a clopreostenol-induced follicular phase, the oestradiol secretion rates from FF ewes with 4.8 ± 0.3 'oestrogenic' follicles, F+ ewes with 3.2 'oestrogenic' follicles and ++ ewes with 1.5 ± 0.02 such follicles were similar as were the mean total numbers of oestradiol-secreting (i.e., granulosa) cells from these follicles, that is 5.4 x 10 6 cells in each genotype.

Collectively these findings show that the Booroola F-gene is expressed in the ovaries of ewes before puberty and during the earliest stages of follicular development. Moreover, as follicles in Booroola ewes with the F-gene mature at smaller diameters, the maturation of 5 or more follicles in FF ewes and 3 to 4 such follicles in F+ ewes may be necessary to produce the same number of oestrogen-producing (i.e. granulosa) cells as that from 1 or 2 mature follicles in ++ ewes.

Keywords: NZSAPAB; Booroola; lambs; ewes; ovarian follicles; granulosal cells; follicle size; cell numbers

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Last Updated 18-03-1997