We hypothesized that the number of microscopic follicles present in the ovaries of cattle selected for twin births (Twinner) would be greater than in the ovaries of contemporary Controls. Ovaries were collected from seven Control and seven Twinner cows at slaughter. The number of Small (1 to 3.9 mm), Medium (4 to 7.9), and Large (> 8 mm) surface follicles was counted and one ovary was fixed for histological evaluation. Fifty to sixty consecutive 6-microm slices were taken from a piece of cortical tissue, approximately 1 cm x 1 cm in area, located between the surface follicles. Microscopic follicles were classified as primordial (oocyte surrounded by a single layer of squamous pregranulosa cells), primary (oocyte surrounded by a single layer of one or more cuboidal granulosa cells), secondary (oocyte surrounded by two or more layers of granulosa cells), or tertiary (oocyte surrounded by multiple layers of granulosa cells with initiation of antrum formation to < or = 1 mm in diameter). The total number of follicles was counted in 200 fields (2 mm x 2 mm) per ovary. A field containing no follicles was classified as empty. There were significantly more secondary follicles in Twinner compared with Control ovaries (12.9 vs 6.3; P < .05). Twinners also tended to have more small surface follicles (35.4 vs 49.0; P < 0.1). We conclude that ovaries of Control and Twinner cows do not differ in the number of primordial follicles or in the number of follicles activated into the growing pool; however, Twinner cows are able to maintain more growing follicles at the secondary and subsequent stages of development.
[1]
R. Cushman,et al.
Superovulatory response of one ovary is related to the micro- and macroscopic population of follicles in the contralateral ovary of the Cow.
,
1999,
Biology of reproduction.
[2]
H. Mizunuma,et al.
Activin from secondary follicles causes small preantral follicles to remain dormant at the resting stage.
,
1999,
Endocrinology.
[3]
R. Rodgers,et al.
Morphological characterization of bovine primordial follicles and their environment in vivo.
,
1996,
Biology of reproduction.
[4]
J. Baker,et al.
Effects of an Igf1 gene null mutation on mouse reproduction.
,
1996,
Molecular endocrinology.
[5]
J. Hammond,et al.
Concentrations of insulin-like growth factor-I in blood and ovarian follicular fluid of cattle selected for twins.
,
1990,
Biology of reproduction.
[6]
J. Kastelic,et al.
Composition and characteristics of follicular waves during the bovine estrous cycle
,
1989
.
[7]
R. Murphree,et al.
Ovarian characteristics and reproductive performance of the aged cow.
,
1976,
Biology of reproduction.
[8]
B. H. Erickson.
Development and senescence of the postnatal bovine ovary.
,
1966,
Journal of animal science.
[9]
B. H. Erickson.
DEVELOPMENT AND RADIO-RESPONSE OF THE PRENATAL BOVINE OVARY
,
1966
.