2. • Dizygotic twins
The most frequent form of twins are the dizygotic ones (7 to 11 in
1000 deliveries), also known as "sibling twins" or "false twins". These
twins stem from two oocytes that matured during the same
menstruation cycle and were fertilized by two different sperm cells. In
other words, genetically, the two zygotes that arose with the
fertilization differ just as much as two normal siblings. Thus dizygotic
twins can be of the same or opposite sex.
Dizygotic twins implant themselves separately and develop
membranes that are independent of each other. Each twin has its
own placenta, its own chorion and its own amniotic cavity.
It sometimes happens that the two placentas lie so close to each
other that they fuse; the same thing can also occur with the chorions
of the two twins. Thus immunologic incompatibility reactions can be
observed since the fusion of the two placentas makes an exchange
between the circulation systems possible.
3. • Day 22 -23 – allantochorion formed
• Day 40 – sexual differentiation
4.
5. • Freemartinism is one of the most commonly found
intersex conditions in cattle although it may also
occur in small ruminants.
• appears in a dizygotic twin pregnancy where one
twin is a male and the other is a female
• Due to precocious anastomoses between the
placental vascular systems of the two fetuses,
masculinising molecules reach the female twin and
disrupt the normal sexual differentiation, whilst in
the male the effects of this association are usually
minimal
6.
7. • A freemartin is, by definition, a genetically
female fetus masculinised in the presence of a
male co-twin, giving rise to a sterile heifer
• A bovine freemartin is usually defined as a
sterile female calf, born co-twin with a male
fetus that shows underdeveloped or
misdeveloped genital tract as a result of early
development of vascular anastomoses
between fetuses of different gender
8. Features of genital tract
• Suppression and disorganization of the ovary,
originating a rudimentary or a testis-like gonad
depleted of germ cells.
• The uterine horns may be hypoplastic or instead
may be reduced to a cordlike structure suspended
in the broad ligament.
• Anatomic continuity between the uterus and the
vagina is frequently absent, and the existence of
rudimentary vesicular glands is typical. The
external genitalia commonly presents enlarged
clitoris, small vulva and a prominent, male-like
tuft of hair.
9.
10.
11. Absence of anatomical continuity between the vagina and the
uterus, hypoplastic or absent uterus, and hypoplastic or streak
gonads, co-existing with vesicular glands, are common findings in
freemartin heifers
12. • As consequence of placental anastomoses
between the heterozygotic twins, blood
chimaerism occurs (60, XX/XY) and passage of
male gonad determinants or hormones (such as
AntiMüllerian hormone and androgens) are
responsible for disrupted differentiation of the
female embryonic gonads and disturbed genital
tract development
13. Diagnosis
• The freemartin condition may be diagnosed
on the basis of physical examination of
suspected animals, as well as by serologic or
cytogenetic testing; the later being more
expensive and not always well accepted by the
farmer, who often considers it an unnecessary
expense.
14. It should be emphasized the importance for
discarding the freemartin syndrome during a
reproductive evaluation whenever a heifer is
intended to be maintained in the farm for
replacement. Its inability to reproduce
demands its early detection and culling from
the herd
