1) In temperate climates, most goats are seasonally polyestrous. They
exhibit cyclic heats during the fall months, under the influence of
decreasing day length. Sometime between January and March, as days
lengthen, the typical goat enters into a period of anestrus. The
physiological differences between the breeding and the anestrus seasons
necessitate the use of different techniques for the control of estrus
during each time period.
2) Reasons for Synchronizing Estrus During the breeding season, estrus synchronization permits the
efficient use of artificial insemination and of a trained technician.
Owners with full time jobs can schedule breedings, artificial or
natural, for weekends or vacation periods. In herds or animals where
heat detection is difficult, goats may be successfully bred even though
they cannot be found in heat. Does may be bred to kid at a certain
time, for instance to take advantage of the Easter market for sale of
buck kids. Five months after synchronized breeding, parturitions will
be closely grouped or can be further synchronized by the use of
hormone injections. Additional advantages are the simplification of kid
rearing and the control of diseases such as bacterial scours and
coccidiosis afforded by an all in, all out, kid raising program.
Finally, estrus synchronization is an important tool for embryo transfer
procedures.
3) Outside the normal breeding season, synchronization has additional
advantages. It permits the breeding of does to freshen in the fall,
thereby assuring a supply of milk when most of the herd is dry. In
areas with a demand for goat milk, there may be an economic incentive
in the form of higher prices paid for winter milk.
4) An alternative to synchronization that permits breeding during the
spring months is the use of lights. If goats are kept under long days
(16-20 hours) for several months (for instance, January and February)
and then returned to ambient day length, many will exhibit fertile
cycles during the next few months. If natural breeding is to be used,
it is imperative that the buck also be subjected to the controlled
lighting. This is not a synchronization technique, as the induced estrus
periods will be somewhat randomly spaced.
5) Methods of Synchronization Does to be synchronized should be placed on a high energy diet 2 to
4 weeks before breeding is desired. Anthelmintics, if needed, also
should be administered in advance. In general, best results will be
obtained with normally fertile does for which the most recent
parturition was without complications. Polled animals with both parents
polled should be examined first before commencing with synchronization
to eliminate intersexes and sterile animals. Polled animals with
masculinized anatomy, masculine behavior, or a total absence of estrus
periods prior to synchronization are poor candidates for
synchronization and the probability of successful breeding is greatly
reduced.
6) The Buck One of the simplest means of synchronization is the sudden
introduction of a buck or his odor early in the fall. It has been shown
that many does will come into estrus approximately 8 to 10 days later.
If a teaser buck is first introduced and then replaced after 3 weeks by
a fertile male, reasonably good synchronization and an increased
ovulation rate will be achieved on the second cycle. If does are
already cycling, the synchronization effect will be largely lost.
7) Vaginal Sponges In France, synchronization of goats is commonly obtained by the use
of intravaginal sponges. They are available commercially abroad and are
impregnated with 45 mg of fluorogestone acetate. Sponges with less
hormone (marketed for sheep) give lower conception rates. The sponge is
coated with an antibiotic powder or ointment and is placed deep in the
vagina for 17 to 21 days. The string designed for removal of the sponge
should be cut short unless each goat is housed separately. When the
sponge is removed, it will be covered with a purulent exudate, but this
exudate does not interfere with conception and no further treatment is
necessary.
8) Hormone injections are used to stimulate follicular development
when the sponge is removed. Pregnant mare serum gonadotrophin (PMSG) is
preferred but is often hard to obtain in the United States. It is
available from Francea (as are the sponges), but a permit from the
USDAb is required for importation of the hormone and may be impossible
to obtain. The dose of PMSG used depends on the age of the goat, the
current milk production, and the season of the year. In dairy breeds,
fertility is poor during the first 4 months after parturition. Adults
for AI giving more than 8 pounds of milk a day receive 700 IU of PMSG
during the period from March 15 to June 14, 600 IU from June 15 to
September 14, and 500 IU during the fall breeding season. Does milking
less heavily receive 100 IU less during each time period, as do adults
that are to be serviced naturally. Overdosing results in superovulation
and potential abortion due to uterine crowding. Doelings receive 400 IU
of PMSG during all seasons, but it is important that these animals
weigh at least 77 lbs (European breeds) before hormonal treatment is
attempted.
9) During the anestrous season, the PMSG is administered 48 hours
before sponge removal. During the breeding season, this treatment is
given simultaneously with sponge removal. The goats are generally in
heat 12 to 36 hours after sponge removal, and are bred within 48 hours.
If fixed time insemination is to be used, 2 breedings at 31 and 55
hours or 36 and 60 hours have been recommended.
10) Limited trials have been performed substituting follicle
stimulating hormone (FSH) for the PMSG, using 2 doses of 2 mg each at
12 hour intervals. The FSH appears to be less effective than PMSG.
11) Progesterone Treatments A removable subcutaneous implant containing progesterone or other progestogen in silastic tubing can be substituted for the vaginal
sponge. This technique avoids vaginal infections as well as the rare
occurrence of adhesions preventing sponge removal, particularly in
doelings. Another technique involves the subcutaneous or intramuscular
administration of progesterone in oil, 20 mg every other day for 18
days. Where it is available, the oral use of
6-methyl-17-acetoxy-progesterone (MAP) at 50 mg/day for 15 to 20 days
is yet another option. With all these products, PMSG will improve
fertility.
aDr. D. Aguer Intervet - SA 43, Avenue Joxe B.P.
235 49002 Angers, France.
bHarvey A. Kryder, Jr. Chief Staff Vet. Organisms & Vectors.
U.S. Dept. Agriculture. Animal & Plant Health
Inspection Service, Federal Center Building.
Hyattsville, Maryland 20782.
12) ++++MISSING DATA++++
13) The donor doe is anesthetized 3 to 5 days after mating, using
halothane or barbiturates. A midventral or flank laparotomy incision
permits flushing of the oviducts and uterine horns for the recovery of
fertilized eggs. Approximately 10 ml of tissue culture medium 199 with
sodium bicarbonate (and, in some studies, 10 2.256835e+199oat serum) at 37
used to flush each oviduct. The fluid is collected in a petri dish and
examined under a binocular dissecting microscope to identify ova that
have undergone cleavage. These fertilized eggs are picked up in a 20
gauge needle or special pipette in preparation for transfer. Recovery
rates of 60 to 80(based on number of corpora lutea) and 80
of recovered eggs have been reported.
14) Meanwhile, recipient does must be prepared. If a large herd of
normal, cycling does is available, animals with natural heats 24 hours
before to 36 hours after the estrus of the donor doe are selected.
Otherwise, recipients are synchronized using any of the techniques
described previously. Both progesterone and prostaglandin treatments have
been ++++MISSING DATA++++
