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“HEAT DETECTION
IN THE COW”
Buddy Faries
DVM and Joe Paschal PhD
Texas Cooperative Extension
Texas A&M University System
"The Mechanics
of Estrus"
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The basics of the estrous
cycle:
The pituitary gland of the
brain secretes the follicle stimulating hormone (FSH) that causes the
ovary to develop follicles. Several follicles develop in what is termed
follicular waves, but only one dominant follicle and egg mature for
ovulation (rupture of the follicle and release of the egg).
As the follicle develops,
estrogen is secreted by the ovary. The egg grows larger as more estrogen
is produced. Estrogen causes estrus ("heat") for 1 day and contractions
of the uterus to aid in transport of sperm.
The pituitary gland of the
brain secretes lutenizing hormone (LH) that causes the ovarian follicle
to rupture and release the egg. The site of rupture becomes a corpus
luteum (CL) that secretes progesterone hormone (the calming hormone) to
inhibit estrus. The ovarian CL matures on Day 6. If the uterine wall
does not get a signal on Day 16 to indicate that a fertilized egg has
been implanted in the uterine wall, the CL regresses on Day 20 by
prostaglandin hormone secreted from the uterus to complete the
reproductive cycle, and the next estrus occurs on Day 21.
After hormones produce an egg
from an ovary and prepare the uterus for pregnancy, an average of 21
days are necessary for the ovary and uterus to be regenerated and the
hormones to be activated for development of an egg by the ovary and an
environment in the uterus for fertilization and pregnancy. These
physiologic and endocrinologic functions and changes regulate a cow to
cycle every 21 days.
The estrous cycle is 18 to 24
days with an average of 21 days. The estrous cycle can be 16 to 25 days
in heifers until they settle down. The period of “no heat” or “out of
heat” is diestrus, about 20 days between cycles or “heats” in cows.
Early maturing breeds like the
English cycle at 12 to 13 months of age, Continental at 14 to 15 months
and Brahman (Bos indicus) at 14 to 18 months. Crossbreeding
greatly reduces age at puberty by at least 1 month.
"Determination
of Timing for A.I."
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Stages of heat and cues that a
cow is in heat:
Cows are in heat for about 18
hours (range 6 to 30 hours).
Early Stage – The cow
is bawling and walking and butting, trailing and mounting other cows and
has swollen vulva with redness inside and little if any, clear mucous
discharge. Her cervix is open
and uterus is rigid.
Middle Stage – The cow
is complacent and restless, has very red and swollen vulva with abundant
and clear mucous discharge and maybe slightly matted hair on tail head.
As ovulation gets closer, she
will continue to ride other cows, begins to be ridden by other cows and
then stands to be mounted (in
standing heat).
Late Stage –
As the cow goes out of heat, she will
continue to mount others and may still be ridden but will not stand.
All signs of nervousness disappear, vulva swelling and mucus decrease,
mucus becomes slightly rubbery and hair on tail head becomes matted.
Ovulation occurs 14 hours (range 6 to 18 hours) after standing heat
ends. About 24 to 48 hours
after standing heat, she will have a slightly bloody mucous discharge.
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Proper timing to increase
conception rates:
Heat checks by an observer are 15 to
30 minute durations and repeated 3 to 4 times a day to determine proper
time to breed the cow. Breed
the cow 8 to 12 hours after first mounting (standing heat) with an
expectation of a 67% conception rate.
When standing heat begins in the morning, breed at night. When standing
heat begins at night, breed in the morning.
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