Ovine estrous cycle:
Anestrus
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Anestrus is considered a problem when cows are not seen in heat.
Failure to observe heat and heat detection must always be ruled out
as the primary problem. Review heat detection procedures and heat
detection efficiency with the producer.
Pregnancy can be a prominent cause of anestrus and must always
be a always be a prime ruleout before anything else. Pregnancy is
often the # 1 cause of cows not being seen in heat.
Rule out true anestrus by palpating the ovaries
'Congenital' Anestrus
Freemartin
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A freemartin is a heifer born twin to bull. 90% are sterile
It is caused by a chimeric condition where hematopoetic cells
intermingle in utero between the fetuses. This results in XX and
XY cells present in a freemartin.
Partial expression of TDF (testicular determining factor) from male
Y chromosome inhibits the female gonad.
MIF (Müllerian inhibition factor) from the male cells prevents
Müllerian duct formation, so no uterus forms.
Clinical Signs
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These animals often have a masculine steer-like appearance.
They may have a small vulva and long vulvar hairs.
Usually the external signs of a freemartin are noticed by the
producer, so the ones you will examine as anestrus heifers will
probably have normal external signs.
Diagnosis
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The 'test tube test' checks the vaginal depth by using a test tube.
In normal animals you can insert a test tube 12-18 cm. In abnormal
heifers the tube will only go about 7.5 cm into the vagina. This test
is only for young heifers, and age can play a big role in how deep
the vagina is.
If they are old enough, palpation is the way to go. These animals
have no ovaries, uterus, or vagina.
A karyotype checks for the XX and XY cell mixture in the blood.
It can be run in animals of any age, and may be cost effective if the
cost of raising the animal to maturity is considered.
Ovarian Aplasia
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This is a rare condition when one or both ovaries are absent.
It is caused when the gonadal ridge does not form correctly.
Palpation is the best diagnostic method.
There may be partial aplasia, when only one ovary does not form.
Ovarian Hypoplasia
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In ovarian hypoplasia, one or both ovaries are smaller than normal.
This is a recessive trait in the Swedish Highland breed and is
caused by a single autosomal recessive gene with incomplete
penetration.
You must ruleout true anestrus.
Again, there may be partial hypoplasia with this condition.
Seasonal Anestrus
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The is some evidence that daylight length (photoperiod) influences
fertility in Brahman breeds, but there is no seasonal anestrus in
cattle.
Summer heat stress, when the THI (temperature humidity index)
combined effects of heat and humidity produce a high "apparent
temperature". If you compare estrus duration at 33.50 vs 18.20 C,
then the estrous cycle is longer and the estrus duration is shorter
and estrus intensity is less.
Anestrus may not really occur here, but since estrus is harder to
detect, it may appear so.
utritional anestrus
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Nutritional anestrus in the most common problem in beef cows.
Producers often try to get by on as little feed as possible to their
cows.
Remember the beef producers' goals is to produce and wean as
many pounds of calves each year as possible.
Postpartum nutrition
o In the postpartum cow, lactation causes a negative energy
balance. This is even more so in first calf heifers which are
also still growing. Therefore, heifers, with the demands of
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lactation, a negative energy balance and still trying to grow,
are affected most by nutritional anestrus.
o It takes cows 90 days to attain a 60% conception rate,
whereas it takes heifers 110 days. This is primarily because
the heifers are not cycling.
o By examining these tables you can see that a cow will cycle
back sooner than a heifer and therefore become pregnant
sooner after parturition.
By feeding cows after they calve, you cannot expect to improve the
number cycling.
Feeding pre-partum is the best way to assure early return to
cyclicity in beef cows.
By providing good pre-partum nutrition, you maintain adequate
pre-partum condition, so the stress of postpartum lactation
produces a shorter duration of negative energy balance.
Control
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A good method that can be used to get the heifers cycling 'earlier',
actually does not really get them cycling earlier. What you do is
breed the heifers 2-6 weeks earlier than the cows, so they will calve
earlier that the cows. If they calve earlier, they will have longer
that the cows to start cycling. If you have a restricted breeding
seasons, the heifers will be cycling when the cows cycle.
You can weigh the cows 100 days before calving. The weight 24
hours after calving should be the same as that 100 days before
calving. This take into account the fetus and placenta being
delivered at parturition. Obviously, this is more of a historical
finding and is not a practical preventative measure.
Body condition scoring at weaning
o This is an ideal method to ensure adequate prepartum
nutrition. You use a system of body score condition when
the calves are weaned. (Calves are generally weaned at about
205 days postpartum, so the cows should be about 100 days
pregnant.)
o The scores are :1-3: emaciated, 4 borderline, 5-7 good fat 89 fat