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F A C T F I L E
The cow has a 21 day oestrus cycle but this can vary between 18
and 24 days. Heifers will begin cycling at the onset of puberty and
will continue to cycle until they are in calf.
MART I N P E AT
The Oestrus Cycle;
detection of, and dealing
with problems with it
The onset of puberty can be affected by
various factors such as breed, nutrition,
growth rate and disease. After calving, cows
will begin to cycle after 20 to 30 days. This
may be extended in high yielding cows or
those affected by disease post calving.
The oestrus cycle is governed by the
complex interactions of various hormones
that are produced in the brain and ovaries,
progesterone and oestrogen being two of
these. The follicle (egg) grows throughout the
cycle and ovulation (the release of the egg)
occurs when the progesterone levels drop
and the oestrogen rises.
A structure called the corpus luteum then
forms on the ovary, which then produces
progesterone.
Oestrus Detection
Oestrus is defined as the period of maximal
sexual activity. The average duration is
thought to be only 8 hours for the modern
dairy cow, however it can range from 2 - 30
hours. There are various signs and different
animals will express these to varying degrees.
Signs include:
l
Increased restlessness and activity.
l
Decreased feed intake and milk yield.
l
Bellowing when isolated.
l
Slight increase (0.1°C) in body
temperature.
l
Clear vulval mucus ('bulling string').
l
Rub marks and sores over the tail head.
l
Mounting other cows, particularly mounting
the cow from head on.
l
Standing to be mounted.
Detection of oestrus involves being able to
observe and record this behaviour. The most
reliable sign is observing a standing response
when ridden.
There are various reasons why heats are
missed. These are usually because cows are
not showing heat strongly or staff are not
observing cows when they are in heat.
The main causes of this are:
l
Increased herd size leading to more cows
per member of staff.
l
Failure to recognise oestrus due to
inadequate staff training.
l
Looking for heat at the wrong time of day.
l
Poor environment; slippery floors and
overcrowding will reduce the chance of
cows exhibiting normal behaviour.
l
Short weak oestrus; the average cow is
in oestrus for a shorter period than she
was 25 years ago. This has partly been
blamed upon increasing milk yields.
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LIVESTOCK MATTERS
WORKING
TOGETHER
FOR A HEALTHIER FUTURE...
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21
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6
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F I GUR E 1 . THE OE S TRU S CYC L E
Castle Veterinary Surgeons