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Oestrus not observed
NADIS
data show that oestrus not observed has been increasing as a problem recently
and that it remains one of the most common problems identified by cattle
veterinarians. This report looks at the causes and solutions for oestrus not observed.
Oestrus not observed
means that the cow has cycled normally, i.e. it has come on heat and ovulated but it has not been seen bulling.
This diagnosis is usually made by detecting a corpus luteum, which only forms
after ovulation, on the ovary by
rectal examination. Milk progesterone measurement can also identify cows that
have ovulated. Causes Cows that have come on
heat are missed because they have not shown bulling behaviour strongly enough
for a long enough time to be seen by the stockperson. Thus a high rate of
oestrus not observed is usually due to a combination of two factors; cows not
bulling strongly and staff not observing cows in heat. The quality of oestrus
detection has deteriorated on UK dairy farms in recent years. There are many
factors responsible for this. The
main 5 are probably: 1)
Increased
herd size In large herds cows
lose their individual identity, and thus small behavioural changes are not
detected. In addition, the larger herd has meant more cows per man, reducing
the time for activities such as oestrus detection 2)
Failure
to recognise oestrus Properly training
staff so that they know the signs of oestrus and ensuring that they are
familiar with the cows can increase oestrus detection rates by over 20%, provided enough time is
allocated to oestrus detection 3)
Looking
for heat at the wrong time Oestrus detection must
be undertaken at times when there is little other activity. Just looking for
bulling cows around milking time and just after feeding will miss most
oestrus behaviour. It must be supplemented by looking at cows at other times
of the day. Setting aside three periods of 30 minutes can result in oestrus
detection rates of over 80% (over 20% higher than the industry average). 4) Poor
environments The environment has a
major impact on oestrus behaviour. For example, cows in straw yards show
oestrus behaviour significantly more strongly than cows in cubicles
Overcrowding, poor lighting, slippy floors and bad building design all reduce
the chances of cows expressing normal oestrus behaviour and the chance of
bulling cows being seen. 5)Short
weak oestrus 25 years ago the
average cow was in oestrus for 15 hours. More recent figures suggest that the
average length of heat is less than 8 hours. Combined with this reduction in
duration, the strength of oestrus also seems to have reduced, with cows on
heat mounting fewer cows for shorter periods. The cause of this is unclear
but it is probably related to increased milk yield. All these factors mean
that the oestrus detection rate in UK dairy herds has fallen. The average
rate is now around 50% which means that half of all bulling cows are missed.
Data from an economic model developed by SAC shows that improving
oestrus detection rate from 50 to 75%
would save on average £15,000 / year in a 100 cow herd. Improving oestrus detection Improving oestrus
detection can pay significant dividends. Available methods for improving
detection include: 1)
Improved
cow identification : If cows
cannot be identified oestrus cannot be recorded 2)
Better
lighting: Improves
identification 3)
Regular
oestrus observation:
Properly planned 30 minute periods can significantly increase oestrus
detection 4)
Regular
milk progesterone measurement:
Return to heat can be anticipated by identifying a fall in milk progesterone.
For most farms, progesterone measurement would need to be automated for this
to be used routinely. 5)
Heat-mount detectors: These are
probably the most widely used aid on UK farms. Their mode of action is
extremely simple. When a cow stands to be mounted (the primary sign of
oestrus), pressure from the cow mounting it causes a change in the detector.
The simplest
heat-mount detectors is tail-paint which is rubbed-off as the cow is mounted.
Other simple versions are plastic domes which change when subject to pressure.
This device glows when pressure
is applied Recent
technological innovation has allowed heat-mount detectors devices to become
more sophisticated. Some detectors now flash to tell you how many times the
cow has been mounted and how long it is since it was first mounted. However, perhaps the most
sophisticated detector comprises a pressure sensitive battery-operated radio
transmitter. When activated, the transmitter emits a radio-signal which is
picked up by a receiver. The signal is then digitised and stored on computer
together with the date and time, duration of each mount and the cows
identity. This has been widely used in the US, but is not yet available in
the UK. 6)
Pedometers Cattle
in heat walk at least twice as much as they do before and after heat. Thus
measuring the distance walked using pedometers can identify bulling cattle.
However, the significant difference in normal activity between cows means that a threshold can’t be set over
which a cow is in oestrus. Comparisons have to be made within cow. This
requires computerisation and greatly increases the costs. Nevertheless,
combining heat checks and pedometer detection will give a high efficiency and
high accuracy of detection.
Pedometers are an effective and
accurate method of heat detection 7)
Electrical resistance The electrical resistance of
vaginal mucous increase during oestrus. Probes are available in the U.S.A.
for measuring the electrical resistance of cows that are thought to be coming
into oestrus. The requirement for twice daily measurement and the lack of
automation means this method is best suited to checking cows after a
synchronised heat for returning non-pregnant animals
Resistance testing: Interesting science but
limited applicability Other
assessments of vaginal mucous including examination of stretch-ability
(‘spinnbarkeit’) and its crystal pattern have been used to detect oestrus but
probably have even less applicability 8)
Temperature milk / body Body temperatures rises during oestrus by about 0.2oC.
Measurement of temperature, either of milk or body, can identify cows in
heat. Unfortunately temperature rises similar to those seen in oestrus
occur at other time. Using
temperature measurement alone results in too many cows that that are not in
heat being identified as in oestrus. It is likely that further research will improve the artificial detection of oestrus. Greater automation of the parlour will allow results from several tests to be added together increasing accuracy and efficiency. Until such time significant improvements in oestrus detection can be achieved with better planning of oestrus observation and the use of heat mount detectors (or for some farms pedometers). Richard
Laven PhD BVetMed MRCVS Copyright © NADIS
2004 |
