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.
Heat detector. This device glows when pressure is applied.
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.
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.
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.
Other assessments of vaginal mucous including examination of stretch-ability 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 0.2o°C. 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).
Article by Richard Laven PhD BVetMed MRCVS
