Australian Livestock Scanning Services Group

The results and recommendations from 23 years of on-property R&D with commercial sheep and cattle producers. We specialise in precision scanning for pregnancy, twinning, and ageing of foetus in sheep and cattle and in helping to raise lamb survival and cow fertility in stud and commercial breeding enterprises.

mob: 0428 667 567, email: fowler.doug@bigpond.com

10. Scanning Accuracy

Scanning will not pay if it is not accurate because pregnant ewes will be called empty and vice versa and the death rate among twin-bearing ewes and their lambs will be increased.

The ALSS Group has been in operation for almost 25 years and has remained as a provider of scanning services because of guaranteed high levels of accuracy.

What are the errors?

  1. Failure to detect a second foetus when the foetus is present, is the most common error (Fowler and Wilkins 1984).
  2. Failure to detect the presence or absence of a pregnancy and finding more foetus than are present, are less common errors.

What are the causes of errors?

The determination of the pregnancy or non pregnancy status is a very simple task. Failure to perform this task with a high degree of accuracy reflects on the competency of the operator.

Assuming total operator competency, two additional factors play a pivotal role in obtaining an accurate scan:

  1. The production of a clear image of the contents of the uterus. This requires the correct coupling fluid. The poorer the coupling, the less clarity there is with the image, so that even a highly competent operator will face difficulty in obtaining a correct diagnosis.
  2. The need to conduct an uninhibited examination of the contents of the uterus. Any factor that stands in the way this will increase the error rate. This factor becomes more important where more detailed scans are required.

Uninhibited examinations are made more difficult:

  1. Where the abdomen is distended in ewes with advanced pregnancies as a result of a joining longer than 6 weeks.
  2. Where supplements have not been ceased one or two days before scanning.
  3. Where ewes have not been taken off feed and water the night before scanning.

These restrictions as sources of errors with the walk through handling system are recognized by the Sheep CRC (Viewed 4 February 2014) http://www.sheepcrc.org.au/ Then click on: "Sheep & Their Management, Pregnancy Scanning, View This Practical Wisdom Note then Successful pregnancy scanning".

Accurate scanning is consistently achievable without restrictions (referred to above) when sheep are scanned on their backs because the entire abdominal area of the ewe is exposed. This enables the conduct a thorough examination of the entire uterus of every ewe presenting for scanning.

What are the consequences of the errors?

  1. The consequences of empty ewes being called pregnant, and the reverse, are obvious. However, declaring a twin-bearing ewe to be single-bearing (the most common error, Fowler & Wilkins (1984) is a serious error.
  2. Twin-bearing ewes classified and managed as “single bearing” and receiving a ration that is correct for single bearing ewes i.e. a carefully controlled/restricted level of nutrition during the last month of pregnancy, are in fact being provided with a nutritional regime the reverse of that needed.
  3. Furthermore, twin-bearing ewes, that are classified as single-bearing ewes and lose one lamb, are seen to be rearing only one lamb, are among the single-lambing ewes and not seen to be scanning errors.

Scanning accuracy benchmarks

  1. Of every 1000 ewes said to be pregnant, 995 should have a lamb.
  2. Of every 1000 ewes said to have a twin, 990 should have a twin.
  3. Of every 1000 ewes said to be singles, 990 should have singles.
  4. With regard to ageing of foetus for AI/ET programs, for identifying earlier and later lambing ewes and for determining exact litter number, nothing less than a close to zero error rate is acceptable and is achievable.

How to achieve consistently accurate scanning

Where a “walk through” handler is used; conduct the scanning operation as soon as possible, but no sooner than 34 days after joining is over and avoid the three sources of errors referred to above.

Accurate scanning is consistently achievable without restrictions (referred to above) when sheep are scanned on their backs. This is because the entire abdominal area of the ewe is exposed and this enables the conduct a thorough examination of the entire uterus of every ewe.

Reference:
Fowler, D.G. and Wilkins, J.F., (1984). Diagnosis of pregnancy and number of foetuses in sheep by real-time ultrasonic imaging. 1. Effects of number of foetuses, stage of gestation, operator and breed of ewe on accuracy of diagnosis. Livestock Production Science 11, 437-450.