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Pregnancy Diagnosis in Beef Cattle

Dr Sandi Jephcott President Elect Aust Cattle Vets

Pregnancy diagnosis in cattle is a very important component of the annual program of any rural business focusing on the breeding aspect of cattle production. It is also an extremely important component of a cattle veterinarian’s business. The producer and the cattle veterinarian should have common economic and production goals.

The image of the vet at the tail end of a cow, glove in hand has been a long and enduring one in the eyes of the farming community, but this image is now under threat. New advances in technology and changes in state government legislation are opening the area of pregnancy diagnosis to non-veterinarians.

Historically, pregnancy testing or diagnosis has been an ‘Act of Veterinary Science’. This means that the procedure can only be legally performed by veterinarians for fee or reward. In recent years, many of these acts have been reviewed (Table 1).

Table 1.

State

Per-rectal pregnancy diagnosis/testing

Ultrasound pregnancy testing

South Australia

Yes*

No*

Queensland

Yes

Yes

Tasmania

No

No

Victoria

No

No

New South Wales

No – trying to differentiate between diagnosis and testing

No

Northern Territory

No

No

Western Australia

Yes – but currently under review

* ‘Yes’ indicates it is an act of veterinary science. ‘No’ indicates it is not an act of veterinary science and is open to the public.

WHY PREG TEST?

Generally producers wish to identify the pregnancy status of their herd for several reasons, including:

  • The identification and marketing of unproductive stock as a major source of income. This is generally referred to as ‘empty testing’, although in tightly managed herds late conceivers are also culled.
  • As a management tool measuring the productivity of the herd; identifying any problems early (6 weeks after bulls are removed); and drafting the herd and applying nutritional regimes according to the expected pattern of calving.  Whole herd pregnancy diagnosis allows the producer to estimate the income generating potential of the herd over the coming two years and manipulate stocking rates according to seasonal conditions. With the introduction of NLIS, this information maybe scanned directly into a database which may improve record keeping, reduce transcription errors and reduce the time spent keeping records.
  • In extensive areas of northern Australia it is used to ‘control mate’. It maybe easier to draft cows according to foetal age at a certain time of the year rather than try and locate and remove all bulls from a paddock.
  • Using the Australian Cattle Vets (ACV) National Cattle Pregnancy Diagnosis Scheme to increase the market value of pregnant breeding females or empty feedlot heifers.
  • Reactive pregnancy testing as a result of poor branding percentages.
  • Identification of heifers, or other breeders, that have been mis-mated due to ‘neighbours’ bulls.
  • Drought management.
  • Identification of females suitable for live export or artificial breeding programs.
  • Measuring the success (or otherwise) of artificial breeding programs.

WHY USE A VET?

  • Early identification of any fertility problems caused by disease, nutritional deficiencies or bull problems.
  • Professional management advice. For example, pregnancy diagnosis will assist with herd modeling, including numbers of heifers required for joining (heifer retention rate) and culling age for mature breeders. Spreadsheet models show that the lower the pregnancy rate, the higher the heifer retention rate necessary to maintain herd structure.
  • Use of ACV National Cattle Pregnancy Diagnosis Scheme
  • Speed and accuracy
  • Legislative requirement

EXAMPLES OF THE REASONS FOR A POOR PREGNANCY RESULT

Controlled mating in Southern Australia

The foetal aging pattern should reflect 60-70% of cows becoming pregnant in the first 3 weeks of the breeding season and around 85-90% being pregnant by 6 weeks. An obvious gap in foetal age may point to a temporary bull breakdown.

Continuous mating in Northern Australia

Extreme variation in foetal ages in breeding herds in northern Australia maybe due to poor rainfall pattern and quantity in the previous two years. This results in irregular calving and conception patterns the year prior to the pregnancy test. In simple terms, look at the calves on the cows and if there is a large range in their ages and size, then expect to get a drawn out calving pattern next season.

CURRENTLY RECOGNISED METHODS USED TO DIAGNOSE PREGNANCY IN CATTLE

  1. Return to Oestrus:
    A mated cow that is seen to come back into oestrus will usually indicate that conception has failed to occur. This method, though heavily relied upon by cattle producers,  particularly in the dairy industry, has proven to be unreliable due to the difficulty in ensuring all heats are observed and the finding that 7-10 per cent of pregnant cows will show signs of oestrus despite being pregnant.
  2. Hormone Testing:
    Two hormones have been used for diagnosis of pregnancy, progesterone and oestrogen, however, for various reasons neither have proven to be accurate. They are also expensive and cannot age the foetus so are rarely used in the beef cattle industry.
  3. Rectal Determination of Pregnancy Status:
    Rectal palpation of the reproductive tract has been the standard method of pregnancy diagnosis for almost 60 years. Currently, the most popular and effective methods of determination of pregnancy status in cattle are manual rectal palpation or B-mode ultrasonography. When performed by experienced personnel, both these techniques can provide a very accurate diagnosis of pregnancy status in addition to information about the gestational age of the foetus.
    To be consistently accurate with rectal palpation, it is important to have a logical and disciplined routine in combination with well refined tactile skills. These tactile skills are developed by regular and repeated pregnancy diagnosis.

DETERMINING THE STAGE OF PREGNANCY

It is generally accepted that estimation of stage of gestation can be extremely accurate between day 35 and day 65.  As the pregnancy progresses, the precision of ageing is reduced. This is in part due to individual animal variation and to difficulties in palpating the whole foetus. It is commonly found that for pregnancies between 84 – 150 days, accuracy may be limited to two weeks of the true gestational age and four weeks in pregnancies from 150 days till term. It is also important to appreciate that cows will naturally show variations in gestational length (up to three weeks either side of predicted calving date), which can further add to the possible incorrectly predicted calving date.

THE USE OF ULTRASOUND FOR PREGNANCY DIAGNOSIS

The use of ultrasonography in bovine reproductive work is rapidly increasing. The technique involved the standard approach of introduction of the transducer into the rectum by hand or a technique where the transducer is introduced into the rectum of the cow attached to a rod or introducer.

  1. Type of ultrasound
    Brightness or B mode ultrasound technology (frequency probe 3.5 or 5 MHz) is best suited to bovine reproductive work. Doppler ultrasound has been promoted to the farming community as an option for ‘Do It Yourself’ pregnancy testing, but its accuracy to achieve this goal in cattle is questionable.
  2. Use of introducer
    The recently developed technique of introducing the transducer into the rectum, via the use of an introducer, has revolutionised pregnancy diagnosis in cattle. The advantages of this technique are related to less stress on palpator and cow, and to a lesser extent, a ‘seeing is believing’ concept for farmers/producers. This approach has been further complemented by the development of portable ultrasound machines worn as a backpack unit and video goggles that allow the image to be projected in front of the operator’s eyes.

Limitations to ultrasonagraphy

Transrectal ultrasonography is most accurate for diagnosing and aging pregnancies between about 35 days and 120 days of gestation. The precision of diagnosis in regards to aging will be influenced by the skill and experience of the operator.

In the second and third trimester the usefulness of ultrasound, particularly with an introducer is reduced, due to the foetus moving cranial and ventral as it grows, hence failure to detect a gravid uterine tract doesn’t imply a non-pregnant animal. The cow may indeed be non-pregnant, but equally she may be very heavily pregnant with the uterus unable to be visualised due to its ventral position. It is strongly recommended that any cow ultrasounded, particularly  using an introducer, that is not determined to be pregnant, be examined by a manual rectal examination to conclusively diagnose the pregnancy status.

Using ultrasonography for very early diagnosis of pregnancy, ie 35 days gestation, may result in larger losses between pregnancy testing and branding, when compared with pregnancy testing undertaken later in the gestational period.

Ultrasonography using an introducer must be performed carefully, taking into consideration the welfare of the cow being examined and the safety of the operator. The rapid insertion of a rigid rod into the rectum increases the likelihood of rectal perforations as the quick insertion may not allow for rectal contractions and spasms to pass.

THE NATIONAL CATTLE PREGNANCY DIAGNOSIS SCHEME

The NCPD Scheme has been developed over a number of years to promote excellence in the skills of pregnancy diagnosis among cattle veterinarians. Cattle veterinarians that have passed a practical examination conducted by an accredited examiner are then accredited to use the following tags (and others not illustrated) on cattle they pregnancy test for their clients.

Red and yellow = over 4 months pregnant
Blue and red = under 4 months pregnant
Green and white = not detectably pregnant

Further Reading

Readers interested in more information on pregnancy diagnosis in cattle are referred to the book, Pregnancy Diagnosis in Cattle which is available from the Australian Cattle Vets (ACV) office (07) 3423 1799.  This book covers southern and northern beef cattle and dairy, and is a detailed account of why, how and what to pregnancy test; facilities; preventing injuries; interpreting results; foetal development; guidelines for schools and the National Cattle Pregnancy Diagnosis Scheme (NCPD).