ULTRASONOGRAPHY - A REPRODUCTIVE MANAGEMENT TOOL IN CATTLE

By Dr. Daniel Ryan, Reprodoc Limited, Cullenagh, Fermoy, Co. Cork

Ultrasonography has been used as a tool in pregnancy diagnosis for the past 25 years.

Developments in the technology during that period have enabled improved image quality and probability of the equipment. These improvements enable a faster set-up time on farm, higher throughput of cattle and faster diagnostic assessment of reproductive status.

Ultrasonography is an integral element of our reproductive management service at Reprodoc Limited. We used ultrasonography as part of a preventative health management programme. The reproductive tract of the cow is affected by environmental stressors. We can detect this aberration in the image using ultrasonography. Lameness, mastitis and dietary imbalances all affect the reproductive tract. 

We use ultrasonography in a herd health management programme and as a reproductive management tool. These roles can be explained as follows: 

We use ultrasonography from 12 days post-calving. The rate of uterine involution can be measured. Metabolic diseases, retained after-births, multiple pregnancy, pre-calving environment and diet all affect the rate of uterine involution. Ovulation within the first three weeks post partum also slows down the rate of involution.

Identification of impaired rate of uterine involution will enable preventative measures be put in place and treatment to improve the rate of uterine repair.

Having completed uterine involution, cows have to reach stage of reproductive fitness between 40 and 80 days, post calving, if a 365 day calving interval is to be maintained.

We use ultrasonography pre-breeding to identify the reproductive status of cows. Targets are set for clients to submit cows for AI, when the stage of the estrous cycle has been identified. The quality of the uterine environment can be identified, thereby differentiating between cows cycling, those with a higher probability of establishing pregnancy. The latter enables use of more expensive semen for cows deemed most fertile.

The stage of the oestrous cycle can be identified using ultrasonography. This information can be used for synchronization of oestrus if not previously identified or as part of a planned breeding programme using AI.

There are various reasons why cows will not resume normal ovarian cycles post calving. The presence of an environmental stressor at the time of breeding will impact adversely on the success rate of an oestrous synchronization programme. Therefore, we use ultrasonography to identify the clinical status of the cow, but have to be able to identify if there is any current environmental stressor in place which will militate against a successful reproductive outcome.

A recommendation to breed cows will be postponed if an environmental stressor is in place. However, the impact of previous environmental stressor may be such that fertility will subsequently be adversely affected. Examples of this are difficult calving giving rise to damage of the reproductive tract, severe malnutrition resulting in severe ovarian dysfunction which will not respond to stimulation of ovarian cycle using exogenous hormones.

The pregnancy rate is similar among cycling and non-cycling cows following oestrous synchronization (Ryan et al, 1994). However, the latter response is dependent on the presence of a functional ovarian follicle at the time of oestrous synchronization in non-cycling cows.

Ultrasonography can be used from 20 days post breeding to identify pregnancy status. We prefer to describe this as non-pregnancy diagnosis as up to 5% of cows pregnant at this stage will subsequently lose their pregnancies. In addition, the purpose of intervention is to identify cows which have not exhibited a return to oestrus. The latter may be explained by either a failure to detect oestrus or embryonic death which delays the interval to resumption of normal ovarian cycles. It is intervention which gives a return to the use of ultrasonography.

Ultrasonography can be accurately used to determine pregnancy status from day 35 post breeding. In our experience, the incidence of embryonic or foetal loss is less than 2% beyond the completion of foetal implantation (day 35). Exceptions to this norm would include either abortion storms caused by neospora, BVD, Leptospirosis or a high incidence of twins from day 20 to 40 which is associated with a higher subsequent incidence of foetal death.

Management of calving intervals requires a rest period prior to parturition. This period varies between 6 and 12 weeks dependent on the production system and the requirements of the individual animal. We use ultrasongraphy to accurately age the pregnancy up to 110 days of gestation, thereby enabling an accurate dry off date to be identified. It is difficult to accurately age the foetus beyond day 110 because either the foetus slips over the pelvic brim and the growth rate of the fetuses vary tremendously.

Identification of twins is also accurate up to day 110 of gestation. Thereafter, the twins are not easily identified because one will be out of view on the image presented. Also, we recommend a 4 week longer dry cow period for cows carrying twins, because the nutritional demands on the cow in the latter stage of pregnancy and the shorter gestation period.

The sex differentiation of the bovine and equine foestus occurs on day 51 of gestation. The genital tubercle differentiates to form the clitoris, which moves candal toward to the tail end or to form the penis, which moves forward toward the umbilical cord. It is the latter phenomenon which we use in ultrasonography to identify the sex of the foetus. We can identify the sex of the foetus with a 99% accuracy rate between day 51 and 110 days of gestation.  The sex of the foetus is used by pedigree breeders to sell stock with a guarantee of sex gender, to sell surplus stock when sex gender is known, to retain cows in the herd with undesired foetal sex which would normally be culled because of other undesirable production traits. Foetal ageing, using ultrasonography is accurate to within 5 days of actual age between 25 and 110 days of gestation in our hands. This is important when future management decisions involve dry off or weaning dates, vaccination pre-calving to protect the calf against various diseases, sale of stock with a given calving date, and nutritional management precalving.

Finally, ultrasonography is used at the end of a breeding period to identify cows which are reproductively sound and could be given another opportunity to enter the breeding program. This is used by milk producers to retain cows in the herd which are young and have desirable production traits.