Early Pregnancy Detection in Dairy Animals: Current Status and Future Prospects

Dr.Dhrubajyoti Das

In any dairy farms, optimising milk yield and fertility is crucial in terms of sustainability and economics.To optimize these parameters, each cow should have a calf every 12–14 months. For this purpose, cows should be pregnant during the earliest postpartum period and undergo pregnancy diagnosis promptly. Early pregnancy detection is crucial for reducing the calving interval by finding nonpregnant animals early and treating and rebreeding them in a timely manner, allowing for a postpartum barren interval of around 60 days, which promotes an optimal reproductive management.

A few common approaches for pregnancy detection are discussed here, along with their advantages and disadvantages.

A) Direct Methods

Direct diagnostic procedures use objective symptoms or visual confirmation to establish the stage of pregnancy.

Per-rectal Palpation:

It can be performed by an experienced veterinarian as early as 35 days after breeding. At this stage of pregnancy, a veterinarian can detect two of the four cardinal signs of pregnancy, including the chorio-allantoic membrane slip and the amniotic vesicle. If the cow is discovered to be "open," the ovaries can also be examined for activity. Despite being the cheapest pregnancy diagnosis method, multiple studies have found that transrectal palpation of pregnant cows early in gestation increases the risk of iatrogenic embryonic death.

Transrectal ultrasonography:

It can be performed by an experienced veterinarian as early as 28 days after breeding. Ultrasound can provide more information than transrectal palpation alone. A veterinarian can monitor the foetus's heartbeat, age and detect twins. The foetus's sex can be ascertained between 55-70 days after breeding. Ovaries can be examined for cysts and other abnormalities.Ultrasound is a minimally invasive, accurate, and efficient technology for detecting early pregnancy, and it may reduce the rare occurrence of palpation-induced abortions. However, veterinary-grade ultrasound equipment fitted with a rectal transducer are expensive in developing countries, hence the high initial cost of this technique partially limits their practical use.

B) Indirect Methods

Indirect diagnostic approaches provide information about pregnancy by using biomarkers generated in the maternal body fluid during pregnancy.

Detection of Progesterone level:

Progesterone levels may be tested using blood or milk samples at least 21 - 24 days post breeding. Bovine milk or serum progesterone concentrations peak at 13-14 days following oestrus, and if the cow is pregnant, they remain increased until day 21 after fertilization and beyond. However, a high progesterone level does not always mean a pregnancy is present. False positives can occur at certain times during the cow’s cycle or incidence of early or late embryonic mortality. While false positives are possible, the test will not yield a false negative result, if the progesterone levels are low, you can be sure that the cow is not pregnant. The benefits of this assay include the non-invasive collection of milk.

Detection of Pregnancy-associated glycoprotein (PAG):

The technique is based on detecting PAGs in blood or milk samples, which are produced by specific cells in the placenta and uterus during pregnancy. Cows must be at least 90 days postpartum and 30 days post-breeding, because the PAGs remain in the body for such a long time that testing before 90 days postpartum can end in a false positive result. False positives may also be seen for several days after a cow has undergone an abortion. It is recommended that cattle be rechecked by a veterinarian at about 60 days of gestation as the chances of abortion dramatically decrease thereafter. Similar to progesterone testing, there are no false negatives associated with PAG testing.

PAGs are used for development of bench-top pregnancy detection methods using an enzyme-linked immunosorbent assay (ELISA), which are now commercially available as BioPRYN (BioTracking, Russia), DG29 (Genex Cooperative Inc., USA), and IDEXX (IDEXX Laboratories, Inc., USA) for pregnancy detection in ruminants.These PAG-based rapid test kits have recently gained popularity among Indian dairy producers, as because the test does not require an expert to perform.

Other, more recent indirect techniques involve measuring biomarkers such as microRNAs (miRNAs), oestrone sulphate, early pregnancy factor (EPF), and interferon stimulated genes (ISGs). However, these techniques require certain laboratory conditions and cannot be performed in the field and are less common.

Future of pregnancy diagnosis may be impacted by the evolving cattle sector. More precise and prompt pregnancy diagnoses are becoming necessary as a result of the use of AI and increased reproductive management. A small number of skilled veterinarians are under pressure to perform a high volume of pregnancy diagnosis due to a lack of specialists. When taken as a whole, these elements are opening up the opportunity of employing indirect or chemical pregnancy diagnostic techniques. In fact, the use of a single blood test for pregnancy has grown rapidly, according to a new report. It is evident that the cattle industry is shifting toward alternative pregnancy diagnosis techniques that do not call for trained professionals or specialized tools.