The Value of Pregnancy Detection

By Shelby Rosasco 

As we move into early fall, the breeding season for spring-calving herds has ended or is close to wrapping up. Pregnancy diagnosis can be an important tool producers can utilize to increase profitability and evaluate reproductive efficiency of the cowherd.  

With drought conditions persisting, management of feed resources will be critical this fall and winter. Many producers will be faced with the tough decision of reducing herd numbers through strategic culling. Identifying and marketing culls, open cows and even late-bred cows can allow producers to save valuable forage and feed resources and decrease feed costs. 

The value of pregnancy detection has been well documented and can provide benefits to producers regardless of if they are looking for ways to reduce cow numbers and stretch forage resources. 

Methods of pregnancy diagnosis 

Producers have several options for pregnancy detection – transrectal palpation, ultrasound or a blood test. Pregnancy detection methods vary in price, difficulty and information that can be ascertained.  

Rectal palpation is the most common method of pregnancy detection utilized. Animals need to be at least 35 to 50 days pregnant for accurate detection.  

The range of how early a pregnancy can be diagnosed depends greatly on experience of the technician or veterinarian; however, the highest accuracy is generally achieved between 45 and 120 days of gestation. An experienced individual can also determine approximate fetal age. 

Ultrasound can be utilized to accurately diagnosis pregnancy as early as 30 days post-breeding. Similar to palpation, pregnancy results are known immediately, allowing producers to make decisions and sort animals as they are being processed.  

Utilizing ultrasound technology can also provide additional information for producers, including presence of multiple embryos, fetal age and fetal sex, which can be determined after day 55 to 60 of gestation. Experience of the technician will determine how early pregnancy can be diagnosed and the information that can be provided. 

Blood-based tests have become a viable option for accurate pregnancy diagnosis and remove the need for specialized equipment or training. Pregnancy can be detected starting at 28 days post-breeding, however for blood tests to be accurate, animals must be at least 75 days post-calving.  

Pregnancy-associated glycoproteins (PAGs) used to diagnose pregnancy are produced by the placenta and can be detected up to 60 days post-calving. If tested too soon after calving, false positive readings can occur due to elevated concentrations of PAGs from the previous pregnancy. Blood samples require a waiting period of two to four days while samples are shipped and processed at a lab. Additionally, blood-based tests cannot determine the age of the fetus, therefore animals cannot be sorted based on expected calving period. 

In a production setting one of the most practical applications for blood-based pregnancy tests may be for determining artificial insemination (AI) conception rates, with a blood sample collected approximately 28 days after AI. Pregnancy diagnosis utilizing palpation or ultrasound can then be conducted at the conclusion of the breeding season to determine overall pregnancy rates – both AI and natural service. 

IDEXX Laboratories has developed a blood-based test that can be completed on the ranch with results acquired in approximately 20 minutes. This method may not be practical in some circumstances, as it would still require animals to be sorted after the samples are processed. Furthermore, the chute-side kit may be more practical for smaller operations where less samples will need to be processed. 

It should be noted, pregnancy detection prior to 40 to 50 days of gestation does incur some risk of pregnancy loss due to stress associated with pregnancy testing. 

Economic considerations 

While prices can vary among the different methods of pregnancy detection, ranging from $3 to $10 per head, the overall cost of pregnancy checking the herd is generally less than the cost to feed open cows through late fall and winter. Identifying open cows and heifers can provide producers with the opportunity to consider different management options. 

The market for cull cows traditionally begins to decline rapidly in the fall around October and remains low until early spring, until February or March. Calculating the cost of gain or opportunity cost of the feed used to retain cows and evaluating the cull cow market can allow for decisions to be made regarding when to market cull cows to maximize profit. 

For spring-calving herds, early pregnancy testing in August and September can allow for non-pregnant cows to be marketed when cull cow prices traditionally tend to be higher. Selling cull and open cows early can also help save additional feed costs.  

Early pregnancy detection of heifers can also allow for additional marketing options for open heifers. Heifers can be marketed immediately or managed and marketed as feeder cattle. Another option, depending on the market, is for open heifers to be rebred for a later calving season and marketed as bred heifers. 

Fertility and management considerations 

Beyond the value of providing producers with the pregnancy status of animals, the additional information provided with pregnancy detection can be extremely useful in increasing reproductive efficiency of the herd and identifying problems that occurred during the breeding season. 

Determining fetal age can allow producers to plan for the upcoming calving season by giving an estimate of how many cows will begin to calve during different portions of the calving season. Determining the age of the fetus can also help identify problems that occurred during the breeding season as well as late-bred cows that have fallen out of a 365-day calving interval. 

A higher-than-normal proportion of late-bred or open cows could be a red flag that problems occurred during the breeding season.  

Factors resulting in late-bred and/or open cows include bull fertility, vitamin or mineral deficiencies, disease, an insufficient bull-to-cow ratio, a low proportion of cows returning to cyclicity prior to the start of the breeding season and inadequate nutrition or body condition. 

 Inadequate nutrition and body condition can significantly influence reproductive performance by increasing the postpartum interval, resulting in a decreased proportion of cows cycling at initiation of the breeding season. Producers should consult with their veterinarian, nutritionist or Extension personnel to discuss issues and find where herd management can be improved. 

Pregnancy has four times greater economic impact than any other production trait, and research has demonstrated heifers that calve in the first 21 days of the calving season have an increase in longevity and productivity. Identification and selection of heifers and cows that breed early in the breeding season and culling females that breed late in the season or failed to breed can increase reproductive efficiency and performance of a cowherd and increase longevity, as well as result in an increase in calf weaning weight and uniformity. 

Shelby Rosasco is the University of Wyoming Extension beef specialist and an assistant professor at the University of Wyoming in the Animal Sciences Department. Rosasco can be reaches at srosasco@uwyo.edu.