Comparison of commercial ELISA blood tests for early pregnancy detection in dairy cows

Evaluation of a Commercial Pregnancy Test Using Blood or Plasma Samples in High-Producing Dairy Cows

This study evaluated a commercial pregnancy-associated glycoproteins (PAGs)-based pregnancy test using whole blood or plasma samples during early pregnancy (28-55 days of gestation) in high-producing dairy cows. Transrectal ultrasonography was used as the gold standard method. The study population constituted of 284 cows. False positive diagnoses were recorded from Day 60 to 89 and from Day 60 to 99 postpartum in blood and plasma samples, respectively. In early pregnancy screening, correct positive diagnoses were recorded in 75% and 100% of blood and plasma samples, respectively. High milk production was associated with negative results in blood samples and with the lowest test line intensity in plasma samples. False positive or negative diagnoses were recorded in 0% of both types of samples in cows previously diagnosed as pregnant and showing signs of estrus. In conclusion, the use of plasma was more effective than the use of blood in early pregnancy diagnosis. In cows previously diagnosed as pregnant and showing signs of estrus, both types of samples showed the same results. Because of large individual variations, normal single pregnancies could not be differentiated from twin pregnancies, from pregnancies with a recently dead conceptus, or from pregnancies that experienced subsequent pregnancy loss.

Development and evaluation of a lateral flow-based portable optical system for determination of the pregnancy status of dairy cows

Our objectives were to develop and evaluate an integrated system consisting of a lateral-flow immunoassay (LFIA) and an electronic portable imaging device for determination of pregnancy status of cows based on plasma concentrations of pregnancy-specific protein B (PSPB). Experiment 1 was conducted to test the performance of the LFIA for PSPB (PSPB-LFIA) whereas experiment 2 was conducted to evaluate the performance of the integrated system including both the LFIA and imaging device. The PSPB-LFIA strips were made of nitrocellulose membrane with polystreptavidin, anti-mouse antibody, Europium-anti-PSPB conjugates, and biotin-PSPB. After adding buffer and plasma in a 96-well plate, strips were dipped to initiate flow and were read in a fluorescence microscope to estimate PSPB concentrations based on the test-to-control line signal (T/C ratio). The T/C ratio of standards was linearly associated with PSPB (R2 = 0.99 in both experiments) concentrations. To test the ability to identify pregnant cows of the PSPB-LFIA only or the integrated system, plasma samples were collected and transrectal ultrasonography (TUS) was conducted 29 to 35 d post AI in lactating Holstein cows (Experiment 1: n = 83; Experiment 2: n = 205). A cow was considered pregnant (Preg) if concentrations of PSPB in plasma obtained by ELISA were ≥2 ng/mL or if an embryo was visible by TUS. In Experiment 1, the accuracy of the PSPB-LFIA compared with ELISA was 92.7% (91.2% Se; 96.1% Sp; 98.1% PPV; 83.3% NPV) and compared with TUS was 90.4% (100% Se; 78.9% Sp; 84.9% PPV; 100% NPV). The agreement between LFIA and ELISA (kappa = 0.84; 95%CI 0.71-0.96) or LFIA and TUS (kappa = 0.80; 95%CI 0.67-0.93) as methods to classify cows as Preg or Non-Preg was high. In Experiment 2, the accuracy of the PSPB-LFIA compared with ELISA was 96.1% (93.8% Se; 100% Sp; 100% PPV; 90.5% NPV) and compared with TUS was 92.2% (99.0% Se; 84.7% Sp; 87.6% PPV; 98.8% NPV). The agreement between LFIA and ELISA (kappa = 0.92; 95%CI 0.86-0.97) or LFIA and TUS (kappa = 0.84; 95%CI 0.77-0.92) as methods to classify cows as Preg or Non-Preg was high. We conclude that a system integrating a fluorescence-based LFIA and an optical reader was effective for classifying cows as pregnant or not pregnant based on estimations of plasma concentrations of PSPB. This novel system serves as a platform for further development of on-farm pregnancy testing tools based on measurement of biomarkers of pregnancy in bodily fluids of cattle.

Dairy heifers have an earlier increase in serum pregnancy-specific protein B compared with lactating dairy cows. Is this an indicator of earlier conceptus attachment?

This study was designed to use within-individual daily increases in circulating pregnancy-specific protein B (PSPB) to determine time to increase in serum PSPB in nulliparous heifers and multiparous dairy cows following artificial insemination (AI). Weekly cohorts of lactating Holstein cows (n = 56) averaging 122 ± 7 d in milk at AI and nulliparous Holstein heifers (n = 23) averaging 16 ± 0.24 mo old at AI were used in this study. Lactating cows received AI to either Ovsynch (n = 38) or at ~12 h following observed standing estrus (n = 18). All heifers were inseminated ~12 h after observed standing estrus. Blood samples for measurement of PSPB were collected daily from d 15 through d 35 postovulation. Nulliparous heifers had increases in serum PSPB earlier compared with both primiparous and multiparous cows. Day of increase in serum PSPB was defined as the day serum PSPB optical density levels initially increased ≥10% from baseline and continued to increase from baseline of ≥10% the following 2 d. Average PSPB were greater in pregnant heifers compared pregnant cows from d 23 through 29. Early lactation nonpregnant cows maintained greater average optical density of serum PSPB from 15 to 35 d postovulation compared with nonpregnant heifers (n = 38). In summary, fertility differences in heifers versus lactating cows may be due to the differences in timing of increases in serum PSPB. This appears to be one of the first publications that used daily PSPB sampling to investigate possible differences in fertility in heifers versus lactating cows.

Using commercial enzyme immunoassay for measuring pregnancy-associated glycoproteins to diagnose pregnancy in dairy cows under field conditions in Algeria

The purpose of the present work was to study effectiveness for early pregnancy diagnosis in cattle of the new enzyme immunoassay (EIA) sandwich kit commercially available based on the measurement of pregnancy-associated glycoproteins (PAGs). 120 Holstein-Friesian cattle of mixed age and parity were comprised from different dairy herds. The pregnant females (n = 68) were diagnosed by ultrasonography at day 35-40 after artificial insemination and confirmed by transrectal exploration at 2-3 months after AI. The non-pregnant females (n = 52) were housed in the absence of males during the experimental period. Blood samples were collected from coccygeal vessels of females into EDTA tubes. The serum was obtained by centrifugation and the serum was stored at - 20 C until assay. The PAG concentrations in pregnant and non-pregnant females were determined in serum by EIA kit. The reproducibility inter- and intra-assay of the PAG-EIA is satisfactory (2.78 and 13.19 %, respectively). The accuracy ( 94.8 %) and the test of parallelism were largely acceptable. No cross-reaction was observed with the different hormones tested at different dilutions. PAG-EIA system gave 100 % sensitivity and negative predictive values. Whereas, specificity and positive predictive value were 91.93 and 71.15 %, respectively. The accuracy of pregnancy diagnosis by PAG-EIA was 87.5 %. In conclusion, the present study shows clearly that the EIA kit can be used to measure PAG in serum cows for the detection of gestation in Algeria. Therefore, this alternative technique could be recommended to replace the radioactive methods in immunoassays to improve the reproductive performances and an efficient tool for reproductive management of dairy cattle.

Effects of mid-gestational l-citrulline supplementation to twin-bearing ewes on umbilical blood flow, placental development, and lamb production traits

The objective of the study was to examine how l-citrulline supplementation to ewes during mid-gestation influences placental activity, placental blood flow, lamb body weight, and carcass characteristics. Two studies were completed. A pharmacokinetic study to compare circulating plasma amino acid concentrations after a single intravenous injection of 155 µmol/kg BW l-citrulline or after an isonitrogenous amount of l-alanine (control; 465 µmol/kg BW). Increases (P < 0.05) in circulating citrulline concentrations were detected for 8 h after l-citrulline injection versus the control. Similarly, increases (P < 0.05) in circulating arginine concentrations were detected for 24 h after l-citrulline treatment. The second study used 12 ewes with twin pregnancies. Daily intravenous injections of either l-citrulline or l-alanine were administered for 39 d from d 42–45 to 81–84 of gestation. Ewes were limit-fed at 85% daily energy requirements during the injection period. A decrease (P < 0.0001) in body weight was observed in both treatment groups during this period. No treatment differences were observed in circulating pregnancy-specific protein B concentrations or placental blood flow during the treatment and post-treatment gestational period. No treatment differences were observed in lamb survival nor in lamb birth, weaning and slaughter weights. Treatment did not influence lamb carcass composition or organ weights. However, there was a tendency (P = 0.10) for an increase in antral follicle numbers in ovaries from ewe lambs derived from ewes treated with l-citrulline. In summary, a daily l-citrulline injection increased both circulating citrulline and arginine concentrations in ewes, but daily l-citrulline injections during mid-gestation did not produce any detectable changes in placental activity and blood flow, neonatal and postnatal lamb development, and lamb carcass composition at slaughter. In conclusion, no benefits in placental function and lamb development were observed after providing l-citrulline during mid-gestation in ewes exposed to a mild energy restriction, but there was an indication that follicle numbers in ewe lambs were positively influenced by l-citrulline treatment during fetal development.

Recent Possibilities for the Diagnosis of Early Pregnancy and Embryonic Mortality in Dairy Cows

Simple Summary

Pregnancy diagnosis plays an essential role in decreasing days open in dairy farms; therefore, it is very important to select an accurate method for diagnosing early pregnancy. Besides traditional pregnancy diagnoses made by rectal palpation of the uterus from 40 to 60 days after AI and measuring the serum or milk progesterone concentration between 18 to 24 days after AI, there are several new possibilities to diagnose early pregnancy in dairy farms. However, it is very important to emphasize that before introducing any new diagnostic test, we need to make sure the accuracy of that particular test to be able to decrease the rate of iatrogenic pregnancy losses caused by prostaglandin or resynchronization treatments. This review focuses on the diagnostic possibilities and limitations of early pregnancy diagnosis in the field.

Abstract

One of the most recent techniques for the on-farm diagnosis of early pregnancy (EP) in cattle is B-mode ultrasonography. Under field conditions, acceptable results may be achieved with ultrasonography from Days 25 to 30 post-AI. The reliability of the test greatly depends on the frequency of the transducer used, the skill of the examiner, the criterion used for a positive pregnancy diagnosis (PD), and the position of the uterus in the pelvic inlet. Non-pregnant animals can be selected accurately by evaluating blood flow in the corpus luteum around Day 20 after AI, meaning we can substantially improve the reproductive efficiency of our herd. Pregnancy protein assays (PSPB, PAG-1, and PSP60 RIA, commercial ELISA or rapid visual ELISA tests) may provide an alternative method to ultrasonography for determining early pregnancy or late embryonic/early fetal mortality (LEM/EFM) in dairy cows. Although the early pregnancy factor is the earliest specific indicator of fertilization, at present, its detection is entirely dependent on the use of the rosette inhibition test; therefore, its use in the field needs further developments. Recently found biomarkers like interferon-tau stimulated genes or microRNAs may help us diagnose early pregnancy in dairy cows; however, these tests need further developments before their general use in the farms becomes possible.

Efficacy of a commercial test kit to determine early pregnancy in cows using whole blood and blood serum

The objective of this study was to determine the efficacy of the Fassisi®BoviPreg visual test kit (Fassisi®BoviPreg) in determining early pregnancies in cows by measuring the pregnancy-associated glycoprotein (PAG) in whole blood and blood serum. The study was conducted on 50 cows, the artificial insemination (AI) dates of which were designated as day 0. Pregnancy diagnosis was performed with transrectal ultrasonography (USG), and serum samples were simultaneously collected and used with Fassisi®BoviPreg to determine pregnancies on 30 days after AI. The results of the Fassisi®BoviPreg test on serum and whole blood samples, respectively, on 30 days after AI were as follows: sensitivity, 61.54% and 50.0%; specificity, 79.17% and 75%; accuracy, 70.0% and 62.0%; positive predictive values, 76.2% and 68.4%; negative predictive values, 65.5% and 58.1%; false-positive diagnoses, 23.8% and 31.6%; and false-negative diagnoses, 34.5% and 41.9%. On day 50 after AI, sensitivities were 63.64% and 50.0%, specificities were 100.0% and 100.0%, and accuracies were 75.0% and 65.62% in serum and whole blood, respectively. Higher pregnancy rates were obtained using Fassisi®BoviPreg in cows with ≥ 5 ng/mL P4 (P < 0.001). In conclusion, the results from the Fassisi®BoviPreg tests on cows on 30 and 50 days after AI showed that the use of blood serum is more accurate and suitable than that of whole blood. The results also showed a higher confidence level in specificity 50 days after AI.

Evaluation of a cattle rapid test for early pregnancy diagnosis in sheep

The early pregnancy diagnosis allows optimizing production and timely management correction, with a greater reproductive output of livestock. The Idexx Rapid Visual Pregnancy Test® consists of an ELISA for visual reading which does not require the use of readers in the laboratory, with satisfactory pregnancy diagnoses at 28 days of pregnancy in cattle. Therefore, the aim of this study was to evaluate this rapid test and to verify the most appropriate day for the diagnosis of pregnancy in the ovine species. For this purpose, 98 serum samples from pregnant sheep and 36 from non-pregnant were used, with duplicate samples, and diagnosis was confirmed by ultrasound examination, used as the gold standard. The numbers of positive samples obtained at 26, 28, and 30 days of pregnancy were 26, 27, and 45, respectively. The Rapid Visual Pregnancy Test correctly identified 100% of the samples as positive at pregnancy of days 26, 28, and 30. The sensitivity and specificity of the test were also 100%. The Idexx Rapid Visual Pregnancy Test, initially indicated for cattle, is effective for the detection of pregnancy in the ovine species, enabling diagnosis of pregnant sheep from the 26th day of pregnancy.

Short communication: Blood samples before and after embryonic attachment accurately determine non-pregnant lactating dairy cows at 24 d post-artificial insemination using a commercially available assay for pregnancy-specific protein B

Early pregnancy diagnosis is critical to reproductive success on dairy farms. Reproductive success depends on cows becoming pregnant before 130 d in milk and then maintaining that pregnancy. The earlier non-pregnant cows are identified, the sooner they can be reinseminated, thus reducing days to pregnancy. Assays for pregnancy-specific protein B (PSPB) and pregnancy-associated glycoproteins can be used to diagnose pregnancy >28 d post-artificial insemination (AI) in lactating cows. The objective of this study was to determine whether percentage change in serum levels of PSPB within cow from d 17 to 24 can be used to identify non-pregnant cows using a commercially available assay. This study was performed on a large commercial dairy. Blood samples were taken at d 17 and 24 post-AI. The d 17 sample served as a baseline based on previous data. Cows with a 10% increase in serum PSPB levels from d 17 to 24 were considered pregnant. Lactating dairy cows (n = 206; 39% primiparous and 61% multiparous) were synchronized using G6G-Ovsynch. The PSPB diagnosis was compared with the herd veterinarian's diagnosis via ultrasound on d 34. The sensitivity for a 10% cutoff as a non-pregnant diagnosis was 100%, and the specificity was 93.58%. The positive predictive value was 93.27%, and the negative predictive value was 100%. Low PSPB levels at d 24 were predictive of early pregnancy loss by 60 d post-AI. To our knowledge no other method can diagnose non-pregnancy with 100% accuracy and predict pregnancy loss earlier than 24 d post-AI. Using comparative PSPB samples at d 17 and 24 post-AI provides an accurate non-pregnancy diagnosis earlier than any other pregnancy diagnosing method.

Recombinant interferon stimulated protein 15 (rISG15) as a molecular marker for detection of early pregnancy in Bubalus bubalis

Early and accurate diagnosis of pregnancy in animals is important for improving the reproductive management of livestock. The buffalo (Bubalus bubalis) is the most important dairy animal in India, but there are reproductive problems resulting from extended calving interval and ovulation occurring in the absence of behavioral estrus. The lack of simple methods for early pregnancy diagnosis intensifies these problems. The present study, therefore, was conducted to ascertain the role of the interferon-stimulated gene, (ISG), 15 in pregnancy detection. The anti-ISG15 Mab based ELISA was developed that could be used for detecting pregnancy at 18 to 20 days after artificial insemination (AI). The ISG15 protein was isolated from a pregnant buffalo and was amplified, and cloned in Escherichia coli by using coding region primers. The ISG15 gene was expressed in the host Escherichia coli BL21 (DE3), and the protocol was standardized for optimum gene expression. Using immortal hybridoma (fused myeloma and B cells) cells, a highly specific and sensitive antibody, anti-ISG15 mAb, for detecting ISG15 (protein) in the serum of pregnant buffaloes was obtained. A blocking ELISA was developed using the anti-ISG15 mAb to detect pregnancy in buffalo within 18 to 21 days after AI. The ISG15 gene was upregulated (P <  0.05) in pregnant buffalo at 18 to 21 days of pregnancy. This assay has an overall diagnostic accuracy of 75.0%. It, therefore, is concluded that recombinant ISG15 retains the potential for detecting pregnancy in B. bubalis and may have applications in ELISA kits for pregnancy detection in closely related species.

Could a bovine pregnancy rapid test be an alternative to a commercial pregnancy-associated glycoprotein ELISA test in dairy cattle?

The aim of the present study was to compare a Bovine Pregnancy Rapid Test (Ubio quickVET; BPRT) with a commercial ELISA-PAG test (Bovine Pregnancy Test DG29®) for early pregnancy diagnosis based on the presence of the PAG (pregnancy-associated glycoprotein) in dairy cattle between 30 and 40 days after artificial insemination (AI). Blood samples were collected from 212 cows between 30 and 40 days after artificial insemination (AI) to quantify the concentrations of PAG in each sample. Transrectal ultrasonography (TRUS) diagnosis of pregnancy was conducted at day 45 ± 3 after AI as the reference standard for the two PAG tests. The results indicated the sensitivity (Se) of the BPRT and DG29 for diagnosing pregnant cattle were 89.4% and 100%, respectively while the specificity (Sp) of the two tests for diagnosis of non-pregnant animals was 89.8% and 81.3%, respectively. Based on these results, the BPRT has a slightly lesser sensitivity and greater specificity than the DG29 test. Moreover, the accuracy of both tests was 94% and 90% respectively for DG29 and BPRT. This implies that the BPRT test could be considered an accurate test when compared to PAG-ELISA test and TRUS at days 30-40 after AI. The BPRT test, therefore, can be used as an alternative to the PAG-ELISA test with some constraints that need to be considered with its use.

Conceptus-induced changes in the gene expression of blood immune cells and the ultrasound-accessed luteal function in beef cattle: how early can we detect pregnancy?

We aimed to identify the functional characteristics of the corpus luteum (CL) by color Doppler ultrasonography and changes in interferon-stimulated gene (ISG) expression in peripheral blood mononuclear cells (PBMCs) during early pregnancy in beef cows. We then aimed to use these features to establish earlier pregnancy diagnosis methods. In experiment 1, the CL size and blood flow were accessed by Doppler ultrasonography, and the PBMCs were isolated on Days 8, 12, 15, 18, 20, 22, 25, 30, 45, and 60 post-timed artificial insemination (TAI) from pregnant (n = 10) and nonpregnant cows (n = 12). The abundance of ISG (OAS1, MX1, MX2, and ISG15) transcripts was measured by quantitative PCR. Analyses of OAS1 and MX2 expression in isolated PBMCs (ISG-PBMC method) and Doppler imaging of CL (Doppler-US method) were performed to test the accuracy of these methods for the diagnosis of pregnancy on Day 20 post-TAI (n = 110; experiment 2). In experiment 1, the luteal volume and blood flow were reduced in nonpregnant cows during the first weeks post-TAI, but an evaluation of CL vascularization and size was efficient in identifying nonpregnant cows on Day 20 post-TAI. The expression of ISGs in PBMCs can be stimulated by the presence of a viable conceptus between Days 15 and 22 post-TAI, and the expression of these genes reaches a peak on Day 20. In experiment 2, the Doppler-US and ISG-PBMC methods resulted in similar specificity (85.5 and 87.7%, respectively). However, only the Doppler-US method resulted in 100% sensitivity. In conclusion, the greatest abundance of ISGs in PBMCs and a high detection of luteolysis by Doppler imaging on Day 20 post-TAI can be feasibly used for the earlier detection of nonpregnant cows in reproductive programs. The level of accuracy for our described pregnancy methods is high on Day 20 (80%-91%), but only the Doppler imaging method results in an absence of false-negative diagnoses.

PreImplantation factor (PIF) detection in maternal circulation in early pregnancy correlates with live birth (bovine model)

BACKGROUND

Early identification of viable pregnancy is paramount for successful reproduction. Detection of specific signals from pre-implantation viable embryos in normal pregnancy circulation would indicate initiation of embryo-maternal interaction and create a continuum to accurately reflect embryo/fetal well-being post-implantation. Viable mammalian embryos secrete PreImplantation Factor (PIF), a biomarker which plays key, multi-targeted roles to promote implantation, trophoblast invasion and modulate maternal innate and adaptive immunity toward acceptance. Anti-PIF monoclonal antibody (mAb-based chemiluminescent ELISA) accurately detects PIF in singly cultured embryos media and its increased levels correlate with embryo development up to the blastocyst stage. Herein reported that PIF levels (ELISA) in early maternal serum correlate with pregnancy outcome.

METHODS

Artificially inseminated (AI) blind-coded Angus cattle (N = 21-23) serum samples (day 10,15 & 20 post-AI) with known calf birth were blindly tested, using both non-pregnant heifers (N = 30) and steer serum as negative controls. Assay properties and anti-PIF monoclonal antibody specificity were determined by examining linearity, spike and recovery experiments and testing the antibody against 234 different circulating proteins by microarray. Endogenous PIF was detected using <3 kDa filter separation followed by anti-PIF mAb-based affinity chromatography and confirmed by ELISA and HPLC. PIF expression was established in placenta using anti-PIF mAb-based IHC.

RESULTS

PIF detects viable pregnancy at day 10 post-AI with 91.3% sensitivity, reaching 100% by day 20 and correlating with live calf birth. All non-pregnant samples were PIF negative. PIF level in pregnant samples was a stringent 3 + SD higher as compared to heifers and steer sera. Assay is linear and spike and recovery data demonstrates lack of serum interference. Anti-PIF mAb is specific and does not interact with circulating proteins. Anti-PIF based affinity purification demonstrates that endogenous PIF is what ELISA detects. The early bovine placenta expresses PIF in the trophoblast layer.

CONCLUSION

Data herein documents that PIF is a specific, reliable embryo-derived biomarker conveniently detectable in early maternal circulation. PIF ELISA emerges as practical tool to detect viable early pregnancy from day 20 post-AI.

Detection of early pregnancy-specific proteins in Holstein milk

Bovine pregnancy is commonly diagnosed by rectal palpation or ultrasonography and changes in progesterone concentration. To determine a simpler and less expensive diagnostic method, we sought to identify early pregnancy-specific proteins in bovine milk by comparing samples collected from pregnant and non-pregnant Holstein cattle. Of the 600-700 protein spots visible on 2-DE gel images, 39 were differentially expressed in milk from pregnant and non-pregnant cattle. Antibodies generated against synthetic peptides of milk whey proteins expressed specifically during pregnancy were used to confirm protein expression patterns. Western blot analysis showed that the levels of expression of lactoferrin (lactotransferrin) and alpha1G T-type calcium channel subunit (alpha-1G) were higher in samples from pregnant than non-pregnant cattle. These findings suggest that assays for pregnancy-specific milk proteins may be used to diagnose pregnancy in cattle.