Early Detection of Pregnancy and Embryonic Loss in Dairy Cattle by ELISA Tests G Ga´bor 1 , F To´th 1 ,LO ´ zsva´ ri 2 , Zs Abonyi-To´th 2 and RG Sasser 3 1 Research Institute for Animal Breeding and Nutrition, Herceghalom, Hungary; 2 Faculty of Veterinary Sciences, SZIE, Budapest, Hungary; 3 Biotracking LLC, Moscow, ID, USA Contents Over a 25-month period 8118 blood samples were assayed for the presence of the serum pregnancy specific-protein B (PSPB) and progesteron (P4) concentrations on three Hungarian large-scale dairy farms. Pregnancy (n ¼ 4085) was checked by BioPRYN assay at 30–36 days post-insemination (PI). Samples from all cows that tested not pregnant and from cows with an optical density (OD) reading in the BioPRYN test that was between 0% and 30% above the cutoff OD value were tested for serum P4 concentration. According to serum P4 concentration, cows were assigned to three categories: high (>4 ng/ml), medium (2–4 ng/ml) and low (<2 ng/ml) serum progesterone. The authors predicted a presumed (low) or possible (medium) late embryonic loss (LEL) or maintenance of the pregnancy (high). A total of 710 LELs were detected (17.4%) and 31.8% of them were predicted because of a low OD value at 30–36 days after insemination. Lower PSPB serum level significantly refers for LEL (p < 0.0001). The prediction rate for the true embryonic loss was 31.8% when OD cutoff from 0% to + 30% of cutoff was examined while it was 62.5% when the threshold was OD cutoff of 0% to 10% of cutoff. The authors conclude that BioPRYN was useful for prediction of a part of LEL in dairy cows and serum P4 concentration in these cows related to the rate of LEL. Introduction Extended postpartum interval, poor heat expression, inefficient detection of oestrus and fertilization failure are major causes of reproductive inefficiency; but early embryonic death is recognized as the major cause of reproductive loss in cattle (Sreenan et al. 2001). O ´ zsva´ ri et al. (2006) analysed the economic data in two Hun- garian large-scale Holstein-Friesian dairy farms using the average output and fertility parameters by a partial budgeting method. The data of calved cows and agro- economic conditions were taken into consideration to quantify the losses. Considering net milk receipts and calf sales, respectively, an average calving interval of 11 months (<350 days) and 12 months were optimal economically. The annual losses due to reproductive failures were 194–276 EUR per cow on the two farms; therefore, the annual economic losses due to reproduc- tive disorders were 160–320 EUR per cow. Early pregnancy detection is one of the key solutions for the decreasing of calving interval. Common methods are (i) rectal palpation [35–42 days post-insemination (PI)], (ii) B-mode ultrasonography (25–30 days PI) and (iii) examination of pregnancy-specific proteins [PSPB; pregnancy associated glycoprotein (PAG), 29–30 days PI] in cattle. BioPryn TM , an enzyme-linked immuno- sorbent assay (ELISA) test has been developed and is distributed for the detection of PSPB in the circulation of pregnant cows. In three experiments BioPryn TM was evaluated and was found to be a practical, reliable and safe system for pregnancy detection in dairy cattle. The BioPryn TM was also examined for the prediction of the embryonic loss between days 30 and 36 after artificial insemination (AI) (Ga´bor et al. 2004). In first-service heifers, the fertilization rate (FR) may approach 100%. Fertility losses in these animals are between 40% and 45% by 17–19 days after insemin- ation. In repeat breeder heifers, losses occur because of fertilization failure (FR 70%) and embryonic mortality that are 30–35% in the same period. The major portion of loss occurs before day 15 after service (Ayalon 1978); therefore, the embryo dies before interferon tau is released to prevent prostaglandin induced luteal regres- sion. Such cows will return to oestrus after the same interval as unmated animals, despite their having been pregnant (Ayalon 1978). The critical period appears to be soon after the embryo enters the uterus, 6–7 days after service, when the morula is developing into the blastocyst. Lamming and Royal (2001) reported an early embryonic loss from 24% to 40%, highlighting the importance of embryo mortality to the dairy industry. Pregnancy detection by BioPryn TM is routinely used in the author’s laboratory in Hungary. Approximately 10 000 tests are performed per year and the results are reported to the farm owners. For all cows of this study, re-check of the assay result by palpation at 60 days is also performed as a routine tool. Differences in preg- nancy status for cows between the early assay results and 60 days were referred to as late embryonic loss (LEL). Alexander et al. (1995), using presence of PSPB as measured by radioimmunoassay, found that from 30 to 45 days after AI until 60 days, there was a 5.4% embryo loss in first-bred dairy heifers. The losses in multi-parous cows are expected to be greater. It is also expected to be greater if time of first measure is reduced to 30–36 days (as is the case in this study). Prediction of embryonic loss by observation of the optical density (OD) response in a test sample on a given day after AI would be of value in dairy management. A low OD would be a reflection of low PSPB in the sample. If it were lower than normal, embryo growth may be retarded resulting in embryo death. The objective of the present study was to develop a means for prediction of embryonic loss at the time of early pregnancy detection (approximately 30–36 days PI) by serum PSPB and serum progesteron (P4) assays. Material and Methods Over a 25-month period, blood samples were collected and assayed for the presence of serum PSPB and Reprod Dom Anim 42, 633–636 (2007); doi: 10.1111/j.1439-0531.2006.00834.x ISSN 0936-6768 Ó 2007 The Authors. Journal compilation Ó 2007 Blackwell Verlag