9 Pregnancy loss in Holstein lactating recipient cows diagnosed pregnant by pregnancy-associated glycoprotein test in blood

Abstract

The objective of this study was to evaluate the pregnancy loss (PL) between Day 30 (P30) and Day 80 (P80) of pregnancy in lactating Holstein recipients that received an in vivo- (flush) or in vitro-produced (IVF) embryo. The recipient cows were located at Maddox Dairy in Riverdale, CA, USA, a Holstein herd that milks 3500 cows with a 305-day mature-equivalent milk production of 12 800 kg. First-lactation cows were enrolled in a Presynch-Ovsynch oestrus-synchronization program and scheduled to be artificially bred for the first time at 80 days after calving or to receive an embryo 7 or 8 days after the expected heat (recipients). The data from 590 pregnancies (1045 embryo transfers) from embryos transferred between January 2018 and March 2019 was analysed. Only grade 1 embryos (from morula to hatched blastocyst stage) produced in vivo or in vitro from Holstein donor heifers, lactating or dry cows, were transferred fresh (in vivo or in vitro) or frozen-thawed (in vivo), and pregnancy rates are shown in Table 1. The ruminant trophoblast produces pregnancy-associated glycoproteins (PAG) that can be detected by enzyme-linked immunoassay (ELISA) in the blood of pregnant cattle as early as 28 days after insemination. Various dairy herds in the USA have been using this test to supplement or replace the use of transrectal ultrasonography for early pregnancy diagnosis. Blood was sampled on P30 after expected heat day (23 days after embryo transfer) from the recipient cows and sent to IDEXX for the PAG Bovine Pregnancy Test, which was reconfirmed on P80 of pregnancy by transrectal ultrasonography. Pregnancy loss was considered to have occurred when a cow was pregnant on P30 but not pregnant on P80. The variable PL was analysed by binary logistic regression in the MINITAB program, and the model included effects of donor status (heifer vs. milk vs. dry) and embryo type. The total PL was 12.2% (72/590) and the details are shown in Table 1. No effect of donor status (P = 0.80) was detected. However, there was effect of embryo type (P = 0.004). The IVF embryos had a PL of 18.0% compared with 9.5% for the in vivo-produced embryos. Further research should be performed to study heifer embryos PL, because currently more embryos are being produced from very young donor cows and sires due to intensive use of genomic testing. In conclusion, there is a higher PL in lactating dairy recipients receiving IVF fresh embryos compared with fresh or frozen in vivo-produced embryos.

Table 1.  Embryo transfer (ET) pregnancy rates (PR, P30) in first-lactation Holstein cows (top) and pregnancy loss (PL) from Day 30 (P30) to 80 (P80) in first-lactation recipient Holstein cows (bottom)