156 THE USE OF THE DG29™ ENZYME-LINKED IMMUNOSORBENT ASSAY KIT TO PREDICT PREGNANCY PRIOR TO EMBRYO TRANSFER IN LACTATING HOLSTEIN COWS

Abstract

Evaluation of postpartum fertility in cows is important for the efficient management of reproduction. DG29™ enzyme-linked immunosorbent assay (ELISA) kit (Conception, Animal Reproduction Technologies, Canada) measures the level of pregnancy–related glycoproteins in blood that are linked to pregnancy in the bovine species. The proteins are known to persist in the postpartum period. Here, we investigated whether the postpartum fertility in Holstein dairy cows can be evaluated through the use of the DG29 kit. We confirmed that genital organs of lactating Holstein cows (n = 119, from Days 56 to 688 postpartum) were normal by a 5.0/7.5-MHz linear array transducer (Tringa, Pie Medical Equipment B.V., Maastricht, The Netherlands), then a progesterone releasing intravaginal device (PRID; CEVA Sante Animale, Libourne, France) was inserted (Day 0) and maintained for 9 days. On Day 7, PGF_2α was administered (2 mL Dalmazine, Kyoritsu Seiyaku, Tokyo, Japan). Blood samples were collected from the tail vein or artery into vacuum tubes at the time of PRID insertion. Serum was separated and stored at –30°C until the ELISA was performed. Oestrus (Day 0) was detected by visual observation. Fresh embryos recovered from Japanese Black cows were transferred to 119 recipient cows in various parities (primiparous = 70, biparous = 27, and multiparous = 22) on Days 6 to 8 of oestrous cycle. Pregnancy was diagnosed between Days 40 to 60 by transrectal ultrasonography. The statistical significance of any differences between various parities was assessed by chi-squared and Student’s t-tests. The pregnancy rate was higher for primiparous cows than for biparous and multiparous cows (64.3, 55.6, and 54.5%, respectively), while concentrations of the pregnancy-related glycoproteins in primiparous cows (135.0 ± 29.8 pg mL^–1) were significantly lower than those of biparous (389.4 ± 175.9 pg mL^–1) and multiparous cows (399.2 ± 203.1 pg mL^–1, mean ± SEM; P < 0.05). In primiparous and multiparous cows, the concentrations of pregnancy-related glycoproteins were significantly lower in pregnant cows compared with nonpregnant cows (primiparous: 81.1 ± 29.9 v. 232.6 ± 59.8 pg mL^–1; P < 0.05; multiparous: 20.8 ± 16.2 v. 853.4 ± 411.5 pg mL^–1; P < 0.05). However, there was no significant difference between pregnant and nonpregnant biparous cows. In conclusion, the DG29 kit may be useful for the prediction of postpartum fertility in lactating Holstein cows. Further studies are needed to test the validity of this observation by using a greater number of various parties’ cows.