Plasma concentrations of pregnancy-associated glycoproteins I and II and progesterone on day 28 post-AI as markers of twin pregnancy in dairy cattle

Carrying twins is the main factor jeopardizing pregnancy maintenance and reducing the lifespan of dairy cows. There is therefore a need to accurately detect twin embryos at the time of pregnancy diagnosis so that twin pregnancies are carefully followed. This study compares in single and twin pregnancies from day 28-42 of gestation, patterns of plasma pregnancy-associated glycoproteins (PAGs) I and II and progesterone (P4), and establishes cut-offs for these hormones on day 28 post-AI that might be useful for twin pregnancy diagnosis. The sensitivity and specificity of the diagnostic capacity of these cut-off values were then determined using ultrasonography findings as the reference standard. A total of 110 lactating dairy cows carrying live singletons or twins from day 28-42 of gestation were enrolled. On day 28 post AI, 56 cows were diagnosed as carrying twins and 54 singletons by ultrasonography. This diagnosis was confirmed ultrasonographically on days 35 and 42 post AI. Among the 54 cows with single pregnancies, those in which the single embryo was accompanied by two corpora lutea (n=23) maintained this condition until day 42 and showed similar plasma PAG-I, PAG-II and P4 levels as those cows with a single embryo and single corpus luteum (n=31). Cows bearing twins showed higher plasma PAG-I, PAG-II and P4 concentrations throughout the study period than cows bearing singletons (between subject effect; P<0.001). Cut-offs for plasma PAG-I, PAG-II and P4 concentrations on day 28 of gestation of 5.5, 0.25 and 14 ng/ml, respectively, were used to determine twin pregnancies. Each of the proposed cut-off values identified twin pregnancies with a precision higher than 70%. In conclusion, the determination of these hormones could be a useful tool to discriminate between single and twin pregnancies.