Correlation between reproductive status and steady-state mRNA levels of the Myxovirus resistance gene, MX2, in peripheral blood leukocytes of dairy heifers

¹ Caine Veterinary Teaching Center, University of Idaho, Caldwell, ID, 83607
² Research and Extension Center, University of Idaho, Caldwell, ID, 83607
³ Dairy and Animal Science Department, Penn State University, University Park, PA 16802

^* To whom correspondence should be addressed. E-mail: rchebel{at}vmtrc.ucdavis.edu.

	Abstract

The objectives of the present study were to evaluate the correlation between reproductive status and steady-state levels of MX2 mRNA in peripheral blood leukocytes (PBL) of dairy heifers and the reliability of using change in MX2 mRNA for identification of non-pregnant heifers 18 to19 d after AI. Holstein heifers (n = 266), 13 ± 1 mo of age, were assigned randomly to be inseminated (BRED; n = 214) or not (NON-BRED; n = 52). Estrous cycles of all heifers were synchronized with an intravaginal insert containing progesterone for 7 d. At insert removal heifers received an injection of PGF₂. Heifers in the BRED group were inseminated on detection of estrus or at a fixed time, 72 h after insert removal concomitant with a GnRH treatment. Heifers in the NON-BRED group received an injection of GnRH 48 h after insert removal. Blood samples collected on d 0 (d of AI or estrus) and 18 were used to determine steady-state levels of MX2 mRNA. Samples collected on d 0, 7, 14, and 21 were analyzed for progesterone concentration. Pregnancy was determined retrospectively by progesterone concentration on d 21 and was diagnosed at 30 ± 1 and 60 ± 3 d after AI. The fold change in levels of MX2 mRNA from d 0 to 18 was greater for heifers classified/diagnosed as pregnant on d 21 (P < 0.05) and 30 ± 1 (P < 0.05) and 60 ± 3 (P < 0.05) d after AI compared with non-pregnant and NON-BRED heifers. Heifers that experienced pregnancy loss from 21 to 30 ± 1 (P = 0.11) or 21 to 60 ± 3 (P = 0.08) d of gestation tended to have smaller fold increases in MX2 mRNA expression than those that maintained pregnancy. The sensitivity (range 57.1 to 65.6%) and negative predictive value (range 47.9 to 57.1%) of determining reproductive status on d 18 according to change in level of MX2 mRNA expression in PBL were low and the level of agreement between diagnosis of pregnancy by change in MX2 mRNA expression and other methods was small (range 0.20 to 0.36). The present study indicates that increased expression of MX2 mRNA in PBL is related to pregnancy around 21, 30, and 60 d after AI in dairy heifers and that losses that occurred later in pregnancy were associated with lower fold increases in MX2 mRNA. However, using change in MX2 mRNA expression was not a reliable method for diagnosis of pregnancy at 18 d after AI because of low sensitivity and negative predictive value.

Key Words: Gene expression, heifers, leukocytes, pregnancy