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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2007-0014v1 85/9/2163    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Stevenson, J. L. Articles by Chebel, R. C. Search for Related Content PubMed PubMed Citation Articles by Stevenson, J. L. Articles by Chebel, R. C.

Correlation between reproductive status and steady-state messenger ribonucleic acid levels of the Myxovirus resistance gene, MX2, in peripheral blood leukocytes of dairy heifers^1,2

J. L. Stevenson^*, J. C. Dalton, T. L. Ott, K. E. Racicot and R. C. Chebel^*,3,4

^* Caine Veterinary Teaching Center, and and Research and Extension Center, University of Idaho, Caldwell 83607; and Dairy and Animal Science Department, Pennsylvania State University, University Park 16802

³ Corresponding author: rchebel{at}vmtrc.ucdavis.edu

The objectives of the current study were to evaluate the correlation between reproductive status and steady-state levels of Myxovirus resistance gene (MX2) mRNA in peripheral blood leukocytes (PBL) of dairy heifers and the reliability of using change in MX2 messenger RNA (mRNA) for identification of nonpregnant heifers 18 to 19 d after AI. Holstein heifers (n = 266), 13 ± 1 mo of age, were assigned randomly to be inseminated (BRED; n = 214) or not (NONBRED; 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 NONBRED 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 and 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 nonpregnant (bred but not pregnant) and NONBRED 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 values (range 47.9 to 57.1%) of determining reproductive status on d 18 according to the change in the level of MX2 mRNA expression in PBL were low, and the correlation between diagnosis of pregnancy by fold change in MX2 mRNA expression and other methods was small (r = 0.20 to 0.36). The current study indicates that increased expression of MX2 mRNA in PBL is related to pregnancy approximately 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 the change in MX2 mRNA expression was not a reliable method for diagnosis of pregnancy at 18 d after AI because of the low sensitivity and negative predictive value.

Key Words: gene expression • heifer • leukocyte • pregnancy