Effects of supplemental progesterone after ai on expression of Interferon-Stimulating genes and fertility in lactating dairy cows

Abstract

Pregnancy per AI (P/AI) and the plasmatic concentration of steroid hormones is less in lactating dairy cows than in dairy heifers. High milk production has been suggested as possible cause of this reduction in P/AI and concentrations of steroid hormones. High milk production and concurrent increase in dry matter intake has been associated with greater catabolism of steroid hormones in sheep and cattle. Progesterone (P4) exposure during diestrus is critical for endometrial function and embryo development. As the conceptus develops, the trophectoderm cells secrete interferon-tau (IFN-t) that blocks the luteolytic cascade and initiates the process of corpus luteum (CL) maintenance. Nevertheless, IFN-t influences gene expression in peripheral leukocytes and induces expression of the so called interferon-induced genes (ISG), which might be used as markers for early detection of pregnancy in cattle, and have been associated with development of the conceptus. Therefore, supplementation with P4 after AI might be an alternative to improve P/AI in lactating dairy cows. The objectives this study will be evaluate the effects of supplemental P4 after AI on CL formation, expression of ISG, and fertility in lactating dairy cows. Lactating Holstein cows will be blocked by parity (primiparous vs. multiparous) and method of AI (timed AI vs. AI on estrus) and, within each block, randomly allocated to receive no supplemental P4 (control), a single controlled internal drug release (CIDR) containing 1.38 g of P4 (EAZI Breed CIDR cattle insert, Zoetis, Madison, NJ) from d 4 to 18 after AI, or a CIDR on d 4 and a second CIDR on d 7 after AI, both of which will remain until d 18. Blood samples will be collected to measure plasmatic concentration of P4 and quantify mRNA for ISGs (ubiquitin-like IFN-stimulated gene 15-kDa protein or IGS-15, 2',5' - oligoadenylate synthetase or OAS-1, myxovirus [influenza virus] resistance 1 Mx or Mx1, and myxovirus [influenza virus] resistance 2 Mx or Mx2) in peripheral leukocytes. Pregnancy diagnoses will be performed on d 32 ± 3 and 60 ± 3 aftet AI to evaluate P/AI and maintenance of pregnancy. (AU)