Effects of time of progesterone supplementation on embryo development and interferon-τ production in the cow

We have investigated the effects of the timing of progesterone supplementation on early embryo development in mature, non-lactating Holstein–Friesian cows. Animals were inseminated 72 h (day 1) and 96 h following prostaglandin injection and were either left as untreated controls (n = 6) or received progesterone supplementation from either days 5 to 9 (early; n = 6) or from days 12 to 16 (late; n = 6). Daily plasma samples were collected until day 16, when cows were slaughtered and reproductive tracts recovered and flushed to collect embryos and to measure interferon-τ activity. Both early and later progesterone supplementation resulted in marked increases in plasma progesterone (P < 0.01). Early, but not late, progesterone supplementation resulted in a fourfold increase in trophoblast length (P < 0.01) and a sixfold increase in uterine concentration of interferon-τ (P < 0.05). The results demonstrate that progesterone supplementation during the postovulatory rise, but not later in the luteal phase, increases embryo development and interferon-τ production.