The first week following insemination is the period of major pregnancy failure in pasture-grazed dairy cows

Abstract

A 60% pregnancy success for inseminations is targeted to optimize production efficiency for dairy cows within a seasonal, pasture-grazed system. Routine measures of pregnancy success are widely available but are limited, in practice, to a gestation stage beyond the first 28 d. Although some historical data exist on embryonic mortality before this stage, productivity of dairy systems and genetics of the cows have advanced significantly in recent decades. Accordingly, the aim was to construct an updated estimate of pregnancy success at key developmental stages during the first 70 d after insemination. Blood samples were collected for progesterone concentrations on d 0 and 7. A temporal series of 4 groups spanning fertilization through d 70 were conducted on 4 seasonal, pasture-grazed dairy farms (n = 1,467 cows) during the first 21 d of the seasonal breeding period. Morphological examination was undertaken on embryos collected on d 7 (group E7) and 15 (group E15), and pregnancy was diagnosed via ultrasonography on approximately d 28 and 35 (group E35) as well as d 70 (group E70). Fertilization, embryo, and fetal evaluation for viability established a pregnancy success pattern. Additionally, cow and on-farm risk factor variables associated with pregnancy success were evaluated. We estimated pregnancy success rates of 70.9%, 59.1%, 63.8%, 62.3%, and 56.7% at d 7, 15, 28, 35, and 70, respectively. Fertilization failure (15.8%) and embryonic arrest before the morula stage (10.3%) were the major developmental events contributing to first-week pregnancy failures. Embryo elongation failure of 7% contributed to pregnancy failure during the second week. The risk factors for pregnancy success that were related to the cows included interval between calving and insemination, and d-7 plasma progesterone concentrations, whereas insemination sire was associated with pregnancy outcome. Most pregnancy failure occurs during the first week among seasonal-calving pasture-grazed dairy cows.

Metabolomic evolution of the postpartum dairy cow uterus

“…Previous work by this group has recently shown a clear increase in the proportion of viable embryos with increased time and number of estrus events after calving (Aranciaga et al, 2021;Berg et al, 2022).…”

“…This is especially true in countries with predominantly grazing dairy systems that have a higher dependence on timely and compact calving seasons (Brownlie et al, 2014). These factors include genetic improvements (Crowe et al, 2018), housing, and quality of feed adjustments peripartum (Sawa & Bogucki, 2011) and setting the voluntary waiting time to about day 24 (Berg et al, 2022; Humblot, 2001) in seasonal pasture‐grazed dairy cows.…”

“…Previous work by this group has recently shown a clear increase in the proportion of viable embryos with increased time and number of estrus events after calving (Aranciaga et al, 2021; Berg et al, 2022). Several proteins were suggested as potential biomarkers of uterine suitability for pregnancy, as well as time‐related changes in immune (e.g., myeloid leukocyte activation) and metabolic (e.g., amino acid metabolism) processes (Aranciaga et al, 2021).…”

“…The most critical period of pregnancy loss in grazing dairy cows is the first week after insemination (Berg et al, 2022; Butler, 2000; Diskin & Morris, 2008). During this period, in the maternal tract, the early embryo is surrounded by oviduct and uterine luminal fluids (ULFs).…”

“…During this period, in the maternal tract, the early embryo is surrounded by oviduct and uterine luminal fluids (ULFs). These fluids and intrinsic oocyte quality determine embryo development, particularly until implantation at around Day 20 (Berg et al, 2022). ULF has been recently shown to possess a much higher degree of regulatory autonomy than previously thought, with enzymatic activity independent of the surrounding endometrial tissue (Simintiras et al, 2022).…”