Oocyte fertilization rates in bovines following
artificial insemination or natural mating are generally
good (~90%). Curiously, only about one third of these
pregnancies remain until 30 days post-AI in dairy cows.
Thus, most pregnancies are lost between fertilization
and early embryonic growth. Although classical
pathways describing that lower progesterone post-AI is
the main culprit to these early embryonic losses, a
number of environmental factors such as heat-stress as
well as novel concepts in bovine physiology including
the effects of excessive negative energy balanced (NEB)
and the insulin-resistant state experienced by high
producing cows during the postpartum period can help
explain the poor reproductive performance, generally
observed in dairy herds world-wide. Thus, expanding
the scientific knowledge in these critical areas in bovine
fertility related to the evident impact of NEB and/or
altered circulating and uterine metabolites in the
postpartum period on oocyte quality, gamete transport,
uterine environment, and early embryonic growth are of
major importance to improve reproductive efficiency in
modern high producing dairy cows.
Oocyte fertilization rates in bovines followingartificial insemination or natural mating are generallygood (~90%). Curiously, only about one third of thesepregnancies remain until 30 days post-AI in dairy cows.Thus, most pregnancies are lost between fertilizationand early embryonic growth. Although classicalpathways describing that lower progesterone post-AI isthe main culprit to these early embryonic losses, anumber of environmental factors such as heat-stress aswell as novel concepts in bovine physiology includingthe effects of excessive negative energy balanced (NEB)and the insulin-resistant state experienced by highproducing cows during the postpartum period can helpexplain the poor reproductive performance, generallyobserved in dairy herds world-wide. Thus, expandingthe scientific knowledge in these critical areas in bovinefertility related to the evident impact of NEB and/oraltered circulating and uterine metabolites in thepostpartum period on oocyte quality, gamete transport,uterine environment, and early embryonic growth are ofmajor importance to improve reproductive efficiency inmodern high producing dairy cows.
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