The Physiology of Pregnancy
Loss: Female Factors
Keith Inskeep explains how hormone levels can cause embryo loss.
by Troy Smith for Angus Journal
STAUNTON, Va. (Oct. 16, 2013) — Cow-calf producers who utilize artificial insemination (AI) often assume that females found open at pregnancy-testing time failed to conceive — that fertilization of an egg did not take place. However, reproductive physiologists say fertilization usually does occur when fertile females are inseminated, either by AI or natural service. In many cases, embryo loss is the reason they are later found to be open.
Keith Inskeep said many early embryo losses occur because the reproductive tract of the cow has concentrations of certain hormones that are too low or too high.
According to Keith Inskeep, a reproductive physiologist at West Virginia University-Morganstown, about 57% of failed pregnancies in cattle actually result from embryo loss. Inskeep talked about reasons why they happen during the Applied Reproductive Technologies in Beef Cattle (ARSBC) symposium Oct. 15-16 in Staunton, Va.
There can be other reasons, including genetic defects, but Inskeep said many early embryo losses occur because the reproductive tract of the cow has concentrations of certain hormones that are too low or too high. Estrogen, for example, is produced in the ovaries to prepare the uterus for pregnancy, but too much estrogen is detrimental.
“The presence of a persistent (aged) ovarian follicle results in higher exposure to estrogen and creates higher potential for embryonic death,” said Inskeep, explaining how detrimental amounts of estrogen can result in defective ovum (eggs) that can be fertilized but resulting embryos soon die. Elevated estrogen at 30-35 days of gestation may also contribute to pregnancy loss. This is the time of placenta formation known as placentation. Though high in dairy cows, Inskeep said losses after onset of placentation are low in beef animals that are free of disease, except in reported cases of inappropriate vaccinations.
Progesterone is also essential to initiation and maintenance of pregnancy. Inadequate levels can cause both early and late embryonic losses.
“Low concentrations of progesterone lead to excessive concentrations of other hormones that may cause embryonic death,” stated Inskeep.
Inskeep reminded producers that body condition affects response to progesterone, emphasizing the need to have heifers properly developed and cows in adequate body condition prior well in advance of breeding.
Inskeep spoke during Wednesday’s ARSBC session focused on dealing with pregnancy and birth losses. Visit the Newsroom at www.appliedreprostrategies.com to listen to his presentation and to view his PowerPoint slides and proceedings paper. This comprehensive coverage of the symposium is compiled by the Angus Journal editorial team. The site is made possible through sponsorship by the Beef Reproductive Task Force.
Editor's Note: This article was written under contract or by staff of the Angus Journal. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.