A common environmental factor in early pregnancy loss is a high heat index (combined heat and humidity). Losses from heat stress occur in the first week or two after breeding, but heat and humidity can also have a long-term effect on egg quality and, thus, embryo quality.

“Changes in the eggs can last a long time. Even when temperature goes back to normal, the cow still has poor-quality eggs in her ovaries,” Tibary explains. It might take several cycles/breedings before she can carry a pregnancy.

Mid to late-term abortion

“Some toxicants affect the fetus – things like lupine, hemlock, locoweed, pine needles, ergot alkaloids, certain molds, etc. For instance, pine needle abortion causes fetal loss in late pregnancy when cows consume needles of Ponderosa pine during the third trimester,” Kasimanickam says. 

The abortion or premature parturition can occur three days to 2-3 weeks after exposure. “The greatest risk is when cows consume pine needles for three days or more, and have a high level of toxicant, which constricts the vascular network in the placenta,” he says. Blood circulation to the fetus can be reduced to 35-50%, with the restricted supply of oxygen and nutrients killing the fetus. The toxicant also increases uterine contractions that lead to expulsion of the fetus.

“Environmental stress can be a factor in how much toxicant a cow consumes; if she stays under a pine tree for shelter during stormy weather, she may eat a lot of pine needles. It’s best to keep cattle out of areas where there are Ponderosa pine trees, at least during the last trimester of pregnancy,” Kasimanickam explains.