The Placenta

Often times we forget that throughout gestation we are not only feeding our cow, but we are also feeding the calf developing within her. The placenta functions as the nutritional conduit between the maternal and fetal units, and the development and functionality of the placenta is critical for the successful gestation of the fetus.

It is only after mid-gestation that the nutrient uptake of the fetus becomes substantial enough to contribute to maternal nutrient requirements. Unlike sheep, where the placenta attains most of its dry tissues, protein, and DNA by mid-gestation, in cattle, the placenta will continue to increase in weight until near term. This continued growth may make the bovine placenta less sensitive to nutritional inadequacy during gestation. In cattle there is a high correlation between the birth weight of the calf and the weight of the placenta, however increases in placental weight do not equate to increased functionality. While research is yet to uncover exactly what drives the functionality of the placenta, it is believed that one major aspect could be, in part, the development of the complex set of blood veins and arties that form in a process called angiogenesis that takes place in the first trimester of gestation.

The perfusion (delivery of blood) of the placenta is a direct result of the angiogenesis that takes place, helping facilitate the placenta’s many duties during gestation. During the second half of gestation, when 75% of the total fetal growth is taking place, there is an exponential increase in umbilical blood flow. This blood flow not only carries nutrients to the fetus, but also works to carry waste product away.

In general the placenta serves 7 major functions:

1. Fetal Gut: serving as a nutrient exchange mechanism between the maternal and fetal units.
2. Fetal Lungs: provides gas exchange for the fetus with oxygen going in and carbon dioxide coming out.
3. Fetal Kidney: working to remove waste for the fetus.
4. Fetal Liver: serving as a filter and detoxification system for the fetus.
5. Endocrine Function: tremendous amounts of hormones are produced by the placenta.
6. Temperature Regulation: serving to maintain a temperature that is slightly warmer than the dam’s internal temperature.
7. Protection: the fluid that is contained within the placenta works as a protective surrounding for the delicate and growing fetus.

The nutritional status and amounts of protein being provided to the dam during the development of the placenta in the first and second trimesters can impact the development of the placenta. Typically it is seen in research that if protein is restricted, the placenta will have enhanced development to compensate for the decrease in available nutrients in the maternal blood supply. In a trial conducted by Rasby and colleagues, and published in the Journal of Animal Science in 1990, they found that cows that were in a thin Body Condition Score (BCS) had greater cotyledonary weights when compared to cows in moderate BCS. In addition, cows that were in thin BCS had greater production of placental hormones. This shows that nutrient intake and body energy reserves influence function of the placenta during late gestation, and producers must manage the cowherd to ensure that proper placental development is taking place.