Bovine Fetal Growth

Cows, like humans, are mammals that give birth to live young; the average length of gestation (pregnancy) in cattle is about 280 days, roughly similar to the average length of pregnancy in humans. Meat and dairy production is a major industry in the United States, so bovine embryology and fetal growth have been extensively studied. Some scientists are currently exploring genetic and other factors that may influence bovine fetal growth and development.

  1. Features-Embryonic Stage

    • After the egg has been fertilized by a sperm and begins to divide, it grows to form eight cells within the first three days of development. The embryo implants in the uterus by about four days; after implantation begins a process called gastrulation, during which the cells are rearranged into three distinct tissue types as the embryo continues to grow. These stages are similar to the process in other mammals including humans.

    Features-Fetal Growth

    • The major organs form over the course of the first three months of development; by about 120 days, the calf will have reached half its final length. Limb development begins as early as the 25th day of pregnancy, while the heartbeat may be audible even sooner. Most of the growth in size takes place during the last three or four months of gestation. While the fetus weighs 15 pounds on average some five months or so into the pregnancy, the average calf weighs 79 pounds at birth. According to the University of Nebraska-Lincoln (UNL), 75 percent of fetal growth takes place during the last two months.

    Considerations

    • Just as in humans, it&'s important that pregnant cows receive adequate nutrition in order to ensure maximum fetal growth. Several studies cited by UNL found that restricting nutrients during pregnancy was linked to an increase in calf mortality and disease susceptibility. This is especially true for the second half of gestation, when the majority of fetal growth takes place.

    Size

    • Although 79 pounds is the average birth weight, it can vary substantially based on breed and other factors. Pregnancy failure or abnormal development is more common in cloned cattle; researchers are still working to understand the reasons why cloned calves have a higher mortality rate.

    Theories/Speculation-Genetics

    • Now that the cow genome has been sequenced, some researchers are working to identify genetic factors that might explain these differences. A study of 733 cows published in the journal "Genetics" in 2009, for example, identified a stretch of DNA on chromosome 6 in one population of cows that was statistically linked to variations in fetal growth. As the tools available to geneticists continue to improve, further research could well identify other important genetic factors.