From the July/August 2020 Beef Newsletter
You found a cow in heat. You catch her in your chute and breed her. Will this bring a calf in nine months and a few days? Here is the process.
At the time we breed the cow, toward the end of standing heat, ovulation has yet to occur. It is triggered by the stimulation of the clitoris (in the fatty tissue at the bottom of the vulva) that sends a signal to the pituitary “release lutenizing hormone to rupture the follicle to release the ovum [egg]”. In OvSynch protocols, a “Fertagyl” injection after breeding is used to do this, but the clitoral stimulation is clearly cheaper… and preferable if you are trying to stay “natural”.
Thus, six to twelve hours after you introduced semen, the sperm cells waiting in the fallopian tube at the end of the uterine horn meet the ovum released from the ovary and the sperm cells begin to rub their acrosomal caps against the enzyme shell of the ovum, until one of them finds penetration inside and the genetic material (half from sire, half from dam) will fuse into a new, unique genotype.
Over the next week, as this fertilized ovum goes through cell division, it migrates down the path of the fallopian tube to the uterine horn, which has a sticky lining from the recent estrus [heat]. If it finds a place to “stick”, an initial attachment forms. A membrane begins to form around the embryo, and fills with protective fluids. Over the next five weeks, the embryo within its sac transitions to a fetus and the fetal attachments (cotyledons and caruncles) become the pathway for nutrition to enter and waste to leave the fetus.
The cow’s body gradually discerns that a pregnancy is in progress, which suspends the estrogen production by the ovarian follicles, and progesterone levels increase to maintain bodily stasis. Between 60 and 90 days, the reproductive tract begins to slide down into the body/flank cavity as the weight of fetus and fluids increases.
In the last trimester of pregnancy, the now fully formed fetus focuses on growth, which is why nutrition is so critical to a healthy, normal size calf (too much starch energy will explode the calf size at the expense of calving ease when fed in the third trimester). High quality hay or pasture is best, as fiber energy meets the nutrient needs without excess weight gain.
In the last two weeks prior to parturition (calving) the calf, to this point suspended upside down inside the uterus, will “turn” to get into a birthing position—head and forelegs forward. Once it begins, the first thing you will see is the udder forming up; next you may see the amber-color cervical plug be passed; then you will see the lateral pelvic muscles relax. From the onset of contractions, it can take five to ten hours before the cervix dilates enough for a safe delivery.
Lost pregnancies occur
At any stage of the above, things can go wrong. None are the fault of your insemination.
The miracle of mammalian pregnancy
It begins with a correct insemination procedure that deposits the germ plasm in the correct location (the body of the uterus, between cervix and the division of uterine horns). From that moment forward, it is your cow’s hormone systems, health status, and nutritional intake that results in a live calf nine months later.
As our breeding seasons come to a close, our statistics of success depend upon the key elements above, and inside you will find a recap of the process as a cow does all the nurturing work of nature.