KIM'S KORNER: Getting the right angle on the timing of pregnancy
By Dr. Kimberly Vonnahme
I don’t know about you, but sometimes I wish I could control time. With school and kids’ activities in full swing, to control the clock is a super power I wish I possessed! I marvel at how seamlessly the days blend into each other, and if you don’t stop to reflect on where you have been, you can miss how far you’ve come in such a short period of time!
I have always loved the fall--- growing up as an Iowa farm girl, harvest was a special time. Who wouldn’t love bringing their dad a hot supper in the middle of the night—I felt such pride in bringing a little nourishment to that hard working farmer I was blessed to call Dad. I also loved school!! I loved the start of each new school year! First as a student-- to show up in my new classroom with my new sneakers and fresh folders, good smelling erasers, and new clothes! And then as a professor—to see the fresh faces on campus, to be greeted by former students bringing back stories of their summer adventures!! So while the fall may seem to be a time of harvest, a time of endings, to me I see fall as a time of new beginnings.
I have had the privilege to witness new beginnings in our sheep flock—both at NDSU as well as at Harvest Hope Farm. God made the timing of pregnancy perfect in sheep: pregnancy is ~5 months long in the ewe—so getting pregnant in the fall allows for lambs to be born in the spring—when the air is warmer and the grass is greener! This new life in the spring began 5 months ago—when our ewes were preparing to become pregnant again—all at the perfect time!
So what controls the timing of pregnancy? Well, ewes are incredible creatures. After the ewes give birth in the spring, they go into a reproductive dormancy—they are busy nursing their lambs, and when the lambs are weaned at ~2 months of age, the ewes do not cycle back to become pregnant like other farm animals do. For many decades, researchers have studied the timing of the estrous cycle (the ovarian cycle of our farm animals), and in sheep, the estrous cycle is largely dependent on day length. As you are well aware, the days are getting shorter now. When an animal (or a human) perceives less light, an organ in our brain (the pineal gland) makes the hormone, melatonin. Lots of people know that melatonin is the hormone that regulates our sleep-wake cycle, and some people will take melatonin to help when they have trouble sleeping. In sheep, melatonin “wakes” up another portion of the brain whose ultimate job is to make sure the ovary will begin to make follicles again. Follicles are blister-like structures on the surface of the ovary that house the egg. Once darkness hours increase, the ovary grows more follicles and, if a ram is nearby, there is a high likelihood of conception occurring.
Ewes that have been pregnant before often ovulate 2 or 3 follicles. This means that the likelihood of having twins or triplets can be greater in our more experienced mothers. When ewes get pregnant for the first time, they often only ovulate one follicle—allowing that younger ewe the ability to nourish herself and the developing lamb inside the uterus. Since making milk is an energy-demanding process, providing milk for only one lamb is an easier transition to make for a new mother… God’s timing is remarkable—giving that new mother the ability to provide for her own well-being as well as nourishing the next generation.
Our ewes at Harvest Hope Farm are surely cycling…. We are planning to introduce a ram in the next few weeks so that our lambs will be born in May! Understanding our ewes’ reproductive cycles allows us to manage the timing of birth… so while we may not be able to control the time for everything… we can control when we will be greeted with new lambs—having the right angle on the timing of pregnancy sure can make our spring a little easier!
Thanks for coming around to Kim’s Korner—where the right angle on animal science can always be found.
Kimberly Vonnahme, PhD, is a mother, lover of agriculture, and an animal scientist. Dr. Vonnahme was a professor at NDSU for 13 years before joining the animal health company, Zoetis. Kim enjoys making lists, analyzing data, hugging her husband and children, and a strong cup of coffee.