Most producers across the Big Sky region are either in the early throws of calving or they are busy preparing for it to begin. Calving season, in its own way, marks the official start of a rancher’s production year. As calving season draws nigh, keep in mind that a cow’s nutritional needs are changing now as well.

“When cows hit that third trimester, the fetus is just growing exponentially and putting a huge demand on all nutrients the cow takes in. She’s got to maintain herself but at the same time the cow is trying to shuttle as many of the nutrients as possible to the fetus,” noted Dr. Megan Van Emon, Extension beef cattle specialist for Montana State University.

Van Emon went on to explain that during the final third of a cow’s pregnancy, nutritional demands increase 30-50 percent. The exact percentage is somewhat dependent on the cow’s body score prior to the third trimester, and of course, the weather plays a huge role as well.

“Like right now, its pretty nice out so a cow may only need a 30 percent increase but when it starts to get really cold out and we’re also trying to help her maintain her body heat and body weight, plus the calf’s, the cow may need closer to a 50 percent increase,” Van Emon said.

That goes for all nutrients. Protein and energy are the big ones, but mamma cows in late gestation may also require a jump in minerals and vitamins.

Van Emon pointed out that a typical calf fetus is about the size of a basketball at the end of middle pregnancy. That fetus will go on to experience exponential growth, increasing from about 20 pounds to a 90- or 100-pound calf in just three short months. So, it is no wonder that cows require such a spike in nutrition.

“All the main systems of a calf are there at the end of middle gestation, everything just fully develops during third trimester,” Van Emon stated.

Van Emon went on to say that nutrition in the last jaunt of pregnancy can play into birth weight. Yes, genetics plays a big role as well but increased protein and energy can mean a bigger calf come birthing.

“That’s the hard part. Usually by the time the cow is entering late gestation it can be extremely cold out so we try to feed those cows extra energy to maintain their body heat so they aren’t putting so much into heat maintenance. But we can see those impacts on birth weights and increased dystocia issues,” said Van Emon.

The take a-way here is, it’s a fine line. Cows need to be fleshy and a good body score entering parturition but if they are over-fed, calving issues may develop.

With so much happening during the final months of a cow’s pregnancy, it is a good rule of thumb to have your cows at a body condition score five or six going into third trimester. Keeping those cows at or about that same score all the way to calving is ideal because a healthy, robust cow is more likely to give birth to a vigorous calf.

With calving just around the bend for so many, Van Emon emphasizes that producers should be cognizant of feed quality. An abundance of range doesn’t necessarily mean it is quality and the same goes for hay. Nutritional preparation in these last few months leading up to calving is something that should not be taken lightly.