For as long as I can remember, observant ranchers have noticed calves will have larger birth weights after a long and cold winter. This observation was confirmed by research conducted by the University of Nebraska back in the 1990s. Prolonged low temperatures and freezing wind chills during pregnancy can cause calves to be larger at birth, which will create more calving problems.

David Colburn conducted this study on 400 first-calf heifers, over three calving seasons. He said, “When a pregnant animal is exposed to cold temperatures the blood flow is concentrated internally to help maintain the body’s core temperature. As a result, the fetus will receive more nutrition during periods of cold weather.” Average birth weights varied 11 pounds from the warmest winter to the coldest winter.

This also explains why calf birth weights are larger in the northern states than they are in the southern states. If you put cows that are genetically similar in Texas and in Montana, birth weights could be as much as 10 to 15 pounds heavier in Montana. This is the result of colder temperatures in Montana. I believe calves born in February and March will have larger birth weights than calves born in May for the same reason.

Just the opposite is true for fall calving. The last trimester of pregnancy for fall-calving cows will often be very hot. When a cow is hot, she will naturally increase blood flow to the outside of her body to get rid of the excess heat. When that happens, the fetus is essentially starved of nutrients. It’s not at all uncommon for fall-born calves to have birth weights that are 20 pounds lighter than they would have been in the spring.

The best way to prevent calving problems is through genetics. Use bulls with proven calving ease. If you don’t have a live, healthy calf at birth, you don’t have much. This is one of many areas Pharo Cattle Company specializes in. Calving season should be easy and enjoyable! Over 70% of the bulls selling in our three spring bull sales can be safely used on virgin heifers. Many are Guaranteed for Calving Ease! You won’t find bulls with this much calving ease in any other program.