Now is the time of year when cattle are grazing crop residues and farm equipment is put away for the winter. Cows that are set to calve on March 1st are moving into their third trimester. This means the nutrient requirement of these cows will go up immensely. The growth of the fetus is exponential until the time of calving. Each day of fetal growth will be greater than the day before—until calving. A complication can be increasing and maintaining their energy as the temperatures drop. More energy is needed for the cows to maintain body condition.
To put this into perspective, let’s say we have a moderate sized, open, non-lactating cow. This cow will need to have approximately 8.5 mega-calories per day (one mega-calorie equals 1000 calories) just to maintain her body condition. This is also assuming she is in a comfortable environment. If that cow is eight months pregnant she could need another 3.5 mega-calories per day. In the weeks before calving, this cow will need more than five mega-calories than if she were not pregnant. That is almost 60 percent more energy needed to grow the fetus into a live calf.
Studies have shown underfeeding cows and heifers during late pregnancy will result in longer intervals between calving and rebreeding, lower milk production, and decreased calf weaning weight. These effects are even more pronounced in heifers compared to cows. There is also research to suggest there is decreased passive immunity to calves in cows that have had inadequate nutrition during the late stages of pregnancy. Passive immunity is acquired by the calf via colostrum and is important early in the calf’s life to fight off infections. It is thought the inadequate nutrition in the late stages of pregnancy hinders the cow’s ability to make immunoglobins, or the calf is unable to absorb the immunoglobins.
With these increased energy requirements for cows during the winter, it is important to know if cows are getting enough nutrients, so we can avoid the negative impacts caused by underfeeding. If your cows are grazing crop residue, then it is difficult to know if their nutritional needs are being met. This is why making notes on the cows’ body condition score before grazing is a good idea. If the average body condition score of the herd is maintaining or increasing, then it would be fair to say energy needs are being met. If the body condition scores are dropping, it is time to rotate to another field, or get them to a dry lot to feed them.
Feeding in a dry lot is much simpler when it comes to feeding cattle. We can balance a ration we know will meet the needs of the cow. If any producer needs help balancing a ration for cows, growing calves, bulls or replacement heifers, stop by the K-State Research and Extension Office in Concordia, call 785-243-8185, or email [email protected].
