Calving season has started for most producers and will be starting for others in the near future. Nutritional management of the cow herd is more important during the periods of late pregnancy and early lactation than any other. It has a huge impact on the performance of both the cow and the newborn calf.
Nutrition for the cow is important during this period because of its effect on subsequent reproductive performance. Nutritional status of the cow at the time that she calves and from calving until initiation of the breeding season will determine if and when she returns to estrus (cycles) and her level of fertility. Thus, it drives if and when cows become pregnant. To make the situation more complex to manage, the cow’s nutrient requirements increase throughout these periods. During late pregnancy, the fetus grows exponentially in the cow’s uterus, causing a directly proportional increase in nutrient requirements. Seventy percent of the fetus’ growth occurs in the last 3 months of pregnancy. As this occurs, the growing fetus is filling an ever-increasing portion of the cow’s body cavity, thus displacing rumen capacity. This often requires the need to provide higher quality feed in late pregnancy to overcome lost capacity for forage intake.
After the calf is born, nutrient requirements rise dramatically to meet the demand of milk production. The amount of increase is directly proportional to the genetic potential to produce milk, so the breed and bloodlines of the cow will influence her requirements for nutrients to produce milk. All of these changing variables make it challenging to manage the nutrient intake to match the nutrient demand. A few tools are available to help with this process. The first tool is to test feeds to know the nutrient content that the cows are receiving. This is relatively straight forward with harvested feeds where representative samples can be collected and sent to a feed testing lab. Once nutrient levels are known, ration balancing programs can be used to balance diets to meet nutrient requirements. Extension livestock specialists can assist with ration balancing. The second tool is to use body-condition scoring (BCS) to evaluate the nutritional status of the cow. The most common BCS system is to numerically score the cows from one (thinnest) to nine (fattest), with a moderate score of 5 being the most desirable at calving. Based on a great deal of research, cows with a BCS of 5 will have a high likelihood of returning to estrus by initiation of calving. Managing BCS from calving until initiation of breeding at calving can also be accomplished. Research suggests that feeding management should be adjusted so that cows that are not at a BCS of 5 at calving move toward a BCS of 5 by initiation of breeding. In other words, thin cows should gain BCS and fat cows should lose BCS. Again, research suggests that movement in nutritional status (BCS) toward a moderate level (BCS=5) will increase fertility so that more cows become pregnant.