By Ken Olson and Adele Harty
Calving season has started or will be starting in the near future for most producers. 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. This means the cow needs to gain about 1.25 lb. per day in fetus and related tissue growth during late gestation. If she doesn’t gain this much, then her own body weight and condition are decreasing. 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 beef and cow/calf field 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 breeding. Managing BCS from calving until initiation of breeding 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.
Nutrition of the cow during late gestation and early lactation is also very important to calf health and performance. Adequate nutrition to the pregnant cow will improve the nutritional status of the growing fetus inside the cow as well as colostrum quality. This will lead to a strong calf that will have good vigor so that it stands quickly and suckles colostrum soon after birth. All of this is important to the early development of the immune system in the calf and will influence its health and performance throughout its life. Cow nutrition after calving will also affect quantity of milk produced; further influencing calf health and performance.
It has been wrongly suggested that under-nourishment of the cow will reduce the birth weight of the calf to decrease calving difficulty. This practice actually backfires, in that undernourished cows are weak and cannot labor as vigorously, and undernourished newborn calves are weak, slow to rise, slow to suckle colostrum and as a result, will suffer increased sickness and death.
Although feeding the cows is the largest production cost in a cow-calf operation, money invested in improving cow nutritional status now will pay for itself in terms of improved cow pregnancy rates this fall and overall calf performance.
Source : sdstate.edu