Manganese plays an important role in the process of energy metabolism and enzyme activation. The amount of manganese required for reproduction is at least 30 percent higher than the requirement for growth. Cows with a manganese deficiency may not exhibit estrus (heat), may have decreased conception rates, may have higher abortion rates, and may breed lightweight calves at birth. Calves may be born weak and may be deformed with twisted legs and enlarged joints. This being said, it is very rare that manganese is deficient enough to cause the type of reproductive problems that you are suggesting. Most grasses contain manganese, so grazing cattle rarely have problems. Corn-based diets are low in manganese and so supplementation is needed. Also, most commercial mineral mixes contain manganese. Consult with your local Cooperative Extension for help in determining the cause of your problem. It is difficult to think that low manganese is the problem even though the cow's ability to store manganese is low.