There are  a number of factors which can contribute to weak calves at birth.  Calves which are easily chilled at birth, slow to stand or have difficulty in standing, and fail to nurse promptly without attention contribute to greater calf losses and considerable work.  Weak calves can be associated with infectious disease as BVD or with large calves which experience hard slow births , but for the most part it is related to cow nutrition in gestation.  

Thin cows which do not get adequate energy in late gestation (often compounded with cold weather) and are thin at calving may produce calves with less fat reserve at birth needed to warn themselves and get up and nursing.  Even cows that appear to have adequate body condition may produce weak calves if their pre-calving diet was lacking protein, vitamin A and E, or minerals as Selenium.  Prevention includes having the cow herd on a vitamin-mineral program as insurance they are receiving what they need.  This may be done by feeding a recommended rate through a delivered ration daily or by a free choice product as loose, blocks, or tubs that is adequately and consistently consumed.  Forage being fed should be analyzed for protein to determine if it will provide adequate late gestation daily protein intake or if it should be supplemented with a protein feed as distillers grain, oil seed meal, or a commercial supplement.   Particularly for young cows the need will be for about 2.5 lbs protein per day or about a 9% crude protein ration.