Bad things often happen to cows during or following periods of negative energy balance. They may develop ketosis or a fatty liver; they may get lame; retained placenta and metritis are more common; mastitis is more likely, as is endometritis. They do not breed back as fast. They are at greater risk for certain infectious diseases, such as Salmonellosis. The underlying connection between negative energy balance and all of these problems is complex, but the bottom line is negative energy balance is bad for cows.
    Considering this fact, it should not be surprising that negative energy balance is not good for dairy calves either. Years ago, veterinarians used to see this in baby calves fed the old standard of two quarts of 20/20 milk replacer twice a day, especially in the winter. The most common complaint was diarrhea, but in reality the poor things did not have enough energy to mount a sufficient immune response to normal day to day challenges. We seldom see that scenario today. Farmers have been quick to adopt what we used to call accelerated feeding programs, which of course we now know are normal feeding programs. Many studies have shown feeding more milk results in better weight gains and better weight gains result in more milk production in first and greater lactations. Wonderful.
    However, we now see the effects of negative energy balance post weaning. The typical picture looks like this: burly, beautiful, energetic hutch calves often gain around 100 pounds or more prior to weaning; then a week after weaning or grouping a pen of weaned calves start to have rough hair coats, diarrhea and coughing. By two weeks, some calves look better but others struggle and may be treated for diarrhea or pneumonia. Fecal samples might be taken where various pathogens including coccidia, Salmonella or coronavirus, are found. Deep pharyngeal swabs might be submitted to find Pasteurella, Mannheimia, Mycoplasma or coronavirus. Other organisms not normally considered pathogens, e.g. Giardia, may be diagnosed. Attempts to improve the environment by better ventilation or bedding management are made. New or different vaccines are introduced into the protocols. Calves are treated with antibiotics, coccidiostats or dewormers. In a few more weeks calves look pretty good, and we might think our interventions have fixed the problem. In most cases, the real problem is plain old negative energy balance, and the calves mostly corrected it on their own. The bad news is in the meantime, calves may have lost the gains in growth produced by the accelerated milk feeding program; some have permanent damage, and we wasted a bunch of time and money.
    The weaning process is important in calves on accelerated milk or milk replacer programs, and it is more important than for calves on the old 20/20 restricted programs. Weaning is more difficult for the accelerated calves because they either refuse to eat enough grain, or they lack sufficient rumen development to properly digest grains, whereas the 20/20 calves had to eat grain to survive to weaning. Eating grain results in development of the lining of the rumen. In adult cows, the rumen and reticulum account for more than 70 percent of the total digestive tract volume by weight. Newborn calves have a small and poorly developed rumen. Milk feeding causes closure of the esophageal groove, which shunts milk to the abomasum, thereby avoiding the rumen entirely. As calves eat solid feed, the rumen changes in size (gets much larger), in morphology (growth of the papillae on the lining), and in function (becomes metabolically active). It is not only the grain itself that is important; volatile fatty acids produced by rumen fermentation of feeds, especially butyrate, are needed to develop rumen papillae. This may explain why forages are not as effective in promoting rumen development as grains. Development does not happen overnight either, which is why experts suggest calves need access to grain at least one month before weaning is started. Early weaning is another risk factor, since early (40- to 50-day-old) calves may have poor rumen development even if eating sufficient amounts of grain.
    Most producers now wean calves in a step-wise fashion to encourage grain intake prior to weaning. Weaning over a one- to three-week period while stepping down milk feeding no more than 30 percent at one time can be helpful to maintain grain intake. Recommendations vary, but calves should be eating at least 2.2 to 4.5 pounds of grain daily for at least three days prior to weaning. Time of moving and grouping is also important, since mixing calves causes stress and may cause cross-suckling. If possible, calves should not be weaned and moved or weaned and grouped concurrently. Group size is important, too. Generally smaller is better, but pens with fewer than 10 calves seem to go through the transition better.
    Another potential pitfall is providing a total mixed ration, or significant amounts of forage to calves that are too young or have incompletely developed rumens. TMR systems are great, but most young calves cannot digest enough nutrients from TMR or high forage diets to meet energy requirements, and thus need to be fed grain for some time after weaning.
    Negative energy balance is not only bad for cows but for calves, too. If your calves struggle with post weaning slump, it might be time to reevaluate the weaning and post weaning periods on your farm because negative energy balance may be the real problem.
    Jim Bennett is a dairy veterinarian at Northern Valley Dairy Production Medicine Center in Plainview, Minn. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.