Fatty livers are still a problem in U.S. dairy herds, accounting for an estimated $60 million in losses each year.
The best solution is prevention, starting with avoiding obesity in both heifers and cows prior to dry off and calving, says Pedro Melendez, a veterinarian with the University of Georgia’s College of Veterinary Medicine.
In a normal liver, the fat content does not exceed 2%. But after calving , when cows are mobilizing fat to support rising milk production, fat levels can rise to 10 to 15% in just 48 to 72 hours. That extreme level can cause problems, even death, he says.
Before calving, a dairy cow will begin to decrease her feed and dry matter intake, with intakes sometimes dropping to zero the day of calving. Intake starts to slowly rise thereafter, but do not reach maximum until 80 to 120 days after calving. At the same time, however, milk production rises quickly.
“As a result, the cow must mobilize fats from her body reserves (subcutaneous fat and abdominal fat) in order to meet the energy requirements of milk synthesis,” says Melendez. “Thus, the mobilization of fat in a post-calving cow is a normal process.”
Fat mobilization is measured by the amount of non-esterified fatty acids (NEFAs) in the blood. NEFAs should be less than 0.3 mEq/L before calving and 0.7 to 0.9 mEq/L at calving and for three days after. Problems occur when concentrations are larger than this because they then accumulate in the liver.
“When the liver is saturated with fat—more than 10% of the liver—treatments are ineffective, and the cow begins to develop other related disorders, such as ketosis, displaced abomasum, mastitis and metritis, among others, which complicate the normal functioning of the body,” says Melendez.
Since treatment is largely ineffective, prevention becomes key:
“An obese cow at calving consumes much less feed than a normal one,” says Melendez. As a result, she will mobilize much more fatty acid from her body, often reaching levels that exceed 0.9 mEq/L. So it’s important that cows dry off with moderate body condition (2.75 to 3.0). This also is true for heifers before first calving.
Heifers should only gain 1.54 to 1.76/lb/day to reach a breeding weight at 13 to 15 months of age and body condition score of 3.0 to 3.25, he says. “During heifer pregnancy, feeding should be moderated since the hormones of pregnancy make the heifer gain weight and condition much faster,” he adds.
Diseases that occur at the time of calving will decrease feed intake and lead animals to mobilize more fat than normal, says Melendez. So have a strategic plan in place to both diagnose and treat sick cows immediately around the time of calving. Even more important is to prevent disease through balanced diets and good management.
“Any stress, such as excessive environmental heat and humidity, lack of shade and comfort, excess mud, over-crowding and lack of animal welfare, will lead to triggered mechanisms that cause more fat mobilization than normal,” he says.
Currently, there are few easy tests to detect fatty liver syndrome. Melendez is currently working to develop molecular techniques to identify biological markers to aid in early diagnosis. In the meantime, he says, prevention is still the best approach to avoiding fatty liver syndrome in early lactation.