Fatty livers account for an estimated $60 million in losses each year. Because treatment for fatty livers is largely ineffective, the best solution is prevention, starting with avoiding obesity in both heifers and cows prior to dryoff 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, Melendez 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. But at the same time, milk production rises quickly.
“As a result, the cow must mobilize fats from her body reserves (subcutaneous fat and abdominal fat) 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,” Melendez says.
Melendez is currently working to develop molecular techniques to identify biological markers to aid in early fatty liver diagnosis.
Causes, prevention and treatment
“An obese cow at calving consumes much less feed than a normal one,” says Pedro Melendez, a veterinarian at the University of Georgia. As a result, she will mobilize more fatty acid from her body, often exceeding 0.9 mEq/L. So it’s important 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 lb. to 1.76 lb. per 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, Melendez says. So diagnose and treat sick cows immediately around the time of calving and prevent disease through balanced diets and good management.
“Any stress, such as excessive environmental heat and humidity, lack of shade and comfort, excess mud, overcrowding and lack of animal welfare, will lead to triggered mechanisms that cause more fat mobilization than normal,” he says.