What are the symptoms of fatty liver in dairy cows?
Nowadays, to give full play to the milk production performance of dairy cows in many countries, continuous feeding of high-concentrate diets has aggravated the prevalence of fatty liver syndrome and diet fatty liver in dairy cows. The disease is common in high-yielding dairy cows. Overfeeding during dry milk makes cattle obese during calving.
After calving, the appetite of cattle decreases and energy deficiency in the body leads to a sharp drop in body weight and fat accumulation in liver cells. A fatty liver syndrome is associated with the persistence of other nutritional and metabolic diseases, infectious diseases and reproductive diseases, such as breast fever, ketosis, mastitis, and placental stagnation.
The fatty liver syndrome is common in dairy cows, which may be related to overfeeding in late pregnancy, especially when the high-energy concentrate is fed in the late dry milk period. Besides, in the season of abundant fresh forage, if the feeding of dairy cows in the dry milk period is not restricted, there is still a risk of obesity, which can lead to fatty liver syndromes.
What is the cause of fatty liver?
Most dairy cows in the early lactation stage are in a state of negative nutritional balance, so they use the energy stored in fat and muscle, which results in weight loss and disease of dairy cows. The mobilization and utilization of energy in vivo mainly includes the conversion of fat storage into free fatty acids and release into the blood and the conversion of stored proteins into sugary amino acids. Free fatty acids enter various tissues through blood, such as kidney, liver, and muscle, and deposit in cells in the form of triglycerides.
As a result, fat content in the liver of dairy cows increases 1-4 weeks after calving. The fatty liver appeared 2 to 3 weeks before calving. This pre-calving fat mobilization may be related to hormone changes in dairy cows near calving. The amount of fat deposition in the liver and other tissues after calving is determined by many factors, such as the potential for high milk production, the amount of fat in the body, body condition during calving and weight loss after calving. When the body fat deposits excessively, the appetite of dairy cows decreases and the mobilization of body fat accelerates, which leads to the increase of liver fat content and weight loss.
The most common clinical fatty liver symptoms of fatty liver syndromes are increased morbidity of diseases during or after childbirth, such as fetal retention, breast fever, mastitis, and ketosis. Studies have shown that fatty liver syndrome will lead to a decline in the fecundity of dairy cows. However, when suspecting the disease, it should be noted that most of the dry cows have excessive body fat (body condition score is greater than 3.5), and most of the cows are thinner (body condition score is less than 2) four weeks after calving.
When fatty liver syndrome occurs, the blood composition of dairy cows will change significantly within one week after calving. The activities of free fatty acids, bilirubin and alanine aminotransferase increased, while the total number of glucose, cholesterol, albumin, magnesium, insulin and white blood cells decreased. In severe cases, the number of white blood cells will decrease to 3 × 10 9/L.
After the death of the diseased cattle, there were a lot of fat deposits in the heart, kidney, pelvic periphery, and omentum. The liver is swollen, obtuse and yellowish-white. Triglyceride deposits were found in the liver, kidney, adrenal gland, skeletal muscle fibers, and myocardial cells. Triglyceride granules were deposited in the cytoplasm of hepatocytes, and the amount of deposition was up to 70% of the volume of hepatocytes. The pathological changes mentioned above can be seen in dairy cows that did not take food 24 to 48 hours before death. Therefore, only combined with the history of the disease, clinical-pathological changes, and postmortem autopsy can contribute to the diagnosis of fatty liver syndrome or obese cow syndrome.
The results of dry milk examination and 3-4 weeks after calving, combined with the history of increased incidence of postpartum dairy cows, can usually clearly indicate whether fatty liver syndrome occurs or not. The exact diagnosis can be obtained by examining the liver tissues of 5-6 cows immediately after calving. Liver biopsy samples can be used to detect the percentage of fat in the liver. A liver biopsy of dairy cows is relatively simple and can be used by every clinical worker. Liver tissue sections were stained with toluidine blue. If the fat content exceeded 20%, it indicated that the cow had developed fatty liver syndromes. When the fat content exceeded 50%, it indicated that the cow had developed severe fatty liver syndromes, then the cattle company should pay more attention to these cows.
Blood biochemical methods can also be widely used to detect the occurrence of fatty liver. Consider different parameters, such as non-esterified fatty acids (NEFA), glucose, alanine aminotransferase, and glycerol. However, these indicators can not fully explain the fatty liver syndrome, the credibility is not high.
There is no definite treatment for fatty liver syndrome or obese cow syndrome. The most routine treatment is to increase blood sugar by intravenous injection of glucose, glycerol or propionate, and glucocorticoid. At the same time, steroids are synthesized to promote protein synthesis, thereby promoting the decomposition of fat in cattle.
Fatty liver can be caused by overweight cows during calving and excessive weight loss in early lactation, and it may affect the milk nutrients. Therefore, the main way to prevent fatty liver is to limit the feeding amount during the dry milk period so that the health score of cows can reach 2.5 to 3.0 points. In recent years, the incidence of fatty liver syndrome in dairy cows with reduced concentrate before calving has been significantly reduced.
During calving, cows with body condition scores of 2.5-3.0 had better appetite than obese cows, so they lost less weight in early lactation. The quality of pasture in spring and early summer in northern China is the best. When cows feed on pasture, dry dairy cows tend to become obese. Dry dairy cows should be restricted to feeding high-quality forage, or to adding low-quality cellulose feed, such as straw or hay.